Application of phaseshifting transformers in UHVDC transmission system under bipolar block faults
ZHANG Zhongchi, TONG Weilin, WANG Jianquan
(School of Electrical Engineering, Zhejiang University, Hangzhou 310027, China)
 

Abstract: The bipolar block faults of UHVDC transmission system can lead to instantaneous large power deficiency in the transmission section, which make part of the tielines heavily overload. Aiming at this problem, installing phaseshifting transformers in particular transmission lines to transfer part of power flow from overload tielines to other lightload tielines was proposed, which can reduce the amount of load that needs to be shed and improve the power supply reliability of the power grid when the bipolar block faults take place. Through discussing the quantity and location problem of phaseshifting transformers, the decisionmaking methods under different circumstances were summarized and a large scale power system whose total load is about 22 000 MW was taken as an example. The type and concrete model of phaseshifting transformer were decided and the relevant parameters of the phaseshifting transformer were derived and calculated. The power flow of each tieline at different phaseshifting angles was simulated using PSASP. The results indicate that phaseshifting transformers can realize power flow transfer between tielines and make full use of the transmission capability of the tielines on the transmission section, which can reduce the tieline overload caused by bipolar block faults of UHVDC transmission system.
Key words: phaseshifting transformer(PST); bipolar block faults in UHVDC; tieline; power flow transfer; power system analysis software package(PSASP)