THE PRINCIPLE OF DIRECTIONAL EARTH FAULT PROTECTION USING ZERO SEQUENCE TRANSIENTS IN NON-SOLID EARTHED NETWORK

Existing earth fault protections in non-solid earthed network are not satisfactory in practical application due to weak fault current and unstable arc. The characteristics of transient zero sequence voltage and current produced by fault are analyzed in this paper. The signal can be decomposed into components in different frequency bands according to angle-frequency characteristics of feeders. In a selected frequency band(SFB), which contains most transient current energy, each healthy feeder can be modeled as a capacitor. The transient zero sequence current or reactive power in the selected frequency band flows from fault to busbar in the faulty feeder, and from busbar to feeder in the healthy feeders. A new protection principle based on measurement of direction of transient zero sequence capacitive current or reactive power is proposed. The feeder, which has negative reactive power flow, is identified as the faulty feeder. This method has higher sensitivity and reliability and free from influences of Petersen coil and unstable arc. Recorded real fault data proved the proposed techniques.