发变组差动保护CT的10%误差曲线校核计算

在系统发生故障的情况下,可能发生CT饱和,因此二次电流不能准确的反映实际一次电流,致使保护装置发生误动。因此我们要求在系统发生短路故障时,CT的变比误差不应大于10%。CT的变比误差与一次电流有关外,还与二次负载阻抗有关。在相同的一次电流作用下,二次负担大,CT的误差同样大。10%误差曲线反映了CT变比产生10%的误差前提下,一次电流与允许的负载阻抗之间产生曲线。从这条曲线我们可以看出在现有的二次负担下,承受的最大短路电流;同时也可计算出在系统发生故障产生最大短路电流下,CT所允许的最大二次负载阻抗。

Calculation of 10% Error Curve Calibration of Differential Protection of Generator Transformer CT

In the condition of system fault,CT saturation may occur,so the secondary current does not accurately reflect the actual primary current,resulting in the protection device malfunction.Therefore,we require that the ratio error of CT should not exceed 10% when a short circuit fault occurs in the system.The CT ratio error is not only related to the primary current,but also to the secondary load impedance.Under the effect of the same primary current,the burden of secondary current is larger,so is the CT error.10% error curve reflects the curve between the primary current and the allowed load impedance under the premise of 10% error produced in CT ratio.From this curve,we can find the maximum short-circuit current in the existing secondary burden,at the same time,we can calculate the maximum secondary load impedance of CT in the situation of the greatest short-circuit current when a system fault occurs.