Optimized PSTN12

8/8/2019 Optimized PSTN12

1/47


2/47

Power T&D Solutions www.abb.com

Power System Technology Navigator (PSTN) Monday, December 13, 2010

Back to Overview V. 1.1

Asynchronous connection

The interconnected AC networks that tie the powergeneration plants to the consumers are in most cases

large. 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 on

the 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 impossible

to 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.

Back to Overview


3/47




Bottlenecks

Constrained transmission paths or interfaces in an

interconnected electrical systemThe term Bottlenecks is often interchangeable tocongested transmission paths or interfaces. Atransmission path or interface refers to a specific set of

transmission 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 operating

conditions 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 market

competition.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 in

the 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.Back to Overview


4/47




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. Slowly

fluctuating periodic flickers, in the 0.5 30.0Hz range,are considered to be noticeable by humans. A voltage

magnitude variation of as little as 1.0% may also benoticeable.

The main sources of flicker are industrial loads

exhibiting 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.

Back to Overview


5/47




Harmonics

Harmonics are associated with steady-state waveformdistortion of currents and voltages

Harmonics are components that make up a waveformwhere each component has a frequency that is anintegral multiple of the fundamental frequency. The termHarmonic is normally applied to waveform componentsthat have frequencies other than the fundamentalfrequency. For a 50 Hz or 60Hz system the fundamentalfrequency is 50HZ or 60Hz. A waveform that contains

any components other than the fundamental frequency isnon-sinusoidal and considered to be distorted.

Nonlinear loads draw currents that are non-sinusoidaland thus create voltage drops in distribution conductorsthat are non-sinusoidal. Typical nonlinear loads includerectifiers, variable speed drives, and any other loadsbased on solid-state conversion. Transformers and

reactors may also become nonlinear elements in a powersystem during overvoltage conditions. Harmonics createmany concerns for utilities and customers alike. Typical

phenomena include neutral circuit overloading in threephase circuits, motor and transformer overheating,metering inaccuracies and control system malfunctions.

Back to Overview


6/47




Interruptions

Occur when the supply voltage drops below 10% of the

nominal 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 decrease

remains 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, and

loss 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.

Back to Overview


7/47




Long lines

Long lines need special consideration in the planning of a

power system.

This transmission carries more than 12,000 MW over 800km. There is an HVDC system with two 600 kV bipoles of3150 MW each is direct route to So Paulo while the three800 kV shunt and series compensated AC lines has twointermediate substations that allow connection to the localgrids.

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 shouldalso consider if an HVDC alternative brings lowerinvestment costs and/or lower losses or if the inherentcontrollability of an HVDC system brings with some otherbenefits.

Another factor to consider is the land useThe figure at the right compares two 3,000 MW HVDC linesfor the 1,000 km Three Gorges - Shanghai transmission,China, to five 500 kV AC lines that would have been used ifAC transmission had been selected.

Go to Long Cables

Back to Overview


8/47




Long cables

Cables have large capacitances and therefore, if fed with AC,

large reactive currents. Cables for DC are also less expensive

than for AC. One must distinguish between submarine cables

and 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 cablesLong 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 a

new 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).

Back to Overview


9/47




Loop Flow

Unscheduled power flow on a given transmission path in an

interconnected 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 neighboring

control 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 assumes

that 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 may

be 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 ownpurposes.

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

Back to Overview


10/47




Power Oscillations

Periodic variations in generator angle or line angle due to

transmission 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 are

usually the result of very light damping in the system and arepronounced at power transfers that approach the lines stability

limit. 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.

Back to Overview


11/47




Reactive Power Factor

Effects of reactive power on the efficiency of transmission and

distribution

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 of

reactive power, which either produce or absorb reactive powerin the systems. To maintain efficient transmission and

distribution, 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 voltage

regulation and power factor correction are also importantespecially for balancing the reactive power demand of large andfluctuating industrial loads.

Back to Overview


12/47




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 ofsags, 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 ride through the sag if it is

short enough in duration.

Back to Overview


13/47




Unbalanced Load

A load which does not draw balanced current from a balanced

three-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 in

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


14/47




Voltage Instability

Post-disturbance excursions of voltages at some buses in the

power 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 power

cannot 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). The

increased 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.

Back to Overview


15/47




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 systems

and 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. 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 Factor

Reduced Transmission Losses

Increased Transmission Capability

Improved Voltage Control

Improved Power Quality

Other applications:

Shunt Capacitors

Back to Overview

more about Harmonic Filters and Harmonics


16/47




Factors / Phenomena: Reactive Power Factor

Technology / System: Harmonic Filters

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

such as rectifiers, 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 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. For

small 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

Back to Overview

more about Harmonic Filters and Reactive Power Factor


17/47




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 the

power system of eastern USA is not synchronous with that of westernUSA. 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 - the

HVDC 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.

