大电流接地系统变比的选择

Large current grounding system change than choice 

中性点接地系统单相接地就是单相短路。变比可以选大一些，如：150/5、150/1以上的变比，不要太小，否则躲不过不平衡电流。注意零线（N）不要穿过CT。

Single-phase grounding neutral grounding system is single phase short circuit. Change is bigger than you can choose some, such as: 150/5, 150/1 or more variable than, not too small, or hide but unbalance current. Don't pay attention to the zero line (N) through the CT. 

零序电流互感器二次额定电流的选择

The choice of zero sequence current transformer secondary rated current 

国标规定有1A、2A、5A。考虑到零序电流互感器一般都是小变比，所以尽量选用1A的，来提高带负载能力。

The nation has 1 a, 2 a, 5 a. Considering the zero sequence current transformer are generally small strain ratio, so try to choose 1 a, to improve the load capacity. 

但是有些综合保护设定1A或5A时是用菜单选择，这时零序电流互感器的二次额定电流就要服从主CT二次额定电流值。

But some comprehensive protection setting 1 a or 5 a menu selection, the zero sequence current transformer secondary rated current shall obey the Lord CT secondary rated current value.