Generally, conventional motor protectors mainly perform protection operation through three-phase current transformers, detection circuits, delay circuits, adjustment circuits, and various components of the relay. Once the detection circuit detects the abnormal current induced by the current transformer, it will output a signal to the executive relay. The relay contacts are connected in series in the power supply circuit of the contactor coil, so the transmitted signal will cause the AC contactor to directly disconnect the power supply, thereby protecting the equipment motor; the delay circuit is used to avoid excessive instantaneous current when the motor starts. Smart motor protectors generally can adjust the duration of this reaction action by themselves; the adjustment circuit is used to set the action current according to the working current accuracy of the protected motor.
Traditional thermal relays are prone to heating points and failure points on the line due to screw connection problems in and out, which will greatly reduce the protection effect. The motor protector, because it is a through-the-core installation method, can reduce breakpoints on the circuit, thereby reducing heating points and fault points, and improving protection accuracy. What's more, the motor protector detects the three-phase operating current and determines different protection methods according to the different properties of the operating current. To a certain extent, it can avoid the impact of harsh environments on the detection accuracy of the equipment.