Fault Transient Analysis Of6-phase Transmission Systems

Six-phase transmission belongs to multiphase transmission..It has muchadvantage, such as increasing the transmission power density, reduced the cost oftower construction, saving the space of line corridor, with more favorableenvironmental indicators, etc. The study of six-phase transmission is sufficientattention in other countries. In our country, the cost of line corridor of UHVtransmission has becoming more and more expensive, at the same time the linecorridors are also limited by geographical constraints and traffic, other industriesconstraints and environmental protection requirements. So six-phase transmission isan idea way for our country’s UHV transmission in theory.Compared to conventional three-phase systems or double lines on the same tower,the arrangement of six-phase transmission systems’ lines is more compact. Thedistributed parameters of line are differences between three-phase systems andsix-phase systems. So, the transient characteristics of six-phase systems are differentfrom the traditional three-phase transmission system. Since the operating time ofrelays on UHV transmission lines is very short, transient process have higher impacton six-phase systems’ relays, but the fault transient analysis of six-phase transmissionis still blank. Six-phase transmission system transient characteristics analysis hasgreat significance for systems’ stable operation and six-phase systems’ protection’studying.The research status of six-phase transmission system fault analysis mainly focuson the steady-state analysis, this paper give deep analysis on fault transient. Usingdecoupling transformation matrix can transform the faulted Six-phase PowerTransmission System into six sequence components. Then this paper prove that theanalysis of six-phase transmission systems’ fault transient based on six-phasecomponent method is correct. Combined with the π-type equivalents circuit, thesix-sequence transient model was establishment and get each sequence component’sfailure sequence network. Then deduce the formula of fault transient current under thecondition of distributed capacitance、capacitor of series compensation or shuntreactors based on the each sequence component failure network. At the same time,compare with double-circuit lines on same tower, the Six-phase Power TransmissionSystems’failure of harmonic have higher frequency and decay more quickly. The model of500KV Six-phase Power Transmission System with the voltage of500kV is established by PSCAD/EMTDC and verify the validity of the analysisunder the condition of distributed capacitance、capacitor of series compensation orshunt reactors.