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Power T&D Solutions www.abb.com

Power System Technology Navigator (PSTN) Friday, March 30, 2012

Back to Overview V. 1.1

- major benefits(link to PPT)

- additionalbenefits

Shunt capacitor

Shunt reactor

Series compensation

Harmonic filters

SVC

TCSC

STATCOM

HVDC

SVR

DVR

MINICOMP(STATCOM)

Energy Storage

Minicap

SVC for Industry

PSGuardWide Area Monitoring

HVDC Light

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Static Freq. Converter

F a c t o r s & P h e n o m e n a

ReactivePowerF

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Loopflow

Unbalancedload

Interruptions

Harmonics

Sags&Swells

Related Links: (online)

Power T&D Solutions

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Motors, Drives & Power Electronics

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Power System Technology Navigator

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Asynchronous connection

The interconnected AC networks that tie the powergeneration plants to the consumers are in most caseslarge. The map below shows the European situation.

There is one grid in Western Europe, one in EasternEurope, one in the Nordic countries. Islands like GreatBritain, Ireland, Iceland, Sardinia, Corsica, Crete,Gotland, etc. also have their own grid with no ACconnection to the continent. The other continents onthe globe have a similar situation.

Even if the networks in Europe have the same nominalfrequency, 50 cycles per second or Hertz (Hz), there isalways some variation, normally less than 0.1 Hz,and in certain cases it may prove difficult or impossibleto connect them with AC because of stability concerns.An AC tie between two asynchronous systems needsto be very strong to not get overloaded. If a stable ACtie would be too large for the economical power

exchange needs or if the networks wish to retain theirindependence, than a HVDC link is the solution.

And in other parts of the world (South America andJapan) 50 and 60 Hz networks are bordering eachother and it would be impossible to exchange powerbetween them with an AC line or cable. HVDC is thenthe only solution.

European interconnected power grids.

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Bottlenecks

Constrained transmission paths or interfaces in aninterconnected electrical system

The term Bottlenecksis often interchangeable tocongested transmission paths or interfaces. Atransmission path or interface refers to a specific set oftransmission elements between two neighboringcontrol areas or utility systems in an interconnectedelectrical system. A transmission path or interfacebecomes congested when the allowed power transfercapability is reached under normal operatingconditions or as a result of equipment failures andsystem disturbance conditions. The key impacts ofBottlenecks are reduction of system reliability,inefficient utilization of transmission capacity andgeneration resources, and restriction of healthy marketcompetition.The ability of the transmission systems todeliver the energy is dependent on several mainfactors that are constraining the system, includingthermal constraints, voltage constraints, and stability

constraints. These transmission limitations are usuallydetermined by performing detailed power flow andstability studies for a range of anticipated systemoperating conditions. Thermal limitations are the mostcommon constraints, as warming and consequentlysagging of the lines is caused by the current flowing inthe wires of the lines and other equipment. In somesituations, the effective transfer capability oftransmission path or interface may have to be reduced

from the calculated thermal limit to a level imposed byvoltage constraints or stability constraints.

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Flicker

A fluctuation in system voltage that can lead tonoticeable changes in light output.

Voltage Flicker can either be a periodic or aperiodicfluctuation in voltage magnitude i.e. the fluctuation mayoccur continuously at regular intervals or only onoccasions. Voltage Flicker is normally a problem withhuman perception of lamp strobing effect but can alsoaffect power-processing equipment such as UPSsystems and power electronic devices. Slowlyfluctuating periodic flickers, in the 0.5 30.0Hz range,

are considered to be noticeable by humans. A voltagemagnitude variation of as little as 1.0% may also benoticeable.

The main sources of flicker are industrial loadsexhibiting continuous and rapid variations in the loadcurrent magnitude. This type of loads includes electricarc furnaces in the steel industry, welding machines,large induction motors, and wind power generators.

High impedance in a power delivery system willcontribute further to the voltage drop created by theline current variation.

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Interruptions

Occur when the supply voltage drops below 10% of thenominal value

An Interruption occurs whenever a supplys voltage dropsbelow 10% of the rated voltage for a period of time nolonger than one minute. It is differentiated from a voltagesag in that the late is not a severe power quality problem.The term sag covers voltage drops down to 10% of nominalvoltage whereas an interruption occurs at lower than 10%.A Sustained Interruption occurs when this voltage decreaseremains for more than one minute.

An interruption is usually caused by downstream faults thatare cleared by breakers or fuses. A sustained interruption iscaused by upstream breaker or fuse operation. Upstreambreakers may operate due to short-circuits, overloads, andloss of stability on the bulk power system. Loss of stabilityis usually characterized by out-of-tolerance voltagemagnitude conditions and frequency variations whichexceed electrical machine and transformer tolerances. This

phenomenon is often associated with faults anddeficiencies in a transmission system but can also be theresult of lack of generation resources. The concernscreated by interruptions are evident and includeinconvenience, loss of production time, loss of product, andloss of service to critical facilities such as hospitals.

