Analysis of the eight reasons for motor heating

As an indispensable power supplier in people's production and life, many motors have a very hot phenomenon in the process of use, but many times they don't know how to solve it. What is more serious is that they don't know why. The resulting motor heat, this should be the first to grasp 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 the rotor is very small, which easily leads to the collision between the stator and the rotor.

In medium and small motors, the air gap is generally 0.2 mm to 1.5 mm. 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, the rotor may be rubbed or collided. Generally, due to the serious tolerance of the bearing and the wear and deformation of the inner hole of the end cover, the bottom of the base, the end cover and the rotor cause the broom, which is easy to cause the motor to heat or even burn. If it is found that the bearing wear should be replaced in time, the end cover is replaced or brushed, and the simpler treatment method is to insert the end cover.

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

This situation belongs to the vibration caused by the motor itself, mostly due to the poor dynamic balance of the rotor, as well as poor bearing, bending of the shaft, different ends of the end cover, the base and the rotor, loose fasteners or uneven grounding of the motor installation, and the installation is not in place. The result may also be transmitted from the mechanical end and should be excluded for specific circumstances.

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

Whether the bearing works properly 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 rod (copper rod) can also be used to contact the bearing box. If the impact sound is heard, it means that there may be one or several balls crushed, if heard The buzzing sound is that the bearing has insufficient lubricating oil, and the motor should be replaced with grease for about 3,000 hours to 5,000 hours.

4, the power supply voltage is high, the excitation current increases, the motor will be excessively hot

Excessive voltage can jeopardize motor insulation and expose it to breakdown. When the power supply voltage is too low, the electromagnetic torque will decrease. If the load torque is not reduced, the rotor rotation number is too low. At this time, the increase of the slip rate will cause the motor to be overloaded and generate heat, and the 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 high or low, it will cause the current of a certain phase to be too large, the motor will heat up, and at the same time, the torque will be “beep” when the torque is reduced, and the winding will be damaged if the time is long.

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

5, winding short circuit, turn-to-turn short circuit, phase-to-phase short circuit and winding open circuit

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

6. Material leaks into the motor to reduce the insulation of the motor, thus allowing the motor to lower the temperature rise.

Solid materials or dust entering the motor from the junction box will reach between the stator and rotor air gaps of the motor, causing the motor to sweep until the motor winding insulation is worn out, causing the motor to be 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 leaks have the following manifestations:

Various container and delivery pipe leaks, pump seal leaks, flushing equipment and floors;

After the mechanical oil leaks, enter the motor from the gap of the front bearing housing;

The oil seal such as the reducer connected to the motor wears, and the mechanical lubricating oil enters along the motor shaft. After accumulating inside the motor, the motor insulation paint is dissolved, so that the insulation performance of the motor is gradually reduced.

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

The lack of phase often causes the motor to be inoperable or the speed is slow after starting, or the rotating forceless current increases the "click" sound. 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 higher of the rated value. The motor will heat up or burn out in a short time. The main reasons for the lack of phase operation are as follows:

A phase failure occurs on the power line due to other equipment failures, and other three-phase equipment connected to the line will run out of phase.

One phase of the circuit breaker or contactor is phase-depleted due to partial voltage burnout or poor contact.

The phase loss of the motor access line due to aging, wear and the like.

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

8, other non-mechanical electrical failure causes

Other motor failures caused by non-mechanical electrical faults may cause motor failure in severe 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, cooling must be forced to ensure ventilation or replacement of blades, otherwise the normal operation of the motor cannot be guaranteed.

In summary, in order to be able to use the correct method for motor fault handling, it is necessary to be familiar with the characteristics and causes of common faults of the motor, seize the key factors, and regularly check and maintain. In this way, it is possible to take fewer detours, save time, eliminate faults as soon as possible, and keep the motor in normal operation. Thereby ensuring the normal production of the workshop.