Back to Overview

more about HVDC & Asynchronous Connection

The Scandinavia - Northern Europe HVDC interconnections

Links:

HVDC transmission for controllability of power flow

HVDC transmission for asynchronous connection

Applications in Power Systems: Interconnection

ABB HVDC Portal


18/47




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 the

inherent 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.

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:



ABB HVDC Portal


19/47




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 from

remote 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

=>G

o 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


20/47




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


21/47




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 areaA 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:



ABB HVDC Portal


22/47




Factors / Phenomena: Power Oscillations


Example of application: Steady State and Transient StabilityImprovement

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 HVDC

projects in operation. It normally takes its input from the phase angledifference in the two converter stations.

Benefits:


Improved Power and Grid Voltage Control


Back to Overview

more about HVDC & Power Oscillations

Links:



HVDC Light System Interaction Tutorial.

ABB HVDC Portal


23/47




Factors / Phenomena: Flicker

Technology / System: MiniCap

Example of application: Installation of a MiniCap to reduce flickerduring 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 voltagevariations 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


24/47




Factors / Phenomena: Long lines & cables


Example of application: Improved voltage profile of long distributionlines 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 series

capacitor 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 line

reactanceImproved voltage profile along the line

Reduced line losses

Back to Overview

more about MiniCap and Long lines & cables


25/47






Example of application: Improved power factor at the utility sourcewith 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 factor

at the sending end of the line.

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


26/47





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 by

giving 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 reliability

Safe 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 MonitoringSystem

and Bottlenecks

PSGuard display: Phase angle monitoring with

early warning and emergency alarm


27/47




Factors / Phenomena: Long lines and cables


Example of application: Line thermal monitoringLoading 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 set

according 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 power

systems 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 (the

phasors 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 l ine 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 average

temperatureof the line is determined.

The obtained temperature is an average, not the spot one. The relation between them

shall be verified, i.e. through consideration of the impact of the various weatherconditions along the line at a given time.

Benefits:

Improvedpower flow control


Other applications:

Power Oscillation Monitoring (POM)

Back to Overview


and Long Lines & Cables

PSGuard display: Line thermal monitoring with early

warning and emergency alarm

PSGuard display: Line temperature pattern computed by PSGuard


28/47




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 different

colors)

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 power

plant in Spain (1000 MW) initiated Wide Area Oscillations

Measurement by PSGuard


29/47






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-area

mode 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 Power

System Stabilizers (PSS) to damp the frequencies appearing most often as dangerousones).

Back to Overview


and Power Oscillations

Example: Estimation of relative frequency and damping


30/47




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 to

voltage stability, that is, the amount of additional active power that can betransported 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 to

improve 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


Optimized utilization of transmission capacitiesBack to Overview


and Voltage Instability

PSGuard display: Voltage stability monitoring P-V Curve


31/47





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-constrained

bottlenecks 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

more about Series Compensation and Bottlenecks


32/47




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 impedance

between area A and area C, the Parallel Path Flow which is routed througharea B is decreased.

Benefits:



Lower Transmission Losses

ImprovedTransient Stability


Other applications:

Transient Stability Improvement

Back to Overview

more about Series Compensation and Loop Flows


33/47





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 voltage

regulation can be obtained during heave power transfer conditions whenthe 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 to

compensate 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


34/47





Technology / System: Shunt Reactor

Example of application: Extra/Ultra High Voltage air insulatedtransmission line and cable line voltage stability

The 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 must

be absorbed by compensation. Otherwise, the receiving terminals of thetransmission lines will exhibit a voltage rise 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.

Back to Overview

more about Shunt Capacitor and Voltage Instability


35/47





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, the

voltage 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 Stability



Other applications:

Power Oscillation Damping

Power Quality (Flicker Mitigation, Voltage Balancing)

Back to Overview

more about Static Var Compensatorand Bottlenecks


36/47




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 the

regulated SVC bus voltage would increase the system damping capability.Figure shows power oscillation prompted by a disturbance on a

transmission 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

more about Static Var Compensatorand

Power Oscillations


37/47






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, the

voltage 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:






Other applications:



Back to Overview

more about Static Var Compensatorand

Voltage Instability


38/47





Technology / System: SVC (Industry)

Example of application: Power Quality Improvement, FlickerMitigation

SVC 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 electric

supply grid, is highly irritating for those affected. The random voltagevariations 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

more about SVC (Industry) and Flicker


39/47






Example of application: Reactive Power Compensation at SteelworksStatic 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 smoothly

over a wide range of operating conditions. This entails the improved powerfactor and sufficient power quality, leading to better process and production

economy.

