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零序电流互感器是一种套在电缆上的CT，它的一次绕组为穿过CT内孔的三相一次导体电缆，它的一次电流是一次三相电流的向量和（在正常、三相平衡时为0），当发生一次系统单相接地时三相平衡关系被打破，这时零序电流互感器的二次就有电流输出，供给保护装置，实现保护和监控。 Zero sequence current transformer is a set of CT on cable, its primary winding is through the CT of inner hole of a three-phase conductor cable, its primary current is a three phase current vector and (0) during normal, three-phase balance, when a system when the single-phase grounding three-phase equilibrium is broken, the zero sequence current transformer secondary is current output, supply protection, protection and monitoring. 零序电流互感器的一次绝缘就是电缆自身绝缘，所以这种零序电流互感器可以套在任一电压等级的电缆上。 One insulation of the zero sequence current transformer is the insulation of the cable itself, so this zero-sequence current transformer can be used on the cable of any voltage grade. 这种零序电流互感器主要用在中性点不接地或经消弧线圈接地的系统。 This type of zero sequence current transformer is mainly used in a system that is not grounded in neutral or is grounded by an arc. 1、小电流选线装置用零序电流互感器 Zero sequence current transformer for small current line 小电流选线装置本身没有整定值，零序电流只是装置的判据之一，要求零序电流互感器在一次接地电流较小时，和非金属性接地时，零序电流互感器也要有一定的输出，来满足装置启动的门坎值。装置本身的负载阻抗并不大，但需要通过电缆将各个零序电流互感器与装置连接起来，所以电缆的阻抗就是零序电流互感器的主要负载阻抗，这种零序电流互感器的负载阻抗一般为2.5Ω左右，经过多年实践和试验得知与小电流选线装置配套的零序电流互感器选用： Small current line selection device itself without setting value, zero sequence current is one of the criterion of device, for zero sequence current transformer in a grounding current is small, and non-metal earthing, zero sequence current transformer is output to a certain extent, to satisfy the operation of threshold value. The load impedance of the device itself is not big, but need through the cable connects the zero sequence current transformer and the device, so the impedance of the cable is the main load impedance zero sequence current transformer, the zero sequence current transformer load impedance is around 2.5 Ω commonly, after many years of practice and test with small current line selection device form a complete set of zero sequence current transformer is chosen: 变比：150/5 容量：5VA Ratio: 15/5 capacity: 5VA 或变比：40/1 容量：2.5VA Or ratio: 40/1 capacity: 2.5 VA 这两种零序电流互感器在负载阻抗2.5Ω时，一次1A，二次输出在20mA左右，一次40A时二次≥1A，没有严格的变比关系。 These two kinds of zero sequence current transformer in the load impedance 2.5 Ω, a 1 a, secondary output in about 20 ma, a 40 a secondary 1 a or higher, no strict than relationship.