基于双端电流波形相关度识别的线路零序差动保护启动元件

对一起线路保护误动案例的分析结果表明:若某侧电流互感器在区外故障时发生轻微暂态饱和,因其电流波形畸变不明显使饱和判据失效,零序差动保护容易误动作。为解决这一问题,对三相电流互感器的暂态饱和特性进行了分析,得到了暂态饱和时间与故障角、故障电流的关系,并采用迭代方法计算出进入饱和的最小时间和使电流互感器饱和的最小全偏移故障电流。在此基础上,以两端零序电流作为识别对象对电流互感器饱和状态进行鉴别,构建了改进的零序差动保护启动元件。在电流互感器有剩磁和无剩磁工况下对各种故障进行了仿真,结果表明该启动元件可大幅提高零序差动保护动作的准确率,证明了其可行性和有效性。

Starting element of line zero-sequence differential protection based on correlation identification of double-terminal current waveform

Analysis results of line protection mal-operation case show that, if a current transformer is in slight transient saturation when external fault occurs, zero-sequence differential protection is easy to malfunction because of the saturation criterion failure due to unobvious current waveform distortion. To solve this problem, transient saturation characteristics of three-phase current transformers are analyzed, by which the relationship between transient saturation time and fault angle and fault current is obtained, and minimum saturation time and minimum fully offset fault current that makes the current transformer saturated are calculated by iterative method. On this basis, improved zero-sequence differential protection starting element is constructed by using double-terminal zero-sequence current as the recognition object to identify the saturation state of current transformers. Simulated by all kinds of faults under residual magnetism and no residual magnetism conditions of the current transformer, the results show that the starting element can greatly improve the accuracy of zero-sequence differential protection by which its feasibility and effectiveness are proved. This work is supported by Science and Technology Project of State Grid Fujian Electric Power Company Limited (No. 52130416001U).