0985 ABB Special Report

PowerTransmission

Special Report

ABBReview

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The case for advanced power technologies. The case for advanced power technologies.

2 Special ReportABB Review

Contents

HVDC superhighways for ChinaNew HVDC transmission lines will carry electricity from the

Three Gorges power plant to China’s coastal regions.

FACTS: improving the performance of electrical gridsHow flexible AC transmission systems let utilities utilize their

existing power lines more efficiently.

ABB static var compensator stabilizes Namibian grid voltageNamibia’s long transmission lines give rise to unusual resonance.

A new SVC has solved the problem.

Advanced transformer control and monitoring with TECABB’s TrafoStar Electronic Control system models a transformer’s

actual state, allowing condition-based maintenance.

Power systems consultingA look at ABB power systems applications that integrate the domain

competence of consulting experts with the latest software tools.

InformIT Wide Area MonitoringPSG modules from ABB optimize asset utilization and can prevent

the collapse of entire power networks.

IndustrialIT and the utility industryHow does the unique business environment of the utility industry

benefit from Industrial IT?

A battery energy storage system for AlaskaThe world’s largest BESS is providing essential back-up power for

90,000 people in the Fairbanks area.

High-voltage cable technologyNew XLPE cable system applications are available that can often

compete with overhead lines.

Powering Troll with HVDC LightTM

New ABB technologies allow power to be supplied from land to

platforms offshore.

SwePol Link: new environmental standards for HVDC transmissionA unique HVDC link connects the electricity networks of Poland

and Sweden.

50 years of HVDC transmissionABB has supplied more than half of the world’s HVDC transmission

capacity.

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3Special ReportABB Review

Editorial

City lights – a ‘power showcase’built on technology and experience

For example, the world’s largest batterysystem, which went into operation inAlaska in 2003, relies on ABB convertertechnology. Such systems bridge thetime between power cuts and the start-up of emergency power generation.Alaska’s new battery is designed toprovide 40 MW of electrical power for15 minutes. Other battery installationsempowered by ABB converter technol-ogy are soon to go into operation inthe United States.

ABB is the undisputed world leader inHVDC transmission. The power con-verters at the heart of this technologycan make a huge contribution to gridstability. An HVDC power transmissionlink between the Three Gorges damand Changzhou in China successfullycompleted all trials in 2003, and has thecapability to operate at power levels ofup to 3300 megawatts – a new worldrecord! In Brazil ABB recently commis-sioned power transmission systems witha total length of 1267 kilometers. Con-struction of the systems, which includ-ed five substations and four series com-pensation banks, was completed in justtwelve months.

The list goes on: the largest-ever gas-in-sulated substation for an important nodein the Saudi Arabian high-voltage net-work; the world’s longest undergroundhigh-voltage cable, developed and in-stalled by ABB, stretching 177 kilome-ters from Victoria to South Australia and the winner of environmental andengineering awards.

ABB also holds the world record in high-power switching with its generator break-ers, which can interrupt up to 200 kA atgenerator voltage levels of around 30 kV.

These records are solid proof of ABB’sability to provide world-class powertechnology, and of our company’sstrong commitment to research anddevelopment. Such performance isbased on R&D programs that investi-gate the physical limits of current inter-ruption and high-voltage insulation, orthe application of semiconductorswitching in our power electronicsdevices.

In addition to device-oriented R&D,ABB also looks at the ‘big picture’. Anexample is our wide area approach tomonitoring power system dynamics andnetwork stability. Engineering tools wehave developed enable us to analyze acomplete grid in a very short time, andpropose significant improvements.

This Special Report is devoted to ABBtechnologies which, by ensuring net-work stability, prevent the emergenceof situations that could cause entirepower systems to collapse. As anoverview of our company’s broad com-petence in this important area, the Re-port demonstrates ABB’s ability to sup-ply the utility industry with each andevery part of its infrastructure. To makesure that electrical energy, upon whichwe depend so much, is available wher-ever and whenever it is needed.

H. Markus BayeganChief technology officerABB Ltd

In the aftermath of the recent poweroutages that plunged northeasternAmerica and parts of Europe into dark-ness, politicians and utility ownersrushed to debate the state of the world’spower infrastructure. The outcome ofthis discussion has been general agree-ment that more investment is needed.But besides pointing out the vulnera-bility of outmoded infrastructure, theblackouts also served to make a point:wherever we live, we can no longerunquestioningly count upon a reliablesupply of electrical power.

While these events gave a full-scaledemonstration of what can happenwhen unstable power systems are dri-ven to their operational limits, it is goodto know that technologies are availablethat could almost certainly have pre-vented them from happening.

ABB is the world’s leading provider of power technology products andsystems. Constant investment in theirfurther development has enabled ourcompany to book several remarkableachievements in recent years.


Reliable grids, with power technologies from the market leader

enced business leaders. ABB has builtits reputation in power technology onthese three strengths.

Invention and innovation have a longtradition at ABB, and many of the keytechnologies upon which the powerindustry is founded were pioneered byour company. Our track record goesback more than a century, and includesthe world’s first three-phase powertransmission system and the world’s firstself-cooling transformer. ABB also pio-neered HVDC technology. To mark thisachievement, our company will cele-brate ‘50 years of HVDC’ together withour customers in spring 2004.

It is this pioneering spirit that still drivesus today. Recent breakthroughs includeour HVDC LightTM technology, whichextends the economical power range ofhigh-voltage direct current transmissiondown to just a few megawatts andopens up new possibilities for improv-ing quality in power grids.

Our utility and industrial customersaround the world rely on proven powertechnologies, researched, developedand made by ABB. In power transmis-sion and distribution, ABB is the recog-nized leader, with a world market shareof some 20 percent.

Every fourth power transformer andhigh-voltage circuit breaker in the worldcomes from ABB. Some of our high-endproducts and systems – generator break-ers, for example – have beaten eventhis proud record and captured morethan half of the world market. The sameis true in other important areas of thepower sector, like high-voltage directcurrent (HVDC) transmission or flexible

The recent blackouts in the US andEurope have made more than just themedia think about the critical impor-tance of a secure and reliable supply ofpower. In our homes and throughoutbusiness and industry, the message isclear: no longer can we take for grant-ed that power will simply be availableeverywhere, always.

Reliable power grids are the result of apartnership between governments, theelectric utilities, consumers and, notleast, the providers of the all-importanttechnology that generates, transmitsand distributes the power so efficiently.Over a country’s power infrastructureflows its lifeblood – the energy that isessential to efficient running of ourhomes and offices, our factories andairports. Much of our future prosperitywill depend on how we look after it.

Modern power systems are the result ofcontinuous development and improve-ment which, over the years, has led tohighly sophisticated and complex tech-nologies. Their reliable operation is atribute to the work of dedicated scien-tists, innovative engineers and experi-

Foreword


Foreword

alternating current transmission systems(FACTS).

State-of-the-art technologies such asHVDC and FACTS have precisely thequalities and capability that arerequired to prevent blackouts.

HVDC lets utilities solve two problemsat the same time: using it to intercon-nect asynchronous power grids notonly increases reliability, but also setsthe stage for power trading acrossthose grids. Most of the world’s powernetworks were designed as nationalgrids or as regional grids within acountry. To facilitate open markets,these networks increasingly requireHVDC interconnections.

With FACTS, utilities have devices at their disposal with which they can bet-ter utilize their existing infrastructure.FACTS provide an alternative to the con-struction of new transmission lines orpower generation facilities by helping to maintain or improve the operatingmargins necessary for grid stability. As aresult, consumers get more power with-out any extra strain being put on theenvironment, and projects are completedin a substantially shorter time.

Wide area monitoring (WAM) systems areanother ABB offering that can preventthe collapse of entire power networks.GPS-synchronized current, voltage andfrequency information gives power sys-tem operators a dynamic overview of thenetwork conditions, and indicates theonset of conditions that, if unchecked,could cause system instability.

The power grids of the 21st centurymust incorporate such high-end tech-

nologies if they are to meet all thechallenges that lie ahead. The black-outs of 2003 have served notice on theutilities, and demonstrated to the widerpublic, that power grids are vulnerable.In many countries, deregulation has alltoo often undermined the will to makenecessary investments in high-endtechnologies.

A first step toward correcting this situa-tion would be for regulators to offer in-vestors, such as utilities and developers,special incentives that encourage themto install technologies which can beimplemented quickly and increase therobustness of their transmission grids.In addition, quality standards for thepower supply are needed to ensurepower reliability and security.

ABB is ready to give its best: proventechnology. But beyond superior powerproducts, systems and services, there isanother decisive contribution that ABBcan make: speed. Short delivery times,guaranteed by a commitment to beingfastest in everything we do, are inkeeping with the prevailing sense ofurgency. Power consumers around theworld do not want to wait, and shouldnot have to wait, one moment longerfor a reliable power supply.

Peter SmitsMember of the Executive CommitteeHead of Power Technologies DivisionABB Ltd


When completed in 2009, the Three Gorges hydroelectric power

plant being built on the middle reaches of the Yangtze river will be

the largest of its kind anywhere in the world. With 26 turbine-

generators, each rated at 700 MW, the total generating capacity will

be a staggering 18.2 gigawatts.

No less challenging was the development of a technically and

economically viable transmission system to carry this power to

China’s coastal regions, where it is urgently needed. After carrying out

feasibility studies, the State Power Grid of China decided to build a

hybrid AC-DC transmission system with over 10,000 km of HVAC and

HVDC lines and about 2475 MVA of transformation capacity. The HVDC

systems leaving the power plant site include bipolar transmission

superhighways with ratings totaling more than 10,000 MW.

HVDC superhighways for China

Leif Englund, Mats Lagerkvist, Rebati Dass


Two of the world’s most powerfuland longest high-voltage direct cur-

rent (HVDC) power transmission high-ways, each with a nominal rating of3000 MW, are currently being installedin China. Being built by ABB in coop-eration with the State Power Grid ofChina, they will eventually carry cleanhydroelectric power from the ThreeGorges power plant, situated on themiddle reaches of the Yangtze river, tomajor load centers near Shanghai andShenzheng on the Chinese coast.

High availability and a low forced out-age rate were key goals from the start ofthe transmission projects. Advancedtechnologies, backed up by solid fieldexperience and featuring built-in opera-tional flexibility and low maintenance,are therefore being used in all thecrucial areas.

To promote and ensure the success ofthe projects at all stages, close coopera-tion among ABB, the client, the client’sdesign and inspection representatives,and local equipment manufacturers, was enshrined in the project contractsin the form of training and transfer oftechnology (see panel).

Three Gorges power plantThe Three Gorges dam across the Yangt-ze river is the largest of its kind in the world. Approximately 1.5 kilometerslong and 185 meters (590 feet) high, itsreservoir, with a normal water level of175 meters (560 feet), will stretch over560 kilometers (350 miles) upstream.The hydroelectric plant, with 26 turbine-

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generators rated at 700 MW, will have a total capacity of 18.2 gigawatts (thenext-largest hydropower plant, Itaipu inBrazil, has a capacity of 12 GW). It isplanned to later install a further six unitsin an underground powerhouse, takingthe total capacity to 22.4 GW. This figurerepresents a more than six percent in-crease in China’s current total installedcapacity of 350 GW. The average yearlyproduction of the Three Gorges plantwill be 84.7 TWh [1,2].

Power evacuation systemThe power generated by the ThreeGorges plant will be transmitted to gridsin central China, east China, Sichuanand Guangdong via the Three GorgesTransmission System. With over 10,000kilometers of HVAC and HVDC lines,this system will form the basis for a new national transmission grid, as thepresent seven regional power networksand five independent provincial net-works will be combined to create two

Location of the Three Gorges power plant on the Yangtze river1

Three Gorges Dam

Beijing

Three Gorges-Changzhou HVDC

Shanghai

Hong Kong

Chongqing

Three Gorges-Shanghai HVDC (planned)

Three Gorges-Guangdong HVDC

Yellow River

Yangtze

Wuhan

Transfer of technology (ToT) and local manufacturing

The contracts for both projects (3GC and 3GG) included extensive co-design, training and ToT programs.

The co-design program calls for the detailed design to be carried out jointly by design engineersand experts representing SPG and ABB.

Training of SPG’s representatives covers maintenance and operation. Its goal is to ensureproper operation and maintenance of the projects by local personnel.

The ToT programs include know-how transfer in HVDC system design, control design andapparatus manufacturing to different organizations, ABB as well as non-ABB, in China. Theseprograms will serve China’s long-term objective of increased self-reliance in the design andproduction of high-tech HVDC equipment.


new regional networks. A national inte-grated grid is planned for 2015.

A major portion of the power will becarried to China’s industrialized coastalareas in Shanghai and Shenzheng bymeans of four HVDC links :

Gezhouba-Shanghai 1200-MW HVDCbipole, in operation since 1991. Three Gorges – Changzhou 3000-MWbipole (3GC), commissioned in May2003.Three Gorges – Guangdong 3000-MWbipole (3GG), currently being com-missioned.Three Gorges – Shanghai, 3000 MW,scheduled to be operating by 2007.

HVDC was chosen to transmit powerfrom the Three Gorges plant for severalreasons. Since the central and eastChina/Guangdong AC networks are not synchronized an AC transmissionscheme would have required coordina-tion, and it would have been verydifficult to ensure adequate stabilitymargins. HVDC allows controlled trans-mission of power between the net-works, which also retain their indepen-dence. DC is also more economic interms of construction costs and losses.Five series-compensated 500-kV AClines would be necessary to transmitthe same amount of power, and eachline would require a larger right-of-waythan one HVDC transmission line for3000 MW.

Unmatched experience with HVDC bulk powerABB’s record of large bipolar HVDC in-stallations is unmatched. Prior to win-ning the ThreeGorges contract,ABB had success-fully built a wholeseries of largebipolar installa-tions worldwide,for example:

Itaipu (Brazil):two bipoles,each rated 3150 MWIntermountain Power Project (USA):one bipole, 1920 MWRihand-Dadri Project (India): onebipole, 1500 MW

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Chandrapur–Padghe Project (India):one bipole, 1500 MWQuebec-New England Multiterminal(Canada/USA): three bipolar stationsrated 2250/2250/2000 MW

Highway construction on scheduleABB was awarded the first contract, tosupply equipment for two converterstations for the 3000-MW HVDC bipolarlink between Three Gorges and eastChina, in April 1999. This entrusted ABBwith overall project responsibility, in-cluding the supervision of site work un-dertaken by the client. The contract alsoincluded ToT, covering HVDC systemdesign, control design and equipmentmanufacturing. Approximately 85% of

the total contractvalue was forequipment or ser-vices provided bythe ABB Group.The installationwas commis-sioned on time inMay 2003.

In October 2001 ABB won a second or-der, this time for the 3000-MW HVDClink between Three Gorges and Guang-dong province. This fast-track projectcuts 30 percent off the normal lead-

Indoor DC yard at Zhengpingconverter station (3GC)

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time, enabling the first pole to be com-missioned 28 months after signing ofthe contract. Similar in scope to the3GC, it provides for more local content.

HVDC allows controlledtransmission of powerbetween the central andeast China/GuangdongAC networks, whichremain independent.

Four HVDC links will carry hydroelectricity from the Three Gorges power plantto China’s coastal area and the industrial region of Guandong

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East China

Guangdong

Left bank

Three Gorges

±500 kV, 3000 MW

±500 kV, 1200 MW

±500 kV, 3000 MW

±500 kV, 3000 MW

Three Gorges – Changzhou

Gezouba – Shanghai

Three Gorges – Shanghai

Three Gorges – Guangdong

Right bank

Central China

14x700 MW

12x700 MW


The transmission systemsThe 3GC and 3GG projects are bothbipolar transmission schemes [3] withidentical main primary and secondaryequipment and operating strategies. The two 3GC converter stations are atLongquan (Hubei province) and Zheng-ping (in Changzhou, Jiangsu province),about 890 km apart. Longquan convert-er station is situated some 50 km fromthe Three Gorges Dam. The receivingstation at Zhengping is approximately200 km from Shanghai. Power will betransmitted eastward during the peakgeneration period and toward the cen-tral power grid whenever reservoirwater needs to be conserved.

The converter station at the transmittingend of the 3GG project is located 16 kmfrom Jingzhou city, about 135 km fromthe Three Gorges power plant. The re-ceiving station is at Huizhou, in Guang-dong province. Power will be transmit-ted over a distance of 940 km.

To keep the AC yard of the 3GG Jingzhouconverter station as small as possible, outdoor gas-insulated switchgear (GIS) isused for all of the ten 500-kV bays .4

500-kV yard with SF6 gas-insulated switchgear, at Jingzhou converter station (3GG)4

The ToT covers HVDC system design aswell as the design of the control andprotection system. This project is welladvanced and on schedule.

3GG benefits from 3GCThe 3GC project has established a worldrecord by transmitting 1650 MW on asingle pole. Since the Zhengping con-verter station is exposed to very heavyindustrial pollution, the DC pole insula-tors had to be longer than those themanufacturers could provide. This andthe difficulty of coordinating the exter-nal and internal insulation of extra-longbushings led to the decision to build in-door DC switchyards . All high-poten-tial DC equipment is installed indoorsand all the DC neutral equipment is out-doors. There are four separate halls foreach pole: one for switches, two for theDC filter capacitor banks, and one forthe DC PLC capacitor bank.

The 3GG project is in a class of its ownwith regard to the very short 28 monthsto commissioning for monopolar and 32 months for bipolar operation. Herethe knowledge and experience baseprovided by the 3GC project proved tobe a huge asset. Areas that profited in-cluded the project engineering phaseand the equipment design and deliverytimes, all of which could be significant-ly reduced. The cost benefit to theclient was also considerable.

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Power circuit arrangement used for the 3GC and 3GG projects5

3000 MW

+500 kV

DC-line

DC-line

Electrode line

–500 kV

y0

y0

y0

y0

y

y

y0

y

y0

y

y0

y0

Converter stationLongquan (3GC)Jingzhou (3GG)

Converter stationZhengping (3GC)Huizhou (3GG)


Power ratings

The links are designed for a normal rat-ing of 2 x 1500 MW under the (relative-ly conservative) specified conditions.They have been designed for a continu-ous overload capability of 3480 MW,and a 5-second overload capability of4500 MW.

To minimize bipole outage the HVDCsystem can be operated with balancedbipolar currents, using the ground matsof the converter stations as temporarygrounding, should the ground elec-trodes or their lines be out of service.

The nominal reverse power transfercapability is 90% of the rated power.The HVDC links are designed to operatecontinuously down to 70% of the ratedDC voltage. The main technical data are given in the table.

Power circuit arrangement

The main circuit arrangement of thetwo links is identical except for thereactive power compensation equip-

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head transmission line. Metallic returntransfer breakers and ground returntransfer switches have been installed tomeet the requirements of monopolarmetallic return operation, and providecapability for uninterrupted transfer.Neutral bus grounding switches arealso installed at the neutral buses ofboth stations to meet temporarygrounding requirements.

Thyristor valves

A double valve scheme was chosento take account of the converter trans-formers being single-phase, two-wind-ing units. Longquan and Jingzhou con-verter stations have 90 thyristors (3 kA,7.2 kV) per valve, while at the receivingstations Zhengping and Huizhou eachvalve has 84 thyristors (same rating).Dry-type damping capacitors and filmDC resistors are used. Comprehensivefire detection and protection is incorpo-rated in the valve hall design.

AC filtering

Four types of filter are used: doubletuned 11th and 13th, double tuned 24th

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ment. Stable steady-state and dynamicoperation of the AC-DC systems is en-sured by optimizing use of the reactivepower capacity of the generators in theThree Gorges power plant and the ACnetworks at each end of the links. One-and-a-half breaker configurations areused on the AC side at both stations.

In addition to the bipolar transmissionscheme, the links can be connected formonopolar transmission with either aground or metallic return. The maincircuit connection on the DC side istypical for an HVDC bipole with over-

The links have beendesigned for a rating of2x1500 MW, a contin-uous overload capa-bility of 3480 MW, anda 5-second overloadcapability of 4500 MW.

Thyristor valve structures6

Main parameters 3GC (3GG)

Nominal power rating, MW 3000

Nominal dc voltage, kV ±500

Transmission distance, km 890 (940)

Power overloads at max

ambient temperatures with

redundant cooling in

service, MW:

Continuous 3150

2 hour 3390

10 seconds 4230

5 seconds 4500

Converter transformers:

Type 1-phase,

2-winding

Power rating, MVA 297.5/283.7

Smoothing reactors:

Type Oil-insulated

Value, mH 290/270 (290)

Thyristor type YST-90

DC filter type Passive

AC filter type Passive

AC system voltage, kV 525/500

AC system frequency, Hz 50


and 36th, double tuned 12th and 24th,and C-type 3rd harmonic. Shunt capaci-tor banks, with and without dampingreactors, balance the reactive powerrequirement at Jingzhou, Zhengping andHuizhou converter stations.

DC filtering

Robust passive DC filtering ensures aperformance level of 500 mAp (bi-pole)/1000 mAp (monopole) for bothprojects. Each terminal pole has twofilter arms designed as double tunedfilters, one tuned to the 12th and 24thharmonics and the other to the 12thand 36th harmonics.

