大容量变频器对电动机继电保护的影响

Analysis on motor protection after applying converter

火力发电厂重要辅机采用大容量变频器调速后,对电动机的传统保护方式产生了很大影响。由于微机型差动保护装置的数字信号处理是基于傅里叶变换,频率范围是45～55Hz,远小于变频器频率变换范围,使其不适用于变频回路,提出采用磁平衡式纵差保护解决变频电动机回路相间短路保护问题;针对传统的零序CT方法检测电动机或电缆单相接地故障非常困难,变频器自身的保护功能也不能检测单相接地故障,提出的谐波注入法可以很好地解决这一难题。

It makes a difference to traditional motor protection ,when the converter with high voltage and large capacity is applied in power plant. The mature differential protection device can not be used in converter circuit, because its digital signal processing based on Fourier transform, and the frequency range wave is from 45Hz to 55Hz,this range is more less than the transforming range of converter frequency. This paper proposes the method that the electric magnetic balance differential protection can resolve the protection problem of inter-phase short circuit faults of large capacity converter motor. It makes difficult to detect single phase earthing of motor or cable through zero-sequence CT, neither the converter self protection, but the harmonic injection method can resolve the difficult problem of single phase earthing protection.