多端线路差动保护改进算法的研究

Study on improved algorithm in differential protection of multi-terminal line

针对传统差动保护在T型以及多端线路保护中出现的问题,以两端输电线路纵向阻抗的计算方法为基础,提出了一种适用于多端线路差动保护的改进算法。所提算法以发生故障时线路各端电流故障分量的相量和作为动作量,以任意两端之间最大的电压故障分量差与该两端线路的串联正序阻抗比值作为制动量。同时,上述数据之间彼此独立且可以相互转化,确保了保护能够在系统正常运行的情况下准确区分出区内、区外故障。通过对三相输电线路合理的解耦算法,达到了消减相间电磁耦合的目的,使所提算法实现分相判别的功能。在EMTP软件中,建立了高压多端输电线路模型,仿真结果表明,所提算法具有良好的状态判别能力,整定简单、判别裕度大,可靠性高,同时能够有效抵御线路电容电流和电流互感器饱和所带来的影响,具有较好的工程推广前景。

Aiming at problems of the traditional differential protection in T-type and multi-terminal line protection,an improved algorithm for differential protection of multi-terminal line based on the calculation method of longitudinal impedance of transmission lines at both ends is proposed. The phasor sum of fault components of the currents at both ends of the line are used as the operating quantity,and the ratio between the maximum voltage fault component between the two ends of the line and the series positive-sequence impedance of the two-terminal line are used as the braking quantity. Meanwhile,the above data are independent and can be transformed to each other,which ensures that the protection can accurately distinguish the internal and external faults under the normal operation of the system. By using the reasonable decoupling algorithm in the three-phase transmission line,the electromagnetic coupling between phases are reduced,so split-phase discriminant function can be realized by the proposed algorithm. A highvoltage multi-terminal transmission line model is established with EMTP software,and the simulative results show that the proposed algorithm has good state distinguishing ability,simple setting,large discriminant margin and high reliability. Meanwhile,it can effectively resist the influence of the saturation of the line capacitance current and current transformer,and has good engineering promotion prospects.