Grounding Fault Protection with Fault Resistance Measuring for Ineffectively Earthed Power Systems

Many power distribution systems have been operated with neutral unearthed, high resistance earthed or resonance earthed, they are usually called ineffectively earthed systems. The ground fault current in the ineffectively earthed systems is usually not more than ten amperes, general over-current relay is difficult to detect the ground fault and isolate the faulted feeder section. Some ground faulted feeder detection schemes have been used by comparing magnitudes or directions of zero sequence currents in all feeders. The schemes need to measure all feeders´ currents, and they cannot be implemented on field terminal unit (FTU), which is installed in distribution automation system and can only measure the current of the protected feeder. In order to improve them, some FTU based ground fault protectors are developed by our research group. Among them, the grounding fault protection scheme with fault resistance measuring is presented in this paper