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Long linesLong lines need special consideration in the planning of a

power system.

This transmission carries more than 12,000 MW over 800

km. There is an HVDC system with two 600 kV bipoles of

3150 MW each is direct route to So Paulo while the three

800 kV shunt and series compensated AC lines has two

intermediate substations that allow connection to the local

grids.

For long AC lines one must consider i.e. the reactive power

compensation, the transient stability and switchingovervoltages and how many intermediate substations one

needs.

If the line length is longer than approx. 600 km one should

also consider if an HVDC alternative brings lower

investment costs and/or lower losses or if the inherent

controllability of an HVDC system brings with some other

benefits.

Another factor to consider is the land use

The figure at the right compares two 3,000 MW HVDC lines

for the 1,000 km Three Gorges - Shanghai transmission,

China, to five 500 kV AC lines that would have been used if

AC transmission had been selected.

Go to Long Cables

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Long cables

Cables have large capacitances and therefore, if fed with AC,large reactive currents. Cables for DC are also less expensivethan for AC. One must distinguish between submarine cablesand land (underground) cables.

Submarine cables

Since no shunt reactor can be installed at intermediate points(in the sea) and DC cables are less expensive, the majority ofcables > 50 km are for DC.

Underground cables

Long underground cables (> 50 km) have been generallyavoided since the cost for an overhead line was deemed to beonly 10 20 % of the cost for the cable. In many parts of theworld it is now almost impossible to get permission to build anew overhead line. HVDC Light has changed the cost relationand the cable solution is less expensive than before.

Laying of the 200 km Fenno-Skan HVDC cable (500 MW).

Laying of the 180 km Murraylink HVDC Light cable (220 MW).

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Loop Flow

Unscheduled power flow on a given transmission path in aninterconnected electrical system

The terms Loop Flow and Parallel Path Flow are sometimesused interchangeable to refer to the unscheduled power flows,that is, the difference between the scheduled and actual powerflows, on a given transmission path in an interconnectedelectrical system. Unscheduled power flows on transmissionlines or facilities may result in a violation of reliability criteria anddecrease available transfer capability between neighboringcontrol areas or utility systems.

The reliability of an interconnected electrical system can becharacterized by its capability to move electric power from onearea to another through all transmission circuits or pathsbetween those areas under specified system conditions. Thetransfer capability may be affected by the contract pathdesignated to wholesale power transactions, which assumesthat the transacted power would be confined to flow along anartificially specified path through the involved transmissionsystems. In reality, the actual path taken by a transaction maybe quite different from the designated routes, determined byphysical laws not by commercial agreements, thus involving theuse of transmission facilities outside the contracted systems.These unexpected flow patterns may cause so-called LoopFlow and Parallel Path Flow problems, which may limit theamount of power these other systems can transfer for their own

purposes.

Transmission Loop Flows for 1000 KW scheduled Transfer fromArea A to Area C in an Interconnected System

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Power Oscillations

Periodic variations in generator angle or line angle due totransmission system disturbances

Oscillations of generator angle or line angle are generallyassociated with transmission system disturbances and canoccur due to step changes in load, sudden change of generatoroutput, transmission line switching, and short circuits.Depending on the characteristics of the power system, theoscillations may last for 3 -20 seconds after a severe fault.Drawn out oscillations that last for a few seconds or more areusually the result of very light damping in the system and are

pronounced at power transfers that approach the lines stabilitylimit. During such angular oscillation period significant cyclevariations in voltages, currents, transmission line flows will takeplace. It is important to damp these oscillations as quickly aspossible because they cause mechanical wear in power plantsand many power quality problems. The system is also morevulnerable if further disturbances occur.

The active power oscillations on a transmission line tend to limit

the amount of power that may be transferred, thus may result instability concerns or utilization restrictions on the corridorsbetween control areas or utility systems. This is due to the factthat higher power transfers can lead to less damping and thusmore severe and possibly unstable oscillations.

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Reactive Power Factor

Effects of reactive power on the efficiency of transmission anddistribution

Reactive power is defined as the product of the rms voltage,current, and the sine of the difference in phase angle betweenthe two. It is used to describe the effects of a generator, a load,or other network equipment, which on the average neithersupplies nor consumes power. Synchronous generators,overhead lines, underground cables, transformers, loads andcompensating devices are the main sources and sinks ofreactive power, which either produce or absorb reactive power

in the systems. To maintain efficient transmission anddistribution, it is necessary to improve the reactive powerbalance in a system by controlling the production, absorption,and flow of reactive power at all levels in the system. Bycontrast, inefficient reactive power management can result inhigh network losses, equipment overloading, unacceptablevoltage levels, even voltage instability and outages resultingfrom voltage collapse. Local reactive power devices for voltageregulation and power factor correction are also importantespecially for balancing the reactive power demand of large andfluctuating industrial loads.

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Sags and Swells

Short duration decrease/increase (sag/swell) in supply voltage

A Voltage Sag or Voltage Dig is a decrease in supply voltage of10% to 90% that lasts in duration from half a cycle to oneminute. A Voltage Swell is an increase in supply voltage of 10%to 80% for the same duration.

