基于故障电阻测量的小电流接地系统保护方法

为解决小电流接地系统高阻接地故障检测的难题,分析了单相接地故障前后相电流变化特征:故障线路的故障相与非故障相电流变化量之差等于接地故障电流,非故障线路的故障相与非故障相电流变化量相等;并由故障相电压与故障电流之比计算出接地故障电阻,发明了基于接地故障电阻测量的高阻接地保护方法。EMTP仿真分析和动模实验测试结果表明,该保护方法能够保护各种高阻接地故障,具有较高的保护精度和可靠性,适合在配电自动化终端单元(FTU)上就地实现。

Grounding Fault Protection Based on Fault Resistance Measurment for Ineffectively Earthed Distribution Systems

Neutral Ineffectively Earthed Power Systems (NIEPS) include neutral unearthed system, neutral earthed with high resistance system and neutral resonance earthed system. Single-phase grounding faults potentially cause cable bombing or phase-to-phase faults in NIEPS, and the safety and power quality of the distribution system will be affected. High impedance grounding faults are difficult to detect with traditional methods in NIEPS because of minor fault current, fault arc, harmonics influence and the protection principle limitation. In order to improve the precision and reliability of traditional grounding fault protection schemes for NIEPS, the characteristics of phase current variations before and after grounding fault occurring are analyzed in the paper. The difference of phase current variations between the fault phase and a normal phase in the faulted feeder equals to the grounding fault residual current, and the difference in the normal feeder equals to zero. The fault resistance equals the ratio between fault phase voltage and fault current. The fault resistance based protection is then put forward. When the fault current is higher than its threshold or the resistance is lower than its threshold, grounding fault occurs in the protected feeder. EMTP simulation and experimental results show that the measurement is with high precision, and the protection is with high sensitivity and robustness to detect high impedance grounding faults. They can satisfy the requirements of distribution automation systems and be implemented on Field Terminal Units (FTU), which is installed in distribution automation system and can only measure the current of the protected feeder.