The most common fault in the current sensor is the short circuit of the current transformer. The current transformer, that is, the number of turns of the CT primary winding is small. When the primary winding is used in series, the secondary winding is connected in series. The number of turns of the secondary winding is large, and it is used in series with the current coils such as measuring instruments and relays. The current coils of measuring instruments and relays have little impedance. Therefore, the CT is close to the short-circuit state during normal operation. The magnitude of the secondary current of the current transformer is determined by the primary current, and the magnetic potential generated by the secondary current balances the magnetic potential of the primary current. If the secondary open circuit, its impedance is infinite, the secondary current is equal to zero, and its magnetic potential is equal to zero, it can not balance the magnetic potential generated by the primary current, then the primary current will all act on the excitation, causing the iron core to be severely saturated. Magnetic saturation increases the iron loss, the current heats up, and the insulation of the current coil is burnt out due to overheating. Residual magnetism is also generated on the core to increase the transformer error. The most serious is that due to magnetic saturation, the sinusoidal wave of the alternating magnetic flux becomes a trapezoidal wave. At the moment when the magnetic flux changes rapidly, a high voltage is induced on the secondary coil, and its peak value can reach several thousand volts, so high. The voltage acts on the secondary coil and the secondary circuit, which poses a serious threat to both the human body and the microcomputer harmonic elimination device. Therefore, the current transformer does not allow the secondary side to open at any time.
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