A Novel Adaptive Protective Scheme For the Single-Phase Earth Fault of the Non-Effectively Grounded Power Systems

The fault current of the faulty feeder is quite low when a single-phase earth fault occurs on a neutral un-effectively grounded grid. The accurate identification of the faulty feeder becomes a difficult task due to many disadvantageous factors. The conventional scheme is implemented with the comparison of the magnitude, polarity or the phase angle among the zero-sequence currents. Therefore, it is hard to be implemented into the feeder protection equipped on the FTU. A novel zero-sequence over-voltage protection scheme based on zero-sequence current compensation is therefore proposed. The fundamental method is based on the measurement of the zero-sequence over-voltage, and the tripping time characteristic adopts the inverse time delay. By virtue of the analysis of distribution of the zero-sequence transient current, a transient RMS value of the zero-sequence current is utilized to form the composite compensation voltage together with zero-sequence voltage. This voltage is utilized to revise the inverse time-delay curve to achieve the selectivity of the protection. The principle is verified with the EMTP simulator.