ee2036 facts unit1

7/21/2019 Ee2036 Facts Unit1

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EE2036 FLEXIBLE AC

TRANSMISSION

SYSTEMS

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UNIT I INTRODUCTION

• The concept of exible AC transmission

• Reactive power control in electrical powertransmission lines

uncompensated transmission line• series and shunt compensation.

• Overview of FACTS devices

• Static Var Compensator SVC!

• Th"ristor Switched Series capacitor TCSC!

• #ni$ed %ower Flow controller #%FC!

• &nte'rated %ower Flow Controller &%FC!.

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R(A)* R(ACT&V( A+, A%%AR(+T

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• (uation/./! comprises two double0freuenc" /1! components. The firstterm has an avera'e value as well asa pea2 ma'nitude of V& cos 3. Thisavera'e value is the active power* %*owin' from the source to the load.

• The second term has a 4ero avera'evalue* but its pea2 value is V& sin 3

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-ritten in phasor domain* the complex power in thenetwor2

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R(ACT&V( %O-(R CO+TRO)

• The reactive power is essential forcreatin' the needed couplin' $eldsfor ener'" devices.

• &t constitutes volta'e and currentloadin' of circuits but does not resultin an avera'e active! power

consumption and is* in fact* animportant component in all ac powernetwor2s.

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• To ma2e transmission networ2soperate within desired volta'e limits*there are man" methods of ma2in'

up or ta2in' awa" reactive power.5ence it is called reactive-powercontrol

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UNCOMPENSATED

TRANSMISSION LINES

• To understand the need for reactive0powercontrol* let us consider a simple case of alossless short0transmission line connectin' asource Vs to a load Z φ (For simplicity, theline is represented only b" its inductivereactance X l )

• To 2eep the volta'es in the networ2 at nearl"

the rated value* two control actions seempossible6 – 7. load compensation* and

– /. s"stem compensation

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Load Compensation5ere the compensation ma2es the power factor to become unit"by adding a parallel capacitive load such that the reactive current

Ix of the load is cancelled (ie) Ic !Ix" The absence of Ix eliminates the voltage drop #V$, bringing Vrcloser in magnitude to Vs% this condition is called loadcompensation" #suall" done b" the customers on their premises.)oads compensation will reduce the line drop but do not eliminate

it8 the" stillexperience a drop of #V& from ' Ir X l "System Compensation This compensator draws a reactive current to overcome bothcomponents of the volta'e drop #V$ and #V& so that thereceivin'0end volta'e* Vr, euals the

sendin'0end volta'e* Vs" To compensate for #V&, an additional capacitive current* #Ic, overand above Ic that compensates for Ix, is dran by thecompensator such that #IcX l #V&Such compensators are emplo"ed b" power utilities to ensure theualit" of suppl" to their customers

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• Reactive0power control for a line is often called reactive-powercompensation.

• *xternal devices or subsystems that control reactive power ontransmission lines are 2nown as compensator s"

• A compensator miti'ates the undesirable e9ects of the circuitparameters of a 'iven line.

• The ob:ectives of line compensation are invariabl"

7. to increase the power0transmission capacit" of the line* and; or

/. to 2eep the volta'e pro$le of the line alon' its len'th within

acceptable bounds to ensure the ualit" of suppl" to theconnected customers as well as to minimi4e the line0insulationcosts.

<. &mprovement in s"stem stabilit".

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For the sa2e of simplicit" ma'nitudes of Vs>Vr>Vm>V

The mid point phasor volta'e Vm and line current phasor & are 'iven b"

lossless line power is same at both ends and mid point so active power % is 'iv

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For reactive power 8 ?r is eual and opposite of ?s. So ? is'iven b" ?s > 0?r

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parameters for controllin' power intransmission line

• Appl"in' a volta'e in the midpoint can increase or

decrease the ma'nitude of power

• Appl"in' a volta'e in series with the line* and inphase uadrature with the current ow* canincrease or decrease the ma'nitude of current

ow. @ecause the current ow la's the volta'e b"BB* there is in:ection of reactive power in series

• &f a volta'e with a variable ma'nitude and a phaseis applied in series* then var"in' the amplitude and

phase an'le can control both the active andreactive current ows. There is a in:ection of bothactive power and reactive power in series

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• &ncreasin' and decreasin' the value if thereactance cause a decrease and increase ofthe power hei'ht of the curves.

for 'iven power ow* var"in' correspondin'l"varies the an'le D between the terminalvolta'es.

