Where should the zero sequence current transformer start?

- May 20, 2020-

Zero sequence current transformer and its characteristics

The zero sequence current transformer is used to detect the zero-sequence current, and its structure is similar to that of the ordinary feed-through current transformer, except that its primary winding is the three-phase conductors of the protected system (three-phase conductors pass through together Transformer ring core), the secondary winding reflects the zero-sequence current of the system.

In a system where the neutral point is not directly grounded, the zero sequence current transformer and grounding relay constitute a single-phase grounding protection device. During normal operation of the system, the vector sum of the three-phase currents on the primary side of the zero-sequence current transformer is zero. When a single-phase ground fault occurs, zero-sequence magnetic flux appears in the core, which induces electromotive force in the secondary winding. The secondary current flows through the grounding relay to make it act.

Zero sequence current transformers are used in conjunction with relay protection devices or signaling devices when the power system generates zero-sequence ground currents. The device components are operated to realize the protection or monitoring function.

Classification of zero sequence current transformer

According to the installation method: integral type and opening and closing type

According to the structure form: busbar type and cable type

According to the coordination protection: small current grounding line selection device, relay, microcomputer protection