Control and protection

The projects’ control and protectionstrategies are realized with ABB’s state-of-the-art MACH2 system. MACH2features high-level perfor-mance, lowmaintenance, avery powerfulprogrammingenvironmentand good inte-gration withSCADA systems.The SCADAsystems enable information about theoperating status of each converterstation to be accessed remotely by dis-

patch centers. These centers have fullremote control capability and can regu-

late powertransmissionon the link.Terminal-to-terminal com-munication isvia opticalfiber groundwire. Capacitynot neededfor communi-

cation is used for dispatch and for datatransfer on the networks, but could alsobe used for commercial purposes.

Control functions such as power ramp-ing, frequency control and dampingmodulation, are also integrated. Thestation engineer can adjust the inter-face and parameters as required by the system.

Converter transformers and

smoothing reactors

The single-phase converter transformersin the Longquan and Jingzhou stations

are rated 297.5 MVA, 525/√3:210.4/√3(210.4 for Y-D) kV, 16% reactance, withan OLTC tap range of +25/-5 (1.25%per step). The Zhengping transformersare rated 283.7 MVA, 500/√3:200.4/√3(200.4 for Y-D) kV, 16% reactance.Here, the OLTC tap range is +26/-2. Inthe Huizhou station the transformersare rated 283.7 MVA, 525/√3:200.6/√3(200.6 for Y-D) kV, 16% reactance, alsowith an OLTC tap range of +28/–4(1.193% per step). Dry-type bushingsare used for the valve hall penetration.The converter transformers at Long-quan, Jingzhou and Huizhou are alsoequipped with electronic control,allowing analysis and reporting, plusintelligent fan control to minimizelosses.

The smoothing reactors are connectedto the valves via the bushing pene-trating the valve hall wall. An electron-ic control system for the reactors atLongquan, Jingzhou and Huizhoufeatures the same capability as thatprovided for the transformers.

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Power will be transmittedeastward during the peakgeneration period and towardthe central power grid when-ever reservoir water needs to be conserved.

Converter transformer arrangement per pole7


DC-side breakers and switches

SF6 breakers are used for all the high-speed DC switches: metallic returntransfer breakers, neutral bus groundingswitches, neutral bus switches andground return transfer switches. Theground return transfer switch is theonly one of these to be of conventionalpassive design. All the others have anactive auxiliary transfer circuit consist-

References

[1] Introduction to China’s Yangtze River Three Gorges Project. The PRC State Council Three Gorges Construction Committee, Ministry of Land and

Resources, State Environmental Pollution Administration, State Bureau of Cultural Relics, September, 2002.

[2] Z. Xiaoqian, D. Gongyang, G. Ricai: The Three Gorges power grid and its development. Cigré 1998, 37–203, Paris.

[3] Z. Xiaoqian, et al: Design Features of the Three Gorges – Changzhou ±500 kV HVDC Project. Cigré 2000, 14–206, Paris.

Leif Englund

Mats Lagerkvist

Rebati Dass

ABB Power TechnologiesSE-771 80 Ludvika

[email protected]

[email protected]@se.abb.com

ing of a capacitor and a charger. Thecharger gives the DC switches extracurrent commutation capability, en-abling them to handle even the highestoverload currents.

Operating configurationsThe links can be operated in many dif-ferent configurations and modes. Emer-gency operation is provided for, as is

Power take-offElectric power generation in China tends to be located in the northeast (coal-fired), and in the

west and southwest (hydropower), while the main consumer areas are in the eastern coastal

area and southern industrial region of Guangdong.

China’s total generating capacity of more than 350,000 MW (end of 2002) needs to grow to at

least 500,000 MW by the end of the decade to cope with increased demand. Due to its fast-

growing economy, many areas, including Shanghai, Guangdong and Zhejiang provinces, are

already today suffering from a significant power supply shortfall. Guangdong province, for exam-

ple, has a deficit of over 30,000 MW, some of which is met through imports from neighboring

Hong Kong.

China now plans to start adding 25,000 to 30,000 MW each year through 2005, for an annual

growth of 7% to 8%. Both AC and DC transmission are foreseen for the extensions. Over the next

ten years, the HVDC market – long-distance transmissions and back-to-back stations to intercon-

nect the regional networks – is estimated at 40,000 MW.

“A remarkable achievement in the history of ABB’s HVDC technology”

The inauguration of the Three Gorges – Changzhou HVDC link in August 2003 in the presence

of representatives of the Chinese government, State Council Three Gorges Office, State Power

Grid Corporation and ABB, marked the successful completion of trials and the start-up of com-

mercial operation. The 500-kV, 890-kilometer long HVDC link can operate at world record levels

of up to 3,480 megawatts, and when the Three Gorges generators begin operating later this

year it will transmit electricity to millions of consumers in eastern China. The largest and longest

bipole DC power transmission link in China was completed on schedule in four years.

“Considering the project’s technical complexity, this is a remarkable achievement in the histo-

ry of ABB’s HVDC technology,” says Peter Smits, head of ABB’s Power Technologies division.

“By delivering this challenging project on time almost to the day, we have demonstrated our

commitment to speed and precision, and to improving the quality of life for millions of Chinese

citizens.”

operation without telecommunication.Through accurate measurement andcontrol it is ensured that in the case ofbipolar balanced operation with localstation ground the unbalance current toground will be zero.

The operating modes are:BipolarMonopolar earth return and metallicreturn Reduced DC voltage (from 500 kV to350 kV)Reverse power operationBipole and pole power controlPole synchronous and emergency(separate) power controlPole backup synchronous control (for modulation of DC current with-out inter-station telecommunication)Pole current control

Meeting China’s energy demand China plans to substantially expand itsgenerating capacity by 2010 in order tocope with the predicted growth indemand (see panel). At the same time,two new regional networks will becreated as the basis for a new nationaltransmission grid. HVDC, with all itsadvantages for long-distance transmis-sion, is expected to play a major role in the extensions.


FACTSRolf Grünbaum, Åke Petersson, Björn Thorvaldsson

Improving the performance of electrical grids

After years of underinvestment in their transmission infrastructure, power utilities are being forced to

look at ways of utilizing their existing transmission lines more efficiently, at possibilities for cross-border

cooperation, and at the issue of power quality. This situation has dramatically increased interest in new

as well as traditional solutions.

FACTS (Flexible AC Transmission Systems), such as SVC, SVC Light®, TCSC and others, are just such

solutions. They take advantage of the considerable technical progress made in the last decade and

represent the latest state of the art. While a typical application would be to increase the capacity of any

given transmission line, this article describes some special cases with unique requirements and how

they were met.

If prestigious projects were ever need-ed to demonstrate FACTS’ credentials

as an improver of T&D performance,none could serve better than the Dafang 500-kV series capacitors helping to safe-guard Beijing’s power supply, the EaglePass back-to-back tie straddling theUS/Mexican border, or the Channel

Tunnel rail link. These, in their differentways, show why FACTS is arousing somuch interest in the electrical supplyindustry today.

Dafang: series capacitors safeguardthe Beijing area power supplyPower demand in the area served by the

North China Power Network, with 140million people and including Beijing, isgrowing at a steady pace. Installing newgeneration plant and transmission lines isnearly impossible due to urban growth.An attractive alternative is to insert seriescapacitors in the existing transmissioncorridor to provide series compensation.


ABB was contracted to do this, and in-stalled two series capacitors (each rated372 MVAr, 500 kV) in the middle of eachline of a 300-km twin-circuit corridorbetween Datong and Fangshan . Theycame on stream in June, 2001, a merenine months after the contract wasawarded and some 3 to 6 months fasterthan for similar installations.

A series capacitor acts to reduce thetransfer reactance of the power line atpower frequency (50 Hz) and suppliesreactive power to the circuit at the sametime. The benefits of this are:

Increased angular stability. Theremust always be a certain differencebetween the voltage phase angles ateither end of the power line to en-able transmission. The phase angledifference increases with powertransmission and the series capacitorkeeps the angular difference withinsafe limits, ie it ensures that the angu-lar difference does not increase somuch that it could jeopardize theangular stability.

1

Improved voltage stability of thecorridor.Optimized power sharing betweenparallel circuits. Without series capac-itors, the line with the least powertransmission capacity would saturatefirst and no additional power couldbe fed into the system, despite thefact that the other line still has capac-ity to spare. The series capacitorsredistribute power between the linesfor better overall utilization of thesystem.

The series capacitors are fully integratedin the power system and benefit from its control, protection and supervisorycapability. They are fully insulated toground.

The main protective devices used areZnO varistors and circuit-breakers. Thefirst is to limit the voltage across thecapacitor and is supplemented by aforced-triggered spark gap to handleexcess current during a fault sequence.The circuit-breakers connect and dis-

connect the series capacitors as re-quired. They are also needed to extin-guish the spark gap, as it is not self-extinguishing.

The capacitors are rated for operationduring normal, steady-state grid condi-tions as well as for severe system con-tingencies, such as loss of one of thetwo parallel 500-kV lines. In such acase, the capacitor of the line remainingin service must be able to take the fullload of both lines for a certain amountof time. This was, in fact, one of thereasons for installing the series capaci-tors in the first place – to ensure thesafe transfer of power to the Beijingarea even with a line down.

Eagle Pass Back-to-Back (BtB) LightSVC Light technology1) has successfullysolved power quality problems in sever-al projects undertaken by ABB. Basedon a common platform of voltagesource converters (VSC), SVC Light alsoprovides solutions for power condition-ing applications in transmission systems.The Eagle Pass tie is a good example of a project in which the VSC platformis configured as back-to-back HVDC,although functionally with priority givento voltage support with the dual SVCLight systems.

Most important in this respect is the factthat installation of active power transfercapability, using HVDC Light across acertain distance or in a back-to-backconfiguration, will provide both bidirec-tional active power and dynamic reac-tive power support simultaneously.Thus, strong voltage support is readilyavailable along with the steady-statepower transfer.

The Eagle Pass substation (operated byAmerican Electric Power, AEP) is locat-ed in a remote part of Texas, on theMexican border, and is connected to theTexas transmission system through two138-kV transmission lines. The nearestsignificant generating station is located

1) SVC Light is a product name for an IGBT-

based static synchronous compensator from

ABB.

The Dafang 500-kV series capacitors1


145 km away and provides very littlevoltage support to the Eagle Pass area.Eagle Pass also has a 138-kV trans-mission line that ties into Piedras Negrassubstation (operated by CommissionFederal Electricas, CFE) on the Mexicanside. This is used mainly in emergenciesto transfer load between power systems,but such transfers involve interruptingthe power as the CFE and AEP systemsare asynchronous (despite both being60 Hz). To overcome this disadvantage,and also solve problems arising fromincreasing demand, a better solutionwas sought.

ABB’s response: voltage source convertersLoad flow studies demonstrated that theinstallation of a 36-MVAr voltage sourceconverter directly at the Eagle Pass sub-station would provide years of respite.Installation of a VSC is ideal for weaksystems as the alternative, reactivesupport provided by shunt capacitors,decreases rapidly when the voltage isreduced. Extending the scenario, twoVSCs connected back-to-back would not only supply the necessary reactivepower but also allow active powertransfer between the two power sys-tems. A BtB scheme would enable the138-kV line between Eagle Pass andPiedras Negras to be continuously ener-gized and allow the instantaneous trans-fer of active power from either system.

Having the capability to control dynami-cally and simultaneously both activeand reactive power is unprecedentedfor BtB interconnections. This feature isan inherent characteristic of the VSC.

As commutation is driven by its internalcircuits, a VSC does not rely on the con-nected AC system for its operation. Fullcontrol flexibility is achieved by usingpulse width modulation (PWM) to con-trol the IGBT-based bridges. Further-more, PWM provides unrestricted controlof both positive- and negative-sequencevoltages. Such control ensures reliableoperation of the BtB tie even when theconnected AC systems are unbalanced.In addition, the tie can energize, supplyand support an isolated load. In the caseof Eagle Pass, this allowed the uninter-

rupted supply of power to local loadseven if connections to one of the sur-rounding networks were tripped. Bothsides of the tie can also be energizedfrom ‘across the border’, without anyswitching that could involve interrup-tions of supply to consumers.

The back-to-back installationA simplified one-line diagram of the BtBtie in Eagle Pass is shown in .2

The BtB scheme consists of two 36-MVA VSCs coupled to a common DCcapacitor bus. The VSCs are of the NPC(neutral point clamped) type, alsoknown as three-level converters. EachVSC is connected to a three-phase setof phase reactors, each connected to a conventional step-up transformer on its respective side of the BtB. Thelayout of the BtB installation is shownin .

BtB operating modesThe two VSCs of the BtB can be con-figured for a wide range of differentfunctions. At Eagle Pass, the main BtBoperating configurations are as follows:

Voltage controlActive power controlIndependent operation of the twoVSCsContingency operation of the BtB

Voltage control

In this mode, both the AEP and CFEsystems are capable of independentvoltage control. The BtB provides therequired reactive power support onboth sides to maintain a pre-set voltage.Active power can be transferred from

3

EaglePass

VSC VSC

PiedrasNegras

Single-line diagram of back-to-back tie at Eagle Pass

2

Eagle Pass back-to-back tieForeground: 138-kV equipment and harmonic filters. Middle: buildings with convert-ers, controls and auxiliaries. Back: cooling towers for water-cooled IGBT converters

3


either side while a constant system volt-age is maintained on both. Any activepower transfers that are scheduled areautomatically and instantaneously low-ered, if required, by the control system

to supply the reactive power needed tomaintain a constant voltage.

Active power control

In this mode, active power can be trans-

ferred between the AEP and CFE sys-tems. Power transfer is allowed whenthe voltage is within a dead-band. If thevoltage lies outside it, the BtB automati-cally reverts to voltage control mode.The active power flow is then automati-cally and instantaneously lowered bythe BtB to provide the required reactivepower support. The dead-band is de-signed so that local capacitor switchingor changes in remote generation thatcause slight voltage swings do not causethe BtB to switch to the voltage controlmode.

Independent operation of the two VSCs

Should maintenance be required on oneside of the BtB, the other side is stillable to provide voltage control to eitherside of the tie. This is done by openingthe DC bus, splitting it into two halves.As the DC link is open, no active powercan be transferred between the twosides of the BtB. Each VSC will then becapable of providing up to ±36 MVAr ofreactive support to either side.

Contingency operation of the BtB

If one of the 138-kV lines into the EaglePass substation is lost, the remaining138-kV line can only support 50 MW ofload at the substation. Should this occur,the voltage falls below 0.98 pu and theBtB switches to the voltage controlmode. Active power is reduced auto-matically and instantaneously to makesure the 50-MW load level at the substa-tion (AEP load plus the export to CFE)is not violated. The BtB supplies therequired reactive support to maintain a1-pu voltage. Load flow studies haveshown that the transmission line contin-gency on the AEP side will have littleimpact on the power transfers from AEPto CFE.

Dynamic performanceThe recording reproduced in illus-trates well the highly dynamic perform-ance of the BtB Light installation atEagle Pass. Plots 1–7 show how the BtBresponded to lightning conditions in aremote area that caused a voltage dip in the AEP network. During the fault,the BtB current (capacitive) was in-creased to almost 1 pu to support thebus voltage at Eagle Pass.

4

-1.5-1.0-0.5

00.51.01.5

PCIA 20000913 17;10;19 Uac Primary Sys A

PCIC 20000913 17;10;19 Iac P1 C

PCIA 20000913 17;10;19 Iac Sys A

PCIA 20000913 17;10;19 Uac Sys A

PCIA 20000913 17;10;19 PQ Ref Sys A

PCIA 20000913 17;10;19 Udc Sys A

PCIC 20000913 17;10;19 Uac S1 C

ABC

-500

-250

0

250

500ABC

-1.5-1.0-0.5

00.51.01.5

ABC

-1.5-1.0-0.5

00.51.01.5

ABC

-40

-20

0

20

40ABC

0.8

1.0

1.2

1.4U+U-

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0-1.0

-0.5

0

0.5

1.0PQ

1

2

3

4

7

6

5

1 AEP 138-kV voltages2 AEP step-down transformer secondary

currents, in amps3 AEP phase reactor currents4 AEP 17.9-kV voltages

5 AEP 17.9-kV phase-to-ground voltages, in kV

6 DC voltages7 AEP converter, active (P) and reactive

power (Q) reference

Eagle Pass back-to-back tie: remote fault case4


Channel Tunnel rail linkWhen the high-speed electrified railwayline between London and the ChannelTunnel to France is finished in 2007 itwill be possible to travel between Lon-don and Paris in just over two hours, at a maximum speed of 300 km/h. Therailway power system is designed forpower ratings in the range of 10 MWand which fluctuate (rapid accelerationand retardation). The traction feedingsystem that was supplied by ABB is amodern 50-Hz, 2 × 25-kV supply incor-porating an autotransformer scheme tokeep the voltage drop along the tractionlines low. Power step-down from thegrid is direct, via transformers connect-ed between two phases .

SVCs for the three traction feedingpointsA major feature of this power system isthe static VAr compensator (SVC) sup-port, the primary purpose of which is tobalance the unsymmetrical load and tosupport the railway voltage in the caseof a feeder station trip – when two sec-tions have to be fed from one station. The second purpose of the SVCs is toensure a low tariff for the active powerby maintaining unity power factor dur-ing normal operation.

Thirdly, the SVCs mitigate harmonicpollution by filtering out the harmonicsfrom the traction load. This is importantas strict limits apply to the traction sys-tem’s contribution to the harmonic levelat the supergrid connection points.

The SVCs for voltage support only areconnected on the traction side of the in-terconnecting power transformers. The

5

supergrid transformers for the tractionsupply have two series-connected medi-um-voltage windings, each with its mid-point grounded. This results in twovoltages, 180 degrees apart, betweenthe winding terminals and ground. TheSVCs are connected across these wind-ings; consequently, there are identicalsingle-phase SVCs connected feeder toground and catenary to ground.

The traction load of up to 120 MW isconnected between two phases. With-out compensation, this would result inan approximately 2 % negative phasesequence voltage. To counteract theunbalanced load, a load balancer (anasymmetrically controlled SVC) hasbeen installed in the Sellindge substa-tion. This has a three-phase connectionto the grid.

The load balancer transfers active pow-er between the phases in order to createa balanced load (as seen by the super-grid). A brief explanation of how theload balancing works is given in thefollowing.

Load current

When the load is connected betweentwo phases (B & C) only, the tractioncurrent can be expressed by two phasevectors, one representing the positivesequence and the other the negativesequence . The summation of the twovectors is the resulting current (currentin phase A is zero and currents in phaseB and C are of equal magnitude, but ofopposite phase). Note that the vectoramplitudes are not truly representative.To compensate the negative sequenceand thus balance the current to be gen-

6

TCR 3rd

25 kV 25 kV 40 MVAr45 MVAr

40 MVAr45 MVAr

400 kV

SVC

Catenary

Feeder

5th 7th

TCR 3rd 5th 7th

=+ Ia

Ib

IcIc

Ib

Ia

Ic

Ib

ILOAD

I+LOAD I-LOAD

=+ Ia

Ib

IcIc

Ib

Ia

Ib

Ic

ILOAD

I ILB LB +ILOAD

Phase-sequence components of the load current6 Load current balancing7

Power feeding system for the Channel Tunnel rail link between England and France. Singlewell substation with two single-phase static var compensators,each rated 25 kV, –5/+40 MVAr

5


erated by the power systems, the loadbalancer generates a (pure) negative-phase sequence current, (ILB), as shownin . This current balances exactly thenegative-phase sequence current fromthe load (I-LOAD in ).

The load balancer in the Sellindge sub-station is optimized to handle a loadconnected between the C and A phas-es. Load balancing theory says that, tobalance a purely active load, a capaci-tor has to be connected between phas-es A and B and a reactor betweenphases B and C. The traction load alsohas a reactive part, which likewise hasto be balanced. In this substation, notonly the asymmetry is compensated butalso the power factor. This is achievedby inserting a capacitor between phasesC and A.

Redundancy

High availability is required, so all criti-cal components are redundant: A com-plete fourth redundant phase has beenadded in the main circuit. All the phasesneed to be as independent of eachother as possible.

These requirements have resulted in a unique plant layout and design forthe control and protection. There arefour fully independent ‘interphases’ (an assembly of components connectedbetween two phases). Each interphasefeatures an independent set of filters,reactors, thyristor valves, thyristor firing

8

6

7

logic circuits, measuring transformers,relay protection devices and coolingsystem. Each of the connections to thesubstation busbars has a circuit-breakerand disconnector inserted in it. Filterscan be connected to or disconnectedfrom the fourth interphase to turn itinto either an inductive or a capacitivebranch.

Two independent control systems acton the three-phase system, while thethyristor firing and logic circuits actdirectly on each interphase. The con-trol systems are strictly segregated, asare the valve-firing logic circuits andthe overall protection system. If aninterphase fails, the control systemtrips it and automatically substitutes the standby unit.

The thyristor valves make use of a newtype of thyristor – a bidirectional devicewith two antiparallel thyristors on acommon silicon wafer. This halves thenumber of units needed in the valves.The thyristor is a 5-inch device with acurrent-handling capability of about 2000 A(rms).

