Introduct|on to Compensat|onCompensation oI transmission lines is meant the use oIelectrical circuits to modiIy the electrical characteristics oI thelines within the prescribed limit.Need of Compensat|on%he line requires the compensation oI transmission lines dueto:#eduction oI power transIer capability oI lines which reducesthe margin between the stable and unstable operation oIsystem.Ferranti eIIect.Sub-synchronous resonance.Var|ous 1ypes of Compensat|on'arious types oI compensation techniques are used Iorcompensating the EH' lines:Series compensationShunt compensation-S'SSynchronous condenserCb[ect|ves of 5er|es and 5hunt Compensat|onain obiective oI series and shunt compensation oI EH' linesIor transmitting bulk power over the long distance may bestated as:%o improve transIer capability along with increased steadystate and transient stability limits.%o obtain Ilat voltage proIile as possible along the length oI theEH' line while maintaining the equal sending end andreceiving end voltage.%o avoid degree oI compensation leading to sub-synchronousresonance.5LkIL5 CCMLN5A1ICN%he series capacitor oIIers an eIIective and economic meansIor improving stability limits oI long distance transmission byreducing the net reactance oI transmission line.In the present case oI 400kv and 600km transmission system,the maximum value oI receiving end power, compensationeIIiciency, optimum value oI series capacitive reactance areobtained using computer program.Series compensation is used in long lines to increasetransmission capacity, improvement oI system stability and toobtain correct load division between parallel circuits.Series capacitors are connected in series with the line to reducethe net impedance oI the transmission line. %his reducedimpedance causes the reduced voltage drop across the line.Series capacitors are generally installed on special platIorms atone or both ends oI the lines.Insta||at|on of 5er|es Capac|torSeries capacitors are generally installed on special platIorms atone or both ends oI the lines.Seiies CapaciioiCuiieni Limiiing ReacioiSpail GapBypass SwiiclMeial Oxide ResisioiAdvantage of 5er|es Compensat|on%here are various advantage oI series compensation:Increase in power transIer capabilityImprovement oI system stabilityLoad division among parallel linesControl oI voltageocat|on of 5er|es Capac|torLocation along the line.Location at one or both ends oI line section on the line sides in the switching stations.Location between Bus Bars and switching station.rob|ems Assoc|ated w|th 5er|es Compensat|onSub Synchronous #esonanceSustain oscillationUnreliable protection oI transmission linesApp||cat|on of 5er|es Compensat|on%hey have been primarily used to improve system stability and to obtain the desired load division among parallel lines.High compensation levels also increase the complexity oI protective relaying and the probability oI sub-synchronous resonance.A practical upper limit to the degree oI series compensation is about 80.Following are some oI the key considerations in the applicationoI series capacitor banks:'oltage rise due to reactive current: 'oltage rise oI on one sideoI the capacitor may be excessive when the line reactive-current Ilow is high, as might occur during heavy powertransIers.Bypassing and reinsertion: provision is made Ior bypassing thecapacitor during Iaults and reinsertion aIter Iault clearing.Speed oI reinsertion may be an important Iactor in maintainingtransient stability.Present trend is to use nonlinear resistors oI zinc oxide whichhave the advantage that reinsertion is essentially instantaneous5nUN1 CCMLN5A1ICN 5V5Shunt compensation may consist oI static (using capacitor andreactor) or synchronous compensation to avoid voltagestability.Shunt capacitors supply reactive power and boost localvoltages. %hey are used throughout the system and are appliedin a wide range oI sizes.%he principal advantages oI shunt capacitors are their low costand their Ilexibility oI installation and operation.%he principal disadvantage oI shunt capacitors is that theirreactive power output is proportional to the square oI thevoltage.unct|on of 5V5 |n LnV 1ransm|ss|on%he most typical Iunction oI S'S in EH' transmission can besummarized as:'oltage support along the lineImproved stabilityControl oI over voltage#eduction oI 'A#s FlowApp||cat|on of shunt compensat|onShunt capacitors are used to compensate Ior the XI2 losses intransmission system and to ensure satisIactory voltage levelsduring heavy loading conditions.Switching oI capacitor banks provides a convenient means oIcontrolling transmission system voltages.1ypes of 5V5SelI Saturated #eactor (S#)%hyristor Controlled #eactor (%C#)%hyristor Switched Capacitor (%SC) Fixed Capacitor (FC), %hyristor Controlled #eactor (%C#)scheme%hyristor Switched Capacitor (%SC), %hyristor Controlled#eactor(%C#) schemeAdvantages of 5V5Increased power transIer capability Enhancement oI transient stability%he dynamic response oI S'S is very IastSteady State and temporary overvoltage can be controlled5NCnkCNCU5 CCNDLN5Lk A synchronous condenser is a synchronous machine runningwithout a prime mover or a mechanical load. By controlling theIield excitation, it can be made to either generate or absorbreactive power. With a voltage regulator, it can automaticallyadiust the reactive power output to maintain constant terminalvoltage.Synchronous compensators contribute to system short-circuitcapacity. %heir reactive power production is not aIIected by thesystem voltage.uring power swings (electromechanical oscillations) there isan exchange oI kinetic energy between a synchronouscondenser and the power system.ANA5I5 C DILkLN1 CCMLN5A1ING 5CnLMLle diffeieni compensaiing sclemes aie analyzed bycompuiing ile maximum ieceiving end powei , opiimumvalue of seiies compensaiion , compensaiion efficiency,Degiee of seiies compensaiion and A, B, C, D paiameieisdepending upon ile ielaiive posiiion of seiies capaciioiand SVS.i) UNCOMPENSAEDLINE:) SERIES COMPENSAIONWIOU SVS) SERIES COMPENSAIONWISVSUNCCMLN5A1LD INL%he 'alues oI A,B,C, parameters are as Iollows:A Zc coshylB Zc sinhylC 1/Zc sinhylA, B, C, D IsVsIRVR5er|es Compensat|on w|thout 5V5%he Series capacitor can be located as:1. At the sending end2. At the middle end3. At the receiving end oI the transmission line without any shunt compensation5er|es Capac|tor at the 5end|ng Lnd of 1ransm|ss|on |neO P#(max) ''#'`2 |K1 Xc`2 K2 Xc K3|O Compensation EIIiciency A1

