交流二次回路中性线阻抗对母线差动保护的影响及防范措施

Analysis of the neutral line impedance influence on bus-bar differential protection and preventive measures

为了提高母线差动保护的正确动作率,通过对现场一起母线差动保护误动事故的原因进行研究,从理论上分析了交流二次回路中性线阻抗的存在对母线差动保护的动作行为可能造成的影响。研究结果表明,当母线上所连支路发生故障时,若线路空载或轻载,故障相的短路电流及非周期分量均达到一定水平时,由于交流二次回路中性线阻抗的存在,会造成非故障相的电流互感器反向饱和,从而可在非故障相中产生异常电流,造成母线差动保护误动作。EMTP仿真结果证明了上述分析结论的正确性和合理性。对此进一步提出了相应的防范措施和建议,以避免现场类似事故的发生。

In order to improve the performance of bus-bar protection, the probable influence of the neutral line impedance of AC secondary circuit on the bus-bar differential protection is analyzed theoretically by investigating a mal-operation of bus-bar differential protection. The analysis shows when a fault occurs on the light-load or unload circuit connected to bus-bar and the non-sinusoidal periodic current reaches to a certain level, the current transformer of sound phase could be saturated reversely because of the neutral line impedance, which can produce an abnormal current in the sound phase and thus cause mal-operation of bus-bar differential protection. The EMTP simulation results validate the correctness and rationality of the analysis. Some appropriate preventive measures are put forward to avoid such real-operation.