Research on Coordination between Single Phase-to-Ground Fault Protection Equipment and Distribution Terminal Unit

To deal with the single phase-to-ground fault quickly in neutral point non-effectively grounded system, a dynamic weighted line selection and automatic sequential isolation protection scheme is designed. At present, the single phase-to-ground fault protection equipment based on the scheme has been widely used in China Southern Grid (CSG) and has achieved very good performance. The application related to the distribution terminal unit is more and more popular because of its good fault isolation by section. The coordination between the single phase-to-ground fault protection equipment and the distribution terminal unit is very important. If the coordination becomes weaker, more trips, which may emerge, cause lower reliability of power supply and breaker close and open alternately. To address the problems, this paper mainly analyzes the typical distribution terminal unit including zero sequence voltage blocking and zero sequence voltage tripping. Furthermore, this paper makes a full risk assessment on the coordination between the single phase-to-ground fault protection equipment and the typical distribution terminal unit combined with 180 typical application scenarios. Considered that a lot of analysis and demonstration, the coordination capabilities of the single phase-to-ground protection equipment and the distribution terminal unit can be effectively improved by optimizing the post-acceleration logic functions. Accordingly, the breaker close and open alternately can be avoid greatly.