How to deal with motor overheating? How to choose a thermal protector?

Before solving the overheating of the motor, we must first understand the cause of the motor heating:

1. Heating caused by motor failure

When the motor is running, it will fail for various reasons. Common faults mainly include: short circuit or grounding of the winding, damage to the insulation of the iron core silicon steel sheet, overload of the motor, lack of phase operation of the winding, and bearing damage caused by overheating of the motor shaft. When these faults occur, the motor may overheat. Therefore, when the motor is running, pay close attention to various fault phenomena, find out and deal with them in time, so as to ensure the normal operation of the motor.

2. The copper loss and iron loss of the motor are converted into heat

The various motors we usually see have iron cores and winding coils inside. The winding has resistance, and loss occurs when power is applied. Losses are proportional to the square of the resistance and current. This is what we often call copper loss. Harmonic losses also occur if the current is not a standard DC or sine wave; the iron core has hysteresis. The eddy current effect will also produce loss in the alternating magnetic field, and its size is related to material, current, frequency and voltage, which is called iron loss. Both copper loss and iron loss are converted into heat, which increases the temperature of the motor, affects the efficiency of the motor, and even damages the motor. Stepper motors generally pursue positioning accuracy and torque output. The efficiency is relatively low, the current is generally relatively large, and the harmonic components are high. The frequency of the alternating current also varies with speed. Therefore, stepper motors generally have heat, and the situation is more serious than that of ordinary AC motors.

3. Effect of voltage change on motor performance

Effect of voltage changes on motor performance. When the motor is powered by the specified AC power supply, it can better meet various performance indicators. However, the performance indicators of the actual power supply often exceed the specified deviation limit, and some regions and departments have quite serious deviations. When the power supply voltage is too high or too low, it will cause the motor to heat up. For example, when the power supply voltage drops, the starting torque will decrease proportionally, which will prolong the starting time, and even fail to start in serious cases, and burn out the motor, which is more prominent in the application of heavy load starting and frequent starting. An increase in the power supply voltage will increase the saturation of the motor's magnetic circuit, resulting in an increase in current and an increase in temperature rise. Therefore, the fluctuation range of the motor power supply voltage should be strictly controlled within the allowable range to ensure the normal operation of the motor.

4. Poor ventilation and heat dissipation cause the motor to heat up

If the ambient temperature around the motor is too high, the ventilation duct of the motor is blocked, and there is too much sludge and dust in the motor, the cooling effect will be affected. Therefore, it is necessary to keep the environment around the motor clean, improve heat dissipation conditions, and reduce the temperature rise of the motor.

In addition, there are frequent start and stop of the motor or frequent forward and reverse rotation, lack of bearing oil, mechanical jamming, motor damping, rotor sweeping, etc., which will cause the motor to heat up to varying degrees.

In case of motor overheating, measures should be taken in time. There are two main causes of motor heating: electromagnetic problems and mechanical problems. After selecting a motor, determine its electromagnetic characteristics. When mechanical problems occur in actual operation, it is necessary to strengthen monitoring, pay attention to the abnormal phenomenon of motor overheating, correctly analyze the cause of motor heating, and take targeted preventive measures. In practical applications, the key is how to protect the motor. Typically, a mechanical temperature control switch can be used for protection.

Motors are often burned out under heavy load and long-running conditions. The thermal switch can be connected in series with the common lead end of the main and auxiliary windings. After winding, wrap the end of the motor winding with insulating paper, and then the discharge motor is close to the casing. When the single-phase motor is connected to the single-phase AC power supply, the motor will heat up due to copper loss and iron loss when the load is running. When the internal temperature of the motor is equal to the working temperature of the temperature control switch, the bimetal thermal protector will automatically jump off the static electric shock and cut off the power to protect the motor.