Voltage sags are one of the most commonly occurring powerquality problems. They are usually generated inside a facilitybut may also be a result of a momentary voltage drop in thedistribution supply. Sags can be created by sudden but brief

changes in load such as transformer and motor inrush and shortcircuit-type faults. A sagmay also be created by a step changein load followed by a slow response of a voltage regulator. Avoltage swellmay occur by the reverse of the above events.

Electronic equipment is usually the main victim of sags, as theydo not contain sufficient internal energy to ride through thedisturbance. Electric motors tend to suffer less from voltagesags, as motor and load inertias will ridethrough the sag if it isshort enough in duration.

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Unbalanced Load

A load which does not draw balanced current from a balancedthree-phases supply

An unbalanced load is a load which does not draw balancedcurrent from a balanced three-phase supply. Typicalunbalanced loads are loads which are connected phase-to-neutral and also loads which are connected phase-to-phase.Such loads are not capable of drawing balanced three-phasecurrents. They are usually termed single-phase loads.

A single-phase load, since it does not draw a balanced three-

phase current, will create unequal voltage drops across theseries impedances of the delivery system. This unequal voltagedrop leads to unbalanced voltages at delivery points in thesystem. Blown fuses on balanced loads such as three-phasemotors or capacitor banks will also create unbalanced voltage inthe same fashion as the single-phase and phase-phaseconnected loads. Unbalanced voltage may also arise fromimpedance imbalances in the circuits that deliver electricity suchas untransposed overhead transmission lines. Such

imbalances give the appearance of an unbalanced load togeneration units.

An unbalanced supply may have a disturbing or evendamaging effect on motors, generators, poly-phase converters,and other equipment. The foremost concern with unbalancedvoltage is overheating in three-phase induction motors. Thepercent current imbalance drawn by a motor may be 6 to 10times the voltage imbalance, creating an increase in losses and

in turn an increase in motor temperature. This condition maylead to motor failure. Back to Overview


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Voltage Instability

Post-disturbance excursions of voltages at some buses in thepower system out of the steady operation region

Voltage instability is basically caused by an unavailability ofreactive power support in an area of the network, where thevoltage drops uncontrollably. Lack of reactive power mayessentially have two origins: firstly, a gradual increase of powerdemand without the reactive part being met in some buses orsecondly, a sudden change in the network topology redirectingthe power flows in such a way that the required reactive powercannot be delivered to some buses.

The relation between the active power consumed in theconsidered area and the corresponding voltages is expressed ina static way by the P-V curves (also called nose curves). Theincreased values of loading are accompanied by a decrease involtage (except in case of a capacitive load). When the loadingis further increased, the maximum loadability point is reached,beyond which no additional power can be transmitted to theload under those conditions. In case of constant power loads

the voltage in the node becomes uncontrollable and decreasesrapidly. This may lead to the partial or complete collapse of apower system.

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Factors / Phenomena: Harmonics

Technology / System: Harmonic Filters

Example of application: Reducing harmonics in heavy industry

Harmonic Filters may be used to mitigate, and in some cases, eliminateproblems created by power system harmonics. Non-linear loads such asrectifiers, converters, home electronic appliances, and electric arcfurnaces cause harmonics giving rise to extra losses in power equipmentsuch as transformers, motors and capacitors. They can also cause other,probably more serious problems, when interfering with control systemsand electronic devices. Installing filters near the harmonic sources caneffectively reduce harmonics. For large, easily identifiable sources of

harmonics, conventional filters designed to meet the demands of theactual application are the most cost efficient means of eliminatingharmonics. These filters consist of capacitor banks with suitable tuningreactors and damping resistors. For small and medium size loads, activefilters, based on power electronic converters with high switchingfrequency, may be a more attractive solution.

Benefits:

Eliminates harmonics

Improved Power FactorReduced Transmission Losses

Increased Transmission Capability

Improved Voltage Control

Improved Power Quality

Other applications:

Shunt Capacitors

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Factors / Phenomena: Reactive Power Factor

Technology / System: Harmonic Filters

Example of application: Regulation of the power factor to increase the

transmission capability and reduce transmission losses as well asreducing harmonics.

Harmonic Filters produced reactive power as well as mitigate, and insome cases, eliminate problems created by power system harmonics.Where the main need is power factor compensation the best solution canstill be a harmonic filter due to the amount of harmonics. Non-linear loadssuch as rectifiers, converters, home electronic appliances, and electric arcfurnaces cause harmonics giving rise to extra losses in power equipment

such as transformers, motors and capacitors. They can also cause other,probably more serious problems, when interfering with control systemsand electronic devices. Installing filters near the harmonic sources caneffectively reduce harmonics. For large, easily identifiable sources ofharmonics, conventional filters designed to meet the demands of theactual application are the most cost efficient means of eliminatingharmonics as well as producing reactive power. These filters consist ofcapacitor banks with suitable tuning reactors and damping resistors. Forsmall and medium size loads, active filters, based on power electronic

converters with high switching frequency, may be a more attractivesolution.

