The zero-sequence current transformer is used to detect the zero-sequence current. Its structure is similar to that of an ordinary through-core current transformer, except that its primary winding is the three-phase wires of the protected system (the three-phase wires pass through together Transformer ring core), the secondary winding reflects the zero sequence current of the primary system.
In a system where the neutral point is not directly grounded, the zero-sequence current transformer and the grounding relay form a single-phase grounding protection device. When the system is operating normally, 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 operate.
Zero sequence current transformers are used in conjunction with relay protection devices or signal devices when the power system generates zero sequence ground current. The device components are activated to achieve protection or monitoring functions.https://www.ctsensorducer.com/