谐振接地系统单相接地故障熄弧时刻识别方法

Identification method of arc extinction time for single-phase grounding fault in resonant grounding system

为了提高单相接地故障保护准确率,部分保护装置使用全过程电气量,而故障点熄弧后电气量与燃弧期间电气量特征不同且对故障保护会产生不利影响,因此准确识别故障点熄弧时刻对提高供电可靠性具有重要意义。通过等效故障全过程的谐振接地系统单相接地故障等值电路,对故障点工频电流熄弧前后的零序电压及电流电气量特征进行了对比分析。分析发现,熄弧前的稳态电气量与熄弧后的暂态电气量难以直接区分,但系统对地电容电流对时间的导数即母线零序电压对时间的二阶导数在熄弧前后发生了突变,存在明显的过渡过程。基于Haar小波分析方法,提出了一种检测母线零序电压二阶导数的小波分解高频分量突变点的故障点熄弧时刻识别方法。最后,通过数字仿真验证了该方法的有效性。

In order to improve the accuracy of single-phase ground fault protection, some protective devices use the electrical quantity of the whole process, while the electrical quantity after arc extinction at the fault point is different from that during arc burning, which will have adverse effects on the fault protection. Therefore, it is of great significance to accurately identify the arc extinguishing time of the fault point to improve the reliability of power supply. The characteristics of zero sequence voltage and current electrical quantities before and after power frequency current arc extinction at fault point are compared and analyzed through single-phase grounding fault equivalent circuit covering the whole fault process of resonant grounding system. The analysis shows that it is difficult to directly distinguish the steady-state electrical quantity before arc extinguishing from the transient electrical quantity after arc extinguishing, but the derivative of the system’s capacitive current to ground against time, that is, the second derivative of the bus zero sequence voltage against time, has a sudden change before and after arc extinguishing, and there is an obvious transition process. Based on the Haar wavelet analysis method, a method for identifying the arcing out time of the fault point by detecting the second derivative of the zero sequence voltage of the bus and the abrupt point of the high-frequency component of the wavelet decomposition is proposed. Finally, the effectiveness of the method is verified by digital simulation.