分频输电系统交交变频器桥臂短路故障研究

Short Fault of Bridge Arm in Cycloconverter for Fractional Frequency Transmission System

根据晶闸管开关特性,对分频输电系统中交交变频器发生桥臂短路后电气量的故障特性进行分析。分析中考虑了整流状态、逆变状态及正反桥切换阶段等3种工况,给出了低频侧电压波形和低频、工频侧电流的计算方法,得到了分频输电系统变频器桥臂短路故障时,系统电气量的特征规律。分析结果表明,分频输电系统在变频器桥臂短路故障时存在着桥臂换相失败、低频侧电压有效值明显降低以及工频侧出现较大的故障电流等特征。与拖动用的交交变频器比较,分频输电系统中变频器主要运行在逆变状态,工频侧的短路电流幅值得到了明显抑制,工频侧的短路电流峰值可能较整流状态减少40%以上。计算结果验证了以上分析的正确性。

In a fractional frequency transmission system （FFTS）, the fault characteristics are analyzed by switching property of thyristor when short-circuit fault occurs in one of the cycloconverter bridge arms. The different operation modes of the cycloconverter, i.e., the rectifier mode, the inverter mode and bridge-switching stage, are taken into consideration. The calculating method for voltage on the lower frequency side and currents on both lower frequency side and industrial frequency side are proposed, and the fault characteristics of the cycloconverter are thus quantitatively described. Analysis shows that in case of short-circuit fault, the bridge arms fail for commutating, the voltage on the low frequency side drops obviously, and the fault current on industrial frequency side gets very large. However the cycloconverter in FFTS usually works in the rectifier mode, the peak value of fault current on its industrial frequency side can be reduced by over 40 %. Simulations verify the above analysis.