Summary and outlookThe importance of improving grid per-formance is growing for economical aswell as environmental reasons. FACTSdevices have established themselves as the most suitable solutions for in-creasing power transmission capabilityand stability.

The Dafang project is a classic exampleof a transmission capacity upgrade pro-viding much-needed power to a fast-growing area, in this case the regionaround Beijing. The project was com-pleted in the extremely short time of nine months and brings existing,remotely generated power to an areawhere it is urgently needed.

The case of Eagle Pass shows the pos-sibilities offered by new technologiesable to combine advanced FACTS prop-erties with network interconnectioncapability. The latest developments insemiconductor and control technologyhave made this possible. Thanks to thisback-to-back tie, existing transmissionfacilities can be utilized to a muchgreater extent than before.

Finally, the Channel Tunnel rail linkillustrates well the flexibility of FACTSdevices by showing how they can alsobe used to solve the problems createdby new, sophisticated types of load. The unbalance caused by new tractionloads, for example, can be mitigated,and downgrading of the electricity sup-ply for other users avoided, by meansof the described solid-state solutions.

These examples show that FACTS de-vices will be used on a much widerscale in the future as grid performancebecomes an even more important factor.Having better grid controllability willallow utilities to reduce investment inthe transmission lines themselves. ABBis currently exploring ways in whichFACTS devices can be combined withreal-time information and informationtechnologies in order to move themeven closer to their physical limits.

TCR

TCR

3rd

25 kV 25 kV

2x42 MVAr

84 MVAr

400 kV

33 kV

Catenary Standbyphase

Feeder

5th

7th

Rolf Grünbaum

Åke Petersson

Björn Thorvaldsson

ABB Power TechnologiesSE-721 64 Västerås

[email protected]

Circuit of dynamic load balancer in Sellindge substation (33 kV, –80/+170 MVAr) 8


The spectacular dune landscapes of Namibia are a key factor in the country’s booming tourist

industry and a valuable source of revenue for the nation. Another, even more important pillar of

the Namibian economy is the power-hungry mining industry. To cope with growing energy demand

in these two sectors and to ensure a reliable power supply for the country as a whole, NamPower,

Namibia’s national electricity utility, has installed a new 400-kV AC transmission system linking its

grid system with the Eskom grid in South Africa. Voltage stability problems, which the new line

would have aggravated, have been resolved by installing a static var compensator from ABB.

Power Rolf Grünbaum, Mikael Halonen, Staffan Rudin

factor!ABB static var compensator stabilizes Namibian grid voltage


While construction of the new linehas brought reliable power to

Namibia, it was not without problems ofits own. The line’s length of 890 km, forinstance, aggravated certain problems –mainly voltage instability and near 50-Hz resonance – that already existedin the NamPower system.

An ABB static var compensator (SVC) rat-ed from 250 MVAr inductive to 80 MVArcapacitive has been installed to solvethese problems. The turnkey project wasconcluded with the successful commis-sioning of the SVC in NamPower’s Auas400-kV substation , just 18 monthsafter the contract was signed.

The case for a new 400-kV gridPower consumption in Namibia is con-centrated in Windhoek and in the north-ern region, where most of the miningand mineral industry is located. Until re-cently, the NamPower grid consisted of aradial network, with bulk power suppliedby the Ruacana hydro-station in the northvia a 520-km 330-kV transmission circuit,linked by an 1000-km 220-kV intercon-nection to Eskom’s system in the south.

This network was often loaded to itsstability limits during low-load periods

1

when Ruacana was not providingpower. The system is also unique forits long 220-kV and 330-kV lines andthe fact that the loads are small incomparison with the generationsources – two features that furtheraggravated the stability problems inlow-load conditions.

To solve these problems, the utility de-cided to build a 400-kV grid. The finalphase of construction – a 400-kV inter-connection between Auas and Koker-boom – was completed in 2000. Thissingle-circuit 400-kV AC transmissionline strengthens the NamPower systemby connecting it to Eskom’s system in

2

Auas static var compensator1

NamPower network2

1, 2 Existing system, with four and no generators3, 4 New system, with four and no generators5, 6 During 400-kV energization, with four and no generators

System impedance/frequency characteristics (a) and system near 50-Hz resonance (b)3

1000

800

600

400

200

0

Ohm

s

0 50 100

f (Hz)

1

5

6

2

1000

800

600

400

200

0

0 100 200

f (Hz)

1

2

34

Ohm

s

a b


the south. However, with a length of890 km it is also very long, in fact oneof the longest lines of its kind in theworld. This and the network’s tree-likeconfiguration, coupled with remote gen-eration and the very long radial linesoperated at high voltage, results in thecharging capacitance being high. Theeffect of this is to shift the existing par-allel resonance closer to 50 Hz, makingthe network more voltage-sensitiveduring system transients, for examplewhen the 400-kV line is energized orduring recovery after a line fault clear-ance. Each of these phenomena mani-fests itself as an extremely high andsustained overvoltage.

Resonance and overvoltagesThe NamPower network has a first nat-ural parallel resonance frequency wellbelow 100 Hz, namely in the 55–70 Hzrange (curves 1 and 2 in ).

The effect of adding the new 400-kVline section (Aries-Kokerboom-Auas)and its four 100-MVAr shunt terminalreactors has been to shift the system’sfirst resonance into the 60–75 Hz fre-quency range (curves 3 and 4). (Thereduction in system impedance at 50 Hz is due to the new 400-kV line,

3

and an indication of how the systemhas been strengthened.)

Curves 5 and 6 in show the networkimpedance as seen at the Auas 400-kVbus the instant the 400-kV line is ener-gized from the northern section (fromthe Auas side) and before the circuit-breaker on the Kokerboom side isclosed.

The impact of the resonance problemin the NamPower system is best illus-trated by simulating the condition atAuas substation, represented by curve6. The voltage situation is shown in ,in which the line circuit-breaker atAuas is closed at time t = 1.0 s and it is assumed that the breaker at Koker-boom is synchronized at t = 1.2 s. Dueto the large charging capacitance of theline the voltage first dips, then over-shoots.

The extremely high overvoltages ap-pearing at Auas, with a peak value inexcess of 1.7 pu and a sustained tran-sient overvoltage (TOV) of more than1.5 pu, attest to the severity of the prob-lem. It is clear that as soon as 50-Hzresonance is triggered very high dynam-ic overvoltages appear with large timeconstants under certain system load andgeneration conditions.

Preliminary studies indicated that over-voltages would appear that would makethe Nam-Powersystem in-operableunlessvery fast,effectiveand reli-ablecountermeasures are taken. Several solu-tions were considered as an answer tothe resonance problem, including fixedand switched reactors, before deciding toinstall a FACTS device in the Auas sub-station. Preference was given to conven-tional, proven SVC technology [1].

SVC design featuresThe Auas SVC has a dynamic range of 330 MVAr (250 MVAr inductive to

4

3

80 MVAr capacitive) and is installedprimarily to control the system voltage,in particular the extreme (up to 1.7 pu)overvoltages expected as a result of thenear 50-Hz resonance. An uncommonfeature of the project is that the SVC isinstalled in a system with very longlines, little local generation and faultlevels lower than 300 MVA.

The SVC that is installed is of a newtype, developed by ABB for power ap-

plications.Its uniquecontrolprinciplehas sincebeenpatented.The in-ductive

power of 250 MVAr is provided by threethyristor-controlled reactors (TCRs), afourth, continuously energized TCR be-ing always on standby . Two identi-cal double-tuned filters, each rated at 40 MVAr, take care of harmonics andsupply capacitive reactive power duringsteady-state operation.

High availability is essential for the AuasSVC. If, for any reason, it should have

5

Studies showed that overvoltagescould make the NamPower systeminoperable unless very fast, effec-tive and reliable countermeasuresare taken.

The blue, green and red curves represent thedifferent phases (instantaneous values).

Energization of the Auas-Koker-boom 400-kV line from thenorthern section, without the SVC

4

600

400

200

0

-200

-400

-600

V (k

v)

0.95 1.00 1.05 1.10 1.15 1.20 1.25

t (s)

X

400 kV Auas substation

400 kV/15kVSVC transformer

15 kV

TCR1 TCR2 TCR3 TCR4 Filter1 Filter2

(spare)

Auxsupply

Single-line diagram of the AuasSVC

5

should be thelast transform-ers in the Nam-Power systemto go into satu-ration.

TCR reactor

and valve

Each TCRbranch consistsof two air-corereactors con-nected on eachside of athyristor valve.The reactorshave specialexterior sur-faces to protectthem from theeffect of sandstorms and sunin the harshdesert environ-ment.

A secondary voltage of 15 kV was cho-sen as an optimum value for both thethyristor valve and busbar design. Thethyristor valves consist of single-phasestacks of antiparallel-connected thyris-


to be taken out of service, the 400-kVtransmission system could not be oper-ated without risking dangerous overvolt-ages. As a result, an availability figure of 99.7 % was specified, and this strong-ly influenced the design, quality, func-tionality and layout of its componentsand subsystems as well as of the SVCscheme as a whole.

Operating range

The Auas SVC provides resonance controlover its entire operating range , whichextends well beyond its continuous range.Controlled operation is possible all theway up to 1.5 pu primary voltage – a nec-essary feature for controlling the reso-nance condition. Besides providing reso-nance control, the SVC also controls thepositive-sequence voltage (symmetricalvoltage control) at the point of connec-tion.

Single-phase transformers

Four single-phase transformers, includ-ing one spare, are installed. Due to thehigh overvoltage demands made onthem during resonance these transform-ers have been designed with a lowerflux density than standard units; they

6

tors (16 thyristors, two of which areredundant, in each valve). Snubbercircuits (series-connected resistors andcapacitors) limit overvoltages at turnoff.The thyristors are fired electrically usingenergy taken directly from the snubbercircuit.

An overvoltage protection device limitsthe voltage that can appear across thevalve, being triggered by control unitsthat sense the instantaneous voltageacross each thyristor level.

Redundant TCR branch

Three TCR units rated at 110 MVAr havebeen installed to cope with the Nam-Power network’s sensitivity to reactivepower and harmonic current injections.A fourth, identical TCR is kept on hotstandby. The SVC control system auto-matically rotates the current standbyTCR unit every 30 hours to ensure equaloperating time for all units.

Redundant cooling system

An unusual feature of the Auas SVC isthat each TCR valve has its own coolingsystem, making four in all. Thus, outagetime is minimized and availability is in-creased. A water/glycol cooling mediumis used to avoid freezing in case of aux-

V/I characteristic, showing the possible steady-state andtransient operating points of the SVC

6

The colored area represents continuous SVC operation. Above this area, the SVC can be operated up to 1.2 pu voltage for 3 s, up to 1.3 puvoltage for 400 ms, and up to 1.5 pu voltage for 300 ms.

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

V(p

u)

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.2 2.5 3.0 3.5 4.0

Capacitive I (pu) Inductive

3 s

400 ms

300 ms


iliary power outages during the colddesert nights.

Filter branches

The required capacitive MVAr are pro-vided by two 40-MVAr filter banks. Eachfilter is double-tuned to the 3rd/5th har-monics and connected in an unground-ed configuration. The double-tuneddesign was chosen to ensure sufficientfiltering even in the case of one filterbecoming defective.

Black-start performanceSince the SVC is vital for operation ofthe NamPower system, everything hasto be done to avoid the SVC breakertripping, even during a network black-

out. In such a case the network couldbe energized from the Eskom side andthe SVC would have to be immediatelyready to control a possible resonancecondition. To handle this task, the SVChas three separate auxiliary supplies,one of which is fed directly from theSVC secondary bus. The SVC is capableof standby operation with its MACH 2controller active for several hours with-out auxiliary power, and automaticallygoes into resonance control mode assoon as the primary voltage returns.

Worst-case situation:energization from north to southThe worst–case scenario for the SVC andthe Nampower system is energization ofthe 400-kV line from the northern section(Auas substation). This system condition,which initiates the critical 50-Hz reso-nance, was therefore simulated in a real-time digital simulator with and withoutthe new resonance controller. As shownin the overvoltage that appears atAuas is 1.62 pu with a conventional PIcontroller. (The two resonance frequen-cies – 56 Hz and 81 Hz – that can beseen in the result correspond to the sys-tem’s first and second pole, respectively.)The new resonance controller has a con-siderable impact on the system’s behav-ior and the voltage controller’s addition-al contribution forces the SVC to be-come inductive. As a result, the peakvoltage appearing at Auas is reduced toa value of 1.32 pu.

7

Real-time digital simulation. 400-kV line energized from the north, with and withoutthe new resonance controller

7

1.8

1.6

1.4

1.2

1.0

0.8

0.6Volta

ge /

400

kV (

pu)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

t (s)

a)

0.5

0.0

-0.5

-1.0

-1.5

-2.0

-2.5

-3.0

Bre

fDI (

pu)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

t (s)

b)

0.5

0.0

-0.5

-1.0

-1.5

-2.0

-2.5

-3.0

Bre

fAdd

(pu)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

t (s)

c)

a Voltage response, 400 kVb SVC controller outputc Impact of resonance controller

Red Conventional PI controllerBlue Resonance controller


Rolf Grünbaum

Mikael Halonen

Staffan Rudin

ABB Power TechnologiesSE-721 64 Västerås

SwedenFax: +46 21 18 31 43

[email protected]

functions and the interconnection pro-tection scheme. The performance ofthe SVC is shown in . As the results

show, theSVC con-trols thevoltageand theresonancecontrollerforces theSVC to

become fully inductive in resonanceconditions. The fault is initiated at t = 4.9 s and is cleared by opening the faulty phase in the Auas-Koker-boom line. A single-phase auto-reclo-sure is initiated after 1.2 s, starting withthe breaker on the Kokerboom side.

8

SVC performance. Results of a phase-to-ground fault in the Auas substation8

1.2

1.0

0.8

0.6

pu

4.5 5.0 5.5 6.0 6.5

1

0

-1

-2

pu

4.5 5.0 5.5 6.0 6.5

BrefDI

1

0

-1

-2

pu

4.5 5.0 5.5 6.0 6.5

t (s)

BrefADD

Voltage response, 400 kV SVC controller output Impact of resonance controller

The overvoltage at Auas is reduced to1.14 pu.

Easier cross-border power sharingAs a result of installing the ABB SVC,the resonance problems that had pre-viously plagued the Namibian grid are a thing of the past. Southern Africa’sstate energy sectors can now be moreeasily integrated and power more easilyshared. And the growing demand forpower – the motor driving the region’seconomic ambitions – can be moreeasily met.

This extreme test was also performedin the field. Comparison of the simula-tion results and the system perfor-mance testshowsvery goodagreementand un-derlinesthe im-provementcapabilityof the new resonance controller underresonance conditions.

Staged fault testAfter the Auas substation had beencommissioned, a phase-to-ground faultwas used to test various SVC control

As a result of installing the ABBSVC, the resonance problems thathad previously plagued theNamibian grid are a thing of thepast.

References

[1] R. Grünbaum, M. Noroozian, B. Thorvaldsson: FACTS – powerful systems for flexible power transmission. ABB Review, 5/1999.


Power transformers at critical nodes inelectricity networks lead stressful

lives. Reliability is everything. Loadpeaks – predictable as well as unexpect-ed – generate high temperatures, whichshorten component lifetime. In the worstcase sudden failure can occur, causinghavoc in the network. It is because of

this risk, and the penalties that can attachto it, that utilities give such a high priori-ty to controlling and monitoring the sta-tus and condition of their transformers.This lets them intervene before failure ormalfunctioning can occur. Increasingly,for many utilities, the watchword is ‘earlydetection of failure conditions’.

Enter the ‘intelligent transformer’Deregulation of the energy markets hasbrought about a paradigm shift andfocused attention on, among otherthings, asset management and remain-ing life management. As a result, anincreasing number of power transform-ers around the world are being equip-

Advanced transformer controland monitoring with TEC

Getting the most out of electrical equipment is

vital to energy enterprises in today’s increas-

ingly deregulated world. With power trans-

formers making up a substantial part of that

equipment, it is little wonder that utilities put a

premium on enhancing the lifetime and perfor-

mance of these industry workhorses.

Conventional control and monitoring schemes

rely on past results – good enough, perhaps,

for routine maintenance and non-critical units,

but not to keep transformers performing con-

stantly, and unfailingly, at the highest level.

Not so ABB’s TrafoStar Electronic Control

(TEC) system. This models the actual state of

the transformer, creating a ‘virtual copy’ that

provides the parameters required to optimize

cooling as well as the data utilities need for

condition-based maintenance.

Transformingtransforming

Lars Jonsson


ped with monitoring devices. As thistrend intensifies and more and morefunctionality is added, transformers arelikely to play a new role – as ‘intelligentunits’ – in future transmission networks.

The trouble with many transformermonitoring systems is that they are notable to control or make decisions andrecommendations based on the avail-able data, forcing engineers to spend alot of time sorting and interpreting theinformation they receive. This is thestrength of TrafoStar Electronic Control(TEC) . TEC receives all the informa-tion it needs for transformer controlfrom just a few multi-purpose sensors;other necessary parameters are calcu-lated. Thus, TEC adds only minimalcomplexity to the transformer.

1

To achieve the goal of making powertransformers ‘intelligent’ and mainte-nance-free, ABB created and integrateda common electronic interface that ex-changes information with the followingapparatus:

Monitoring and diagnostics devices ofthe transformer and componentsTransformer control cabinetTap-changer motor-driveOverall protection system

Through this interface, TEC provides ex-act status information to enable utilitiesto extend transformer lifetime and savecosts by reducing maintenance and in-creasing availability.

It does this by generating a model ofthe transformer and its working condi-

tion and then comparing the measuredparameters with the simulated values.Discrepancies are detected and potentialmalfunctions and/or normal wear in thetransformer and its ancillaries are indi-cated.

As ABB’s fully integrated control andmonitoring solution making use of oneoriginal set of multi-purpose sensorsand employing specific transformerdesign data, TEC is the latest addition toa product portfolio that already includesthe ABB T-Monitor. The T-Monitor is aproven retrofit solution that providesadequate predictive power by means ofeasily fitted add-on sensors and modelsthat require less detailed informationabout the transformer and its compo-nent design.

TEC architectureThe system hardware and softwarefeatures proven ABB technology andhas been designed to allow extra func-tionality to be added in the future. Be-ing microprocessor-based, the systemhas more flexibility than a PLC andprovides a more stable platform than aPC solution.

TEC gets its capability to control andmonitor not only from its superiorsoftware, but also from the fact that ithas unlimited access to all the infor-mation it requires. It knows everything

The main parameters can beviewed on-line on the TEC frontpanel or on a PC terminal.

2

TEC receives the information it needs for transformer control from just a few multi-purpose sensors.

1


about your transformer. This ‘knowl-edge’ begins with the transformerdesign data. Next, temperatures andloss-related parameters obtained fromthe transformer heat-run test are fed in.So much data is transferred to the TECsystem that it becomes a virtual trans-former copy. Each transformer has its own fingerprint, with all the para-meters needed for optimized control.The model created by TEC works insimulated conditions but reacts in thesame way that a real transformer would.

The main parameters are processed inthe TEC cabinet and transferred to the station PC via a single optic fiber. They are made available to theoperator via easy-to-use software and a display.

TEC and IndustrialIT

IndustrialIT [1] has been introduced byABB as an architecture for seamlesslyinterconnecting all our Group’s prod-ucts, solutions and processes. More thanthat, it allows our customers, servicepartners and third parties to connectwith them too. Industrial IT enables thetotal integration of business processeswith real-time and lifetime data manage-ment. As a consequence, utilities will beable to substantially improve the effi-ciency of their business.

Utility assets, such as power transform-ers, are prime candidates for such real-time integration. And TEC is an idealmeans of integrating them. It will becertified to Level 2 (Integration), mean-ing that it will not only be informationenabled and capable of connection toand working well in an Industrial ITsystem, but also be able to exchangeextended data, like status and mainte-nance data, via defined protocols. Sys-tems with Industrial IT Enabled com-ponents offer a variety of advantages,including ‘plug and produce’ capability.Disturbances are reduced at the sametime that flexibility is increased.

Feature overviewTEC offers a whole range of functionsdesigned to let utilities use their trans-formers to the maximum. Until now,service criteria have been based on loadassumptions and the results of the lastservice. TEC changes all this. Real-timeinformation opens up new possibilitiesfor optimizing operation and mainte-nance.

Cooling/overload forecastTraditionally, transformer cooling is atwo-step system, with the option of50 % or 100% capacity. With TEC, sixsteps are possible, according to load,ambient conditions and cooler status.

The coolers are controlled individuallyand can be started prior to an anticipat-ed load increase. This reduces thermalstress and adds hours of operation atmaximum capacity.

TEC advanced cooling control is basedon algorithms that calculate the heatlosses and the number of coolers re-quired to dissipate them. It also keepstrack of the number of hours each fan isin operation and runs all motors accord-ingly. As input, TEC receives data onthe actual and/or predicted load andambient conditions. Armed with this in-formation, the system is able to respondimmediately to load peaks, and thecooling capacity can be better adaptedto actual demand. Further, it can simu-late the results for a specific load condi-tion or forecast the maximum overloadduration based on the hot-spot results.

