Grounding Fault Protection with Sampling Value Difference in Ineffectively Earthed Power Systems

Traditional protection schemes are difficult to detect and isolate grounding faults in ineffectively earthed power systems, especially to detect generator stator grounding faults with selectivity in multi-generator-system. In order to improve them, two novel protections with sampling value difference is proposed by comparing different phase´s current variations before and after single-phase grounding fault occurring in the paper. One is feeder grounding fault protection for distribution networks, and the other is generators stator grounding fault protection for multi-generator-system. The two protections are verified with EMTP simulations. Results show that the proposed feeder protection can correctly detect all kinds of grounding faults with high reliability, and the proposed generator protection can detect the generator with stator grounding fault selectively. The feeder protection can be implemented easily in field terminal unit (FTU) and satisfy the requirement of distribution automation.