• %ower ow can also be controlled b" re'ulatin'

the ma'nitude of sendin' and receivin' endvolta'es Vs and Vr. This t"pe of control has much

more inuence over the reactive power owthan the active power ow

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Therefore* we can conclude that thepower ow in a transmission line canbe controlled b"

7! appl"in' a shunt volta'e Vm at

the midpoint

/! var"in' the reactance

<! appl"in' a volta'e with a variablema'nitude in series with line

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S5#+T CO=%(+SAT&O+

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• The ob:ective of appl"in' shuntcompensation in a transmission s"stem isto suppl" reactive power to increase the

transmittable power and to ma2e it morecompatible with the load demand.

• The shunt compensator should be able tominimi4e the line overvolta'e under li'htload conditions* and maintain volta'elevels under heav" load conditions

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• An ideal shunt compensator %>B! is connected at themidpoint of the transmission line* as shown in Fi'ure.

• The compensator volta'e that is in phase with themidpoint volta'e Vm has amplitude of V identical to that of

the sendin'0 and receivin'0end volta'es. That is Vm > Vs >Vr > V.

• The midpoint compensator in e9ect se'ments thetransmission line into two independent parts6

7! the $rst se'ment* with an impedance of :;/* carries

power from sendin'0end to the midpoint* and/! the second se'ment* also with an impedance of :;/*carries power from the midpoint to the receivin' end.

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S(R&(S CO=%(+SAT&O+

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F)O- OF %O-(R &+ A+ AC SST(=

%ower Flow in %arallel %aths

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%ower Flow in a =eshedSstem

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)&=&TS T5( )OA,&+G CA%A@&)&T

• @asicall"* there are three 2inds of limitations6

• Thermal

– Thermal capabilit" of an overhead line is a function of the ambienttemperature* wind conditions* condition of the conductor* and 'roundclearance

• ,ielectric

– ,ielectric From an insulation point of view* man" lines are desi'nedver" conservativel". For a 'iven nominal volta'e ratin'* it is oftenpossible to increase normal operation b" H7BI volta'e i.e.* JBB 2V toJJB 2V! or even hi'her. Care is then needed to ensure that d"namicand transient over volta'es are within limits

• Stabilit"

– There are a number of stabilit" issues that limit the transmission

capabilit".

– These include6

• Transient stabilit"

• ,"namic stabilit"

• Stead"0state stabilit"

• Freuenc" collapse

• Volta'e collapse

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CO+V(+S&O+A) R(ACT&V( %O-(RCO+TRO);VO)TAG( CO+TRO);

• Static VAR compensation – Switched capacitor;reactor ban2s

• Rotatin' VAR compensation – S"nchronous condenser K which is a unloaded s"nchronous motor

connected to AC s"stem* whose reactive0power output can be

continuousl" controlled b" var"in' its excitation current. -hen it isunder excited* it behaves li2e an inductor* absorbin' reactive powerfrom the ac s"stem. 5owever* when it is overexcited* it functionsli2e a capacitor* in:ectin' reactive power into the ac s"stem

• Tap chan'in' transformers

%hase shiftin' Transformers• )ine compensation

– Series compensation

– Shunt compensation

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Opportunities for FACTS

• These opportunities arise throu'h the abilit" of

FACTS Controllers to control the interrelated

parameters that 'overn the operation of

transmission s"stems includin' series impedance*

shunt impedance* current* volta'e* phase an'le*and the dampin' of oscillations at various

freuencies below the rated freuenc".

• These constraints cannot be overcome* while

maintainin' the reuired s"stem reliabilit"* b"

mechanical means without lowerin' the useable

transmission capacit".

@" providin' added exibilit"* FACTS Controllers

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@AS&C T%(S OF FACTS

CO+TRO))(RS

• &n 'eneral* FACTS Controllers can bedivided into four cate'ories6 – Series Controllers

– Shunt Controllers

– Combined series0series Controllers

– Combined series0shunt Controlle

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Series Controller

• The series Controller could be avariable impedance such as capacitor*reactor* etc.* or a power electronicsbased variable source of mainfreuenc"* sub s"nchronous andharmonic freuencies or acombination! to serve the desiredneed.

• &n principle* all series controllers in:ectvolta'e in series with the line.

• As lon' as the volta'e is in phase

uadrature with the line current* theseries Controller onl" supplies orconsumes variable reactive power. An"other phase relationship will involvehandlin' of real power as well

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Shunt controller

• the shunt Controllers ma" bevariable impedance* variablesource or a combination

• &n principle* all shunt Controllersin:ect current into the s"stem atthe point of connection

• As lon' as the in:ected current isin phase uadrature with the linevolta'e* the shunt Controlleronl" supplies or consumesvariable reactive power. An"other phase relationship willinvolve handlin' of real power aswell.

