What are overcurrent, overvoltage and undervoltage
Electrical control systems often encounter short-circuit, overcurrent, overload, zero voltage, undervoltage, overvoltage and other fault phenomena! The general electrical control system has at least two protection links of short circuit protection and overload protection, and on the contrary, it cannot be called a complete electrical control system.
Overcurrent: For example, the motor does not start in the correct way or the load torque increases sharply
The addition will cause the motor to run over current. Compared with the short circuit current, the overcurrent is smaller than the short circuit current, and it is certainly larger than the rated current of the motor, although the short circuit is not serious, it will also damage the motor.
Undervoltage: For example, the normal operation of the motor, the reduction of the power supply voltage causes the release of the appliance, resulting in the abnormal work of the control circuit, and even an accident. Assuming the motor load is constant,
The power grid voltage is too low. Because of the electromagnetic torque and voltage of the three-phase asynchronous motor
In direct proportion to the quadratic, it will cause a reduction in electromagnetic torque and a stationary load
If the motor stops and the motor current increases, the motor heats up and seriously damages the motor.
Overvoltage: The phenomenon of voltage fluctuation in which the power frequency AC voltage increases by the square root value, exceeds the rated value by 10%, and lasts for more than one minute. This phenomenon generally belongs to the electromagnetic disturbance phenomenon of power system.
In summary, overcurrent may be due to incorrect starting mode or load torque
Caused by a sharp increase, undervoltage is the reduction of the supply voltage to the allowable value of the motor
Electromagnetic torque is reduced with stationary load.
