Topics Facts, Rpc, Svc

7/31/2019 Topics Facts, Rpc, Svc

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BY,MUHAMMAD UMAIR SHAHID


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FACTS(Flexible AC Transmission Systems)RPC(Reactive Power Control)SVR(Static Voltage Regulator)


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IntroductionControl of power flowThree phase thyristor controlled compensatorDigital protection scheme for the advanced series compensator

Proposed fuzzy logic control of a power system stabilizerPhase angle regulator


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The rapid advancements in power electronics andmicroprocessors over the last decade has had and will havea significant impact on the way utillities operate theirpower systems. The use of power electronics andmicroprocessors will help to dre the transmission anddistribution of electricity more reliable, controllable, andefficient. The term FACTS is an acronym for Flexible ACTransmission Syste:m. FACTS is the word used to describethe use of high speed power electronic controllers tocontrol the electric power system. The use of FACTStechnology will allow greater coritrol of power flows,increase the loading on power lines so as the lines operatemore closely to their thermal limits , enhance the system'sability to transfer power between conmolled areas, anddamp power system oscillations.


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Power flow through a systemdepends on transmission lineimpedance. Unfortunately, itdoes not depend on thermal

limits or ownership.Consider the example inFigure 1.


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Figure 1 (a), lines AB, BC, and AC have ratings of 1000MW, 1250 :MW, and 2000 MW, respectively. With thegiven impedances the three lines should carry ,600MW, 1600 MW, and 1400 MW, respectively. Notice

that line BC: is overloaded. By inserting a capacitor whose reactance is -5 ohms, the impedance c)f line ACgoes from 10 ohms to 5 ohms. The new power flows will be 250 MW, 1250 MVV, and 1750 :MW,respectively. This system could be mechanically controlled, but such a breaker would eventually faildue to the stress that many switching would place onthe breakers mechanical components.


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The Western Area Power Administration has installed the world's first three phase thyristor controlled compensationscheme. This device has continuously variable impedance.It can reduce the transmission line's impedance thusincreasing the power to the thermal limit of 400 MW. It isbecoming more difficult for utilities to build newtransmission lines due to the environmental impact andrestricted space. FACTS technology allows us to increasethe loading capability of existing systems. The advanced

series compensator (ASC), shown in Figure 2, allows theutility to set a scheduled load on the transmission line withautomatic control. The ASIC also provides protection forthe conventional series capacitors to which it is connected .


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Another use of a variable series and/or shunt compensator is toimprove the damping of electromechanical oscillations and transients.Due to the power system's highly nonlinear nature, it is difficult tomodel the dynamics of a power system which changes its characteristic

with operating points. Using a series and/or shunt compensator willincrease the power capability of a transmission line. However, in orderto make such compensators effective, intelligent and fast acting controltechniques have to be developed.

A fuzzy logic controller is proposed to operate a variable seriescapacitor compensator. The controller uses the steady state relations of machine rotor angle and electrical power as the input signals. Test

disturbances were applied to the system under three differentcontroller configurations: (i) with a typical PSS, (ii) with a typical PSSand a varia.ble series reactor, and (iii) with a typical PSS, a variableseries reactor, and a fuzzy logic controller.


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SHUNT FACTS DEVICES IN POWER SYSTEM:

Shunt FACTS devices are classified into two categories,namely variable impedance type (SVC) and switchingconverter type(STATCOM).


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The SVC uses conventional thyristors to achieve fast control of shunt connected capacitors and reactors. The configuration of the SVC is shown in Figure 1, which basically consists of a fixedcapacitor (C) and a thyristor controlled reactor (L). The firing

angle control of the thyristor banks determines the equivalentshunt admittance presented to the power system.


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Static Voltage Regulator (SVR) which is connectedbetween mains and consumers machine removes thenegative effects of the mains fluctuation to theconsumers machine.SVR is based on coil selecting principle, which meanssupplying the consumer machine with autotransformer coils inside of it. SVR ensure machines(like motors, rectifier, and air conditioner) to operateproperly and safely with selecting coil if a fluctuationand a deviation occurs in mains.


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If an overload (more than the 150% of nominal power)occurs, consumer machines (loads) are directly supplied with Bypass from the mains. After the normalconditions restate, machines again begin to besupplied with SVR.SVR contains a communication interface unit. By thehelp of this units signs it is possible to get informationfrom SVR.


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SVR regulates the voltage through the tapping selection by means of semi-conductor static switching devices viz. Thyristors, IGBTs whichrespond instantaneously. In addition, microprocessor-based controlcircuitry along with Thyristors results in high correction speed andhigher efficiency. There is no moving part inside SVR and it is a fully electronic & automatic unit.


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Topics Facts, Rpc, Svc