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零序电流互感器变比：额定一次电流与额定二次电流之比

Zero sequence current transformer is variable ratio: the rated primary current to the rated secondary current 

零序电流互感器的应用一般都选用较小变比，常用的如：50/5、75/5、100/5、150/5、200/5、20/1、50/1、100/1、150/1、200/1等，因为只有发生一次接地故障时，零序电流互感器才有输出。人们不会让接地电流很大时才使保护动作。（不用考虑躲过负荷电流）可是由于一次绕组是电力电缆，仅有一匝，这样，50/5的零序电流互感器的二次额定匝数，仅10匝，所以50/5的零序电流互感器负荷特性较差，实际负载阻抗和零序电流互感器的容量不一致时将会出现较大的误差，而且在低于额定电流时误差也会加大，所以在允许的情况下尽量选用大一些的变比。

The application of zero sequence current transformer is generally choose smaller than, the commonly used such as: 50/5, 75/5, 100/5, 75/5, 200/5, 20/1, 50/1, 100/1, 150/1, 100/1, etc., because only a ground fault occurs, zero sequence current transformer is output. People don't let the earth current is large to make the protection action. (don't consider from load current) as the primary winding is power cable, however, only one turn, so, 50/5 of the zero sequence current transformer secondary rated number of turns, only 10 turns, so 50/5 of the zero sequence current transformer load characteristic is poorer, the actual load impedance and the capacity of the zero sequence current transformer is not consistent, there will be a larger error and error just below the rated current is increased, so as far as possible under the condition of the allowed to choose a few bigger than.