零序电压产生机理及过渡电阻测量和选相方法

Transition Resistance Measurement and Fault Phase Selection Under Single-Phase Ground Fault Based on Producing Mechanism of Zero-Sequence Voltage

不对称电网高阻接地故障相的选择和过渡电阻的测量较为困难。文章从新的角度阐述电网零序电压的产生机理和物理意义:不对称电网将自适应的产生零序电压,零序电压在零序阻抗上产生的电流完全补偿电网的"零序不对称电流"。根据零序电压产生的机理,解释中性点不接地系统不存在零序电流的原因,给出中性点经阻抗接地电网零序电压的等效运算电路图,实现接地故障电流的预测。通过比较各相电压与故障电流的相位可判别出故障相,然后根据故障相电压和故障电流的幅值计算过渡电阻。理论分析及仿真验证表明所述方法不受电网不对称和负荷电流变化的影响,精度高,应用方便。

It is difficult to selection the fault phase and to measure the transition resistance under single-phase high.resistance ground fault in asymmetrical power network. From a new viewpoint, the producing mechanism of zero-sequence voltage in power network and its physical meaning are expounded： asymmetrical power network produces the zero-sequence voltage adaptively, and the current produced by zero-sequence voltage on zero-sequence impedance completely compensates the zero-sequence asymmetrical current in the power network. According to the producing mechanism the reason why there is not zero-sequence current in power network with isolated neutral system is explained, and a circuit diagram for equivalent calculation of zero-sequence voltage in power network with neutral grounded via impedance is given to implement the prediction of the current of grounding fault. Because the voltage of the fault phase is the same as the phase of the current in the fault phase, the fault phase can be distinguished by comparing the phase of three-phase voltages with the phase of the fault current, and then the transition resistance can be calculated. Results of theoretical analysis and simulation show that the proposed method is not affected by the asymmetry of power network and the variation of load current, so it possesses high accuracy and is easy to apply.