Real-time status/availabilityThe parameters measured during serviceare compared with the simulated values.The transformer model detects discrep-ancies and indicates potential malfunc-tions and/or normal wear in the trans-former itself, the cooling equipment andthe tap-changer.

Real-time information from temperaturesensors and from optional moisture sen-

Start panel showing a transformer model with basic data

3TEC users can easily access more detailed informationas well as transformer or tap-changer documentation.

4


sors is stored by the TEC system. If re-quired, a hydrogen detector can bemounted on the tank to obtain an earlyindication of potential problems in atransformer winding.

A rolling LCD on the front panel showsthe main parameters together with athree-lamp status ‘traffic light’ (green/yellow/red). The same information canbe viewed on a PC terminal, either inthe substation control room or at aremote location .

LifetimeTemperature control, based on overloadforecasting and winding hot-spot calcu-lations, allows the consumed lifetime tobe computed in accordance with the lat-est IEC and IEEE standards.

Event recordingTEC also keeps track of transformertrips and alarms, recording the actualevents as well as the sequence to assist

2

operators in determining their rootcause.

Condition-based maintenanceThe status traffic light identifies themost heavily worn contact in the tap-changer, based on the actual loadduring each operation. The user seeswhen the next service is due.

Oil treatment is condition-based, beingdependent on the development of mois-ture as indicated by the temperatureand (optional) moisture sensor in thetap-changer compartment.

Early warning is given of any increasein tap-changer temperature beyond thenormal value.

Operation and updatesThe user interface runs in the Windowsenvironment. The PC start panel shows a transformer model with basicdata such as the top-oil and bottom-oil

3

temperatures, up to three hot-spot tem-peratures, the apparent power and thetap-changer position and operations.More detailed information can be ob-tained by clicking on the object on thetransformer model or by pressing one ofthe status information buttons.

All of the transformer and tap-changerdocumentation, including instructionfilms, can be viewed on the PC in thecontrol room or any other place ofconvenience .

Tried and provenEnvironmental tests, hardware/softwarefunctional tests and on-site tests in vari-ous parts of the world have shown thatthe system is well suited for substationenvironments.

ABB’s extensive experience with elec-tronic equipment in harsh industrial envi-ronments has also been incorporated inthe design of the TEC . For example, itis EMC compliant and vibration proof.

A modular systemTEC is the first of a generation, andABB continues to investigate new ap-proaches and ways to improve thesystem as a whole and in part. Furtherparameters for the transformer, tap-changer and bushings will be includedin the future. TEC’s modular designmakes this easy, and provides theflexibility that will ensure its success asan innovative and cost-saving product.By giving utilities the means to monitor,and thereby optimize, the way theyoperate their power transformers, TECcan be said to be truly transformingtransforming.

5

4

Reference[1] C. Rytoft, B. Normark: IndustrialIT and the utility industry. ABB Review 3/2002, 23–28.

Lars Jonsson

ABB Power TechnologiesPower Transformers

Ludvika, [email protected]

TEC electronics – tried and tested5


Power Systems Consulting

Amid the regulatory transformation that is revolutionizing the utility market,

reliability and economics stand out as the factors driving financial and

operating performance. To get the best return on their assets and perform

at the highest level, utilities are turning to solutions that integrate the

domain competence of consulting experts with the very latest software

tools. New methods for optimizing performance costs have been developed

in the course of several recent projects undertaken by ABB.

Rana Mukerji

Power systems consulting is a keyABB offering, enabling customers to

plan, operate and maintain their systemsin a more economical and reliable way.Consulting work in which ABB is en-gaged covers a broad spectrum, and in-cludes:

Planning for grid upgradesSystem performance issues related tovoltage, thermal and dynamic stabilityconstraintsEvaluating and enhancing grid relia-bilityForecasting demand growth for distri-bution companiesBenchmarking of utilities relative toglobal ‘best in class’ peer groupsAsset evaluation and reliability cen-tered maintenance planningTechnical due-diligence in support ofmergers and acquisitions

The ABB Consulting group is a globalteam of more than one hundred powersystems experts with local presence inthe USA, UK, Germany, Spain, Sweden,Italy, India and China. ABB consultantsare backed up by over 6000 product,systems and service specialists in loca-tions close to our customers, enablingthe company to identify and implementtotal system solutions.

Changes for the betterJust as the rest of the power industryhas changed dramatically within the lastdecade, the art and science of transmis-sion and distribution planning is fun-damentally different from what it wasten years ago. Deregulation and perfor-mance-based regulations are changingthe framework within which plannersand system operators work. Considera-

tion has to be given to new technolo-gies on both the load side and the sup-ply side. The changes cover the spec-trum of regulatory policy, technology,competition and industry economics.

In recent years, a strong global econo-my has resulted in demand growth inmost companies’ service territories. Inthe majority of companies, even thosewith overall flat growth, there are pock-ets of relatively strong load growth inthe system for which planners mustspecify the infrastructure. More thanever, utility planners need to be awareof the equipment installed in the sys-tem, as well as its current condition.

Generally, customers also expect a levelof reliability as good as, or better than,the reliability they have been used to in


the past. An increasing number of cus-tomers operate businesses today thatare sensitive to reliability and the quali-ty of service. It is therefore importantfor utilities to have the tools to system-atically analyze cost/performance trade-offs within the financial constraints im-posed on them. Similarly, the benefits ofavailable funds should be maximized.This often implies changes to standards,guidelines and procedures.

Interpreting such changes and develop-ing new optimization methods andstate-of-the-art software to assist utilitiesin meeting these challenges is whereABB has vast experience. In just the lastfive years, new methods for optimizingperformance costs have been developedthat allow the domain competence ofconsulting experts and software tools tobe integrated in a web-based data ware-housing tool. These new methods let usfocus on the most cost-effective ways to obtain maximum performance for asystem and utilization of assets.

The following two examples show howABB’s experience can be the key factor

in creating optimal, cost-effectivesolutions for customers based on keyperformance indicators.

Reuniting BerlinOn March 5, 1952, as a result of thepolitics of the time, the electrical supplysystem of Berlin was divided into twosections, one for the eastern and onefor the western zone. Now, five decadeslater, the two networks, like the twohalves of the city, are reunited, havingbeen incorporated in the German inter-connected grid. For Berliner Kraft- undLicht (Bewag) AG, the utility respon-sible for running the network in thewestern half of the city, joint operationof the two networks posed certainproblems. Besides the obvious need forstandardization – different systemphilosophies had developed over theyears – it was also apparent that a con-cept was needed for the city’s electricitysupply in the longer term.

Investigations were carried out to findan optimal concept for the reunited dis-tribution networks of Berlin that took all factors into account. Bewag and

ABB formed a joint planning group todevelop the approach. Its main objec-tive was to make the two networksmore compatible so that the city wouldbe able to cope with future electricitydemand.

One of the issues looked at especiallyclosely was the reliability of the down-town area networks, and at ways toincrease it without making any basicchanges to the supply concept. In par-ticular, it was necessary to find out if,and what, additional investments mightbe required to achieve the goal ofhigher reliability.

With the help of advanced mathematicalmodeling of the system componentsand special programs for the calcula-tions, certain system components wereloaded beyond their conventional nomi-nal power. This showed which compo-nents could be utilized more economi-cally. As a result of this study, Bewagdecided to increase the capacity oftransformers and underground cablesused in the networks.

Utility gets resultsThe second example involves an elec-trical utility company providing powerto several regions in Europe. In order tobenchmark some of their guidelines,practices and power quality indexes,they wanted a comparison with utilitiesin Germany and the United States thatwould identify ‘best practices’. To thisend, studies were carried out in theareas of maintenance, transmission anddistribution planning, and engineeringand operations.

In addition to providing a benchmarkfor these four areas, ABB undertookreliability calculations for the utility’spower distribution system. This wasdone to obtain a baseline for its distri-bution design practices at the time, aswell as an on-site diagnosis of certainfacilities.

ABB found differences between the util-ity’s practices and typical practices inGermany and the USA, especially in themaintenance area. It was seen that achange in procedures could result in

Distribution transformer density data, imported from a utility’s transformer load managementprogram and used in load forecasting


considerable cost savings without signif-icantly affecting reliability. The studyalso recommended use of some of thenewer probabilistic approaches to sys-tem planning which help minimize thecost of new investments.

After receiving the study results, theutility indicated that it was “very impres-sed by ABB’s ability to set up a cross-border team in such a short time tocope with a challenging project with avery tough deadline.”

Business processes and assetutilizationIn another example, ABB instituted ‘bud-get-constrained’ planning policies andmethods appropriate for a regulated US‘wire company’ operating in a compe-titive environment. The project included:

A review of all engineering planningand budgeting procedures, reliabilityrequirements, engineering criteria,planning guidelines, and appropriatestandards, as well as planning, bud-geting and engineering results fromthe past ten years. Development and implementation ofa new planning/budgeting/projectprioritization method based on mar-ginal benefit/cost optimization usingcustomer service quality costs as well as budget cost as an element ofperformance evaluation. Design of an entirely new planningprocess and organization, compatible

with the new planning methodologyand tailored to the company’s newgoals and needs. Seminars and workshops for over 220 engineers, managers and super-visors from 14 operating districts, toconvey the concepts and skills neces-sary to implement the new approach.

Another project undertaken by ABB in-volved investigating the operations andmaintenance history and procedures of aTexas utility’s underground distributionand transmission cable systems in theDallas, Fort Worth and DFW airport ser-vice areas. The investigation includedreliability assessments of the transmis-sion and distribution systems using anetwork model. Also included were in-spections of parts of the utility cable net-works, substations and pumping stations,as well as interviews with utility opera-tions, engineering, and maintenance per-sonnel. The investigation further includ-ed a review of utility standards, guide-lines and documentation relevant to theoperation of the cable network.

Power system performance researchAnother area in which ABB is active is inresearch into power system performanceand the development of new technolo-gies for its improvement. In one suchproject, named ‘Wide Area Disturbance’,we examined, among other things, volt-age instability, overload and out-of-step.

Based on this, we developed a newalgorithm for estimating the proximity to voltage collapse. The method em-ploys only local measurements – busvoltage and load current – and is simpleenough to be implemented in a numeri-cal relay. The relay’s estimation can beused for a number of applications, forexample to enhance local controllers(SVCs, etc) or to direct load shedding.Alternatively, the estimation can be sentto a computing center as support forsystem coordination.

Other completed projects, eg ‘RobustControl of FACTS Devices’ and ‘Controlof Nets, Drives and Converters’, haveexamined the algorithms for dampingpower oscillations under uncertainoperating conditions. Uncertainties

included transmission outages andvarying load profiles. New algorithmsand software for centralized anddecentralized robust controllers weredeveloped and tested by means ofsimulations on realistic system models.

Backing up ABB’s consulting business isdomain expertise and field experienceaccumulated over decades in the powerindustry, plus a global presence thatallows us to bring best practices from all over the world together to help ourutility customers improve their businessperformance.

Load forecast study performed using a commercially available GIS database asstarting point

Screenshot taken from a budget-constrainedplanning software simulation

Rana Mukerji

ABB Power TechnologiesABB Inc.

Raleigh, NC, [email protected]

Special ReportABB Review32

The big pictureDetecting power system instabilities and optimizing asset utilization with InformIT Wide Area Monitoring PSG 850Joachim Bertsch, Cédric Carnal, Andreas Surányi


Developments in the world’s power markets are compelling utilities

to place greater emphasis on asset utilization in order to operate

more profitably. But there is an equal need, as the recent massive

blackouts in North America and Europe showed, to have safeguards

in place that ensure total reliability for the transmission networks.

Increasing attention is therefore being given to the monitoring of

power system dynamics. This requires information of higher accura-

cy and with update rates faster than those normally provided by tra-

ditional SCADA systems. In addition, it has to be synchronized over a

wider geographical area than traditional protection systems allow.

With the introduction of phasor measurement units and recent ad-

vances in communication and computing it has become technically

feasible to take a wide area approach to monitoring power system

stability on-line. InformIT Wide Area Monitoring PSG 850 was devel-

oped as a state-of-the-art platform for just such an approach.

IT-based, it offers solutions designed to optimize asset utilization

as well as to prevent entire power networks from collapsing.

The world has come to depend onelectricity so much that huge efforts

– and investments – have to be made toensure that it flows uninterruptedly.Apart from having to find the capital forthis, the electric utilities are faced withanother problem: market pressures areforcing them to maximize their prof-itability. Together, these factors providea strong incentive for utilities to installtechnology that combines functionalityfor optimizing asset utilization and coststructures with that required to preventpower system outages. This is preciselywhat InformIT Wide Area MonitoringPSG 850 – one of a family of PSG mod-ules/packages that also include widearea protection and control (PSG 870),wide area measurement (PSG 830) andwide area connectivity (PSG 810) (seefigure on page 34) – was developed for.Inherent benefits of the PSG 850 solu-tion include:

Transmission capacity enhancement,achieved by on-line monitoring of thesystem safety or stability limits.

Power system reinforcement (invest-ment planning), based on feedbackobtained during analysis of systemdynamics.Introduction of a coordinated ap-proach to stabilizing actions in casesof severe network disturbance.Triggering of additional functions,such as var compensation. Better understanding of a system’sdynamic behavior.Installation of an early warning sys-tem designed to prevent potentialblackouts.

Data utilization in wide area monitoringMonitoring of entire power systems withPSG 850 is based on dynamic phasormeasurement – increasingly being seenas the ultimate in data acquisition tech-nology. Phasor measurement units(PMUs), located in critical areas of a net-work, allow fast measuring of the volt-age and current phasors (ie, their magni-tude and phase angles) and optimizeprocess control on the basis of a dynamic,


a 4 to 6 % increase in transmission ca-pacity achieved by deploying a widearea monitoring system could help topostpone or even avoid major invest-

mentsworth 10to 100millionUSD. PSG 850is there-fore alsoan im-portant

decision support tool for congestionmanagement and investment planning.

Disturbance analysis and system extension

planning

The continuous data storage function-ality provided by PSG 850 is a veryvaluable source of information for theanalysis of incidents and disturbancesoccurring in the power system. Besidesimproving the efficiency of power sys-tem analyses, it helps to determine andeliminate the actual causes of such inci-

highly accurate system overview. Severalelectrical utilities have already deployedPMUs in their grids, mainly for manualdata acquisition and processing.

A key feature of wide area monitoringsystems is the central acquisition ofdata from PMUs, enabling utilities toutilize phasor information wherever it is needed. PSG 850 provides the follow-ing customized forms of data utilizationin support of utilities’ asset manage-ment targets.

Monitoring of dynamic system behavior –

stability assessment

At present, power system operationtends to be based on static or quasi-dy-namic information extracted from rmsmeasurements, mostly using SCADA sys-tems. Phasor measurements at importantnodes help system operators gain adynamic view of the power system andinitiate any necessary stabilizing mea-sures in good time. Significant support is provided by stability assessment algo-rithms, which are designed to take ad-vantage of the phasor measurement in-formation. This increases the efficiencyof power system operation and helps tomaintain security at the desired level.

Monitoring of transmission corridors –

congestion management

Energy is often traded over the trans-mission corridors interconnecting thepower systems – an activity that adds

significantly to the cost, and thereforeprice, of energy in liberalized markets.However, the transmission capacity ofsuch corridors is often constrained bystabilityconcernshavingtheir ori-gin inuncer-taintyabout theunderly-ing sys-tem status. The traditional solution – toreinforce transmission path capacity byinstalling new lines – has the advantageof offering high availability, but also the substantial disadvantage that lineconstruction is time-consuming andrequires huge new investments.

An alternative solution is to significantlyimprove asset utilization through widearea monitoring. This reduces uncertain-ties and, consequently, the operationalrisks. Under certain conditions, such aslower-than-assumed ambient tempera-tures, the dynamic capacity increase canbe significant. The smaller invest-ment makes the ABB solutionfar more cost-effectivethan installing newlines. For ex-ample,

Phasor measurements at importantnodes help system operators gain adynamic view of the power systemand initiate any necessary stabilizingmeasures in good time.


Configuration of a wide area monitoring system with synchronized phasor measurements from PMUs used as input for the system monitoring center

1

System monitoring center GPS satellite

Transmission network

PMUPMU

PMU

dents. This accurate identification pro-vides a sound basis for the planning ofsystem expansions and future systemreinforcements.

System platform overview

Phasor measurement as basic technology

Wide area monitoring systems are es-sentially based on new data acquisitiontechnology. Unlike conventional controlsystems, which use, for example, RTUsto acquire the rms values of currentsand voltages, a wide area monitoringsystem acquires GPS1)-synchronized cur-rent, voltage and frequency phasor in-formation measured by PMUs at select-ed locations in the power system. Themeasured quantities include both mag-nitudes and phase angles, being time-synchronized via GPS receivers with anaccuracy of one microsecond. Untilnow, critical nodes in transmission gridshave usually been monitored using stat-ic or quasi-dynamic data based on rmsmeasurements. Phasors, measured at thesame time, provide instant snapshots ofthe status of the monitored nodes. Bycomparing these snapshots, both thedynamicandsteadystate ofcriticalnodes intransmis-sion andsub-trans-missionnetworkscan beobserved. The result is dynamic moni-toring of the power systems.

System architecture of the wide area

monitoring platform

The platform architecture for monitoringis made up of the following hardware:

Phasor measurement unitsCommunication linksSystem monitoring center

PMUs are placed in the substations toallow the power system to be observedunder all the different operating condi-

tions (network islanding, line or genera-tor outage, etc). Some redundancy isprovided to secure this information inthe event of certain data being unavail-

able, forexampledue toPMU out-age orcommuni-cationfailure.The mea-sured dataare sentvia dedi-

cated communication channels to thePSG 850’s system monitoring center(SMC) – a central computational unit inwhich the collected data are synchro-nized and sorted . This provides asnapshot of the power system’s status.

In the case of meshed network topolo-gies, the snapshot is then processed by the basic monitoring (BM) package,which is part of the SMC. BM denotesthe set of algorithms included in allinstallations of the wide area platformas the basis for different software appli-cations. This solution package has thefollowing capabilities:

1

Ability to provide consistent inputdata for all PSG 850 applications.Fast execution, leaving sufficient timeto run additional applications withinthe sampling interval.Robustness – the system is resistant tothe poor quality of some of the inputdata (availability, range, synchroniza-tion)

The reference phasor can be chosenfrom various points in the grid. Softwareapplications, which are linked to the BMoutput, address various dynamic phe-nomena occurring in power systems.They predict the state of the power sys-tem and suggest appropriate action tobe taken by the system operators whenan emerging instability is detected. Anergonomic graphical user interface (GUI)

displays the output information.

Historical data can also be accessed,allowing phasor data to be retrieved forsubsequent analysis. A navigation facili-ty is provided for easy selection anddisplay of the required information.

Implementation activities andadvanced software applicationsTo take full advantage of InformIT WideArea Monitoring PSG 850, a step-wise

2

Wide area monitoring is essentiallybased on new data acquisitiontechnology, with GPS-synchronizedcurrent, voltage and frequencyphasor information measured byPMUs at selected locations.

1) GPS Global Positioning System


approach is recommended: First, theutility and the PSG 850 supplier carryout an initial study to identify typicalnetwork problems and the most endan-gered of the areas in which the system isto be deployed. Afterwards, the appro-priate monitoring algorithms and mostsuitable locations for installing the PMUscan be chosen. ABB has developed acomplete set of algorithms that ensureoptimized procedures during the variousstages.

The fundamental software modules in-clude a GUI(with single-line diagram,pop-up win-dows, trenddisplays),easily scal-able PMUconnectivitypackage, data storage capability andexport functions for further analysis.

The following software applications areoffered with InformIT Wide Area Moni-toring PSG 850:

Advanced monitoringVoltage stability monitoring for trans-mission corridorsLine temperature monitoringPower oscillation monitoringFrequency stability monitoringControl action suggestions

Customer feedback has been goodSeveral systems with up to 16 PMUshave already been installed or engi-neered for practical application in high-voltage power grids. Feedback fromprototype applications on customer

sites is dili-gentlyrecorded,and con-tinues toconfirmimprove-ments inpower

system performance. Evaluation of thefeedback shows that customer benefitsinclude:

Cost-effective grid operation basedon observation of critical networkareas.

Increased grid utilization, facilitated byon-line monitoring of critical nodes.Detection and elimination of causesof power quality problems, madepossible by the high accuracy of theunderlying system of measurement.Thorough investigation of criticalincidents.Provision of additional strategic infor-mation for the utility’s grid planningdepartment.

As a result of this positive feedback, sev-eral wide area monitoring pilot projectsare now having their status upgraded to‘ready for commercial exploitation.’

Wide-ranging benefitsExperience with installed prototypesshows that wide area monitoring sys-tems help to significantly improve gridutilization, especially during peak de-mand periods. Just as importantly, theyfacilitate detection of the critical factorsinfluencing a network’s fundamentalstability.

When a wide area monitoring system isinstalled, utilities that operate powerlines at high load levels can reduce theircosts substantially by postponing invest-ment in new infrastructure while stillmaintaining high grid availability.

In this context, InformIT Wide AreaMonitoring PSG 850 goes well beyondthe capability of existing local monitor-ing and protection equipment. It raisesthe level of asset utilization and cansignificantly contribute to future costsavings in a utility’s long-term strategicinvestment planning.