Benefits:



Harmonic Filtering

Other applications:

Power Quality Improvement, Flicker mitigation

Power Quality Improvement, Voltage Balancing

Back to Overview

more about SVC (Industry) and

ReactivePower Factor


40/47




Factors / Phenomena: Unbalanced Load


Example of application: Railway Feeder connected to the Public GridThe 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 to

counteract the unbalances and mitigate the harmonics such that the powerquality within the transmission grid is not impaired. Figure shows a typical

traction 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

more about SVC (Industry) and

Unbalanced Load


41/47





Technology / System: STATCOM

Example of application:Grid Voltage SupportSTATCOM, 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 network

losses and provision of sufficient power quality to the electric energy end-users.

Benefits:






Other applications:


Back to Overview

more about STATCOM and Bottlenecks


42/47






Example of application: Power Quality Improvement, flickermitigation

STATCOM 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 necessary

to continuously measure and compensate rapid changes by means ofextremely fast reactive power compensation. STATCOM uses voltage

source 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 Balancing



Other applications:


Power Quality Improvement

Back to Overview

more about STATCOM and Flicker


43/47




Factors / Phenomena: Unbalanced Load


Example of application: Railway Feeder connected to the Public GridModern 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, the

STATCOM can elegantly be used to restore voltage and current balance inthe grid, and to mitigate voltage fluctuations generated by the traction

loads. 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


44/47






Example of application:Grid Voltage SupportSTATCOM, 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 network

losses and provision of sufficient power quality to the electric energy end-users.

Benefits:






Other applications:


Back to Overview

more about STATCOM and Voltage Instability


45/47





Technology / System: TCSC

Example of application: Transient Stability ImprovementBottlenecks may be effectively relieved by the use of entirely or partiallythyristor controlled series compensation. As with conventional SCtechnology, TCSC can improve stability of power transmission, reactivepower balance, and load sharing between parallel lines, thus mitigating theimpact of transmission bottlenecks. Figure shows a two-areainterconnected system where the power transfer from area A to area B is

limited to 1500MW due to stability constraints. Additional electricity can bedelivered from area A to area B if series compensation is applied to

increase the maximum stability limits. High degree of series compensationlevel is permitted with the controlled series compensation achieving furtherimproved transmission capacity utilization.

Benefits:



Improve Dynamic Stability


Immunity against Subsynchronous Resonance

Other applications:


Subsynchronous Resonance Mitigation

Back to Overview

more about TCSC and Bottlenecks


46/47




Factors / Phenomena: Loop Flows


Example of application: Power Flow ControlLoop Flows, or Parallel Path Flows, may be effectively alleviated by the useof entirely or partially thyristor controlled series compensation.

In interconnected power systems, the actual path taken by a transactionfrom one area to another may be quite different from the designated routesas the result of parallel path admittance, thus diverting or wheeling powerover parallel connections. Controlled series compensation is a usefulmeans for directing power flows along contracted paths under variousloading and network configurations. Figure shows parallel path flowalleviation by the use of controlled series compensation. With a reductionin the direct interconnection impedance between area A and area C, theParallel Path Flow which is routed through area B is decreased.

Benefits:



Lower Transmission Losses

ImprovedTransient Stability


Other applications:


Subsynchronous Resonance Mitigation

Back to Overview

more about TCSC and Loop Flow


47/47






Example of application: Power Oscillation DampingThyristor Controlled Series Capacitors may be used to damp bulk powersystem oscillations. A TCSC, in effect, has the ability to increase thedamping torque (or damping power) on a bulk power system which isexperiencing angular oscillations between the two terminals of thecompensated transmission line. It does so by effectively modulating theamount of power that flows through the line. When an angular increase

occurs between the two terminals of a line during an oscillation, the TCSCwill increase power flow in order to oppose the increase in angle; likewise,

the TCSC will decrease power flow through the line during the angulardecrease portion of the oscillation cycle. Figure shows angular oscillationprompted by a temporary short circuit on a transmission system. Theuncompensated system undergoes substantial oscillations following theshort circuit while the same system with TCSC experiences much improvedresponse.

Benefits:



Improved Transient Stability


Immunity against Subsynchronous Resonance

Other applications:

Transient Stability Improvement

Interconnections between grids

Subsynchronous Resonance Mitigation Back to Overview

more about TCSC and Power Oscillations

Optimized PSTN12

Documents

Transcript of Optimized PSTN12