At what temperature can the motor work normally?

Summary of motor "fever" reasons and "fever reduction" methods

The insulation grade of the motor refers to the heat resistance grade of the insulating material used, which is divided into A, E, B, F, and H grades. The allowable temperature rise refers to the limit of the temperature rise of the motor compared with the ambient temperature.

Temperature rise refers to the value of the temperature of the stator winding higher than the ambient temperature under the rated operating state of the motor (the ambient temperature is specified as 35°C or below 40°C, if the specific value is not marked on the nameplate, it is 40°C)

Insulation temperature class	Grade A	Class E	Class B	Class F	Class H
Maximum allowable temperature (°C)	105	120	130	155	180
Winding temperature rise limit (K)	60	75	80	100	125
Performance reference temperature (°C)	80	95	100	120	145

In electrical equipment such as generators, insulating materials are the weakest link. Insulating materials are especially vulnerable to accelerated aging and damage due to high temperature. Different insulating materials have different heat resistance properties, and electrical equipment using different insulating materials have different resistance The ability of high temperature is different. Therefore, general electrical equipment stipulates the maximum temperature of its work.

According to the ability of different insulating materials to withstand high temperatures, seven allowable maximum temperatures have been stipulated, which are arranged according to the temperature: Y, A, E, B, F, H and C. Their allowable operating temperatures are: 90, 105, 120, 130, 155, 180 and above 180°C. Therefore, Class B insulation means that the heat-resistant temperature of the insulation used by the generator is 130°C. When the generator is working, the user should ensure that the insulation material of the generator does not exceed this temperature to ensure the normal operation of the generator .

Insulation materials with insulation class B are mainly made of mica, asbestos, and glass filaments glued or impregnated with organic glue.

Q: At what temperature can a general motor work normally? How high the motor can withstand

temperature?

Answer : 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. Generally, the temperature rise of the motor should be below 20 degrees. Generally, the motor coil is made of enameled wire, and when the temperature of the enameled wire is higher than about 150 degrees, the paint film will fall off due to the high temperature, resulting in a short circuit of the coil. When the coil temperature is above 150 degrees, the motor casing exhibits a temperature of about 100 degrees, so if the casing temperature is used as the basis, the maximum temperature the motor can withstand is 100 degrees.

Question: The temperature of the motor should be below 20 degrees Celsius, that is, the temperature of the motor end cover should exceed the ambient temperature.

What is the reason why the motor heats up more than 20 degrees Celsius when it is less than 20 degrees Celsius?

Answer : The direct cause of the motor heating is due to the large current. Generally, it may be caused by short circuit or open circuit of the coil, demagnetization of the magnetic steel or low efficiency of the motor. The normal situation is that the motor runs at a high current for a long time.

Q: What causes the motor to heat up? What kind of process is this?

Answer : When the motor is running under load, there is power loss in the motor, which will eventually turn into heat energy, which will increase the temperature of the motor and exceed the ambient temperature. The value by which the motor temperature rises above the ambient temperature is called warm-up. Once the temperature rises, the motor will dissipate heat to the surroundings; the higher the temperature, the faster the heat dissipation. When the heat emitted by the motor per unit time is equal to the heat dissipated, the temperature of the motor will not increase, but maintain a stable temperature, that is, in a state of balance between heat generation and heat dissipation.

Q: What is the allowable temperature rise for a general click? Which part of the motor is most affected by the temperature rise of the motor? How is it defined?

Answer : When the motor is running under load, from the perspective of exerting its function as much as possible, the higher the load, that is, the output power, the better (if mechanical strength is not considered). However, the greater the output power, the greater the power loss, and the higher the temperature. We know that the weakest temperature-resistant thing in the motor is the insulating material, such as enameled wire. There is a limit to the temperature resistance of insulating materials. Within this limit, the physical, chemical, mechanical, electrical and other aspects of insulating materials are very stable, and their working life is generally about 20 years. If this limit is exceeded, the life of the insulating material will be shortened sharply, and it may even be burned. This temperature limit is called the allowable temperature of the insulating material. The allowable temperature of the insulating material is the allowable temperature of the motor; the life of the insulating material is generally the life of the motor.

Excessive temperature is one of the common fault types of motors, so what causes the temperature of the motor to be too high?

The following are the common causes and treatment methods of high motor temperature:

1. When the instantaneous voltage of the motor exceeds the rated voltage by more than 10%, or the instantaneous voltage of the motor is lower than the rated voltage by more than 5%, it will cause the motor to generate heat and temperature rise under the rated load. In this case, the voltage should be checked and adjusted.

2. The unbalance of the three-phase power supply voltage of the motor will also cause the motor to heat up. This is because when the unbalance of the three-phase power supply voltage exceeds 5%, it will cause the unbalance of the three-phase current. The countermeasure is to check and adjust the voltage.

3. The contact problem of the power switch of the motor and the open circuit of one-phase fuse will cause the lack of phase operation, which will cause the temperature of the motor to rise. The solution is to repair or replace the damaged parts.

4. There is an error in the winding wiring of the motor, which causes the motor running under the rated load to overheat. The solution is to correct the wiring error of the winding wire.

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

6. The broken bars of the cage rotor of the motor or the loosening of the coil joints of the wound rotor will cause the current of the maintenance network to increase and cause the temperature to rise. The countermeasure is to repair or replace the rotor.

7. When the bearings of the motor are severely worn, there will be large friction and heat generation. The solution is to check whether the bearings are loose and whether the stator and rotor are poorly matched.

8. Excessive load of the motor is also the cause of overheating. Reducing the load or replacing a high-power motor can solve the overheating problem.

9. Too frequent starting of the motor, high ambient temperature, poor ventilation, etc. will also cause the temperature of the motor to be too high, reducing the number of starts, lowering the ambient temperature, ensuring smooth air ducts, eliminating dust and oil, and maintaining good fan operation are all important. Can help with similar overheating issues.

For a running motor, if the current does not exceed the rated current of the motor, it means that there is basically no problem in the circuit. If the original load has not been changed, it is necessary to check whether the voltage is higher than the rated voltage. Generally, 380V is plus or minus 5%. See if the ambient temperature is too high. Whether the bearing is short of oil. Whether the cooling fan is damaged.

(1) The load is too large. The load should be reduced or a motor with a larger capacity should be replaced.

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

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

(4) The ambient temperature rises. Cooling measures should be taken;

(5) Turn-to-turn or phase-to-phase short circuit of the stator winding. Use a megohmmeter or multimeter to check the insulation resistance between the two-phase windings; use the current balance method to check the three-phase winding current, the phase with a large current is a short-circuit phase, and a short-circuit detector can also be used to check whether there is a short circuit between the turns of the winding;

(6) The stator winding is grounded. It can be checked with a multimeter or an indicator light, and the phase with zero resistance is the ground phase;

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