Benefits:

Improved power factor, Reduced transmission losses, Increased transmission capability

Improved voltage control, Improved power quality, Eliminates harmonics

Other applications:

Shunt capacitors

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Factors / Phenomena: Asynchronous connection

Technology / System: HVDC and HVDC Light

Example of application: Interconnection of power systems

It is sometimes difficult or impossible to connect two AC networks due tostability reasons. In such cases HVDC is the only way to make anexchange of power between the two networks possible.

Several HVDC links interconnect AC system that are not running insynchronism with each other. For example the Nordel power system inScandinavia is not synchronous with the UCTE grid in western continentalEurope even though the nominal frequencies are the same. And thepower system of eastern USA is not synchronous with that of western

USA. There are also HVDC links between networks with different nominalfrequencies (50 and 60 Hz) in Japan and South America.

Direct current transmissions in the form of classical HVDC or HVDCLight are the only efficient means of controlling power flow in a network.HVDC can therefore never become overloaded. An AC network connectedwith neighboring grids through HVDC links may as the worst case loosethe power transmitted over the link, if the neighboring grid goes down - theHVDC transmission will act as a firewall against cascading disturbances.

Benefits:

The networks can retain their independence

An HVDC link can never be overloaded

HVDC transmission will act as a firewall against cascading disturbances.

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more about HVDC & Asynchronous Connection

The Scandinavia - Northern Europe HVDC interconnections

Links:

HVDC transmission for controllability of power flow

HVDC transmission for asynchronous connectionApplications in Power Systems: Interconnection

ABB HVDC Portal
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Factors / Phenomena: Bottlenecks


Example of application: Interconnection of power systems

Bottlenecks may be relieved by the use of an HVDC or HVDC Light link inparallel with the limiting section of the grid. By using the inherentcontrollability of the HVDC system the power system operator can decidehow much power that is transmitted in the AC-link and how much by theHVDC system.

Longer AC lines tend to have stability constrained capacity limitations asopposed to the higher thermal constraints of shorter lines. By using theinherent controllability of an HVDC system in parallel with the long AC

lines, the power system can be stabilized and the transmission limitationson the AC line can be increased.

Benefits:

Increased Power Transfer Capability

Additional flexibility in Grid Operation

Improved Power and Grid Voltage Control

An HVDC link can never be overloaded!

.

Back to Overview

more about HVDC & Bottlenecks

Links:


Applications in Power Systems: InterconnectionABB HVDC Portal
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Phenomena / Factor: Long lines

Technology / System: HVDC

Example of application: Expressway for power

A HVDC transmission line costs less than an AC line for the sametransmission capacity. However, the terminal stations are more expensivein the HVDC case due to the fact that they must perform the conversionfrom AC to DC and vice versa. But above a certain distance, the so-called"break-even distance", the HVDC alternative will always give the lowestcost. Therefore many long overhead lines (> 700 km) particularly fromremote generating stations are built as DC lines.

Benefits:

Lower investment cost

Lower losses

Lower right-of-way requirement for DC lines than for AC lines

HVDC does not contribute to the short circuit current

=> Go to Long Submarine Cables

.

Back to Overview

more about HVDC & Long Lines

Links:

HVDC transmission for lower investment cost

HVDC transmission has lower losses

Applications in Power Systems: Connection of

generation

ABB HVDC Portal
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Phenomena / Factor: Long submarine cables

Technology / System: HVDC

Example of application: long distance water crossing

In a long AC cable transmission, the reactive power flow due to the largecable capacitance will limit the maximum possible transmission distance.With HVDC there is no such limitation, why, for long cable links, HVDC isthe only viable technical alternative. There are HVDC and HVDC Lightcables from 40 km up to 580 km in operation or under construction withpower ratings from 40 to 700 MW.

Benefits:Lower investment cost

Lower losses

.

Back to Overview

more about HVDC & Long Submarine Cables

Links:

HVDC submarine cables

ABB HVDC Portal
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Factors / Phenomena: Loop Flow


Example of application: Interconnected power systems

Loop Flows, or Parallel Path Flows, may be alleviated by the use of HVDCor HVDC Light. In interconnected power systems, the actual path taken bya transaction from one area to another may be quite different from thedesignated routes as the result of parallel path admittance, thus divertingor wheeling power over parallel connections.

The figure shows how parallel path flow can be avoided by replacing anAC line with a HVDC/HVDC Light link between area A and area C

Benefits:HVDC can be controlled to transmit contracted amounts of power andalleviate unwanted loop flows.

An HVDC link can alternatively be controlled to minimize total networklosses


.

