Jul 19, 2023

How to solve the high motor temperature?

     Insulation is the weakest link in electrical equipment such as generators. Insulation materials are especially susceptible to high temperatures that can accelerate aging and damage. Different insulation materials have different heat resistance properties, and electrical equipment with different insulation materials has different abilities to withstand high temperatures. Therefore, the general electrical equipment is specified in the maximum temperature of its work.

    People according to the ability of different insulation materials to withstand high temperatures of its seven allowable maximum temperatures, according to the temperature of the size of the arrangement are: Y, A, E, B, F, H, and C. Their allowable working temperature are: 90, 105, 120, 130, 155, 180 and 180℃ or more. Therefore, the B-class insulation indicates that the generator uses insulation with a heat-resistant temperature of 130℃. The user should ensure that the generator insulation does not exceed this temperature when the generator is in operation in order to ensure that the generator works properly. Insulation class B is mainly made of mica, asbestos, and glass yarn by organic glue or impregnation.

At what temperature can a motor normally operate? What is the maximum temperature that the motor can withstand?

      If the measured temperature of the motor cover exceeds the ambient temperature by more than 25 degrees, it indicates that the temperature rise of the motor has exceeded the normal range, and the general motor temperature rise should be below 20 degrees. Generally, the motor coil is made of enameled wire, and the enameled wire will fall off when the temperature is higher than 150 degrees, causing the coil to short circuit. When the coil temperature is above 150 degrees Celsius, the motor casing shows a temperature of about 100 degrees Celsius, so if the casing temperature is used as the basis, the maximum temperature that the motor can withstand is 100 degrees Celsius. The temperature of the motor should be below 20 degrees Celsius, that is, the temperature of the motor end cover should be less than 20 degrees Celsius above the ambient temperature.

What is the reason for the motor to be hotter than 20 degrees Celsius?

      The direct cause of motor heating is caused by high current. Generally, it may be caused by short circuit or open circuit of coil, demagnetization of magnet or low efficiency of motor, etc. The normal situation is that the motor runs with high current for a long time.

      Motor load running with power loss in the motor, will eventually become heat, which will make the motor temperature rise above the ambient temperature. The value of the motor temperature higher than the ambient temperature is called temperature rise. Once there is a temperature rise, the motor must be dissipated to the surrounding area; the higher the temperature, the faster the heat dissipation. When the heat emitted by the motor unit time is equal to the heat dissipated, the motor temperature no longer increases, but maintains a stable and constant temperature, that is, in a balanced state of heat generation and heat dissipation.

      Motor load operation, from the maximum play its role, with the load that the output power the greater the better (if not consider the mechanical strength). But the greater the output power, the greater the power loss, the higher the temperature. We know that the weakest thing in the motor temperature resistance is the insulation material, such as enameled wire. Insulation material temperature resistance has a limit, within this limit, the physical, chemical, mechanical, electrical and other aspects of the insulation material performance is very stable, its working life is generally about 20 years. Beyond this limit, the life of the insulating material will be sharply shortened, or even burned. This temperature limit is called the permissible temperature of the insulation material. The allowable temperature of the insulation material is the allowable temperature of the motor; the life of the insulation material is generally the life of the motor.

Common causes of high motor temperature and treatment methods

1、If the instant voltage of the motor exceeds the rated voltage by more than 10%, or if the instant voltage of the motor is lower than the rated voltage by more than 5%, it will cause the motor to heat up and increase the temperature under the rated load, such a situation should be checked and adjusted the voltage.

2、Imbalance in the three-phase power supply voltage of the motor will also cause the motor to heat up, this is because when the three-phase power supply voltage imbalance exceeds 5%, it will cause the three-phase current imbalance, the response method is to check and adjust the voltage.

3、The motor's power switch contact problem and one phase fuse break will cause the motor to run out of phase, which will cause the motor's temperature to rise.

4、The motor winding wiring is wrong, which makes the motor overheat under rated load, the solution is to correct the wrong winding wiring.

5、The stator winding of the motor is short-circuited between turns or phases or grounded, which will cause the motor current to increase and produce temperature rise, the solution is to add insulation to the center or replace the winding directly.

6、The cage rotor of the motor is broken or the winding rotor coil joint is loosened, which will lead to the increase of the current of the maintenance network and produce the temperature rise, the solution is to weld the patch or replace the rotor.

7、When the bearing of the motor is worn out seriously, it will produce large rubbing and heat, the solution is to check whether the bearing is loose and whether the stator and rotor are poorly matched.

8、The overheating problem can be solved by reducing the load or replacing the high power motor.

9、The motor starts too frequently, the temperature of the environment is too high, and the ventilation is not good, etc. will also lead to the high temperature of the motor. Reducing the number of starts, lowering the ambient temperature, ensuring the air duct is smooth, eliminating the accumulated dust and oil, and keeping the fan running well can help solve a similar overheating problem.


If the current of the running motor does not exceed the rated current of the motor, it means there is basically nothing wrong with the circuit. If the original load is not changed, test whether the voltage is at the rated voltage, generally, 380V is plus or minus 5% normal. See if the ambient temperature is too high. Whether the bearing is short of oil. Whether the heat sink fan is damaged.

(1) The load is too large. Reduce the load or replace the motor with a larger capacity.

(2) Two-phase operation. Check whether the fuse is fused and the contact point of the switch is in good contact, and eliminate the fault;

(3) The motor air duct is blocked. The air duct should be cleared of dust or grease;

(4) The ambient temperature rises. Take cooling measures;

(5) Short circuit between turns or phases of stator winding. Use a megohmmeter or multimeter to check the insulation resistance between the two-phase winding; use the current balance method to check the three-phase winding current, the current phase for the short-circuit phase, also available short-circuit scout to check whether the winding turns are short-circuited;

(6) stator winding grounding. Available multimeter or indicator check, the resistance is zero for the grounded phase;

(7) Power supply voltage is too low or too high. Use the voltage file of a multimeter or voltmeter to check the power supply voltage at the input of the motor.


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