New design of ground fault protection

Ground fault protection is widely used to protect transmission and distribution lines in case of ground faults. Combined with a directional element and used in a teleprotection scheme, ground fault protection can detect and isolate even high resistive ground faults not detected by distance protection. However, there are a lot of maloperations due to the incorrect result of the directional element of the ground fault protection using either zero sequence or negative sequence quantities. After analysing numerous fault records, it seems obvious that these problems with the directional elements cannot be solved using either zero sequence or negative sequence because these quantities are sometimes very small or not related to the fault. This study suggests a new design of ground fault protection using additional information given by numerical relays. With the new design, the ground fault protection takes a lot of advantages regarding phase selection and directional element from the distance protection. The main difference between the distance protection and the ground fault protection remains the different grading. For the distance protection, the sensitivity is limited by the resistive reach. The basic principle for the grading of ground fault protection remains a simple threshold of zero-sequence current.