Back to Overview

more about HVDC & Loop Flow

Links:


Applications in Power Systems: Interconnection

ABB HVDC Portal
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Factors / Phenomena: Power Oscillations


Example of application: Steady State and Transient Stability

Improvement

Long AC lines tend to have stability constrained capacity limitations asopposed to the higher thermal constraints of shorter lines. By using theinherent controllability of an HVDC system in parallel with the long AClines, the power system can be stabilized and the transmission limitationson the AC line can be increased.

The HVDC damping controller is a standard feature in many HVDCprojects in operation. It normally takes its input from the phase angle

difference in the two converter stations.

Benefits:


Improved Power and Grid Voltage Control


Back to Overview

more about HVDC & Power Oscillations

Links:


Applications in Power Systems: Interconnection

HVDC Light System Interaction Tutorial.

ABB HVDC Portal

P T&D S l i
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Factors / Phenomena: Flicker

Technology / System: MiniCap

Example of application: Installation of a MiniCap to reduce flicker

during large motor starting

Voltage flicker can become a significant problem for power distributorswhen large motor loads are introduced in remote locations. Installation ofa series capacitor in the feeder strengthens the network and allows suchload to be connected to existing lines, avoiding more significantinvestment in new substations or new distribution lines.

The use of the MiniCap on long distribution feeders provides self-regulated reactive power compensation that efficiently reduces voltage

variations during large motor starting.

Benefits:

Reduced voltage fluctuations (flicker)

Improved voltage profile along the line

Easier starting of large motors

Self-regulation

Back to Overview

more about MiniCap and Flicker

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Factors / Phenomena: Long lines & cables


Example of application: Improved voltage profile of long distribution

lines by adding a MiniCap

The voltage profile on a radial circuit depends on the circuit parametersand the load characteristics. The voltage profile can be significantlyimproved by installing a MiniCap along the line. A typical voltage profilefor a radial circuit with and without a series capacitor is shown below.Note that the voltage profile curve has a jump at the location of the seriescapacitor which represents a large voltage rise downstream of the seriescapacitor.

The use of the MiniCap on long distribution feeders provides improvedvoltage profile for all loads downstream of the installation.

Benefits:

Increased power transmission capability through decreased total linereactance

Improved voltage profile along the line

Reduced line losses

Back to Overview

more about MiniCap and Long lines & cables

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Example of application: Improved power factor at the utility source

with a MiniCap

The reactive power produced by the series capacitor is proportional to thecapacitor impedance and the line current. With the series capacitorsupplying a significant portion of the reactive power requirements of thedistribution line and of inductive motor loads, much less reactive power isdrawn from the utility source, resulting in a greatly improved power factorat the sending end of the line.

The use of the MiniCap on a distribution feeder provides self-regulated

reactive power for improved power factor at the utility source.

Benefits:

Increased power factor at the utility source

Easier starting of large motors

Improved voltage regulation and reactive power balance

Self-regulation

Back to Overview

more about MiniCap and Reactive Power Factor

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Technology / System: PSGuard Wide Area Monitoring System

Example of application: Phase angle monitoring

The phase angle monitoring application facilitates the monitoring ofnetwork stresses caused by heavily loaded lines. It provides operatorswith real-time information about voltage phase angle deviations a crucialissue e.g. for the successful reclosing of transmission lines.

Its main function is to supply sufficient information to the power systemoperator to evaluate the present angle difference between two locations.Upon detection of an extraordinary status, PSGuard alerts the operator bygiving an early warning or, in critical cases, an emergency alarm.

The present version provides monitoring functionality, and its outputs areintended as mature decision support for operators in taking stabilizingmeasures. Actions that the operator may take to improve grid stabilityrange from generation rescheduling or actions on the reactive powercompensation, blocking of tap changers in the load area and loadshedding in extreme cases.

Benefits:

Improved system stability, security and reliabilitySafe operation of power carrying components closer to their limits

Optimized utilization of transmission capacities

Enhanced operational and planning safety

Other applications:

Line Thermal Monitoring (LTM)

Voltage Stability Monitoring (VSM)

Power Oscillation Monitoring (POM) Back to Overview

more about: PSGuard Wide Area Monitoring System

and Bottlenecks

PSGuard display: Phase angle monitoring withearly warning and emergency alarm

Power T&D Solutions bb
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Factors / Phenomena: Long lines and cables


Example of application: Line thermal monitoring

Loading of power lines or HV cables is in many cases constrained by thermal limitsrather than by voltage instability concerns. A thermal limit of a line is usually setaccording to conservative and stabile criteria, i.e. high ambient temperature and calmair. This yields assumptions of very limited cooling possibilities and thus low loadability.However, the ambient conditions are often much better in terms of possible cooling andwould allow higher loading of a line with a minimal risk. This can be achieved if an on-line tool for line temperature assessment is available. One of the algorithms of PSGuardserves this purpose. However, its functionality and applicability on the real powersystems should be tested in the practice.

The algorithm works as follows

The voltage and current phasors measured at both ends of a line are collected (thephasors have to be measured at the same instant, which is possible through the GPS-synchronization of the phasor measurement units, PMUs)

Actual impedance and shunt admittance of a line are computed.

