天生桥—广州直流系统换流阀过电压机制研究

基于天广500 kV高压直流输电工程,分析了阀过电压产生的机制,结果表明,在以下2种情况下阀两端会产生较大过电压:1)最上层换相组的阀全部关断后,在该层换流阀两端可能产生严重过电压,而其他几层阀关断时一般不会在阀两端产生过电压;2)交流相间操作冲击将在阀两端产生较大过电压。据此对换流变高压端Y/Y绕组阀侧单相接地和交流相间操作冲击2种典型故障进行了仿真分析,结果表明:当直流系统以最小输送功率运行时,整流站换流变高压端Y/Y绕组阀侧单相接地故障在阀两端产生较大过电压,通过阀避雷器的能量最大,但随着输送功率的增加,能量会减小;整流站的换流变变比要比逆变站大,因而相同幅值的交流相间操作冲击在整流站换流阀两端产生的过电压相对严重。

Overvoltage Mechanism of Converter Valves for HVDC Power Transmission Project From Tianshengqiao to Guangzhou

Based on the HVDC power transmission project from Tianshengqiao to Guangzhou the mechanism leading to converter valve overvotage is analyzed and analysis results show that overvoltage will appear at both terminals of the valves under two conditions: the first one is that after turning-off all valves in uppermost layer of commutating group overvoltages appear at both terminals of the valves belonging to this layer,whereas when all valves belonging to other layers of commutating groups are turned-off there in general will not be overvotlages appearing at both terminals of these valves;the second one is that the switching surge due to interphase operation in AC-system will lead to higher overvoltage appearing at both terminals of valves.According to the analysis results,simulation analysis on two typical faults,namely the single-phase short-circuit occurred at upper-half rectifier bridge side of wye-wye connected winding of converter transformer and switching surge caused by interphase operation in AC-system,is performed.Simulation results show that when HVDC system is operated in minimum power transmission mode,the single-phase short-circuit fault occurred at upper-half rectifier bridge side of wye-wye connected winding of converter transformer will lead to higher overvotage at both terminals of valves while the energy passing through valve arrester reaches its maximum value,however,along with the increase of transmitted power the energy passing through valve arrester will decrease;in view of the fact that the transformation ratio of converter transformer configured in rectifier station is higher than that in inverter station,the swithching surge caused by interphase operations in AC system,which possess the same amplitude,will lead to relatively serious overvotlage appearing at both terminals of converter valves in rectifier station.