分段比率制动的电流差动保护

通过对一起高压输电线光纤电流差动保护误动事故的分析，论述了在故障暂态过程中，非周期分量电流将使电流互感器铁心中的磁通显著增大，并形成大量剩磁。铁心剩磁的存在使电流互感器在 B-H曲线上的起始工作点发生变化，加重了饱和程度和缩短进入饱和时间，这是差动保护误动的重要原因。经过分析电流互感器误差和比率制动系数的关系，指出不考虑暂态剩磁的影响，仅依据制动电流的大小对差动保护特性进行分段，或者盲目地提高制动系数都是不完善的，以铁心磁感应强度的大小为依据进行比率制动特性的分段是克服电流互感器饱和、提高保护灵敏度和可靠性的更合理的方式。最后给出了一种工程实用解决方案。

Study of Sectional Ratio Restraint Characteristic in Current Differential Protection

By analyzing a misoperation accident of a current differential protection using fiber communication channel on a high voltage transmission line, it is discussed that residual magnetic flux intensity in current transformer is created in large quantity by transient non-periodic current component. The residual magnetic flux intensity makes the starting work point of current transformer change on B-H curve, and hence the magnetic saturation state is aggravated in shorter time, which is the main reason to cause the misoperation accident of differential protection. The relationship between error curve of current transformer and ratio restraint coefficient is analyzed. The analytical result shows that it is inappropriate to study characteristic of differential protection piecewise only based on stalling current amplitude and to increase retain coefficient blindly without taking account of the influences of residual magnetic flux intensity. It can be concluded that it is a more reasonable way to take the magnetic induction intensity in current transformer as the basis to study the sectional ratio restraint characteristic of current differential protection. Finally, a new type of practical scheme is produced.