Resistance of the line/cable is extracted

Based on the known properties of the conductor material (reference temperature anddependency coefficient are usually supplied by the manufacturer), the actual averagetemperature of the line is determined.

The obtained temperature is an average, not the spot one. The relation between themshall be verified, i.e. through consideration of the impact of the various weatherconditions along the line at a given time.

Benefits:

Improved power flow control

Safe operation of power carrying components closer to their limits

Other applications:

Power Oscillation Monitoring (POM)

Back to Overview


and Long Lines & Cables

PSGuard display: Line thermal monitoring with earlywarning and emergency alarm

PSGuard display: Line temperature pattern computed by PSGuard

Power T&D Solutions www abb com


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Factors / Phenomena: Oscillations


Example of application: Power oscillation monitoring

Power oscillation monitoring is the algorithm used for the detection ofpower swings in a high voltage power system. The algorithm processes theselected voltage and current phasor inputs and detects the various powerswing (power oscillation) modes. It quickly identifies the frequency and thedamping of swing modes. The algorithm deploys adaptive Kalman filteringtechniques.

Displayed results

Damping of the dominant oscillatory mode (time window, i.e. trend display)

Frequency of the dominant oscillatory mode (time window, i.e. trend display)

Amplitude of the oscillation (time window, i.e. trend display)

Optional

Damping of other oscillatory modes (all in one time window, distinguished by differentcolors)

Frequencies of other oscillatory modes (all in one time window, distinguished by differentcolours

Alarms

When the damping of any oscillation mode decreases to below a predefined value (in twosteps, first is alert, the second emergency alarm)

Read more

Back to Overview

Measurements by PSGuard WAMS: The loss of a powerplant in Spain (1000 MW) initiated Wide Area Oscillations

Measurement by PSGuard

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Factors / Phenomena: Oscillations


Example of application: Power oscillation monitoring

Benefits:

Increased power transfer

Enhanced security

Short-term operation benefits:

Immediate awareness of the power system state in terms of the presence of oscillations,thus an operator sees the urgency of the situation

Indication of the frequency of an oscillation which may then be associated with the knownexisting mode of the power system, i.e. the operator may distinguish if a local or inter-areamode is excited

Long-term benefits:

With the help of the stored data, long-term statistics can be collected and, based on theirevaluation, the system reinforcements can be performed (such as retuning of PowerSystem Stabilizers (PSS) to damp the frequencies appearing most often as dangerous

ones).

Back to Overview


and Power Oscillations

Example: Estimation of relative frequency and damping



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Factors / Phenomena: Voltage instability


Example of application: Voltage stability monitoring

The voltage stability monitoring application facilitates the monitoring of thegrids dynamic behavior and provides stability calculations for steady statesituations as well as stability predictions in contingency cases. It builds onand extends the basic functionality of PSG830 with functions related to themonitoring of voltage stability for a transmission line / corridor.

Its main function is to provide the operator of the power system withsufficient information to evaluate the present power margin with respect tovoltage stability, that is, the amount of additional active power that can be

transported on a transmission corridor without jeopardizing the voltagestability. The present version provides monitoring functionality, and itsoutputs are intended as mature decision support for operators in takingoptimizing resp. stabilizing measures. Actions that the operator may take toimprove voltage stability range from generation rescheduling or actions onthe reactive compensation, blocking of tap changers in the load area and toload shedding in extreme cases.

Applied directly, the application is assigned to a single line or cable.

However, on a case-by-case basis, the method can be applied also totransmission corridors with more complex topologies.

Benefits:

Improved system stability, security and reliability

Reduced cost and greater functionality of Protection & Control systems

Safe operation of power carrying components closer to their limits

Optimized utilization of transmission capacitiesBack to Overview


and Voltage Instability

PSGuard display: Voltage stability monitoring P-V Curve



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Technology / System: Series Compensation

Example of application: Transient Stability Improvement

Bottlenecks may be relieved by the use of Series Compensation. Longerlines tend to have stability-constrained capacity limitations as opposed tothe higher thermal constraints of shorter lines. Series Compensation hasthe net effect of reducing transmission line series reactance, thuseffectively reducing the line length. Series Compensation also offersadditional power transfer capability for some thermal-constrainedbottlenecks by balancing the loads among the parallel lines. Figure showsa two-area interconnected system where the power transfer from area A to

area B is limited to 1500MW due to stability constraints. Additionalelectricity can be delivered from area A to area B if Series Compensation isapplied to increase the maximum stability limits.

Benefits:



Improved Grid Voltage Control

Other applications:

Power Flow Control

Back to Overview

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Factors / Phenomena: Loop Flows

Technology / System: Series Compensation

Example of application: Power Flow Control

Loop Flows, or Parallel Path Flows, may be alleviated by the use of SeriesCompensation. In interconnected power systems, the actual path taken bya transaction from one area to another may be quite different from thedesignated routes as the result of parallel path admittance, thus diverting orwheeling power over parallel connections.

