In power system, CT is widely applied in one time measurement and control of current. In normal working condition, the secondary side of CT is almost short circuit, and output voltage is very low. During operation, if the secondary winding is open circuit, or abnormal current flows the primary winding (such as lightning current,

CTKB-IV series CT overload protector is mainly applied in various CT secondary side abnormal over voltage protection, CT secondary side differential winding, over current winding, measurement winding, generatrix protection winding, spare winding etc.

The basic apparatus of CT secondary open circuit over voltage protection is ZnO voltage dependent resistor, and parallel connection with secondary winding. In normal working condition, voltage dependent resistor is at the sate of high resistance, and the leakage current is very low, while the sample signal is "0'. The control circuit is off operation, and the CT is at the normal working condition. In general condition, secondary winding just has several voltage, and the max. voltage is less than 20V.

When CT is secondary return open circuit or primary winding comes forth abnormal over current, the voltage emerged from secondary winding is far higher than the normal condition voltage. Then the voltage dependent resistor is on state ( over 150V), the sample voltage signal is a little higher, and the inner automatic control circuit controls secondary winding short circuit, and active display on the panel. At the same time, it will output remote no power contact signal. When the malfunction is removed, it can operate. There're two reposition methods: one is the malfunction removing of power off, it automatically reposition when restarting the power; another is after the malfunction removing of power on, pushing "reposition" button, it'll remove the malfunction and the circuit will recover before.