Eight reasons why motors get hot


Motor as people’s production and life indispensable important power provider, in the use of the process of many motor will appear very serious heat phenomenon, but many times do not know how to solve, more serious is not know what causes the motor heat, which should be the first to master in the use of the motor process, the following we come together to understand why the motor heat is very serious common causes.

1, the air gap between the stator and rotor of the motor is very small, which will easily lead to the stator and rotor touching each other

2, the abnormal vibration or noise of the motor will easily cause the motor to heat up

In the small and medium-sized motor, air gap is generally 0.2mm ~ 1.5mm. air gap is large, the excitation current is required, thus affecting the power factor of the motor; air gap is too small, the rotor may occur friction or collision. Generally due to bearing serious over poor and end cover bore wear deformation, so that the seat, end cover, rotor three different axis cause sweeping, it is easy to make the motor hot or even burned. If the bearing is found to be worn out, it should be replaced in time, and the end cap should be replaced or brushed, a simpler way to deal with the end cap is to set the sleeve.

This situation belongs to the vibration caused by the motor itself, most of them are due to bad dynamic balance of the rotor, as well as poor bearing, bending of the rotor, end cap, seat, rotor different axis, loose fasteners or motor installation foundation is not level, installation is not in place, may also be the mechanical end passed over, should be excluded for the specific situation.

3, bearing work is not normal, must cause the motor to heat up

Whether the bearings work normally can be judged by hearing and temperature experience.

Available hand or thermometer to detect the bearing end to determine whether its temperature is within the normal range; can also be used to listen to the rod (copper rod) contact bearing box, if you hear the impact sound, said there may be one or several ball rolling broken, if you hear a sizzling sound, that is to say that the bearing lubricant is not enough, the motor should be in operation 3,000 hours ~ 5,000 hours or so for a grease.

4, the power supply voltage is high, the excitation current increases, the motor will overheat

Excessive voltage will endanger the insulation of the motor and put it at risk of breakdown. When the power supply voltage is too low, the electromagnetic torque will be reduced, if the load pitch is not reduced, the rotor rotation number is too low, then the increase in the rate of difference will cause the motor to overload and heat up, and a long time 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 high or low, it will lead to excessive current in a certain phase, the motor will heat up, and at the same time, the reduction of the rotation distance will issue a “humming” sound, which will damage the winding over time.

In short, whether the voltage is too high, too low or asymmetric voltage will increase the current, the motor will heat up and damage the motor. Therefore, according to the national standard, the change of the motor supply voltage should not exceed ±5% of the rated value, and the motor output power can be maintained at the rated value. Motor power supply voltage is not allowed to exceed the rated value of ± 10%, the difference between the three-phase power supply voltage should not exceed the rated value of ± 5%.

5、Winding short circuit, turn-to-turn short circuit, phase to phase short circuit and winding break

The insulation between two adjacent wires in the winding is damaged, so that the two conductors touch each other, known as a winding short circuit. A short circuit in a winding occurring in the same winding is called an inter-turn short circuit. A short circuit in the winding occurring between two phases of the winding is called a phase short circuit. Either way, it will cause an increase in current in one or both phases, causing local heating and damage to the motor due to insulation aging. A winding break is a fault caused by the stator or rotor winding of a motor being touched or burnt off. Whether the winding is short-circuited or broken, it may cause the motor to heat up or even burn up. Therefore, after the occurrence of this situation must immediately stop processing.

6, material leakage into the motor inside, so that the motor insulation is reduced, so that the motor allows the temperature rise to reduce

Solid materials or dust from the junction box into the motor inside, it will reach the motor stator, rotor air gap between, resulting in motor sweeping, until the abrasion of motor winding insulation, so that the motor damage or scrap. If the liquid and gas medium leak into the motor, will directly cause the motor insulation drop and tripping. General liquid and gas leaks have the following forms of expression:

Leakage from various containers and transport pipes, leakage from pump body seals, flushing of equipment and ground.

Mechanical oil leaks into the motor through the front bearing box gap.

With the motor connected to the reducer and other oil seal wear, mechanical lubricating oil along the motor shaft into, after the motor internal accumulation, dissolve the motor insulation paint, so that the motor insulation performance gradually reduced.

7, almost more than half of the motor burned are caused by the motor is out of phase operation

Lack of phase often causes the motor can not run or start after the slow speed, or rotating powerless current increases with “hum” phenomenon. If the load on the shaft does not change, the motor is in a serious overload state, the stator current will reach two times the rated value or even higher. Within a short time the motor will become hot or even burned. The main causes of out-of-phase operation are as follows:

Power line due to other equipment failure caused by a phase power failure, connected to the line of other three-phase equipment will be out of phase operation.

Circuit breaker or contactor a phase due to partial voltage burn or poor contact caused by the lack of phase.

Motor connected into the line due to aging, wear and tear caused by the lack of phase.

Motor a phase winding break, or junction box in a phase connector loose.

8, other non-mechanical electrical fault causes

Other non-mechanical electrical fault causes the motor temperature to rise, when serious may also lead to motor failure. If the ambient temperature is high, the motor lacks a fan, the fan is incomplete or lacks a fan cover. In this case cooling must be forced to ensure ventilation or replacement of the fan blades etc., otherwise the normal operation of the motor cannot be guaranteed.

To sum up, in order to be able to adopt the correct approach to motor troubleshooting, it is necessary to be familiar with the characteristics and causes of common motor faults, to seize the key factors and to regularly check and maintain them. In this way, we can take fewer detours, save time, troubleshoot as soon as possible, so that the motor is in normal operation. Thus ensuring normal production in the workshop.

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