小电流接地系统自适应单相接地保护方案

针对国内外在小电流接地系统中单相接地保护方法,提出了一种新的基于零序电流补偿的零序过电压保护方案,其基本保护采用零序过电压保护,动作时间采用反时限特性:在分析接地故障零序暂态电流分布特点的基础上,利用线路的零序电流暂态有效值与一个可整定的补偿电抗相乘,形成补偿电压,并与零序电压幅值合成复合补偿电压,利用该电压对基本的反时限动作特性曲线进行修正,实现选择性保护。仿真实验验证了算法的有效性。

Novel Adaptive Protective Principle for the Single-phase Earth Fault of the Non-effectively Grounded Power Systems

During normal system operation,the grounding method does not have a relevant impact.However,consequences of single-phase faults on the system depend to a large extent on the grounding method chosen.In the case of grounding using a resonant coil,the fault current is reduced to a minimum,because the inductive reactance of the coil compensates the capacitive reactance of the system at all times.Using resonant-grounded systems,transient outages are automatically canceled with no activity on the switches or fuses within the system;therefore,the service is not interrupted.Thus,supply may be maintained during the outage.On such a neutral un-effectively grounded grid,the fault current of the faulty feeder is quite low when a single-phase earth fault occurs.The accurate identification of the faulty feeder becomes a difficult task due to many disadvantageous factors.The conventional scheme is implemented with the comparison of the magnitude,polarity or the phase angle among the zero-sequence currents.Therefore,it is hard to be implemented into the feeder protection equipped on the FTU.A novel zero-sequence overvoltage protection scheme based on zero-sequence current compensation is therefore proposed.The fundamental method is based on the measurement of the zero-sequence overvoltage,and the tripping time characteristics adopt the inverse time delay.By virtue of the analysis of distribution of the zero-sequence transient current,it is demonstrated in this paper that the transient maximum of the faulty feeder should be greater than all of transient maximum of sound feeders.In such a situation,a transient RMS value of the zero-sequence current is utilized to form the composite compensation voltage together with zero-sequence voltage.This voltage is utilized to revise the inverse time-delay curve to achieve the selectivity of the protection.The principle is verified with the EMTP simulator.