Vs < -iXc'# 05er|es Capac|tor at the M|dd|e Lnd of 1ransm|ss|on |neO P#(max) ''#'`2 |K1 Xc`2 K2 Xc K3|------------'Bo'`2O Compensation EIIiciency |A1`2 A2`2|

Vs < -iXc'# 05er|es Capac|tor at kece|v|ng Lnd of 1ransm|ss|on |neO P#(max) ''#'`2 |-A1(KA2) Xc K B2- A1B1|------------'Bo'`2O Compensation EIIiciency A1

Vs < -iXc'# 05er|es Compensat|on w|th 5V5%he Series capacitor with S'S can be located as:1. At the sending end2. At the middle end3. At the receiving end oI the transmission line5er|es Capac|tor and 5V5 at the 5end|ng Lnd

Vs < -iXc'# 0SVSib5er|es Capac|tor and 5V5 at the M|dd|e Lnd

Vs < -iXc'# 0SVSib5er|es Capac|tor and 5V5 at the kece|v|ng Lnd

Vs < -iXc'# 0SVSibD@Degree of Series Compensation(s)PR(max) (p.u.)Case 1 (a) Case 1 (b) Case 1 (c)10 8.61 8.88 8.6520 9.29 9.79 9.3930 10.07 10.89 10.2640 10.96 12.26 11.2850 11.96 13.98 12.5160 13.05 16.98 13.9670 14.10 18.92 15.6480 14.64 21.53 17.3690 12.99 14.76 18.21Case No. PR(max) (p.u.) n c(opt) Xc(opt)(p.u.) S (opt) 1 (a) 14.64 79.00 0.1032 80.001 (b) 21.53 90.00 0.1002 80.001 (c) 18.21 79.00 0.1167 90.002 17.85 0.85 0.0848 80.003 24.79 96.00 0.0456 80.004 22.87 77.00 0.1220 90.005 21.70 1.14 0.0854 70.006 24.00 79.00 0.1178 90.00Invn ov^vnicv ,:)v.nvn 1vnv 200+1102^v.nin 1vnv ^nvnv 200+110!^vni ^v.cnv 200+110!1ic.n 1vnv v.vni,v 200+110