Figure shows parallel path flow alleviation by the use of SeriesCompensation. With a reduction in the direct interconnection impedancebetween area A and area C, the Parallel Path Flow which is routed through

area B is decreased.

Benefits:



Lower Transmission Losses

Improved Transient Stability


Other applications:

Transient Stability Improvement

Back to Overview

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Technology / System: Shunt Capacitor

Example of application:

Regulation of the power factor to increase the transmission capability andreduce transmission losses

Shunt capacitors are primarily used to improve the power factor intransmission and distribution networks, resulting in improved voltageregulation, reduced network losses, and efficient capacity utilization. Figureshows a plot of terminal voltage versus line loading for a system that has ashunt capacitor installed at the load bus. Improved transmission voltageregulation can be obtained during heave power transfer conditions when

the system consumes a large amount of reactive power that must bereplaced by compensation. At the line surge impedance loading level, theshunt capacitor would decrease the line losses by more than 35%. Indistribution and industrial systems, it is common to use shunt capacitors tocompensate for the highly inductive loads, thus achieving reduced deliverysystem losses and network voltage drop.

Benefits:

Improved power factor

Reduced transmission losses

Increased transmission capability

Improved voltage control

Improved power quality

Other applications:

Harmonic FiltersBack to Overview

more about Shunt Capacitor and Reactive PowerFactor

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Technology / System: Shunt Reactor

Example of application: Extra/Ultra High Voltage air insulated

transmission line and cable line voltage stabilityThe primary purpose of the shunt reactor is to compensate for capacitivecharging voltage, a phenomenon getting more prominent for increasing linevoltage. Long high-voltage transmission lines and relatively short cablelines (since a power cable has high capacitance to earth) generate a largeamount of reactive power during light power transfer conditions which mustbe absorbed by compensation. Otherwise, the receiving terminals of thetransmission lines will exhibit a voltagerise characteristic and many types

of power equipment cannot withstand such overvoltages. Figure shows attop level voltage at the receiving end when transmission line is loaded withrated power. Then shunt reactor is not needed. Next figure shows a voltageincrease when line is lightly loaded and bottom figure shows what happenswhen a shunt reactor is connected. The voltage stability is kept due to theinductive compensation from the reactor.

A better fine tuning of the reactive power can be made by the use of a tapchanger in the shunt reactor. It can be possible to vary the reactive powerbetween 50 to 100 % of the needed power.

Benefits:

Simple and robust customer solution with low installation costs andminimum maintenance

No losses from an intermediate transformer when feeding reactivecompensation from a lower voltage level.

No harmonics created which may require filter banks.

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Power T&D Solutions




Technology / System: Static Var Compensator (SVC)

Example of application: Grid Voltage Support

Static Var Compensators are used in transmission and distributionnetworks mainly providing dynamic voltage support in response to systemdisturbances and balancing the reactive power demand of large andfluctuating industrial loads. A Static Var Compensator is capable of bothgenerating and absorbing variable reactive power continuously as opposedto discrete values of fixed and switched shunt capacitors or reactors.Further improved system steady state performance can be obtained fromSVC applications. With continuously variable reactive power supply, thevoltage at the SVC bus may be maintained smoothly over a wide range ofactive power transfers or system loading conditions. This entails thereduction of network losses and provision of adequate power quality to theelectric energy end-users.

Benefits:



Improved Grid Voltage StabilityImproved Grid Voltage Control

Improved Power Factor

Other applications:

Power Oscillation Damping

Power Quality (Flicker Mitigation, Voltage Balancing)

Back to Overview

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Power T&D Solutions



Factors / Phenomena: Power Oscillations


Example of application: Power Oscillation Damping

Static Var Compensators are mainly used to perform voltage and reactivepower regulation. However, when properly placed and controlled, SVCscan also effectively counteract system oscillations. A SVC, in effect, hasthe ability to increase the damping factor (typically by 1-2 MW per Mvarinstalled) on a bulk power system which is experiencing power oscillations.It does so by effectively modulating its reactive power output such that theregulated SVC bus voltage would increase the system damping capability.Figure shows power oscillation prompted by a disturbance on atransmission system. The uncompensated system undergoes substantialoscillations following the disturbance while the same system with SVCexperiences much improved response.

Benefits:



Improved Dynamic Stability

Other applications:


Grid Voltage Support

Back to Overview

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Power Oscillations

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Static Var Compensators are used in transmission and distributionnetworks mainly providing dynamic voltage support in response to systemdisturbances and balancing the reactive power demand of large andfluctuating industrial loads. A Static Var Compensator is capable of bothgenerating and absorbing variable reactive power continuously as opposedto discrete values of fixed and switched shunt capacitors or reactors.Further improved system steady state performance can be obtained fromSVC applications. With continuously variable reactive power supply, thevoltage at the SVC bus may be maintained smoothly over a wide range ofactive power transfers or system loading conditions. This entails thereduction of network losses and provision of adequate power quality to theelectric energy end-users.

