交流系统接地故障对直流换相失败的影响分析

摘要

换相失败是高压直流输电系统中常见的故障之一,而受端交流系统故障是诱发换相失败的重要原因. 利用序分量法详细推导了交流系统发生不同接地故障时换相电压与线电压过零点偏移的变化情况,比较系统地分析了各种交流侧接地故障对换相失败的影响. 分析结果表明:不同的故障类型对阀的换相过程影响不同;随着过渡电阻的变化,换相电压过零点偏移可能会从超前转为滞后;并基于理论分析结果对关断角的表达式进行了相应的修正. 最后以天广直流输电系统为原型,利用PSCAD搭建了双极HVDC仿真模型,验证了结论的正确性;并利用仿真结果对影响换相失败的两大因素,即换相电压和过零点偏移的影响程度进行了探讨.%As one of the most common faults in HVDC transmission system, commutation failure is considered to be caused mostly by AC system faults in the receiving-end.A detailed analysis of the relationship between commutation voltage reduc-tion and line voltage zero-crossing point drift is given when various types of grounding faults occur in AC system by using se-quence components method.Thus the systemic analysis about the impacts of grounding faults on commutation failure is presen-ted.The results indicate that the influence on commutation process varies with fault types, and the phase of commutation volt-age may change from lead to lag compared to the voltage before the faults as the transition resistance changes.The expressions for extinction angle is modified correspondingly based on the theoretical analysis results.A bi-polar HVDC simulation model is established with PSCAD/EMTDC based on Tian-Guang HVDC transmission system, which verifies the correctness of the conclusion.A further discussion is presented about the effects of commutation voltage reduction and line voltage zero-crossing point phase shift on the commutation failure according to the simulation results.