CO=@&+AT&O+ OF

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CO=@&+AT&O+ OFCO+TRO))(RS

• Two methods of operation; Control6 – Co ordinated manner 0 This could be a

combination of separate seriescontrollers* which are controlled in acoordinated manner

#+&F&(, =anner 0 the term Luni$edLhere means that the dc terminals of allController converters are all connectedto'ether for real power transfer

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#+&F&(, S(R&(S 0 S(R&(S

CO+TRO))(R

• &n $'ure* series Controllers provideindependent series reactivecompensation for each line and alsotransfer real power amon' the linesvia the power lin2 .

• The real power transfer capabilit" ofthe uni$ed series0series Controller*referred to as &nterline %ower FlowController* &%FC!.

• &%FC ma2es it possible to balanceboth the real and reactive powerow in the lines and thereb"maximi4e the utili4ation of thetransmission s"stem.

S(R&(S S5#+T

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S(R&(S KS5#+TCO+TRO))(RS

• The" also operate in coordinated or #ni$ed manner

• &n principle* combined shunt andseries Controllers in:ect currentinto the s"stem with the shunt

part of the Controller andvolta'e in series in the line withthe series part of the Controller.

• 5owever* when the shunt andseries Controllers are uni$ed*

there can be a real powerexchan'e between the seriesand shunt Controllers via thepower lin2

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,(F&+&T&O+S

• Flexibilit" of (lectric %ower Transmission0 The abilit"to accommodate chan'es in the electric transmissions"stem or operatin' conditions while maintainin'suMcient stead" state and transient mar'ins

• Flexible AC Transmission S"stem FACTS!0 Altenatin'current transmission s"stems incorporatin' powerelectronic0based and other static controllers toenhance controllabilit" and increase power transfercapabilit".

• FACTS Controller0 A power electronic0based s"stemand other static euipment that provide control ofone or more AC transmission s"stem parameters.

Sh t C t d

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Shunt ConnectedControllers

• Static Var Compensator SVC !

• Static S"nchronous Compensator STATCO=!

• Static S"nchronous Generator SSG!

• @atter" (ner'" Stora'e S"stem @(SS!

• Supercondactin' =a'netic (ner'" Stora'e S=(S!

• Th"ristor Controlled Reactor TCR!

Th"ristor Switched Reactor TSR!• Th"ristor Switched Capacitor TSC!

• Static Var Generator or Absorber SVG!

S i C t d

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Series ConnectedControllers

• Th"ristor Controlled Series CapacitorTCSC!

• Th"ristor0Switched Series Capacitor

• Th"ristor0Controlled Series ReactorTCSR!

• Th"ristor0Switched Series ReactorTSSR!

• Static S"nchronous Series

Compensator SSSC!

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@(+(F&TS FRO=

FACTS T(C5+O)OG

• Control of power ow as ordered. The use of control ofthe power ow ma" be to follow a contract* meet theutilitiesN own needs* ensure optimum power ow* ridethrou'h emer'enc" conditions* or a combination

thereof.• &ncrease the loadin' capabilit" of lines to their thermal

capabilities* includin' short term and seasonal.

• &ncrease the s"stem securit" throu'h raisin' thetransient stabilit" limit* limitin' short0circuit currents

and overloads* mana'in' cascadin' blac2outs anddampin' electromechanical oscillations of powers"stems and machines.

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TSSC VS TCSC

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• &n #%FC which combines a STATCO= and an SSSC .

• This is a complete Controller for controllin' active and reactivepower control throu'h the line* as well as line volta'e control..

• The ener'"0sortin' capacit" of the dc capacitor is 'enerall" small. Therefore* the active power drawn 'enerated! b" the shunt

converter should be eual to the active power 'enerated drawn!b" the series converter. Otherwise* the dc0lin2 volta'e ma" increaseor decrease with respect to the rated volta'e* dependin' on the netpower in the shunt or series converter.

• On other hand the reactive power on the series and shuntconverter can be choosen independentl"* 'ivin' a 'reater exibilit"

to the power ow control .• Additional stora'e such as a superconductin' ma'net connected to

the dc lin2 via an electronic interface would provide the means offurther enhancin' the e9ectiveness of the #%FC

ee2036 facts unit1

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