What about motor heating?

Motors are indispensable and important power providers in people’s production and life. Many motors will generate serious heat during use, but many times do not know how to solve them, and what is more serious is that they do not know why. The resulting heating of the motor should be the first to be grasped during the use of the motor. Let’s take a look at the common reasons why the motor is very hot.

 

1. The air gap between the stator and rotor of the motor is very small, which is easy to cause collision between the stator and rotor
In medium and small motors, the air gap is generally 0.2mm to 1.5mm. When the air gap is large, the excitation current is required to be large, thereby affecting the power factor of the motor; if the air gap is too small, the rotor may friction or collision. Generally, due to the severe over-tolerance of the bearing and the wear and deformation of the inner hole of the end cover, the different axis of the base, the end cover and the rotor will cause the bore, which can easily cause 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 cover should be replaced or brush-plated. The simpler treatment method is to set the end cover.

2. The abnormal vibration or noise of the motor can easily cause the motor to heat up
This situation belongs to the vibration caused by the motor itself, most of which are due to poor rotor dynamic balance, poor bearing, bent shaft, end cover, frame, rotor different axis, loose fasteners or motor installation foundation is uneven, and the installation is not in place The cause may also be transmitted from the mechanical end, which should be eliminated according to specific circumstances.

3. Abnormal bearing operation will inevitably cause the motor to heat up.

Whether the bearing works normally can be judged by hearing and temperature experience. You can use your hand or a thermometer to check the bearing end to determine whether the temperature is within the normal range; you can also use a listening rod (copper rod) to contact the bearing box. If you hear an impact sound, it means that one or several balls may be crushed. The sizzling sound means that the lubricating oil of the bearing is insufficient, and the motor should be changed once every 3,000 to 5,000 hours of operation.

4. The power supply voltage is too high, the excitation current increases, the motor will overheat  
Excessive voltage will endanger the motor insulation and cause it to be broken down. When the power supply voltage is too low, the electromagnetic torque will decrease. If the load torque is not reduced and the rotor speed is too low, the increased slip will cause the motor to overload and generate heat. Long-term overload will affect the life of the motor. When the three-phase voltage is asymmetrical, that is, when the voltage of one phase is too high or too low, it will cause a certain phase current to be too large, the motor heats up, and at the same time the torque decreases will make a “buzzing” sound, which will damage the windings for a long time.
In short, no matter the voltage is too high, too low or voltage asymmetry, the current will increase, and the motor will heat up and damage the motor. Therefore, according to the national standard, the change of the motor power supply voltage should not exceed ±5% of the rated value, and the motor output power can maintain the rated value. The motor power supply voltage is not allowed to exceed ±10% of the rated value, and the difference between the three-phase power supply voltage should not exceed ±5% of the rated value.

5. Winding short-circuit, inter-turn short-circuit, phase-to-phase short-circuit and winding open circuit  
After the insulation between two adjacent conductors in the winding is damaged, the two conductors collide, which is called a winding short circuit. A winding short circuit that occurs in the same winding is called an inter-turn short circuit. A winding short circuit that occurs between two phase windings is called an interphase short circuit. Either way, it will increase the current of one or two phases, causing local heating, and aging the insulation and damaging the motor. Winding open circuit refers to the fault caused by the broken or blown stator or rotor winding of the motor. Whether the winding is short-circuited or open, it may cause the motor to heat up or even burn. Therefore, it must be shut down immediately after this happens.

6. The leakage of materials into the motor reduces the insulation of the motor, thereby reducing the allowable temperature rise of the motor
Solid materials or dust enter the inside of the motor from the junction box, and will reach the air gap between the stator and rotor of the motor, causing the motor to sweep the cavity, until the motor winding insulation is worn out, and the motor is damaged or scrapped. If liquid and gas medium leak into the motor, it will directly cause the motor insulation to drop and trip. Generally liquid and gas leakage has the following manifestations:
(1) Leakage of various containers and pipelines, leakage of pump body seal, flushing equipment and ground, etc.
(2) After the mechanical oil leaks, it enters the motor from the gap of the front bearing box.
(3) The oil seal of the reducer connected to the motor is worn, and the mechanical lubricating oil enters along the motor shaft. After it accumulates in the motor, it dissolves the motor insulation paint, which gradually reduces the motor insulation performance.

7. Almost more than half of the motor burns are caused by the lack of phase operation of the motor   .
The lack of phase often causes the motor to fail to run or the speed to be slow after starting, or to rotate weakly, the current increases and there is a “humming” phenomenon. If the load on the shaft does not change, 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 will cause the other three-phase equipment connected to the line to run without phase.
(2) One phase of the circuit breaker or contactor is missing due to burnout of the bias voltage or poor contact.
(3) Phase loss caused by aging, wear and other reasons of the incoming wire of the motor.
(4) One-phase winding of the motor is open, or one-phase joint in the junction box is loose.

8. Other non-mechanical and electrical fault causes  
The temperature increase of the motor caused by other non-mechanical and electrical failure causes may also cause the motor to malfunction. If the ambient temperature is high, the motor lacks a fan, the fan is incomplete, or the fan cover is missing. In this case, it is necessary to force cooling to ensure ventilation or replace the fan blades, otherwise the normal operation of the motor cannot be guaranteed.
To sum up, in order to be able to use the correct method to deal with motor faults, it is necessary to be familiar with the characteristics and causes of common motor faults, grasp the key factors, and regularly inspect and maintain. Only in this way can we avoid detours, save time, troubleshoot as soon as possible, and keep the motor in normal operation. So as to ensure the normal production of the workshop.

2020-09-04T16:34:55+08:00September 4th, 2020|

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