Maximum benefit is gained fromwide area monitoring when theutility and ABB jointly identifytypical network problems and themost endangered areas.

Example of graphical user interface display provided by PSG 850. The popup linemonitoring faceplate (on right) compares voltage phasors.

2

Joachim Bertsch

Cédric Carnal

Andreas Surányi

ABB Power TechnologiesCH-5400 Baden/Switzerland

[email protected]@ch.abb.com

[email protected]


The utility industry is undergoing a fundamental transformation. The

change from a vertically integrated in-dustry, often under national control andwith only limited competition, if any atall, to a fully competitive, deregulatedindustry is dramatic in all its implica-tions. On top of all this, the product in-volved, electrical energy, is vital to thedevelopment of nations. The US Depart-ment of Energy has put this clearly intoperspective by stating: “Electricity is a cornerstone on whichthe economy and the daily lives of ournation’s citizens depend. This essentialcommodity has no substitute. Unlikemost commodities, electricity cannoteasily be stored, so it must be producedat the same instant it is consumed. Theelectricity delivery system must be flexi-ble enough, every second of the day andevery day of the year, to accommodatethe nation’s ever-changing demand forelectricity. There is growing evidencethat both private and public action isurgently needed to ensure our trans-mission system will continue to meet thenation’s need for reliable and afford-able electricity in the 21st century.

IT solutions will be a key area for utili-ties in this new and fast-changing mar-ket. Only IT solutions can successfullyprovide enough flexibility and intelli-gence to accommodate changes in themarket such as price erosion, invest-ment uncertainty and demand for higherreliability.

Price erosionThe introduction of competition has, inmost cases, led to significant reductionsin electricity prices, as in Europe, wherethe electric utility industry has beenundergoing restructuring for the last tenyears .

Industrial customers are usually the firstto benefit from increased competition.Subsequent opening of the individualconsumer market is accompanied bystrong pressure on electricity pricesacross the board; in Sweden more than30% of customers have changed theirelectricity supplier since reform wasintroduced just a few years ago.

The consequences of the increasedcompetition are that the utilities have

1

to better utilize existing investments,which are very capital intensive, toenhance their value, and also ensure thehighest possible return on future invest-ments. At the same time, operation andmaintenance costs are becoming morecritical.

Investment uncertaintyIn a non-competitive environment,planners had only to consider the loadgrowth per region and structure theinvestments accordingly. The regulatoryframework and the customer base werestable and this made planning easy. Themain focus was on security of supply,and costs for investments, operation andmaintenance were simply passed on tothe consumer.

With the unbundling of generation,transmission and distribution activities,totally new conditions were created for the utilities. Competition is normallyintroduced in the generation business,whereas transmission is often left regu-lated. Different models are applied todistribution, but as a rule the regulatorpressures the distributor to be com-

IndustrialITand the utility industry

Claes Rytoft, Bo Normark

ABB’s IndustrialIT has been discussed often in the pages

of ABB Review, and its benefits, especially for automation,

manufacturing and production applications, have been

explained in detail. But what about the utility industry?

How is Industrial IT contributing to this important area of

ABB business and how can the unique business environ-

ment of the utility industry profit from it?


petitive. This has resulted in a largeincrease in investment uncertainty.

Electricity is fast-becoming the largesttraded commodity in the world. The keysto success in this marketplace are theability to master real-time market dataand information about the capabilitiesand limitations of resources, and havingefficient tools for asset management.

One initial reaction of the utilities hasbeen to cut back on investments, butthis is not a sustainable strategy. Publicresponse to somespectacular black-outs and supplyshortages has re-sulted in pressurefor more stringentregulation.

Reliabilityexpectationshave grownThe traditional utility could provide asecure supply of electricity since costwas not considered to be too important.However, in the new competitive busi-ness environment, strict cost control hasto be given equal attention. Somethingelse making supply security increasinglyimportant is the fact that the loads are

becoming more and more sensitive tosupply quality.

Inadequate reliability not only puts acompany’s image on the line, it can alsodamage its balance sheet by making itliable to pay penalties to customers.

How IndustrialIT supports utilities inthe new business environment

Information

The most fundamental prerequisite forall performance enhancements based

on IT is ac-cess to in-formation.However, thetraditionalmix of mutu-ally incom-patible andslow infor-mation cre-ation, storage

and retrieval methods simply have noplace in the new, fast-changing energyworld.

ABB’s IndustrialIT concept will make itpossible to create, store and retrieve, inreal time, all the information that a sys-tem will need to operate as efficiently

as possible. There will be none of thebarriers that have traditionally separatedinformation provinces, such as mechani-cal and electrical, technical and busi-ness, operation and maintenance, andsoftware and hardware.

The key to ABB’s Industrial IT is AspectObjectTM technology [1]. An Object isdefined as a software container whichkeeps together all the characteristics,called Aspects, of a piece of equipment,be it switchgear, a transformer or anyother device. Aspect Objects can becombined to model a complete station,as shown in .

When multiple products are combinedto form a system or solution, physicallyputting each device into place is theeasy part. The difficult part is collecting,and keeping up-to-date, all the relatedinformation (configuration, drawings,maintenance records, etc), as this isoften stored in different formats and indifferent locations.

Industrial IT from ABB will change this.Once the physical device is put intoplace, the operator can simply copy andpaste the model Aspect Object into theoverall system monitoring and controlstrategy. No matter where each realobject is deployed, one ‘click’ on themodel Object provides a link to itsAspect information.

Although certain Aspects (drawings,instructions, etc) may not change overtime, others (eg, configuration, efficien-cy, cost of ownership) must be frequen-ly updated. The Industrial IT architectureprovides a way to automate this process,and to help various devices ‘learn’ fromeach other by exchanging real-timeAspect information.

Integration

ABB’s common Industrial IT architecturemakes it possible to integrate many dif-ferent applications as Aspects, allowingthem to be seamlessly linked in realtime. It is even possible to integrate theapplications without any changes and itis not even necessary for the differentapplications to be aware of each other.In addition, they could be from ABB,

2

1995

1996

1997

1998

1999

2000

Source: Eurostat.

60

70

80

90

100

110

Electricity price development for industrial customers in Europe 1995–2000(1995=100). The blue, green and red curves assume a 100%, <100% and <40%market liberalization, respectively.

1

Success in the powermarket depends on havingreal-time information aboutthe capabilities of resources,and efficient tools for assetmanagement.


but could just as well be any third-partyor customer application such as Word,Excel, ERP, a web camera, or a Comput-erized Maintenance Management System(CMMS) .

This, in turn, engenders entirely newconceptual solutions. It is well knownfrom other industries that when com-ponents, systems and solutions areadapted for integration, totally new and much more efficient solutions aremade possible.

Normally, the first step in integration is to copy the traditional products andsystems into one common system.Since the different functions can shareinterface and computing capability, asaving in both hardware and softwareis certain.

The second step in the integration is tostart utilizing the available informationto build completely new functionality in the integrated system. The biggest

3

advantages arise from combining theintegration with added functionality andoptimization.

The integration functionality of theIndustrial IT architecture is unique inthat it allows logical integration of

Power system installation

Aspect Object model

Switchgear

Real-time aspects

Aspect Object

The Aspect Object is a key element of ABB’s IndustrialIT architecture.2

AspectDirectory

Database Database

MicrosoftCOM

activex

UI UI UI

GIS OCS CMMS

Applications communicate via the Aspect Directory3


independent applications without re-quiring any changes to them. A practi-cal example of this could be to inte-grate an OCS system with a CMMS, thusallowing an operator to issue an errorreport in the CMMS when somethinghappens in the plant. The report can be

initiated by just right-clicking with themouse on the faulty object and thenselecting the CMMS Aspect .

In the ABB Object architecture, suchflexibility is provided by an AspectDirectory which interfaces between

4

applications. When an application isinstalled in the system it registers allinterfaces that it supports with theAspect Directory. When any applicationwants to perform an operation that in-volves action by other applications, itqueries this Aspect Directory for refer-ences to all interfaces that implementthe operation, and then invokes theseinterfaces, one by one.

To copy and paste an object, for exam-ple, all applications that implementAspects defined for the object must beinvolved and perform their part of theoperation, each application copying andpasting its Aspect respectively.

Industrial IT based automationplatformABB utilizes the Aspect Object techno-logy both as an integrated part of thenew automation platform and as a solu-tion for integration of hitherto indepen-dent applications, thus providing animproved workflow for ABB customers.

The automation platform will span tradi-tional functions such as DCS, PLC andSCADA functionality. In the platform,the Aspect Object system will be usedto keep track of all information aboutan object connected to the system, eg acontroller, where the different Aspectsmight be an alarm list, control logic,documentation, graphics, etc.

Importantly, the operator is providedwith a tool with a familiar ‘feel’ foreasy navigation through the informationhierarchy. This ‘Plant Explorer’ is abrowser that allows navigation throughthe various structures and viewing ofthe Aspects defined for each object.

Optimization by integrating solutionsAdvantage may be taken of the addedfunctionality arising from an integratedsolution to optimize the performance of the entire system. This opens upspectacular possibilities, such as com-bining real-time information and addedfunctionality. For example, starting from

Production cost forecastingCapability limitations in productionStatic and dynamic capability, withmargins in the system for both

5

The Plant Explorer lets users navigate through the information in a way they are familiar with.

5

OperatorPump alarmCheck control loopCheck cooling systemWrite error report

Control

Cooling system

Work order

Spare parts

Error report

Control

Cooling system

Error report

Integrating a SCADA/EMS system with a Computerized Maintenance ManagementSystem allows an operator to issue an error report in the CMMS when somethinghappens in the plant.

4


Information needed for demand-driven maintenanceInformation needed for disturbanceprevention and mitigation,

it is possible for users to take thisinformation and start combining asfollows:

Market prices, current and future.How can I combine this with produc-tion cost forecasting?Demand forecasting. How can I usethis information together with capa-bility limitations, maintenance sched-uling and disturbance prevention?Maintenance scheduling. How canthis be combined with market pric-ing, demand forecasting and capabili-ty limitations to minimize the conse-quential cost of maintenance?Capability limitations. How can this be combined with static and dy-namic capability margins to ensuremaximum utilization without reducingthe reliability?

Industrial IT certificationTo ensure all ABB products adhere tothe Industrial IT architecture, a certifica-

tion program has been launched. It isplanned to certify all ABB products,including all power technology devicessuch as transformers, switchgear, etc.By mid-2003 over 30,000 ABB productswere certified at the basic certificationlevel. More advanced certification levels(Information, Connectivity, Integrationand Optimization are foreseen) as wellas certification of solutions will follow.The certification program is open forthird-party products and it is ABB’sambition to establish the Industrial ITarchitecture as an industry de factostandard.

Structured customer offerings All offerings compliant with the Indus-trial IT architecture will have a consis-tent naming structure that is descriptivein its nature. That means that nameswill directly guide the reader to what-ever application or use is addressed.For ABB’s utilities business, the namingpolicy has been applied according tothe following structure (with exam-ples):

Solution Portfolio (Industrial IT forPower Generation) Solution Suite (Industrial IT forCombustion Management) Solution (Industrial IT Carbon in Ash Monitor)Product (ControlIT, Process Controller,AC 800M)

Market introductionIndustrialIT for Utilities will be intro-duced to the market in a step-wise fash-ion, with products and solutions beinggradually certified to comply with thefour levels of Industrial IT compliance.The first, smaller power plant and waterautomation systems based on the newautomation platform are already up andrunning.

A key goal in the introduction programis to develop new solutions around theAspect Object architecture.

IndustrialIT for utilities

Industrial IT is an overall strategy for ABB with major benefits for the utility industries:

A new, modern automation platform in which Aspect Objects is an integrated feature and

which will be introduced for power plants, water applications and substation control and

protection.

A unique integration architecture that will make it possible to integrate existing utility

applications.

A certification process that guarantees that ABB, and many third-party, products will fit

seamlessly into the Industrial IT architecture.

A new transparent naming strategy that makes it easy to understand ABB’s product and

solution offerings.

Claes Rytoft

Bo Normark

ABB Power TechnologiesCH-8050 Zurich


Reference

[1] The ABCs of IndustrialIT. ABB Review 1/2002, 6–13.


Golden Valley Electric Association(GVEA) is a rural electric cooper-

ative based in Fairbanks, Alaska, serv-ing 90,000 residents spread over 2200square miles. A reliable supply of elec-tricity is essential to the local populationsince many residents live in remoteareas and winter temperatures can fallas low as minus 50 °C. Back-up powertherefore has to be available in theevent of an outage.

Traditional solutions for providing re-serve power require building and main-taining transmission and generation ca-pacity well in excess of normal demand.

GVEA’s decision in favor of a batteryenergy storage system (BESS) reflects itscommitment to installing a system thatis a cost-effective and efficient alter-native to these solutions.

15 important minutes At the heart of the world’s most power-ful storage battery system are two corecomponents: the converter, designedand supplied by ABB, and nickel-cadmi-um (Ni-Cd) batteries, developed by Saft.The converter changes the batteries’ DCpower into AC power, ready for trans-mission over the GVEA grid. The batter-ies constitute the energy storage medi-

um. They can produce up to 27 MW ofpower for 15 minutes, giving the utilityenough time to get back-up generationon line. While the BESS is capable ofproducing up to 46 MW for a shorttime, the client’s primary need is for thesystem to cover the 15-minute periodbetween sudden loss of generation andstart-up of back-up generation.

Although the BESS is initially configuredwith four battery strings, it can readilybe expanded to six strings to provide afull 40 MW for 15 minutes. The facilitycan ultimately accommodate up to eightbattery strings, providing flexibility that

Alaskan winters are cold. Where temperatures

can drop to minus 50 °C, power outages are

very bad news indeed. A reliable supply of elec-

tricity is given a high priority when your

water pipes can freeze solid within hours if the

power goes down!

One way to prevent this happening is

to have an emergency power source feed

energy into the grid until back-up generation

can be made available. An economically and

ecologically more viable alternative to ‘spinning

reserve’ – gas turbines kept running in case of

an emergency – is battery back-up. In August

this year, the world’s largest-ever battery

energy storage system was inaugurated in

Fairbanks, Alaska. In addition to stabilizing the

local grid, it will reduce power outages in the

area by 65%. A consortium led by ABB

supplied and installed the system.

Cold storageThe battery energy storage system for Golden Valley Electric Association

Tim DeVries, Jim McDowall, Niklaus Umbricht, Gerhard Linhofer


will allow the client to boost output orprolong the useful life of the systembeyond its planned 20 years.

System and project requirementsThe final specification required that thevendor provide a turnkey solution andguarantee for twenty years that the BESScould supply 40 MW for 15 minutes,with a 4 MW/min ramp-down after the15-minute mark. The system is requiredto be capable of operating in all fourquadrants (ie, the full power circle) andto provide continuous, infinitely ad-justable control of real and reactivepower over the entire operating range.The specification also required that theBESS be able to operate in an automaticmode, as GVEA does not plan to manthe facility.

Rated output had to be provided for thefollowing power system characteristics:

Nominal voltage of 138 kV (1.0 pu)Normal sustained voltage of 0.90 pu(min) and 1.1 pu (max)Normal frequency of 60 Hz, withnormal deviation of +/- 0.1 Hz Sustained frequency range of 59.0 Hz(min) and 60.5 Hz (max)

Seven operating modesThe BESS is able to operate in sevendistinct modes:

Var support: The BESS provides volt-age support for the power systemunder steady-state and emergencyoperating conditions. Spinning reserve: In this mode, theBESS responds to remote generationtrips in the Railbelt system. It is initia-ted at a system frequency of 59.8 Hz,with the BESS loading to full outputat 59.4 Hz if system frequency contin-ues to drop. Spinning reserve has thehighest priority of all the modes andwill interrupt any other mode theBESS is operating under.Power system stabilizer, included todamp power system oscillations.Automatic scheduling, used to pro-vide instantaneous system support inthe event of a breaker trip on either atransmission line or a local generator.The BESS has thirty independentlytriggered inputs, which will be tied re-motely to the trip circuits of breakers.

Scheduled load increase: This is initi-ated and terminated by SCADA andputs the BESS in a frequency andvoltage regulation mode to allow it to respond to the addition of largemotor loads. Automatic generation control: In thismode the BESS is capable of operat-ing by AGC, similar to that of rotatingmachinery.Charging: The SCADA dispatcher cancontrol the MW rate at which the BESSwill be charged and when charging isto start after a BESS discharge.

The batteryThe Alaskan BESS battery comprises13,760 Saft SBH 920 high-performancerechargeable nickel-cadmium cells,arranged in four parallel strings to pro-vide a nominal DC link voltage of 5000 Vand a storage capacity of 3680 Ah. Thecells are built into 10-cell modules formounting in a drive-in racking system.An aisle between the racks providesinstallation and service access for aswing-arm fork truck.

The complete battery weighs some 1300 tons and the hall in which it islocated measures 120 meters by 26 meters – about the size of a soccerfield. The initial battery configurationhas four individual strings operating in parallel, but can be expanded toaccommodate eight strings. Each stringhas 3440 cells connected in series.

The battery features a pocket plate con-struction with thin, high-performanceplates. This design allows the full 20–25year life to be attained without any loss of the beneficial characteristics ofNi-Cd batteries. The type of cell usedcan deliver 80% of its rated capacity in20 minutes.

Ni-Cd pocket plate cells can withstandrepeated deep discharges with littleeffect on battery life. The graph in shows the cycling characteristics of theSBH battery.

The chosen design has several advantages:Compact arrangement: More rackdepth can be utilized, minimizing thespace taken up by aisles.

1

Easy installation: 90% of the connec-tions are made in the factory; onlythe inter-module connections aremade on site.Quick change-out: If there is a prob-lem with an individual cell, the mod-ule containing that cell can be re-placed by another complete modulein less than 30 minutes .Minimum power losses: 99% of theinter-cell connections are made withsolid copper bars; power lossescaused by flexible cable connectionsare therefore minimized.Spill isolation: The cells sit on a plas-tic grating, allowing spills to drain in-to the base of the module. The traycan hold the electrolyte content of allten cells.

2

World record

During commissioning tests, ABB’s powerconversion system and the Saft battery setan unofficial world record by achieving a peakdischarge of 26.7 MW with just two strings inoperation, making use of the short-time over-load capability of the battery modules. Thismakes the Alaskan BESS more than 27 per-cent more powerful than the previous recordholder – a 21-MW BESS commissioned byPREPA (Puerto Rico Electric Power Authority)at Sabana Llana, Puerto Rico in 1994.

10000

1000

100

0 10 20 30 40 50 60 70 80 90

Depth of discharge (%)

Cycling characteristics of theBESS battery. No. of charge/discharge cyclesvs depth of discharge

1

Number of cycles


A PE liner on the inside of the modulecase (between the battery cells andmetal tray) provides the necessary insu-lation. Each module is fitted with a self-contained, single-point filling system,allowing all 10 cells to be topped up ina single operation without removing themodule from the rack.

Battery monitoring systemThe battery monitoring system was sup-plied by Philadelphia Scientific Inc. Itmeasures, records and reports the mod-ule voltage, string current, cell elec-trolyte level (one cell per module) andcell internal temperature (also one cellper module).

Data collection and transfer are orga-nized hierarchically. The lowest-leveldevice in the hierarchy is the sentryunit. There is one for each 10-cell mod-ule, and its task is to measure the mod-ule voltage, cell electrolyte level andcell internal temperature. Each sentryunit reports its collected data to asergeant module. Every string has itsown sergeant module, which also mea-sures the string float current. In turn,the sergeant module reports its collect-ed data to the supervisory computer,which analyzes and displays the data.This computer is also responsible forforwarding summary data to the HMIand is the main terminal for BESS per-

sonnel who need to access the monitor-ing system.

Optical couplers carry the data from thesentry units to the data bus, which isinsulated to withstand a minimum of5000 V. 5560 readings are taken every30 seconds – a total of 5.8 billion read-ings per year. These numbers can bedoubled if required.

The electrical systemFour battery strings are currently in-stalled . All preparations have beenmade for extension at a later stage, withup to eight battery strings possible. Everystring (and sub-string) can be switchedoff and completely isolated from the restof the system by DC switches. In addi-tion, two disconnectors allow separationof the battery and the DC link of theconverter when maintenance work hasto be carried out on the batteries. Theconverter can then remain in operationand provide reactive power to the gridfor voltage control. Filter circuits in theDC link eliminate the risk of resonancesat higher frequencies should any har-monics be generated in the grid by non-linear loads. The voltage source convert-er at the heart of the electrical systemcomprises standardized PEBBs (PowerElectronic Building Blocks). One double-stack PEBB in NPC (Neutral PointClamped) connection forms a single-phase H-bridge Four H-bridges areinstalled per phase, for a total of twelvesingle bridges. The stacks are cooled bydeionized water in a closed-loop circuit.

Each bridge is connected to its dedicat-ed transformer winding. The voltagecontributed by the bridges is added inthe transformer by series-connecting theline-side partial windings, resulting in avoltage wave shape similar to the quali-ty that could be expected from rotatingmachines. Voltage limiters prevent anyovervoltages due to sudden load rejec-tions or possible disturbances in theelectric grid from damaging the DC link.

