Eight major causes of motor heating

1. The air gap between the stator and rotor of the motor is very small, which is easy to cause the collision between the stator and rotor

In medium and small motors, the air gap is generally 0.2mm ~ 1.5mm. When the air gap is large, the excitation current is required to be large, which affects the power factor of the motor. If the air gap is too small, friction or collision may occur to the rotor. Generally, due to the serious out-of-tolerance of bearings and the wear and deformation of the inner hole of the end cover, the three different axes of the base, end cover and rotor cause sweeping, and it is easy to make the motor heat or even burn down. If the bearing is found to be worn, it should be replaced in time, and the end cover should be replaced or brushed. The relatively simple treatment method is to insert the end cover.

2. The abnormal vibration or noise of the motor is easy to cause the heating of the motor

This situation belongs to the vibration caused by the motor itself, most of it is due to the rotor dynamic balance is not good, and the bearing is bad, the shaft bending, the end cover, the frame, the rotor different axis, the fastener is loose or the motor installation foundation is uneven, the installation is not in place, it may also be the mechanical end passed over, should be excluded for the specific situation.

3. Bearing work is not normal, must cause motor heating

Whether the bearing works normally can be judged by hearing and temperature experience.

The bearing end can be detected by hand or thermometer to determine whether the temperature is within the normal range; It can also be used to contact the bearing box with the listening rod (copper rod). If you hear the impact, it means that there may be one or several ball crushed. If you hear the hiss, it means that the lubricating oil of the bearing is insufficient.

4.The power supply voltage is on the high side, the excitation current is increased, and the electric machine is excessively heated

Excessive voltage will endanger the motor insulation, making it has the risk of breakdown. When the power supply voltage is too low, the electromagnetic torque will be reduced. If the load pitch is not reduced and the rotor rotation is too low, then the increase of slip will cause the motor to overload and heat, and the overload for a long time will affect the life of the motor. When the three-phase voltage is asymmetrical, that is, when the one-phase voltage is high or low, it will lead to a phase current is too large, the motor is heated, and the rotation distance will be reduced to issue a "buzzing" sound, and the winding will be damaged for a long time.

In short, whether the voltage is too high, too low or voltage asymmetry will increase the current, motor heating and damage the motor. Therefore, according to national standards, the change of motor power supply voltage should not exceed ±5% of the rated value, the output power of the motor can maintain the rated value. The power supply voltage of the motor shall not exceed ±10% of the rated value, and the difference between the three-phase power supply voltages shall not exceed ±5% of the rated value.

5.Winding short circuit, inter-turn short circuit, phase short circuit and winding break

When the insulation between the two adjacent conductors in the winding is damaged, the two conductors collide, which is called the winding short circuit. The winding short circuit occurring in the same winding is called interturn short circuit. The winding short circuit occurring between two - phase windings is called phase - phase short circuit. No matter which one, will make a phase or two phase current increase, cause local heating, so that the insulation aging damage to the motor. Winding breakage refers to the fault caused by the stator or rotor windings of the motor being broken or burned off. Whether winding short circuit or open circuit may cause motor heating and even burn down. Therefore, this situation must be immediately shut down for processing.

6. Material leakage into the motor, the motor insulation is reduced, so that the allowable temperature rise of the motor is reduced

When solid material or dust enters the motor from the junction box, it will reach the air gap between the stator and rotor of the motor, causing sweeping of the motor until the insulation of the motor windings is worn out, and the motor is damaged or scrapped. If the liquid and gas medium leak into the motor, it will directly cause the motor insulation drop and trip. General liquid and gas leakage has the following manifestations:

Leakage of various containers and conveying pipes, leakage of pump seals, flushing equipment and ground;

Mechanical oil leakage from the front end of the bearing box gap into the motor;

The oil seal of the reducer connected with the motor is worn, and the mechanical lubricating oil enters along the motor shaft. After accumulating in the motor, the insulation paint of the motor is dissolved, so that the insulation performance of the motor is gradually reduced.

7. Almost more than half of the motor burning is caused by the lack of phase motor operation

The lack of phase often causes the motor to be unable to run or start the speed is slow, or the inability to rotate the current to increase the "buzzing" sound phenomenon. If the load on the shaft does not change, the motor is in a state of severe overload and the stator current will reach twice the rated value or more. In a short time, the motor will heat up and even burn down. The main reasons for phase loss are as follows:

If one phase is cut off due to other equipment failure on the power line, the other three-phase equipment connected to the line will run out of phase.

Loss of phase of a circuit breaker or contactor due to bias voltage burning or poor contact.

Lack of phase due to aging, wear and tear of the incoming line of motor.

One phase winding of the motor is broken, or one phase connector in the junction box is loose.

8. Other non-mechanical and electrical faults

The motor temperature rise caused by other non-mechanical electrical failure causes may also lead to motor failure in serious cases. If the ambient temperature is high, the motor lacks a fan, the fan is incomplete or the fan cover is missing. In this case must be forced cooling to ensure ventilation or replace the blade, otherwise the normal operation of the motor cannot be guaranteed.

To sum up, in order to be able to use the correct method for motor fault processing, it is necessary to be familiar with the characteristics and causes of common motor faults, grasp the key factors, regular inspection and maintenance. In this way, we can avoid detours, save time and troubleshoot the faults as soon as possible, so that the motor is in normal operation. In order to ensure the workshop normal production.