Most motor applications will be equipped with overload holding devices, that is, when the motor current exceeds the set value due to overload, the holding instruction will be executed to implement protection.
When the motor is mechanically stuck, or there are electrical faults such as ground, phase-to-phase, and turn-to-turn, the protection instruction will also be effective due to the increase of current. However, when the current has not increased to the protection setting value, the protection device will not execute the corresponding instruction.
Especially for the case of electrical faults in the winding, due to different fault states, it first manifests as current imbalance. In some cases where the fault is not serious, the motor may continue to work in a state of slight current imbalance until a serious problem occurs; therefore, after an electrical fault occurs in the motor winding, the current will be unbalanced to varying degrees, and the current of a certain phase will increase, but the increase depends on the degree of the fault, and it may not necessarily trigger the motor protection device; when the fault undergoes a serious qualitative change, the winding will instantly explode, and the motor will be in a circuit-breaking state, but the power supply may not be cut off.
For the current setting of overload protection, when the setting is too small, protection will be executed when there is a slight overload, affecting normal operation; if the setting is too large, it will not play a protective role; some protection devices can not only take action in the case of large current, but also implement protection for excessive unevenness problems.