Site experiences with earth fault protection of non-solidly earthed distribution networks

Non-solidly earthed system for distributed network reduces earth fault current and allows the system to work with the fault present, thus increasing supply availability to customers. However, the risk to life and igniting fires cannot be ignored, hence there is a need to quickly detect and isolate permanent faults. The low earth fault current is a challenge to protection. This paper describes the existing protection techniques for non-solidly earthed network and presents a new transient reactive power method. A pilot project has been set up by Tai'an Power Authority of China State Grid in Shandong province to demonstrate the scheme. In August 2019, Shandong province was struck by Typhoon Lekima. 50 faults were experienced by the pilot network and the protection scheme has performed correctly for these incidents. Some of the fault incidents were presented in this paper.