消除剩余电流保护动作死区的理论与方法

Theory and Method of Eliminating Operating Dead Zone of Residual Current Protection

研究了漏电保护技术,在分析剩余电流保护技术基础上,指出该技术在原理上存在重要缺陷。当线路中存在正常漏电,而设备又发生故障漏电或有人触电,正常漏电电流与故障漏电(或触电)电流存在相角差,造成剩余电流反而减小,因此存在故障漏电保护动作死区。本文建立了一种新型漏电保护模型,提出用2到5个周时间间隔的剩余电流变化量表示故障漏电,并采用剩余电流和剩余电流变化量双重判据,实现故障漏电的正确保护。通过分析剩余电流的相位关系,推导出剩余电流在各相上分量及剩余电流变化量的计算公式,实现了故障漏电电流的检测。最后,采用单片机进行软硬件设计,并试验验证了对故障漏电的正确保护性,且不会引起误动作。

The leakage current operated protective technique is studied and its major defects in principle are discussed based on the thorough analysis of residual current operated protection theory. If leakage current exists in power lines under normal condition, there will be a phase angle difference between the normal leakage current and the fault leakage current when an electric shock hazard occurs. The residual current will decrease consequently, thus a dead band of protection exists. A new method using the residual current variation during 2 to 5 cycles to express the fault leakage current is presented. The new leakage current operated protective model is established in which not only the residual current but also its variation is taken into consideration as a bi-criteria to represent the fault current so that a correct protection can be implemented. On the basis of residual currents＇ phase analysis, the calculation formula of the residual current and its variation in each phase is obtained and the detection of fault current is fulfilled. Finally prototype based on microcontroller is designed and its correct protection without mis-tripping is verified by experiments.