Short circuit fault of electric motor is a serious type of fault with great harm. Short circuit faults include phase to phase short circuits in the stator winding and turn to turn short circuits in one phase winding. The phase to phase short circuit of the stator winding is the most serious fault of the motor, which can cause serious damage to the motor itself, significantly reduce the voltage of the power supply network, and affect the normal operation of other electrical equipment. One phase turn to turn short circuit is a common short-circuit fault, which initially manifests as asymmetric three-phase current, causing an increase in the phase current of the faulty phase. In severe cases, it can lead to the complete burning of the insulation of the turn to turn coil, resulting in a short circuit of all one phase windings of the motor. At this point, the non faulty phase of the load star connection will bear the line voltage, while the load delta connection will generate a phase to phase short circuit, which will cause serious damage to the motor.
The most obvious characteristic of motor phase to phase short circuit fault is the occurrence of high current in the fault phase of the three-phase power supply line, which poses great harm and should be protected by quick break protection. The setting value of short-circuit protection should be greater than the maximum stable starting current of the motor, generally taking 8-10 times the rated current of the motor. When carrying out short-circuit protection, it is achieved by detecting the current of the three-phase wires of motors A, B, and C. After exceeding the set value, power off protection is directly carried out. The principle of short-circuit protection is that when the maximum three-phase current exceeds K times the rated line current of the motor within a certain time limit (of course, it is very short) (K is the short-circuit overcurrent multiple, usually taken as 8-10), it is considered that the motor has a short-circuit fault and should be protected with quick break.
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