Benefits:



Improved Grid Voltage StabilityImproved Grid Voltage Control


Other applications:

Power Oscillation Damping


Back to Overview

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Voltage Instability

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o e & So ut o s




Technology / System: SVC (Industry)

Example of application: Power Quality Improvement, Flicker

MitigationSVC is used most frequently for compensation of disturbances generatedby the Electrical Arc Furnaces (EAF). With a well-designed SVC,disturbances such as flicker from the EAF are mitigated. Figure shows theflicker mitigation effect of a SVC installed at a steel making plant.

Flicker, the random variation in light intensity from incandescent lampscaused by the operating of nearby fluctuating loads on the common electricsupply grid, is highly irritating for those affected. The random voltage

variations can also be disturbing to other process equipment fed from thesame grid. The proper mitigation of flicker is therefore a matter of powerquality improvement as well as an improvement to human environment.

Benefits:

Reduced Flicker

Harmonic Filtering

Voltage Balancing

Power Factor Correction

Furnace/mill Process Productivity Improvement

Other applications:

General Reactive Power Compensation at Steelworks


Back to Overview

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Example of application: Reactive Power Compensation at Steelworks

Static Var Compensators provide dynamic voltage support to balance thereactive power demand of large and fluctuating industrial loads. A StaticVar Compensator is capable of both generating and absorbing variablereactive power continuously as opposed to discrete values of fixed andswitched shunt capacitors or reactors. With continuously variable reactivepower supply, the voltage at the SVC bus may be maintained smoothlyover a wide range of operating conditions. This entails the improved powerfactor and sufficient power quality, leading to better process and productioneconomy.

Benefits:



Harmonic Filtering

Other applications:

Power Quality Improvement, Flicker mitigationPower Quality Improvement, Voltage Balancing

Back to Overview

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Reactive Power Factor

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Factors / Phenomena: Unbalanced Load


Example of application: Railway Feeder connected to the Public Grid

The traction system is a major source of unbalanced loads. Electrificationof railways, as an economically attractive and environmentally friendlyinvestment in infrastructure, has introduced an unbalanced and heavydistorted load on the three-phase transmission grid. Without compensation,this would result in significant unbalanced voltage affecting mostneighboring utility customers. The SVC can elegantly be used tocounteract the unbalances and mitigate the harmonics such that the powerquality within the transmission grid is not impaired. Figure shows a typicaltraction substation arrangement with a load balancer (an asymmetricallycontrolled SVC). The load balancer transfers active power between thephases such that the balanced voltage can be created (seen from the grid).

Benefits:

Voltage Balancing

Harmonic Filtering


Other applications:

Power Quality Improvement, Flicker Mitigation


Back to Overview

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Unbalanced Load

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Technology / System: STATCOM


STATCOM, when connected to the grid, can provide dynamic voltagesupport in response to system disturbances and balance the reactivepower demand of large and fluctuating industrial loads. A STATCOM iscapable of both generating and absorbing variable reactive powercontinuously as opposed to discrete values of fixed and switched shuntcapacitors or reactors. With continuously variable reactive power supply,the voltage at the STATCOM bus may be maintained smoothly over a widerange of system operation conditions. This entails the reduction of networklosses and provision of sufficient power quality to the electric energy end-users.

Benefits:



Improved Grid Voltage Stability



Other applications:


Back to Overview

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Example of application: Power Quality Improvement, flicker

mitigationSTATCOM is an effective method used to attack the problem of flicker.The unbalanced, erratic nature of an electric arc furnace (EAF) causessignificant fluctuating reactive power demand, which ultimately results inirritating electric lamp flicker to neighboring utility customers. In order tostabilize voltage and reduce disturbing flicker successfully, it is necessaryto continuously measure and compensate rapid changes by means ofextremely fast reactive power compensation. STATCOM uses voltagesource converters to improve furnace productivity similar to a traditionalSVC while offering superior voltage flicker mitigation due to fast responsetime. Figure shows the flicker mitigation effect of an STATCOM installed ata steel making plant.

Benefits:

Eliminated Flicker

Harmonic Filtering

Voltage BalancingPower Factor Correction


Other applications:


Power Quality Improvement

Back to Overview

more about STATCOM and Flicker



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Factors / Phenomena: Unbalanced Load


Example of application: Railway Feeder connected to the Public Grid

Modern electric rail system is a major source of unbalanced loads.Electrification of railways, as an economically attractive andenvironmentally friendly investment in infrastructure, has introduced anunbalanced and heavy distorted load on the three-phase transmission grid.Without compensation, this would result in significant unbalanced voltageaffecting most neighboring utility customers. Similar to SVC, theSTATCOM can elegantly be used to restore voltage and current balance inthe grid, and to mitigate voltage fluctuations generated by the tractionloads. Figure shows a conceptual diagram of STATCOM application fordynamic load balancing for traction.

Benefits:

Voltage Balancing

Harmonic Filtering


Other applications:

Power Quality Improvement, Flicker Mitigation


Back to Overview

more about STATCOM and Unbalanced Load



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