What to do if the motor is hot

Issuing time:2020-02-20 16:20

The air gap between the stator and the rotor of the motor is very small, which easily leads to collision between the stator and the rotor.

In medium and small motors, the air gap is generally 0.2mm to 1.5mm. When the air gap is large, a large excitation current is required, which affects the power factor of the motor; if the air gap is too small, the rotor may be subject to friction or collision. Generally, due to the serious tolerance of the bearing and the wear and deformation of the inner hole of the end cover, the different shaft centers of the machine base, the end cover and the rotor cause sweeping, and it is easy for the motor to heat up or even burn. If the bearing is found to be worn, it should be replaced in time, and the end cap should be replaced or brushed. The simpler method is to insert an end cap.

2. The abnormal vibration or noise of the motor easily causes the motor to heat up

This situation belongs to the vibration caused by the motor itself, most of which are due to the poor dynamic balance of the rotor, as well as poor bearings, curved shafts, different shaft centers of the end caps, bases, and rotors, loose fasteners, or uneven installation foundations of the motors and improper installation. It may be caused by the mechanical end and should be excluded according to the specific situation.

3. The bearing does not work properly, which must cause the motor to heat up

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. The bearing box (copper rod) can also be used to contact the bearing box. If an impact sound is heard, it means that one or more balls may be crushed. A snoring sound means that the bearing has insufficient lubricant, and the motor should be changed once every 3,000 hours to 5,000 hours.

4. The power supply voltage is too high, the excitation current increases, and the motor overheats.

Excessive high voltage will endanger the insulation of the motor and risk of breakdown. When the power supply voltage is too low, the electromagnetic torque will be reduced. If the load torque is not reduced, the number of rotor revolutions will be too low. At this time, the increased slip rate will cause the motor to overload and generate heat, and prolonged overload will affect the life of the motor. When the three-phase voltage is not symmetrical, that is, when the voltage of one phase is too high or too low, the current of one phase will be too large, and the motor will heat up. At the same time, the "torque" will be emitted when the torque is reduced, and the winding will be damaged for a long time.

In short, no matter the voltage is too high, too low, or the voltage is asymmetric, the current will increase, and the motor will heat up and damage the motor. Therefore, according to national standards, the change of the motor power supply voltage should not exceed ± 5% of the rated value, and the output power of the motor can maintain the rated value. The motor power voltage must not exceed ± 10% of the rated value, and the difference between the three-phase power voltages should not exceed ± 5% of the rated value.

5. Winding short circuit, interturn short circuit, interphase short circuit and winding open circuit

After the insulation between two adjacent wires in the winding is damaged, the two conductors are in contact with each other, which is called winding short circuit. Winding shorts that occur in the same winding are called inter-turn shorts. A winding short-circuit that occurs between two-phase windings is called an inter-phase short. No matter which one, it will increase the current of one phase or two phases, cause local heating, and cause the insulation to age and damage the motor. Winding break refers to the failure caused by the stator or rotor winding of the motor being broken or burned. Whether the winding is short-circuited or disconnected, it may cause the motor to heat up or even burn out. Therefore, you must stop processing immediately after this happens.

6. Material leaks into the inside of the motor, which reduces the insulation of the motor and reduces the allowable temperature rise of the motor.

When solid materials or dust enter the motor from the junction box, they will reach the air gap between the stator and rotor of the motor, causing the motor to scavenge until the insulation of the motor windings is worn out, causing the motor to be damaged or scrapped. If liquid and gaseous medium leaks into the motor, it will directly cause the motor insulation to drop and trip. General liquid and gas leaks have the following manifestations: (1) leaks in various containers and pipelines, leaks in pump body seals, flushing equipment and the ground. (2) After the mechanical oil leaks, it enters the motor through the gap in the front bearing box. 3 (3) Oil seals such as the reducer connected to the motor wear out, mechanical lubricant enters along the motor shaft, and after it accumulates inside the motor, it dissolves the motor insulation paint, which gradually reduces the motor's insulation performance.

7. Almost half of the motors are burned due to lack of phase operation of the motor

The lack of phase often causes the motor to fail to run or the speed of the motor to start slowly, or the current will increase when there is no buzzing. If the load on the shaft is not changed, the motor is in a severe overload state, and the stator current will reach 2 times or more of the rated value. The motor will heat up or even burn out in a short time. The main reasons for the lack of phase operation are as follows:

(1) One-phase power failure caused by other equipment failure on the power line, other three-phase equipment connected to the line will run out of phase.

(2) One phase of circuit breaker or contactor is missing due to bias voltage burnout or poor contact.

(3) Phase loss due to aging, wear, etc. of the motor's incoming line.

(4) One phase winding of the motor is open, or one phase connector in the terminal box is loose.

8. Other non-mechanical electrical failure causes

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