Novel techniques for earth fault feeder detection based on negative sequence current in industry power systems

Many industrial power systems have been operated with floating neutral or high resistance earthed neutral. In the occurrence of single-phase earth faults, the fault current is usually not more than ten amperes. Traditional earth fault detection schemes based on zero sequence current usually have poor sensitivity in detecting high impedance faults (HIF) and arcing faults. Analysis on negative sequence current caused by earth faults shows that the negative sequence current is slightly bigger than the zero sequence current in the fault feeder. In the sound feeder, the negative sequence current is approaching to zero, and is much smaller than the zero sequence current, Negative sequence current is therefore more sensitive in detecting faulted feeders than zero sequence current in theory. Some fault detection schemes based on negative sequence current are presented in this paper. They have been verified by EMTP simulation. The prototype has been developed and tested. Results show that these protection schemes have high sensitivity and robustness in detecting HIF and arcing faults.