ABB Review Special Report - ABB - ABB Group

41.51.00.50-0.5-1.0-1.55002500-250-5001.51.00.50-0.5-1.0-1.51.51.00.50-0.5-1.0-1.540200-20-401.41.21.00.81.00.50-0.5Eagle Pass back-to-back tie: remote fault caseeither side while a constant system voltageis maintained on both. Any activepower transfers that are scheduled areautomatically and instantaneously lowered,if required, by the control systemPCIA 20000913 17;10;19 Uac Primary Sys APCIC 20000913 17;10;19 Iac P1 CPCIA 20000913 17;10;19 Iac Sys APCIA 20000913 17;10;19 Uac Sys APCIC 20000913 17;10;19 Uac S1 CPCIA 20000913 17;10;19 Udc Sys APCIA 20000913 17;10;19 PQ Ref Sys A-1.00 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.01 AEP 138-kV voltages2 AEP step-down transformer secondarycurrents, in amps3 AEP phase reactor currents4 AEP 17.9-kV voltagesABCABCABCABCABCU+U-PQ5 AEP 17.9-kV phase-to-ground voltages,in kV6 DC voltages7 AEP converter, active (P) and reactivepower (Q) referenceto supply the reactive power needed tomaintain a constant voltage.1234567Active power controlIn this mode, active power can be transferredbetween the AEP and CFE systems.Power transfer is allowed whenthe voltage is within a dead-band. If thevoltage lies outside it, the BtB automaticallyreverts to voltage control mode.The active power flow is then automaticallyand instantaneously lowered bythe BtB to provide the required reactivepower support. The dead-band is designedso that local capacitor switchingor changes in remote generation thatcause slight voltage swings do not causethe BtB to switch to the voltage controlmode.Independent operation of the two VSCsShould maintenance be required on oneside of the BtB, the other side is stillable to provide voltage control to eitherside of the tie. This is done by openingthe DC bus, splitting it into two halves.As the DC link is open, no active powercan be transferred between the twosides of the BtB. Each VSC will then becapable of providing up to ±36 MVAr ofreactive support to either side.Contingency operation of the BtBIf one of the 138-kV lines into the EaglePass substation is lost, the remaining138-kV line can only support 50 MW ofload at the substation. Should this occur,the voltage falls below 0.98 pu and theBtB switches to the voltage controlmode. Active power is reduced automaticallyand instantaneously to makesure the 50-MW load level at the substation(AEP load plus the export to CFE)is not violated. The BtB supplies therequired reactive support to maintain a1-pu voltage. Load flow studies haveshown that the transmission line contingencyon the AEP side will have littleimpact on the power transfers from AEPto CFE.Dynamic performanceThe recording reproduced in 4 illustrateswell the highly dynamic performanceof the BtB Light installation atEagle Pass. Plots 1–7 show how the BtBresponded to lightning conditions in aremote area that caused a voltage dipin the AEP network. During the fault,the BtB current (capacitive) was increasedto almost 1 pu to support thebus voltage at Eagle Pass.16Special ReportABB Review