不同电流互感器混用对线路差动保护的影响及对策的研究

分析了电磁式电流互感器和电子式电流互感器暂态特性的差异,提出了采用差分虚拟制动CT饱和开放的办法来解决不同互感器混用时线路光纤差动保护饱和误开放的问题。该方法能够有效解决因暂态传递特性不一致引起的饱和误开放问题。此外由于电子互感器二次时间常数与常规互感器有较大差异,导致在故障切除后电子互感器侧电流拖尾,会造成开关跳开后线路保护仍计算有差流,同时保护各侧电流互感器的二次电流衰减时间常数不一致也存在导致差动保护在区外故障电流切除时误动作。提出使用全周差分傅氏计算保护跳开相的电流,以避免造成线路保护跳令不能及时收回导致误启动失灵以及区外故障切除引起差动误动的问题。

Influence of mixing different types of current transformers on line differential protection and the countermeasures

This paper analyzes the difference of transient characteristics of magnetic current transformer and electronic current transformer, and proposes to adopt the method of difference virtual brake CT saturated open to solve the problem of saturation mis open of line optical differential protection when different CTs are used mixedly. This method can effectively solve saturation mis open caused by inconsistent transient transfer characteristics. In addition, secondary time constant of electronic transformer has great difference from that of conventional current transformer, and it results in the current trailing of electronic transformer after fault excision, which can cause line protection still has calculation of differential flow after switch off. And the inconsistent secondary current attenuation time constants of CT at each side of protection can lead to misoperation of differential protection in cutting off the external fault. This paper puts forward the full-circle differential Fourier to calculate the current of jumped phase of protection, in order to avoid mal-start failure caused by not withdrawing jump command of line protection in time and the differential maloperation owing to cutting off external fault.