Eight causes and solutions for motor heating


Motors are an important power provider indispensable in […]

Motors are an important power provider indispensable in people's production and life. Many motors will generate serious heat during use, but many times do not know how to solve them. What is more serious is that they do not know what causes the motor. Heat, which should be grasped first during the use of the motor, let's take a look at the common reasons why the motor heats up very seriously.
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. 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, mostly due to poor rotor dynamic balance, poor bearing, bent shaft, end cover, frame, rotor with different axis, loose fasteners, or uneven or improper installation foundation of the motor. It may also be caused by the mechanical end, which should be eliminated according to specific circumstances.
3. Abnormal bearing work 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 indicates 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 increase in 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 over time.
In short, no matter the voltage is too high, too low or voltage asymmetry, the current will increase, and the motor will generate heat 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 and winding open circuit
After the insulation between two adjacent wires in the winding is damaged, the two conductors will touch each other, which is called a winding short circuit. Winding short circuits that occur in the same winding are called inter-turn short circuits. 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 entering the motor from the junction box 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 gaseous media 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 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 rotate slowly after starting, or rotate weakly, the current increases, and there is a "buzzing" 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 the failure of other equipment 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 the one-phase connector in the junction box is loose.
8. Other causes of non-mechanical electrical faults
The temperature increase of the motor caused by other non-mechanical and electrical failure causes may also cause the motor to fail in severe cases, such as high ambient temperature, lack of fan, incomplete fan or lack of fan cover. In this case, it is necessary to force the refrigeration but 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, eliminate faults as soon as possible, and keep the motor in normal operation, thereby ensuring normal production in the workshop.