Zero Sequence Current Transformers for Switchgear Safety

Core Balance Current Transformers (CBCT), also known as Zero Sequence Current Transformers (ZSCT), are critical components for earth fault protection in low and medium voltage electrical systems. These transformers detect unbalanced or residual currents by monitoring the sum of currents in three-phase conductors passed through the transformer’s core. CBCTs operate on the principle that, under normal conditions, the vector sum of phase currents equals zero. If an earth fault occurs, this balance is disturbed, producing a net current that the CBCT detects. This net current induces a voltage in the secondary winding, activating an earth fault relay to isolate the affected part of the circuit.