The converter and transformers havebeen designed and built to handle thetotal power should the battery beextended from four to eight strings at a later stage.

4

3

Battery module, comprising 10 cells, on the move2


The active switching devices used in theconverter are integrated gate commutatedthyristors (IGCTs), an advanced type ofgate turn off thyristor (GTO). Comparedwith other devices that can be turned off,IGCTs have the advantage of lower con-duction and switching losses, plus superi-or switch-off characteristics that allow asnubberless converter design.

Advantages of this converter designinclude:

The three-level medium-voltage mod-ules are proven, highly reliable prod-ucts. Low FIT values are obtainedwhen these modules are used.Use of double-stack modules shortensthe distances between the powersemiconductors, keeping stray induc-tances low, and reduces the spacerequired for the complete converter.Since the clamp diodes and capacitorsare integrated in the semiconductorstack, the stray inductance in theclamp circuit is also minimized,allowing use of higher IGCT switch-off currents.Using a single clamp for two phasesreduces the need for bulky and costlyclamp inductors and resistors.

Ease of serviceability was a primaryconsideration during the mechanicaldesign. All power semiconductors inthe stack are readily accessible, allow-ing easy replacement.

Power and reactive powerperformanceThe system is designed for four-quad-rant operation. It can charge as well asdischarge the battery and it can absorb

Basic diagram of the electrical system3

Battery strings 1 to 4

Filter circuits12 x 2-phase

modules3 x 1-phasetransformers

Voltagelimiter unit

to 138 kV/60 Hz grid

to 138 kV/60 Hz grid

4 units

4 units

4 units

2 units

AC 1

Rsym

DC+

DC–

CC+

CC–

AC 2

Rsym

DC+

DC–

CC+

CC–

=

Building block. A double-stack water-cooled PEBB in NPC connection, forming one H–bridge

4


reactive power from or supply reactivepower to the grid. Each of these modesis possible with the DC link voltagevarying as the battery’s charging condi-tion changes.

The operating range of the system interms of active and reactive power for90% and 100% of the nominal grid volt-age is shown in .5

The control systemLocal system control is provided by anABB SPIDER MicroSCADA humanmachine interface (HMI) based on theMicrosoft Windows operating system .The system is operated via pictures,windows and function keys using amouse and a keyboard. Sequence andclosed-loop control as well as overallprotection are provided by ABB’sprogrammable high-speed controller(PHSC), which can be programmedusing the graphic function plan pro-gram FUPLA. The PHSC is well provenand its reliability has been shown to besuitable for both system control andprotection in numerous applications.

The converter control incorporates thefollowing functionality:

Sequence controlControl of the main breakersSignal conditioningProcessing of measurement signalsFast current control for ride-throughin the event of external faultsPower and reactive power controlLoad managementInterlocking of local control andSCADA/RTU controlRedundant protection functions

6

BESS – a stabilizing factorWhile fulfilling its overall mission ofreducing power outages in the Fairbanksarea, the Alaskan BESS has specificbenefits in the areas of transmission anddistribution, generation and strategicplanning:

Transmission and distribution benefitsinclude voltage regulation, first swingstability and loss reduction.

In the generation area the BESS offersspinning reserve, ramp-rate constraintrelief, load following, black starts, loadleveling, and a reduction in deferredturbine starts.

Strategic benefits include improvedpower quality, reduced demand peaks,and enhanced service reliability throughreduced power supply generated out-ages.

The principal benefit, however, is the ability of the BESS to instantly con-tribute to system stability following theloss of a major transmission line orgenerator. The spinning reserve it pro-vides has the potential to allow genera-tion units to be run at lower levels orbe shut down entirely, resulting in sig-nificant savings. Almost instantaneousactive power is available. This is impor-tant in cases where the BESS has toramp up before the impact of a genera-tor loss becomes noticeable at the pointof common coupling.

Tim DeVries

Golden Valley Electric [email protected]

Jim McDowall

[email protected]

Niklaus Umbricht

Gerhard Linhofer

ABB Automation TechnologiesCH-5300 Turgi


1.5

1

0.5

0

-0.5

-1

-1.5

Rea

ctiv

e po

wer

[pu]

Indu

ctiv

e

C

apac

itive

-1.5 -1 -0.5 0 0.5 1 1.5

Charge DischargeActive power [pu]

Operating range of BESSP/Q diagram 1 pu corresponds to 40 MVA

5

= V_grid = 100% = V_grid = 90%

Overview of control and protection system6

Convertercooling unit

Converter Transformer 138 kVswitchgear

138 kV gridBattery string

1

Battery monitoringsystem

Local HMI(ABB MicroSCADA) GVEA SCADA

Programmable High Speed Controller

RTU

Protection

Control

1

8

Deregulation of the electricity supply markets and growing environmental awareness are creating

exciting new markets for power transmission solutions based on extruded cable

technology. At the same time, improvements on all

fronts are extending the use of XLPE (cross-linked

polyethylene) insulated cable systems up to

500 kV. Today’s cable system applications are

often competitive with overhead lines, while

new manufacturing methods are enabling

submarine cables with integrated optical

fibers and flexible joints to be supplied in

longer lengths than ever before. Further devel-

opment of extruded insulation systems is also

contributing to the success of ABB’s innovative

HVDC LightTM concept.


High-voltage cable systems rated 220 kV and above have become

part of the very backbone of modern-day power transmission infrastructure.This importance carries with it, howev-er, a special responsibility on the partof the suppliers to ensure that thesystems exhibit the highest reliabilityand, because of the high electricalstresses at such voltage levels, that thecables and accessories are properlycoordinated.

Deregulation – changing the rulesIn today’s deregulated electricity mar-kets, the rules that used to govern gen-eration, transmission and distributionhave changed for both the power utili-ties and the suppliers. Suddenly, it isthe customer who is in the spotlight.

Accordingly, the market has to listenmore to public opinion, and there is a strong possibility that this will in-clude a call for a less ‘visible’ T&Dinfrastructure.

All the actors in this new market haveto reduce their costs and at the sametime guarantee high reliability for thetransmission and distribution systems. A likely scenario is that new cable in-terconnections will be built and opera-tional margins will be utilized morefully in order to get maximum technicaland economic benefit from the electri-cal network.

Extruded cable systems have a majorpart to play in this new, competitiveenvironment, especially when it comes

to replacing overhead lines with under-ground cables. XLPE cable systemscosts have decreased during the lastdecade and are likely to fall even fur-ther. At the same time, XLPE cable per-formance has increased enormously.The new message is therefore thatXLPE cable systems are able to competewith overhead lines, technically, envi-ronmentally and commercially. This isparticularly true in the voltage range of12–170 kV .

Extruded insulation – performance and improvementsThe well-established trend toward asmaller insulation thickness will contin-ue, resulting in a leaner cable withmany advantages, among them longerdispatch lengths, fewer joints, easier

1

Björn Dellby, Gösta Bergman, Anders Ericsson, Johan Karlstrand

XLPERFORMANCEHigh-voltage

cable technology


installation, and reduced thermal con-traction/expansion of the insulating ma-terial. Experience accumulated duringEHV XLPE cable system development,improvements made in materials andprocesses, and the excellent servicerecord of XLPE, have reduced the thick-ness of cable insulation to 12–15 mmfor 132-kV cable systems. This placesthe XLPE cable systems versus over-head line transmission scenario in anew light, where the cable solutionoften can be an attractive alternative.

Underground cables versus overhead linesThere are, of course, many operational,security, environmental, reliability and

economic parameters that distinguishXLPE cable systems from overheadlines [1]. For modern XLPE cable sys-tems, the reduced cost ratio and envi-ronmental and reliability benefits arethe most obvious and important con-siderations. Due to their larger cross-sectional areas, cables usually exhibitfewer losses per MVA than comparableoverhead lines. A summary of the ben-efits of XLPE cable systems is given inthe table on page 52.

The ratings of the overhead lines aresometimes dictated by high winterloads, which include a lot of electricalheating equipment. During hot summerdays the overhead line carries some

50% less electricity than in winter, mak-ing them less attractive if load profileshave to be smoothed out in the future.In areas where there are many air-con-ditioning units, for example, the bene-fits of XLPE underground cables makethem a genuine alternative .

Underground transmission lines alsohave a better overload capacity forperiods of time shorter than 90 minutesdue to the high thermal mass of thesurrounding soil.

Qualification of 400–500 kV cablesystemsThe IEC emphasizes the importance ofreliability and coordination of the cablesand accessories by recommending thatthe performance of the total system,consisting of cable, joints and termina-tions, be demonstrated. The compre-hensive test program, including a ‘pre-qualification’ test, is described in detailin IEC 62067.

ABB qualified as a supplier of cablesystems for the 400-kV voltage level in1995.

Quality, materials and manufacturingOnly certified suppliers are contractedto deliver essential materials. All ABBmanufacturing sites for HV cables andaccessories are ISO 9001 and 14001 cer-tified. The XLPE cable core is producedon a dry curing manufacturing line. Thecable insulation system, including theconducting layers, is extruded in a sin-gle process using a triplex extrusioncross head located, together with thethree extruders for the insulating andconducting materials, in a clean-room .

Cable designshows a 400-kV XLPE cable. The

cable’s copper conductor, which has across-sectional area of 2500 mm2, isdivided into five segments to reduceskin effect losses. ABB uses segmented(Milliken) conductors made of strandedwires for cross-sections greater than1000 mm2. For cross-sections smallerthan 1000 mm2, the conductors arehighly compacted to obtain a rounder,smoother surface.

4

3

2

5

10

15

20

25

30

01986 2000199819961994199219901988

CR

400 kV

130 kV

Comparison of cost ratio (CR) for XLPE cable systems and overhead transmission lines

1

Air/soil temperature

Am

pac

ity

Soil

OHTL

XLPE cables

Rating of overhead line (OHTL) versus underground XLPE cable. The dashed lineindicates that higher powers could be transmitted if the daily load cycle profile istaken into account.

2


The metallic screen consists of copperwires on a bedding of crepe paper to re-duce the mechanical and thermal impacttransferred to the insulation. The numberof wires and the total cross-section de-pend on the short-circuit requirements ofthe network. Longitudinal water tightnessis achieved by filling the gaps betweenthe screen wires with swelling powder.

External protection against mechanicalimpact and corrosion is provided by atough, extruded, laminated sheath madefrom HDPE (high-density polyethylene).A bonded metal foil on the inside of thesheath stops water from diffusing intothe cable.

The resulting lean, low-weight cable hasseveral advantages: a greater length ofcable can be wound onto any givendrum; high eddy-current losses in thecable sheath are avoided; the current-carrying capacity is optimized.

Possible oversheath options are:An extruded conductive layer forouter sheath measurementsAn extruded flame-retardant layer forextra safety in hazardous environ-ments

Another option the cable design offers isspace-resolved temperature monitoringwith optical fibers. The fibers are con-tained in a stainless-steel tube, approxi-mately the same size as a screen wire,which is integrated in the cable screen.Monitoring the temperature in this wayenables the cable load to be optimized.

Cable accessoriesIn the early 1990s ABB developed pre-fabricated joints for HV and EHV cableswhich are totally dry, ie with neithergaseous nor liquid materials, and main-tenance-free. The main electrical partscan therefore be pre-tested in the facto-ry, speeding up on-site installation andreducing the attendant risks. The jointshave integrated sheath insulation inorder to comply with the CIGRE recom-mendation contained in Electra 128,which requires them to withstand im-pulse voltages of 125 kV between thetwo joint sections and 63 kV to earth.This permits cross-bonding of the cable

screen, which reduces the inducedscreen currents and losses in the AC ca-ble system. The complete cable systemwith joint, outdoor terminations and GISterminations, fulfills the requirements ofIEC 62067 in every respect.

Testing of 220–500 kV cable systemsIn the case of medium-voltage cables itis usual to think in terms of compo-nents. Even if these come from differentsuppliers, they can be joined together

Vertical extrusion of XLPE cable insulation3

400-kV XLPE cable. The copper conductor is divided into five segments to reduceskin effect losses.

4


and the system as a whole will stillwork. This is why limits are given forthe electrical stresses in the constructionrequirements in IEC 60502.

HV and EHV cables and accessories, onthe other hand, are designed as systems.No construction requirements exist forcables for these voltage levels, just thetest requirements in IEC 60840 and IEC 62067.

400-kV XLPE cable projectsIn 1996 ABB received an order from thepublic utility Bewag (now VattenfallEurope) to supply and install a 400-kVXLPE cable system in a 6.3-km longunderground tunnel in the center ofBerlin. The ventilated tunnel is situated25 to 35 meters below ground and has adiameter of 3 meters . The cable sys-tem, with a 1600 mm2 segmented copperconductor, has a transmission capacity of1100 MVA and forms part of a diagonaltransmission link between the transmis-sion grids west and east of the capital.

5

The cable is installed with the threephases arranged vertically, one abovethe other, on specially designed cablesaddle supports7.2 metersapart, with ashort circuit-proof spacer in the middle of each span.The cable routewas dividedinto nine sec-tions, eachapproximately 730 meters long. GISterminations were installed at the twosubstations and the new ABB joint wasused to interconnect the cable lengths.The laid cable consists of three maincross-bonded sections, with three mi-nor sections within each main section.The cable circuit went into service inDecember 1998.

The Bewag utility subsequently award-ed a second 400-kV XLPE cable con-

tract to ABB, this time for a 5.4-kmlong system, again in an undergroundtunnel. This cable circuit completes the

diagonal link be-tween the transmis-sion grids west andeast of Berlin, andwas handed over to the customer inJuly 2000.

Further 345–400 kVcable projectsawarded to ABB

include orders for 200-km XLPE cables,accessories and installation. Commis-sioning of these projects is scheduled to take place during 2003–2004.

New submarine cable projectsIn 1998 ABB was awarded the ChannelIslands Electricity Grid Project, whichreinforces the power supply fromFrance to Jersey and, for the first time,connects Guernsey to the Europeanmainland grid. The submarine part

400-kV cable system in a 6.3 km underground tunnel running through Berlin’s city center5

Greater lengths of low-weight XLPE cable canbe wound onto anygiven drum, while higheddy-current losses inthe sheath are avoided.


of this project was completed in July2000.

The main components delivered for theproject were:

Submarine cables between Franceand Jersey and between Jersey andGuernsey (approx 70 km)Underground cables on Jersey andGuernseyGIS substationsNew transformers and reactors

The two submarine cables are of thesame basic design, ie three-core, sepa-rate lead-sheathed, and with triple-extruded XLPE insulation. Each has afiber optic cable with 24 fibers integrat-ed in it for system communication andinter-tripping. The cables have doublewire armor (ie, an inner layer of tensilearmor and an outer, so-called rockarmor) to protect them from damagethat could be caused by tidal currentsand fishing.

The cables have a diameter of ap-proximately 250 mm and weigh about 85 kg/m in air.

Both cables were delivered by the facto-ry in their full lengths .

Because of the risks posed by fishingactivities, the cables between Jersey andGuernsey and the fiber optic cables be-tween Jersey and France were jetted in-to the seabed for extra protection.

Another submarine cable project is theMa Wan and Kap Shui Mun Cable,which crosses a channel in Hong Kong.Due to the heavy traffic in this channel,it was decided to forgo conventionalinstallation of the 132-kV and 11-kVsystems, which would probably havedisturbed shipping even if modern tech-niques were used. The problem wassolved by drilling under the seabed andinstalling ducts through which thecables were pulled. This has the extraadvantage of allowing upgrades to becarried out in the future.

Separate control systems were installedto monitor operation of the cable link,which was completed in 2003.

6

A new submarine cable project hasrecently been awarded to ABB byAramco. The cable, which is 53 kmlong, is rated 110 kV with 3 × 500 mm2

copper conductors. It will be commis-sioned in 2004.

HVDC LightTM

HVDC LightTM, which was launched in1997, is another ABB innovation in theT&D field that incorporates advancedHV cable technology. High VoltageDirect Current (HVDC) cables are em-ployed for bulk power transportationover long distances, mainly underwater.

Traditional cable technology is basedon paper insulation systems impregnat-ed with highly viscous oil. While thesecables have many technical advantages,the manufacturing process is slow andthe end-product is mechanically sensi-tive. The industry had therefore beenlooking for a long time for an extrudedHVDC cable of the kind used in ACsystems.

With HVDC Light [2], ABB has intro-duced to the market an extruded cablesystem, together with new transistor-based converters, that makes HVDC

Storage of submarine cable prior to laying6


transmission competitive even at lowpower ratings. The first commercialsystem, a link rated at 50 MW, wasinstalled on the Swedish Island ofGotland, where it transmits power froma wind power plant to the town ofVisby [3].

Other major projects that have beencompleted are:

The Directlink, rated 180 MW at 80 kV, which transfers power be-tween the states of New South Walesand Queensland in Australia.The Murraylink, rated 200 MW at 150 kV, built to transfer power be-tween Victoria and South Australia [4].The Cross Sound Cable, rated 330 MW at 150 kV, which transferspower between New England andLong Island.

The latest HVDC Light project, to supplypower to an offshore platform in theNorth Sea (Troll A), is due to be com-missioned in 2004. (See article startingon page 53.)

Applications for HVDC Light include:Feeding of isolated loads (eg, off-shore platforms)Asynchronous AC grid connection

Transmission of power from smallgeneration units (eg, wind powerplants)DC grids with multiple connectionpointsNetwork reliability enhancementthrough voltage stability and blackstarts

Tomorrow’s electrical infrastructure – here nowExtruded cable systems are available astotal solutions, with a ‘cradle to grave’supplier commitment. Such systems areturnkey offerings in the commercial aswell as the technical sense. They maystart with the permit application, contin-ue with the removal of the overheadlines and the supply and installation ofthe cable system, and end with theenvironmentally friendly disposal of theold equipment.

Complete cable system applications canalso be seen as intelligent combinationsof monitoring equipment, converters,load-sharing devices, series and/orshunt compensation devices. Financing,too, can be arranged; here, leasing anda new type of availability guaranteecould resolve several commercial uncer-tainties.

Together, these ‘thumbnail’ sketches of the future add up to a new cus-tomer-value-based market. Extrudedinsulated cable system applications aredestined to play a key role in thisevolving market by meeting not onlythe transmission and distribution net-work requirements of today but alsothose of tomorrow.

Environment

No visual impact

Low/no electromagnetic fields

High level of personnel safety,

low risk of flashover in air

Good working conditions

Grid security

Not affected by wind, snow, ice,fog, etc

Nothing can be stolen

Economy

Low maintenance

Minimum investment for lake/river crossings

Land use minimized

Value of land/buildingsunaffected

Operation

High availability, few faults

Usually low losses/MVA

High short-time overloadcapacity

References

[1] D. Karlsson: Comparison of 130 kV XLPE cable systems and OH lines – loading capability, reliability and planning criteria. CIGRÉ 2002.

[2] K. Eriksson: HVDC Light DC transmission based on voltage sourced converters. ABB Review 1/98, 4–9.

[3] M Byggeth, et al: The development of an extruded HVDC cable system and its first application in the Gotland HVDC Light project. JICABLE 1999.

[4] T. Worzyk, et al: The Murraylink Project – the first commercial 150 kV extruded HVDC cable system, JICABLE 2003.

Dr. Björn Dellby

Gösta Bergman

Dr. Anders Ericsson

Johan P. Karlstrand

ABB Power TechnologiesHigh Voltage Cables

SE-371 23 KarlskronaSweden

[email protected]

Benefits of underground transmission lines

Powering Troll

Troll A platform (Photo: Øyvind Hagen, Statoil)

with HVDC Light™Tom F. Nestli, Lars Stendius, Magnus J. Johansson, Arne Abrahamsson, Philip C. Kjaer

Now, new technologies from ABB are making it easier than

ever before to deliver electrical power to offshore installations,

lowering operating costs and reducing environmental impact

at the same time. Seventy kilometers off the Norwegian coast,

two of these technologies – HVDC Light™ and Motorformer™

– are helping to power 40-MW compressor units on Statoil’s

Troll A platform without any local power generation.

With its compressors, motors and

electrical systems devouring many

tens of megawatts, an offshore

installation can be a power-hungry

beast indeed. The onboard gas

turbines or diesel generators that

usually supply this power, however,

manage no more than about 25%

efficiency – way off the dazzling

75–80% efficiencies of, say, land-

based combined cycle power

plants. This inefficiency isn’t just

costly in terms of excessive fuel

consumption, either; high emis-

sions can rack up the cost still

further, for example where CO2

taxation applies.

Special ReportABB Review 53


HVDC Light™ and Motor-former™ join the offshore clubTroll A is the largest gas pro-duction platform on the Nor-wegian shelf. Some 40% ofNorway’s total annual gasproduction comes from TrollA, which can produce up to100 million cubic meters ofgas per day. Today, the reservoirpressure drives the gas to the onshoreprocessing plant at Kollsnes, where thecondensate, water and gas are separat-ed. The gas is then compressed andtransported through pipelines to theEuropean continent .

As the gas is taken out of the reservoir,the pressure inevitably decreases. Thismeans that to maintain productioncapacity, offshore precompression of thegas will eventually become necessary.ABB has been awarded two contracts aspart of Statoil’s Troll A PrecompressionProject: a US$ 185 million contract forthe compression equipment and a US$85 million contract for the electric drivesystems for compressors. The new instal-lation is due to go into commercial oper-ation in the fall of 2005 as part of a pro-gram introduced to maintain and expandthe platform’s production capacity.

