Zero sequence current transformers, which are also know as core balance current transformers (CBCT), residual current transformers, ground current transformers or leakage current transformers. Zero sequence ct detects the presence of zero sequence currents during short circuit fault conditions, usually used in power fire protection equipment, such as residual current circuit breaker, earth leakage protection switch, leakage circuit protection breaker, leakage circuit protection plug. When the power system generates zero-sequence grounding current, it is used in conjunction with the relay protection device for pre-protection Or monitor.

Based on Kirchhoff's current law: the algebraic sum of the complex current flowing into any node in the circuit is equal to zero. When the circuit and electrical equipment are normal, the vector sum of each phase current is equal to zero, Ia+Ib+Ic=0.

The secondary winding of the zero sequence current transformer has no signal output,without actuator operation.

Once a ground fault occurs, the vector sum of the phase currents is not zero, Ia+Ib+Ic=Io>0, Io is the zero sequence current /leakage current/fault current. The fault current makes the zero sequence current transformer Magnetic flux is generated in the toroidal core, and the induced voltage on the secondary side of the zero-sequence current transformer causes the actuator to act, drive the tripping device, switch the power supply network, and achieve the purpose of ground fault protection.

The features of Zero-sequence current transformer

High sensitivity

Close to zero load shift and zero phase shift

Excellent balance characteristics

Perfect temperature stability

Small change for output voltage after passing the heavy current IDC

A variety of configuration and output characteristics