小电阻接地配电网零序保护的改进研究

中性点经小电阻接地系统发生高阻接地故障时,由于传统零序过流保护达不到定值而无法跳闸,导致故障长时间存在,而且此时无故障告警信号,因此存在危害系统可靠运行及人身安全的隐患。对中性点经小电阻接地系统发生接地故障时的零序电流电压特征进行了分析,提出了利用阻容比闭锁条件改进零序保护的方案。阻容比闭锁条件的本质在于通过分析零序电流阻性部分和容性部分的不同组成进行故障线路的识别。阻容比闭锁条件不受电压互感器和电流互感器极性的影响,因此能够可靠使用专用零序电流互感器。加入阻容比闭锁条件后不改变原有的保护配置,易于实施,能够提升零序保护的高阻接地故障检测能力,及时切除故障,保证系统的可靠运行以及人身安全。

The Research on the Improvement of the Zero-sequence Relay for the Low Resistance Grounded Distribution Network

In the low resistance grounded power grid,when a high-impedance grounding fault occurs at a distribution line,the zero-sequence current is not big enough to achieve the setting values of the zero-sequence over-current relays,and thus the fault would exist for a long time with no alarm signal.As a result,there would be a hidden danger that the grounding fault might cause further faults or cause harm to personal safety.To solve the problem,in the paper,the features of zero-sequence current and voltage when the high-impedance grounding fault occurs are analyzed,and an improved zero-sequence over-current relay with the resistance-capacitance ratio condition restriction is proposed.The resistance-capacitance ratio restriction condition is based on the different structure of the resistant part and the capacitive part of zero-sequence currents,and the faulted line can be identified with the resistance-capacitance ratio criterion.The resistance-capacitance ratio criterion are not influenced by the polarity of voltage transformer(TV)and current transformer(TA)and will not be affected by reversed polarity of the special zero-sequence TA.The resistance-capacitance ratio criterion is used to improve the zero-sequence over-current relay,and the relay structure is not changed.Thus the new method can be carried out easily.With the zero-sequence over-current relay with the resistancecapacitance ratio restriction,the ability of identifying high-impedance grounding faults can be improved,and the fault area can be isolated quickly,to ensure the reliable operation of the power grid and the safety of people.