Choosing conventional systems for thisproject would have meant that gas tur-bines would drive the compressors. Inthat case, it is estimated, annual emis-

1

sions of some230,000 tons ofCO2 and 230 tonsof NOx would re-sult. Besides theirimpact on the envi-

ronment, the CO2

taxation in effecton the Norwegian

shelf means that suchemissions would also be

a significant cost factor.Working with Statoil, ABB developed analternative system based on two inno-vative ABB technologies – HVDC Light™and Motorformer™. These have beensuccessfully employed on shore since1997 and 1998, respectively, but neverbefore on an offshore installation ortogether as an electric drive system. Thesystem uses power from the onshoreelectrical grid to drive the compressorson Troll A, thus eliminating greenhousegas emissions from the platform.

HVDC Light – rectifying, inverting and controllingHVDC Light [1], by using series-connect-ed power transistors, enables voltagesource converters to be connected tonetworks at voltage levels higher thanever before for power transmission,reactive power compensation and har-monic/flicker compensation.

On Troll A, an HVDC Light converter(inverter) feeds the variable-speed syn-chronous machine driving each com-pressor with AC power obtained byconverting the incoming DC, which istransmitted from shore over submarinecables. As their speed is variable, thecompressors are supplied with power atvariable frequency and voltage, rightthrough from zero to maximum speed(at 63 Hz) and from zero to maximumvoltage (56 kV), including starting, ac-celeration and braking. The drive sys-tems perform equally well at each endof the frequency spectrum. Small filtersat the converters’ outputs keep themotor winding stress at a safe level.

The inverter control software is adaptedfor both motor speed and torque con-trol. The motor currents and voltagesand the rotor position are measured and

2

On most offshore installations, thepower generators and large com-

pressors are driven by onboard gas tur-bines or diesel engines with total effi-ciencies that can be as low as 20–25 %even under ideal conditions. As aresult, fuel consumption and CO2 emis-sions are unnecessarily high. Ever sincethe Kyoto Protocol, which allows trad-ing of greenhouse gas emissions, highCO2 emissions have become a costfactor. On top of this, as on the Nor-wegian shelf, there may be CO2 taxa-tion, making emissions costly evenwithout trading.

If the electrical power for all this equip-ment can be supplied from shore, theCO2 emissions of offshore installationsare eliminated, saving operators a con-siderable sum of money. But that isn’tall; transmitting electrical energy fromshore is also more efficient in terms ofequipment maintenance, lifetime andavailability.

The overall environmental bonus ofeliminating low-efficiency offshorepower plants is considerable. A land-based combined cycle gas powerplant, which utilizes the gas turbine’swaste heat, can have an efficiency ofas much as 75 to 80%. Even if highlosses of 10% are assumed for a longtransmission line to an offshore instal-lation, the saving will still be signifi-cant for most installations.

Gas from Troll A is processed at Kollsnes before being transported to the European continent.

1


used together with an advanced modelof the machine’s electromagnetic para-meters to calculate converter switchingpulses in much the same way as forsmaller industrial variable-speed drives(ACS 600/ACS 1000/ACS 6000). Unitypower factor and low harmonics areassured, along with a sufficiently highdynamic response, over the motor’sentire operating range. Protection andmonitoring of the converters and syn-chronous machines, as well as controlof the excitation converter feeding thelatters’ field winding, are handled byABB’s well-proven IndustrialIT HVDCControl, MACH 2.

Overall control of the rectifier station atKollsnes is also handled by the MACH 2.

There is no need for communication be-tween the rectifier control system onland and the motor control system onthe platform; the only quantity that canbe detected at each end of the transmis-sion system is the DC link voltage. Asthe DC link cannot store much energy,the motor control system is designed tofollow even rapid changes in powerflow at the opposite end without dis-turbing motor operation. Nuisance trip-ping is generally kept to a minimum.

The HVDC Light converter for Troll isbased on a two-level bridge withgrounded midpoint. Only extremely lowground currents are induced duringsteady state and dynamic operation, thisfeature being one of the main reasonsfor using HVDC for the power supply.No cathode protection of any kind hasto be provided for this installation.

HVDC Light cable – the power carrierThe HVDC Light concept includes a fur-ther innovation: the HVDC Light extrud-ed polymer cable. The shift in high-volt-age AC technology from paper-insulatedto extruded polymer cable was the in-centive for ABB to develop and producean extruded cable offering the samebenefits – flexibility and cost-effective-ness – for HVDC transmission.

Troll A’s importance as a major gas pro-ducer called for an extremely reliabletransmission link. The actual cable hasa 300-mm2 copper conductor surround-ed by a very strong and robust poly-meric insulating material . Wateringress is prevented by a seamless layerof extruded lead, over which there aretwo layers of armor – steel wire wovenin counter helix – to provide the re-quired mechanical properties. This de-sign ensures that the cable has thestrength and flexibility necessary forlaying in the North Sea. The two elec-tric drive systems require an HVDCLight cable system with two cable pairs

3

Motorformer

Motorformer [2] features conventional rotor,

exciter, control and protection technologies.

Most of the stator technology is also conven-

tional – the exception is the winding, which is

made of XLPE-insulated cable. The stator’s

cable slots are designed for low electrical

losses, high-strength cable clamping,

efficient cooling and simple installation.

The first Motorformer to go into commercial

operation, at the AGA plant in Sweden,

has verified the many benefits of using HV

cable technology in large electric motors.

Motorformer is suitable for most applications

where conventional technology is used today.

HVDC Light

In the past, high-voltage DC links have been

used almost exclusively to transmit very high

powers over long distances. HVDC Light [1]

is a new transmission technology based on

voltage source converters that extends the

economical power range of HVDC transmis-

sion down to just a few megawatts.

HVDC Light also offers power quality

improvements, for example reactive power

compensation and harmonic/flicker com-

pensation. Thanks to fast vector control,

active and reactive power can be controlled

independently, with harmonics kept low,

even in weak grids.

From the rectifier station at Kollsnes, subsea HVDC cables transmit power to the Troll A Platform, where the inverter station andMotorformer™ are located. Two identical systems are to be installed.

2

132-kV switchboard Rectifier station

Power

transformer

HVDC Light

rectifier

HVDC Light

inverter70 km

HVDC Light cable

Inverter station Motorformer

40 MW56 kV

Gear

Pre-compressor

Kollsnes Subseacable

Troll A platform


Dr. Tom F. Nestli

Magnus J. Johansson

ABB Automation [email protected]

Lars Stendius

Arne Abrahamsson

Dr. Philip C. Kjaer

ABB Power Technologies

[1] G. Asplund, K. Eriksson, K. Svensson: HVDC Light – DC transmission based on voltage sourced converters. ABB Review 1/1998, 4–9.

[2] G. L. Eriksson: Motorformer – A new motor for direct HV connection. ABB Review 1/2001, 22–25.

(one for each drive), physically separat-ed from each other on the sea floor.The two cables in each pair are operat-ed in bipolar mode, one having a posi-tive and the other a negative polarity.

To make sure that the cables will notbe damaged by anchors or trawling,they are laid in trenches on the sea bedformed by water jetting, or coveredwith rocks where this is not practicable.

Motorformer™ drives the compressorsFollowing the introduction in 1998 ofnew, innovative cable winding technol-ogy, ABB’s engineers soon began toconsider the possibility of using HV

cable windings in place of conventionalwindings in electrical motors in orderto radically increase the motors’ voltageratings. Such a motor can then be con-nected directly to the HV grid, doingaway with the need for a costly step-down transformer.

The first product to be based on thisprinciple was an HV cable-wound gen-erator. Shortly afterwards, the same con-cept was applied to motors, resulting inthe development of a synchronous ma-chine, dubbed Motorformer™ (see panelon page 55). The first unit was installedin 2001 at an air separation plant inSweden, where it drives a compressor.This motor is directly connected to a 42-kV bus. In the meantime, ABB offersHV motors of this kind for voltages upto 70 kV. Work is currently under way to develop units rated at 150 kV.

Apart from eliminating the step-downtransformer and related switchgear,Motorformer reduces the total systemlosses by as much as 25% . Beingepoxy-free, it also has important envi-ronmental benefits, including easy recy-clability. And fewer components meanhigher system reliability and availability,plus reduced costs for service, mainte-nance and spares.

A challenging environment for high-voltage equipmentOffshore equipment design is con-strained by the need to keep both foot-print and weight to a minimum. HVDCLight and Motorformer offer importantadvantages in precisely these areas:

Smaller filters and the absence of syn-chronous condensers make HVDCLight more compact and lighter thantraditional HVDC systems.No large, heavy transformer is re-quired to connect the Motorformerto the HVDC Light converter.

Other design considerations in connec-tion with this project were:

Safety: Troll A produces large quanti-ties of hydrocarbon gas, which is not

4

allowed to come into contact withhigh-voltage equipment.Environment: The high-voltage equip-ment must be protected from thedamp, salt-laden sea air.Availability: Given the daily productionof gas worth US$ 10–15 million, highequipment availability is essential.

HVDC Light and Motorformer are inno-vative technologies with all the qualitiesneeded to power offshore platformsfrom shore for maximum economicaland environmental benefit. Troll A isthe first such platform anywhere to bepowered in this way, the electric drivesystem being part of a program tomaintain and expand production capac-ity. The elimination of CO2 emissionsand a smaller equipment footprint arejust two of the benefits enjoyed byStatoil as a result.

HVDC Light™ extrudedsubmarine cable, with doublearmoring (80 kV rating)

3Use of MotorformerTM eliminatestransformer losses (A). Only motorlosses (B) remain.

4

Conventionalsystem

Motorformersystem

Inputpower

Shaftpower

A B

B


The reason for all these links is thevital need to secure power system

reliability in each of the participatingcountries. They make it easier to opti-mize power generation in an area inwhich different countries use differentmeans of power generation and havedifferent power demand profiles over a 24-hour period. Wet summers in theNordic region result in a considerablepower surplus, which can be sold tocountries that rely on more expensivefossil fuel-fired power plants. Con-versely, any surplus power can be soldback during periods of low load.

Power system reliability in the region isincreased by the addition of new HVDCcable links. In the event of grid disrup-tions, the rapid power balancing abilityof these links can be used to compen-sate for fluctuations in frequency andvoltage. For example, it is technicallyfeasible to reverse the entire 600 MWpower throughput of the SwePol Link in just 1.3 seconds, although this is not a feature that will be used in practice.Nevertheless, a typical emergency powermeasure could call for a ∆P ramp-up of

300 MW within a few seconds to preventgrid failure if the voltage in southernSweden drops below 380 kV.

All previous links of this kind use elec-trode stations off the coast to transmitthe return current under the sea, andthis has worked perfectly well. The firstsuch cable link was laid in 1954 be-tween Västervik, on the Swedish main-land, and the Baltic island of Gotland.Since then, the power rating has beenincreased and the original mercury arcvalves in the converter stations havebeen replaced with thyristor valves.

In the case of the SwePol Link, returncables were chosen as an alternativeto electrodes in order to pacify local

resistance to the project, particularlyaround Karlshamn. The environmentalissues that were raised during planningof this link may also apply to futureinstallations.

Lower emissions benefit theenvironmentThe power link between Sweden andPoland is the latest example of the

growing economic cooperation betweenthe countries bordering the Baltic Sea.The cable, which was taken into com-mercial service in June 2000, is a steptoward the large-scale power distribu-tion partnership that is known as theBaltic Ring [1].

The new link allows power generationto be stabilized in both countries, wherethe seasonal and daily variations in de-mand can differ considerably. The sur-plus that builds up in the Nordic regionduring wet years has already been men-tioned. In a really cold year it makesfinancial sense for this region to importPolish electricity generated from coalrather than start up a condensing oil-fired power plant or a gas turbine.

Polish imports of electricity via the linkwill in turn reduce environmental im-pact in that country. The predicted an-nual net import of 1.7 TWh is expectedto reduce emissions from Polish powerplants by 170,000 tonnes of sulfur diox-ide and 1.7 million tonnes of carbondioxide, according to calculations by theSwedish power company Vattenfall.

Leif Söderberg, Bernt Abrahamsson

Six cable links – all of them HVDC (high-voltage direct current) – are

currently in service between the power grids of continental Europe

and the Nordic region, with another five planned. The latest to be

brought on line is the SwePol Link, which connects the electricity

networks of Poland and Sweden. It is unique in that, unlike previous

installations that depend on electrode stations to transmit the return

current under ground or under water, it uses

cables to carry this current.

SwePol Link sets new environmental standard for HVDC transmission


Poland’s forthcoming admission to the EU will reinforce measures to re-duce its enviromental impact, therebypromoting the import of Swedishhydropower.

Cable company is set upSwePol Link AB was formed in 1997 toinstall, own and operate the cable linkbetween Sweden and Poland. It is apower transmission company that willsell electricity transmission servicesacross the link.

A Polish subsidiary was formed in 1998 to handle the local business. Onthe Swedish side the link will be usedprimarily by state-owned Vattenfall,although other companies will be able to sign transmission agreements withSwePol Link.

The new link is approximately 250 kmlong. It runs from Stärnö, just outsideKarlshamn in Sweden, past the Danishisland of Bornholm, and returns to landat the seaside resort of Ustka on theBaltic coast of Poland , .

The Swedish converter station was sitedat Stärnö because a 400-kV station andthe Swedish main grid are nearby. Thisavoided having to build new overheadlines that would have marred theSwedish countryside. The Polish con-verter station is connected to thePolish 400-kV grid at Slupsk, about 12 km from the coast.

The link involved around 2500 man-years of work for ABB, primarily at itsplants in Ludvika and Karlskrona. Bothstations are unmanned, although on-callpersonnel will be able to provide cover-age at short notice.

DC circuitThe land-based power grid is, of course,an AC system. However, for long under-water links DC is the only viable solu-tion on account of the high capacitanceof submarine cables.

Most cable links are monopolar sys-tems, in which the return current is car-ried through the ground and the sea.Power is transmitted over a high-volt-age cable. It is a common misconcep-tion that sea-water carries the returncurrent because of its high conductivity.However, most of the current travels at a considerable depth through theearth.

3

21

In the case of the SwePol Link the re-turn current is carried by two insulatedcopper conductors rated at 20 kV. Theuse of these conductors eliminates theneed for environmentally controversialelectrodes.

The high-voltage cable is around 140 mm in diameter, of which the cen-tral conductor takes up 53 mm. Instead of being solid, this consists of coppersegments to make it more flexible. The segments are shaped individually, then rolled as a unit to achieve an effec-tive copper cross-section in excess of99%. The rest of the cable consists of various layers of insulation, sealantand armor. The 250-km long cable ismade up of four sections which are laidindividually and joined by the layingbarge.

Visible parts of the linkThe visible parts of the link are the two converter stations at Stärnö andSlupsk. Located just a small distancefrom the center of Karlshamn, theStärnö station is next to an oil-firedpower plant that completely dominatesthe landscape. By siting the tall valvebuilding in a former quarry some 10 meters deep, the station’s impact on the skyline is reduced even more.The power cables run 2.3 km from thestation to the sea.

At the Polish end, the valve building isa prominent, but by no means ugly,landmark in the flat agricultural country-side. The Slupsk station is just over 20 meters high and is situated about 12 km from the Polish coast.

Both the high-voltage and return cablesrun underground almost all the waybetween the stations. On land thisrequired clearing a five-meter wideswathe through the landscape when thecables were being laid. This will soonbe hidden, partly thanks to forest re-planting. At sea about 85% of the cablecould be laid in a trench about onemeter deep to avoid damage by trawlersand anchors.

The converter stations cannot only beseen, but heard too. This is because the

4

KarlshamnKarlskrona

Bornholm

Ronneby

UstkaDarlowo

1 x 2100 mm2

HVDC

2 x 630 mm2

Return

Baltic Sea

SwePol Link between Swedenand Poland.

1

The power cable (blue) and the return cables(red) run on the same route, spaced 5 to 10 mapart in shallow water and 20 to 40 m apart indeep water.

Hemsjö

Dunowo

Krajnik

Karlshamn

Slupsk Gdansk

Oskarshamn

Malmö

Ringhals

The 250-km SwePol Linkexchanges power between 400-kVAC grids in Sweden and Poland.

2

The converter stations are near Karlshamn insouthern Sweden and at Slupsk, 12 km fromthe Polish coast.


eddy currents that flow in all powertransformers generate noise at a fre-quency of 100 Hz. Converter stations also produce higher-frequency noise that can be irritating to people livingnearby. It was clear that special sound-proofing would be necessary. Followingcalculations and measurement of thenoise level and noise propagation, thetransformers and reactors were enclosed.The filter capacitor cans are equippedwith a noise-reducing device.

A magnetic field with minimal effect on the surroundingsWhenever electricity is transmittedthrough a conductor it generates amagnetic field around it. Since DC isused, the field is of the same type as theearth’s natural magnetic field. This iscompletely different to the AC fieldsnormally produced, for example,around overhead lines.

Measurements have shown that the mag-netic field around the cable at a distanceof six meters is equal in strength to theearth’s natural magnetic field, while at adistance of 60 meters its intensity dropsto just one tenth of that field.

The magnetic field resulting from thecombination of 1 + 2 cables varies withthe depth and relative spacing of thecables. It is not practicable to lay the

high-voltage cable at the same time asthe two return cables, which meansthat they cannot be laid right next toeach other. They also have to be sepa-rated because of the heat they gener-ate. In shallow water the HV cable islaid 5–10 meters from the returncables. The resulting magnetic fieldmeasured on the surface of the sea istypically 80% of that obtained around ahigh-voltage cable in a monopolarinstallation. The equivalent figure at100 meters depth with 20–40 metersseparation is typically 50%.

Further away from the cables there is an even greater percentage reduction in the magnetic field, added to the fact that the absolute value of the mag-netic field at this distance is insignifi-cant compared with the earth’s mag-netic field. Thus, the use of returncables has no major effect on magneticfield strength. And, anyway, modernships no longer depend on magneticcompasses.

But what are the possible effects onanimal life? Experience with previouscable links has shown that they do not affect fish or other marine organ-isms. Nor do they affect the vital hom-ing ability of eels and salmon. This is especially important since these fishmigrate regularly during the course

of their lives and it is essential thattheir sense of direction remain unim-paired.

Back in 1959 a study was carried out to determine how the Gotland cablehad affected the marine environment[2]. This was followed by exhaustivestudies on the Fenno-Skan link (Swe-den–Finland) and the Baltic Cable(Sweden–Germany) [3]. The reportswere unanimous: marine life is affectedneither by the magnetic field nor byany chemical reactions. The facts speakfor themselves. Eels continue to findtheir way to the Baltic Sea, despitehaving to cross seven cables on theway [4, 5].

No chlorine formationThe originally proposed monopolarsolution, which would have used elec-trodes to transmit the return currentundersea, has been replaced by analternative solution in which returncables form a closed circuit. Any con-cerns about chlorine formation havetherefore been entirely eliminated,since no electrolysis can occur.

1

23

5

6

7

9

4

8

SwePol Link power cable, rated600 MW and 450 kV DC. Itsoverload capacity is 720 MW attemperatures below 20°C.

4

1 Conductor 2 Conductor screen3 Insulation4 Insulation screen5 Metal sheath

6 Protection/bedding7 Reinforcement8 Armor9 Serving

Valve building in the Slupsk (Poland) converter station3


The electrodes that would have beenused have an anode made of fine titani-um mesh and copper cables for thecathode. The following competing reac-tions take place at the anode:

2 H2O ⇒ 4H+ + O2 (g) + 4e-

2 Cl- ⇒ Cl2 (g) + 2e-

(g) in the above formulae indicates thatthese elements are in gaseous form.

The amount of chlorine gas generateddepends on the temperature, thechloride content of the seawater andthe reaction energies. It reacts almostexclusively with water as follows:

Cl2 (g) + H2O ⇒ HClO + Cl- + H+

At low pH the hypochlorous acid that is formed could be ionized, but in sea-water it mostly occurs in molecularform. In time it breaks down into itscomponent parts.

There was a suspicion that the chlorinegas and hypochlorous acid that are for-med would react with biological materialin the vicinity of the electrodes, resultingin the formation of compounds such aspolychlorinated hydrocarbons, which in-clude PCBs. Studies on the Baltic Cable

have ruled out this concern [3]. No accu-mulation of organic chlorine was ob-served in the surrounding biomass.

To put things in the right perspective it is worth comparing the described pro-cess with the common chlorination ofdrinking water, in which the hypochlo-rite concentration is at least 100 timeshigher than the value measured at theanode.

No corrosionThe return cables used for the SwePolLink eliminate the risk of corrosion, andthis would seem to be the only tangibleadvantage they offer.

DC cable links that use electrodes dolead to leakage currents in the earth. Thereturn current passing through the earthtakes the shortest path. On its route be-tween the electrodes some of the currentmay pass through long metal objects,such as railway tracks, gas pipes and ca-ble shielding. Electrolytic reactions couldoccur between this metal and its sur-roundings, possibly leading to corrosion.During the planning of the SwePol Linka list was therefore made of all the metalobjects that could be at risk (see table).

