基于主保护不平衡电流有效值的转子匝间短路故障监测

Monitoring of Field Winding Inter-turn Short Circuit Based on Unbalanced Current Effective Value in Main Protection

为利用发电机主保护所配电流互感器来监测励磁绕组匝间短路故障,以三峡VGS发电机为例,采用多回路方法对故障后进入各主保护的不平衡电流进行了计算与分析;在此基础上,指出利用不平衡电流中的单次谐波进行故障监测的不足,由此提出基于主保护不平衡电流有效值的励磁绕组匝间短路故障监测原理;通过对不同短路匝比故障的计算与理论分析,指出流过中性点间的不平衡电流不适合用来反应于励磁绕组匝间短路故障,而应采用反应于每相绕组内部不平衡电流的监测方法;最后阐述了励磁绕组匝间短路监测与其他常规保护之间的配合,为发电机转子匝间短路故障的在线监测奠定了基础。

In order to use current transformer installed for the generator main protection to monitor inter-turn short circuits of field winding, taking Three Gorges VGS generator as an example the after-fault unbalanced current entering into various main protections is calculated and analyzed with multi-ldop method. Then the defects of fault monitoring using single harmonic in unbalanced current are pointed out and a monitoring principle of field winding inter-turn short circuit based on unbalanced current effective value for the main protection is proposed. Through the calculation and theoretical analysis of faults with different short circuit turn ratios of field winding, it is pointed out that unbalanced current flowing between two neutral points is not suitable for reflecting inter-turn short circuits fault of field winding, and the monitoring method reflecting the internal unbalanced current of each phase winding should be adopted instead. Finally the coordination between the inter-turn short circuits monitoring of field windings and other conventional protections is illustrated, laying a theoretical foundation for the field windings inter-turn short circuit fault on-line monitoring.