小电流接地故障暂态方向保护原理研究

分析了小电流接地系统接地故障暂态零序电压电流特征。根据线路的相频特性将频率分为不同区段，论证了在一选定的低频区段内，所有健全线路分别可用一集中电容等效；在该选定频段内，故障线路暂态零序电流或无功功率方向与非故障线路相反。据此提出了检测暂态零序容性电流或无功功率方向的暂态方向保护算法。该方法灵敏度、可靠性高，不受消弧线圈和不稳定电弧的影响。实际故障数据验证了该方法的正确性。

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.