Objects that are at risk of corrosion dueto leakage currents require some form

of active protection, such as sacrificialor cathodic protection.

The return current can also find a routethrough other power distribution sys-tems that have multiple earth pointsclose to the electrode. This gives rise toa DC component in the AC grid, whichcan lead to undesirable DC magnetiz-ation of transformers. The problem cangenerally be solved by modifying thegrounding of the AC system.

Benefits versus costUsing the described return cables does,of course, have some advantages,among them the reduced magnetic fieldstrength along the cable route and thefact that they cause neither chlorine for-mation nor corrosion of undergroundmetal objects. And they also allowed asolution that addressed the environmen-tal concerns of various groups of soci-ety. In any final count, however, thesebenefits have to be measured againstthe extra cost. In the case of the SwePolLink, for example, they added about 5%to the cost of the project.

Metal objects on Swedish coast that could have been affected by the SwePol Link

Object length Distance from electrode Example

More than 25 m Less than 5 km Cable support

More than 200 m 5 – 10 km Sewage pipe Ø 1.2 m

More than 1000 m 10 – 20 km 10-kV cable

District heating

Copper shield around building

More than 5000 m 20 – 50 km Protective shield (Cu)

References

[1] The making of the Baltic Ring. ABB Review 2/2001, 44–48.

[2] W. Deines: The influence of electric currents on marine fauna. Cigré study committee no 10, 1959.

[3] Anders Liljestrand: Kontrollprogram bottenfauna, bottenflora (Inspection program: bottom flora and fauna). Baltic Cable. Marin Miljöanalys AB,

1999.

[4] Håkan Westerberg: Likströmskablar, ålar och biologiska kompasser (DC cables, eels and biological compasses). Fiskeriverkets Kustlaboratorium,

1999.

[5] E. Andrulewicz: Field and laboratory work on the impact of the power transmission line between Poland and Sweden (SwePol link) on the marine

environment and the exploitation of living resources of the sea. Sea Fisheries Institute Report, Gdynia, Feb 2001.

Leif Söderberg

SwedPower ABSE-162 16 Stockholm

[email protected]

Fax: +46 (0) 8 739 62 31

Bernt Abrahamsson

ABB Power TechnologiesSE-771 80 Ludvika

[email protected]

Fax: +46 (0) 240 807 63


With the arrival of the electric lightbulb in the homes and factories

of late 19th century Europe and theUSA, demand for electricity grew rapid-ly and engineers and entrepreneursalike were soon busily searching forefficient ways to generate and transmitit. The pioneers of this new technologyhad already made some progress – justbeing able to transmit power a fewkilometers was regarded as somethingfantastic – when an answer to growingdemand was found: hydroelectric pow-er. Almost immediately, interest turnedto finding ways of transmitting this‘cheap’ electricity to consumers overlonger distances.

First direct, then alternating currentThe first power stations in Europe andthe USA supplied low-voltage, direct cur-rent (DC) electricity, but the transmissionsystems they used were inefficient. Thiswas because much of the generated pow-er was lost in the cables. Alternating cur-rent (AC) offered much better efficiency,as it could easily be transformed to high-er voltages, with far less loss of power.The stage was thus set for long-distancehigh-voltage AC (HVAC) transmission.

In 1893, HVAC got another boost withthe introduction of three-phase trans-mission. Now it was possible to ensurea smooth, non-pulsating flow of power.

Although direct current had been beat-en at the starting gate in the race to de-velop an efficient transmission system,engineers had never completely givenup the idea of using DC. Attempts werestill being made to build a high-voltagetransmission system with series-connect-ed DC generators and, at the receivingend, series-connected DC motors – allon the same shaft. This worked, but itwas not commercially successful.

AC dominatesAs the AC systems grew and power in-creasingly was being generated far fromwhere most of its consumers lived andworked, long overhead lines were built,

In 1954, at a time when much of Europe was busy expanding its electricity supply infrastructure

to keep pace with surging demand, an event was quietly taking place on the shores of the Baltic

Sea that would have a lasting effect on long-distance power transmission. Four years earlier, the

Swedish State Power Board had placed an order for the world’s first commercial high-voltage

direct current (HVDC) transmission link, to be built between the Swedish mainland and the island

of Gotland. Now, in 1954, it was being commissioned.

50 years on, ABB proudly looks back at its many contributions to HVDC technology. Since the

laying of that early 90 kilometers long, 100-kV, 20-MW submarine cable, our company has gone

on to become the undisputed world leader in HVDC transmission. Of the 70,000 MW of HVDC

transmission capacity currently installed all over the world, more than half was supplied by ABB.

50 years

Gunnar Asplund, Lennart Carlsson, Ove Tollerz

ABB – from pioneer to world leader

HVDC


over which AC at ever-higher voltagesflowed. To bridge expanses of water,submarine cable was developed.

Neither of these transmission media waswithout its problems, however. Specifi-cally, they were caused by the reactivepower that oscillates between the ca-pacitances and inductances in the sys-tems. As a result, power system plan-ners began once again to look at thepossibility of transmitting direct current.

Back to DCWhat had held up high-voltage directcurrent transmission in the past was,first and foremost, the lack of reliableand economic valves that could convertHVAC into HVDC, and vice versa.

The mercury-arc valve offered, for a longtime, the most promising line of develop-ment. Ever since the end of the 1920s,when the Swedish ASEA – a foundingcompany of ABB – began making staticconverters and mercury-arc valves for volt-ages up to about 1000 V, the possibility of developing valves for even higher volt-ages had been continually investigated.

This necessitated the study of new fieldsin which only a limited amount of exis-

tent technical experience could beapplied. In fact, for some years it wasdebated whether it would be possible at all to find solutions to all the variousproblems. When HVDC transmissionfinally proved to be technically feasiblethere still remained uncertainty as towhether it could successfully competewith HVAC in the marketplace.

Whereas rotating electrical machinesand transformers can be designed veryprecisely with the aid of mathematicallyformulatedphysicallaws, mer-cury-arcvalve designdepends to alarge degreeon knowl-edge ac-quired em-pirically. As a result, attempts to in-crease the voltage in the mercury-vapor-filled tube by enlarging the gap be-tween the anode and cathode invariablyfailed.

The problem was solved in 1929 by aproposal to insert grading electrodesbetween the anode and cathode. Subse-

quently patented, this innovative solu-tion can in some ways be considered asthe cornerstone of all later developmentwork on the high-voltage mercury-arcvalve. It was during this time that Dr.Uno Lamm, who led the work, earnedhis reputation as ‘the father of HVDC’.

The Gotland linkThe time was now ripe for service trialsat higher powers. Together with theSwedish State Power Board, the compa-ny set up, in 1945, a test station at Troll-hättan, where there was a major powerplant that could provide energy. A 50-kmpower line was also made available.

Trials carried out over the followingyears led to the Swedish State PowerBoard placing, in 1950, an order forequipment for the world’s first HVDCtransmission link. This was to be builtbetween the island of Gotland in theBaltic Sea and the Swedish mainland.

Following on this order, the companyintensified its development of the mer-cury-arc valve and high-voltage DC ca-ble, while also initiating design work onother components for the converter sta-tions. Among the equipment that bene-fited from the increased efforts weretransformers, reactors, switchgear andthe protection and control equipment.

Only some of the existing AC systemtechnology could be applied to the newDC system. Completely new technology

was there-fore neces-sary. Spe-cialists inLudvika,led by Dr. ErichUhlmannand Dr. Harry

Forsell, set about solving the many verycomplex problems involved. Subsequent-ly, a concept was developed for the Got-land system. This proved to be so suc-cessful that it has remained basically un-changed right down to the present time!

Since Gotland is an island and thepower link was across water, it was

Even when HVDC transmissionfinally proved technically feasible,it was doubted for a long timewhether it could compete withHVAC in the marketplace.

Analog simulator used in the design of the early HVDC transmission systems


also necessary to manufacture a subma-rine cable that could carry DC. It wasseen that the ‘classic’ cable with massimpregnated paper insulation that hadbeen in use since 1895 for operation at 10 kV AC had potential for furtherdevelopment. Soon, this cable wasbeing developed for 100 kV DC!

Finally, in 1954, after four years of innov-ative endeavor, the Gotland HVDC trans-mission link, with a rating of 20 MW, 200 A and 100 kV, went into operation.A new era of power transmission hadbegun.

The original Gotland link was to see 28 years of successful service beforebeing finally decommissioned in 1986.Two new links for higher powers havemeanwhile been built between theisland and the Swedish mainland, onein 1983 and the other in 1987.

Early HVDC projectsThe early 1950s also saw the British andFrench power administrations planninga power transmission link across theEnglish Channel. High-voltage DCtransmission was chosen, and the com-pany won its second HVDC order – thistime a link for 160 MW.

The success of these early projects gen-erated considerable worldwide interest.

During the 1960s several HVDC linkswere built: Konti-Skan between Swedenand Denmark, Sakuma in Japan (with50/60 Hz frequency converters), theNew Zealand link between the Southand the North Islands, the Italy – Sar-dinia link and the Vancouver Island linkin Canada.

The largest mercury-arc valve HVDCtransmission link to be built by thecompany was the Pacific Intertie [1] inthe USA. Originally commissioned for1440 MW and later uprated to 1600 MWat ±400 kV, its northern terminal is sitedin The Dalles, Oregon, and its southernterminal at Sylmar, in the northern tip of the Los Angeles basin. This projectwas undertaken together with GeneralElectric, and started operating in 1970.

In all, the company installed eight mer-cury-arc valve based HVDC systems for a total power rating of 3400 MW.Although many of these projects havesince been replaced or upgraded withthyristor valves, some are still in opera-tion today, after 30 to 35 years ofservice!

The semiconductor ‘takeover’ beginsMercury-arc valve based HVDC hadcome a long way in a short time, but itwas a technology that still harboredsome weaknesses. One was the difficul-

ty in predicting the behavior of thevalves themselves. As they could notalways absorb the reverse voltage, arc-backs occurred. Also, mercury-arcvalves require regular maintenance,during which absolute cleanliness iscritical. A valve that avoided thesedrawbacks was needed.

The invention of the thyristor in 1957had presented industry with a host ofnew opportunities, and HVDC transmis-sion was soon seen as a promising area

Early mercury-arc valve for HVDC transmissionMercury-arc valves in the first Gotland link,1954

Gotland 1 extension, with the world’s first HVDC thyristor valves


of application. As part of its activities inthe semiconductor field, the companyhad continued to work at developinghigh-voltage thyristor valves as an alter-native to the mercury-arc type. In thespring of 1967, one of the mercury-arcvalves used in the Gotland HVDC linkwas replaced with a thyristor valve. Itwas the first time anywhere that thiskind of valve had been taken into com-mercial operation for HVDC transmis-sion. After a trial of just one year, theSwedish State Power Board ordered acomplete thyristor valve group for eachconverter station, at the same time in-creasing the transmission capacity by 50 percent.

Around the same time, tests were car-ried out on the Gotland submarine ca-ble, which had been operating withoutany problems at 100 kV, to see if itsvoltage could be increased to 150 kV –the level needed to transmit the higherpower. The tests showed that it could,and this cable was subsequently operat-ed at an electrical stress of 28 kV/mm,which is still the worldwide benchmarkfor large HVDC cable projects today.

The new valve groups were connectedin series with the two existing mercury-arc valve groups, thereby increasing the transmission voltage from 100 to 150 kV. This higher-rated system wastaken into service in the spring of 1970

– another world’s ‘first’ for the Gotlandtransmission link.

With the advent of thyristor valves itbecame possible to simplify the convert-er stations, and semiconductors havebeen used in all subsequent HVDClinks. Other companies now began toenter thefield.BrownBoveri(BBC) –which lat-er mergedwith ASEAto formABB – teamed up with Siemens andAEG in the mid-1970s to build the 1920-MW Cahora Bassa HVDC linkbetween Mozambique and South Africa.The same group then went on to buildthe 2000-MW Nelson River 2 link inCanada. This was the first project toemploy water-cooled HVDC valves.

The late 1970s also saw the completionof new projects. These were the Skager-rak link between Norway and Denmark,Inga-Shaba in the Congo, and the CUProject in the USA.

The Pacific Intertie was also extendedtwice in the 1980s, each time with thyris-tor converters, to raise its capacity to3100 MW at ±500 kV. (ABB is currently

upgrading the Sylmar terminal by replac-ing the converters and control system.)

Itaipu – the new benchmark The contract for the largest of all HVDCtransmission schemes to date, the 6300-MW Itaipu HVDC link in Brazil,was awarded to the ASEA-PROMON

consortiumin 1979.This projectwas com-pleted andput intooperation inseveralstages be-

tween 1984 and 1987. It plays a key rolein the Brazilian power scheme, supply-ing a large portion of the electricity forthe city of São Paulo.

The scale and technical complexity ofthe Itaipu project presented a consider-able challenge, and it can be consideredas the start of the modern HVDC era.The experience gained in the course ofits completion has been in no small wayresponsible for the many HVDC ordersawarded to ABB in the years since.

After Itaipu, the most challenging HVDCproject was undoubtedly the 2000-MWQuébec – New England link. This wasthe first large multi-terminal HVDCtransmission system to be built any-where in the world.

HVDC cables have kept paceAs the converter station ratings in-creased, so too did the powers and volt-age levels for which the HVDC cableshad to be built.

The most powerful HVDC submarinecables to date are rated 600 MW at 450 kV. The longest of these are the230-km cable for the Baltic Cable linkbetween Sweden and Germany, and the 260-km cable for the SwePol linkbetween Sweden and Poland.

HVDC todayThe majority of HVDC converter stationsbuilt today are still based on the princi-ples that made the original Gotland linksuch a success back in 1954. Station de-

Foz do Iguaçu converter station with the Itaipu 12,600-MW power station in the background

The scale and complexity of theItaipu project presented a consid-erable challenge, and it can beconsidered as the start of themodern HVDC era.


sign underwent its first big change withthe introduction of thyristor valves inthe early 1970s. The first of these wereair-cooled and designed for indoor use,but soon outdoor oil-cooled, oil-insulat-ed valves were also being used. Today,all HVDC valves are water-cooled [2].

Good examples of modern bulk powerHVDC transmission are the links ABB isinstalling for the Three Gorges hydro-electric power plant project in China.(See article starting on page 6.)

In 1995 ABB presented a new genera-tion of HVDC converter stations: ‘HVDC2000’ [3]. HVDC 2000 was developed to meet stricter electrical disturbancerequirements, to provide better dynam-ic stability where there was insufficientshort-circuit capacity, to overcomespace limitations, and to shorten deliv-ery times.

A key feature of HVDC 2000 was theintroduction of capacitor commutatedconverters (CCC). This was, in fact, thefirst fundamental change to have beenmade to the basic HVDC system tech-nology since 1954!

HVDC 2000 also includes other ABB in-novations, such as continuously tunedAC filters (ConTune), active DC filters,outdoor air-insulated HVDC valves, andthe fully digital MACH2™ control system.

The first project to employ HVDC 2000with CCC and outdoor valves was theGarabi 2200-MW HVDC back-to-backstation in the Brazil – Argentina HVDCInterconnection.

HVDC LightTM

HVDC technology has become a maturetechnology over the past 50 years andreliably transmits power over long dis-tances with very low losses. This begsthe question: where is developmentwork likely to go in the future?

It was conceived that HVDC develop-ment could, once again, take its cuefrom industrial drives. Here, thyristorswere replaced a long time ago by volt-age source converters (VSC), with semi-conductors that can be switched off aswell as on. These have brought manyadvantages to the control of industrialdrive systems and it was realized thatthey could also apply to transmissionsystems. Adapting the technology of volt-age source converters to HVDC, how-ever, is no easy matter. The entire tech-nology has to change, not just the valves.

As development of its VSC converter gotunder way, ABB realized that the insu-lated gate bipolar transistor, or IGBT,held more promise than all the otheravailable semiconductor components.Above all else, the IGBT needs only

very little power for its control, makingseries connection possible. However, forHVDC a large number of IGBTs wouldhave to be connected in series, some-thing industrial drives do not need.

In 1994, ABB concentrated its develop-ment work on VSC converters in a pro-ject that aimed at putting two convertersbased on IGBTs into operation forsmall-scale HVDC.

An existing 10-km-long AC line in cen-tral Sweden was made available for theproject.

At the end of 1996, after comprehensivesynthetic tests, the equipment was in-stalled in the field for testing under ser-vice conditions. In 1997 the world’s firstVSC HVDC transmission system, HVDCLight™ [4], began transmitting powerbetween Hellsjön and Grängesberg inSweden.

In the meantime, seven such systemshave been ordered, and six of them arenow in commercial operation in Swe-den, Denmark, the USA and Australia.HVDC Light is now available for ratingsup to 350 MW, ±150 kV.

ABB is to date the only company thathas managed to develop and build VSCHVDC transmission systems [5].

Submarine cable for the 600-MW BalticCable HVDC link between Germany andSweden

Baltic Cable HVDC converter station


One advantage of HVDC Light is that itallows an improvement in the stabilityand reactive power control at each endof the network. Also, it can operate atvery low short-circuit power levels andeven has black-start capability.The HVDCLight cable ismade of poly-meric materialand is thereforevery strong androbust. Thismakes it possi-ble to use HVDC cables where adverselaying conditions might otherwise causedamage. Extruded cable has also madevery long HVDC cable transmission onland now economically viable. An ex-ample is the 180-km-long HVDC Light™interconnection ‘Murraylink’ in Australia.

And the next 50 years?HVDC transmission has come a long

way since that first Gotland link. Butwhat does the future hold for it?

Bulk transmission is likely to rely onthyristor-based technology for many

years sinceit is reliableand low incost, pluslosses arelow. In-creasing the voltageis one way to go

here as it would allow much higherpowers and very long distances for the links.

HVDC Light has the potential to bedeveloped further. One direction mightbe toward higher voltages and powers,but low power and relatively high volt-ages are also conceivable for systemsfor smaller loads and generators.

The development of HVDC Light cablehas made it possible to link up networksacross very deep waters that have previ-ously made such schemes unthinkable.The most interesting prospects forHVDC Light, however, lie in its potentialfor building multi-terminal systems. Inthe long term it might offer a genuinealternative to AC transmission, whichtoday completely dominates this sector.

References

[1] L. Engström: More power with HVDC to Los Angeles. ABB Review 1/88, 3–10.

[2] B. Sheng, H. O. Bjarma: Proof of performance – a synthetic test circuit for verifying HVDC thyristor valve design. ABB Review 3/2003, 25–29.

[3] B. Aernlöv: HVDC 2000 – a new generation of high-voltage DC converter stations. ABB Review 3/1996, 10–17.

[4] G. Asplund, et al: HVDC Light – DC transmission based on voltage sourced converters. ABB Review 1/1998, 4–9.

[5] T. Nestli, et al: Powering Troll with new technology. ABB Review 2/2003, 15–19.

Further information on HVDC can be found at www.abb.com/hvdc

Shoreham station, 330-MW HVDC LightTM Cross Sound Cable link, USA HVDC Light land cable

The introduction of capacitorcommutated converters wasthe first fundamental changemade to the basic HVDCtechnology since 1954!

Gunnar Asplund

Lennart Carlsson

ABB Power TechnologiesLudvika/Sweden

[email protected]@se.abb.com

Ove Tollerz

ABB Power TechnologiesKarlskrona/Sweden

[email protected]


ABB Review

Special Report

Power Technologies

Editorial board

Markus BayeganGroup R&D and Technology

Georg Schett ABB Power Technologies

Klaus Treichel ABB Power Technologies

Nils Leffler Chief Editor, ABB Review

Publisher and copyright © 2003

ABB LtdZurich/Switzerland

Publisher’s office

ABB Schweiz AGCorporate ResearchABB Review / RD.REVCH-5405 Baden-Dä[email protected]

Printers

Vorarlberger Verlagsanstalt AGAT-6850 Dornbirn/Austria

Design

DAVILLA Werbeagentur GmbHAT-6900 Bregenz/Austria

Partial reprints or reproductions are permittedsubject to full acknowledgement. Complete reprints require the publisher’swritten consent.

ISSN: 1013-3119

www.abb.com/abbreview

a

Think of all the ideas you put on paper.In China, that’s a lot of paper.

w w w . a b b . c o m

That’s why we helped Asia Pulp and Paper

build the fastest mill in the world.ABB

also created a new generation of integrated

automation that can monitor and operate

the entire plant from a single screen. At ABB,

we believe the most important thing

we build today is knowledge. Because the

power that will drive the next hundred

years is the power of ideas.

Don’t let your city lose its shine.

Proven power technologiesintegrated in record time

ABB’s cutting edge technologies for grid reliability include HVDC

and FACTS: High Voltage Direct Current (HVDC) technology by

ABB has built-in overload control and can be loaded fully without

increasing the risk of cascaded line tripping. Our Flexible AC

Transmission Systems (FACTS) allow more power to flow on exis-

ting lines with minimum impact on the environment, substantially

shorter project implementation times, and this at lower costs.

Contact the worldwide market leader in power technologies:

www.abb.com/poweroutage

©ABB 2003

0985 ABB Special Report

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