Causes of overload of valve electric actuator:

One is that the power supply voltage is low and the required torque can not be obtained, which makes the motor stop rotating;

Second, the torque limiting mechanism is mistakenly adjusted to make it greater than the stop torque, resulting in continuous excessive torque and stopping the motor;

The third is intermittent use, resulting in heat accumulation, which exceeds the allowable temperature rise of the motor;

Fourth, for some reason, the circuit of torque limiting mechanism fails, which makes the torque too large;

Fifth, the use of high ambient temperature, the relative thermal capacity of the motor decreased.

In the past, fuse, over-current relay, thermal relay and thermostat were used to protect the motor, but these methods have their own advantages and disadvantages. There is no absolutely reliable protection method for the electric device, which is a variable load equipment. Therefore, we must take a variety of combinations, summed up in two ways: one is to judge the increase or decrease of motor input current; the other is to judge the motor itself heating. Either way, the time margin given by the thermal capacity of the motor should be considered.

Generally, the basic protection methods for overload are as follows:

1. For overload protection of continuous operation or inching operation of motor, thermostat is adopted;

2. Thermal relay is used to protect the motor from locked rotor;

3. For short circuit accident, fuse or over-current relay shall be adopted

Valve electric actuator is an indispensable equipment to realize valve program control, automatic control and remote control. Its movement process can be controlled by the stroke, torque or axial thrust. It is very important to select the valve electric device correctly to prevent overload (the working torque is higher than the control torque).