Fault analysis and treatment of poor heat dissipation of motor

An AC induction motor was burnt out and the fuse was blown. The motor operated well after installation, but half a year later, the operator found that the temperature of the motor was higher than normal, and the temperature of the motor became higher and higher with the increase of service date. The operator asked the electrician to check and found no other abnormalities. The electrician thought that the current, voltage, speed and sound were normal and could continue to use. However, after a few days of continuous use, the motor was burnt out and the fuse was blown. After disassembling the motor, it was found that unburned cotton wool remained in the ventilation duct.

Fault analysis:

When the voltage of the motor is normal and the load current is greater than the rated current, the temperature rise exceeds the allowable value, which causes the motor to overheat and burn out. Most of the reasons are due to poor ventilation, which affects the heat dissipation of the motor. Unburned cotton wool remains in the ventilation duct of the motor, which indicates that the cotton wool blocks the ventilation duct, affecting the heat dissipation and increasing the temperature rise of the motor. With the increase of service date, the degree of blockage is more and more serious, the heat dissipation conditions are worse and worse, and the temperature rise is higher and higher, so that the temperature rise of the motor exceeds its allowable value, resulting in the burning of the motor.

After the motor was burned out, the cause of the burning was further verified from the burning of the motor winding. If the motor winding coil is locally short circuited or grounded, the winding is burned at the local position. When the motor is overloaded (the current value is greater than the rated current) and the temperature rise exceeds the allowable value, all stator windings are burned and all insulation is burnt. The load current of the motor does not exceed the rated value, all windings are burned, and unburned cotton wool remains. Therefore, it can be concluded that the ventilation duct is blocked, and the temperature rise is increased due to the heat dissipation difference of the motor, resulting in burning.

The common causes of motor overheating are as follows:

① The ambient temperature is too high. When the ambient temperature is high (generally more than 35 ℃), the heat dissipation efficiency of the motor decreases. At this time, if the output power of the motor is not reduced, the temperature of the motor will rise.

② There is too much dust inside and outside the motor, which affects the heat dissipation.

③ The fan is damaged or installed reversely, and the cooling air volume is reduced.

④ The hot air discharged from the motor cannot be dispersed and cooled quickly, and is immediately sucked into the motor fan, resulting in thermal circulation and overheating of the motor.

Troubleshooting:

In order to avoid similar accidents, the following measures shall be taken.

① Open or protective (J-type) motors shall not be used in places with more dust.

② The dust and sundries in the motor ventilation duct shall be blown and cleaned frequently to keep the ventilation and heat dissipation of the motor in good condition.

③ Once it is found that the voltage of the motor is normal, the load current does not exceed the rated current value, and the temperature rise increases, it shall be shut down for inspection. If necessary, it shall be disassembled for inspection and cleaning. Do not start production blindly until you find out the reason for the increase in temperature rise. If it is determined that the ventilation is poor and the machine is started after cleaning, the operation monitoring shall still be strengthened. The fault can be considered to have been eliminated only after the temperature rise does not increase 2h after the machine is started and loaded.