Why and how to deal with abnormal heating of motor
1. Motor overload
When the motor of compressor works under overload, it will generate abnormal heat. The main reasons for overload are as follows:
(1) The motor power selected for the compressor does not meet the requirements. At this time, it is necessary to find out the machine brand and instructions, and select the motor with enough power according to its provisions.
(2) When the compressor works at a pressure higher than the rated air pressure, the motor will be overloaded and heated. If such a condition is found, the normal operation conditions shall be restored immediately, and the safety valves of each section and the final section shall be readjusted properly to avoid overload.
The opening pressure of the safety valve shall be adjusted to 1.05 ~ 1.1 times of the rated air pressure. It is better to use gas instead of water for the test safety valve, because water is easy to make the valve port scale and rust, resulting in the failure of valve action.
2. Poor cooling of motor
Poor cooling of the motor will cause temperature rise and abnormal heating. Therefore, the following points should be noted:
(1) For small and medium-sized motors without separate ventilation and cooling system: to check whether the fan blades are complete, the direction of rotation shall make the motor itself get wind cooling.
The cooling fins on the motor shell shall be cleaned, and no plaster, oil stain, etc. shall be accumulated to avoid affecting the heat dissipation.
(2) For large synchronous motor with separate ventilation and cooling system, check whether its air ventilator works normally, and adjust and repair it if necessary to ensure enough cooling air volume and air pressure.
The blades on the rotor shall be installed correctly to ensure the air inlet cooling.
Check whether the air precooler is normal. The temperature difference between the cooling air and the water entering the cooler is the main index determining the cooling effect of the air precooler. The temperature difference under the rated load is generally 7-10 ℃. The temperature difference between the inlet water temperature and the outlet water temperature determines the regulated cooling water volume. When the temperature difference between the inlet water and the outlet water is 2-3 ℃, it indicates that the water consumption is normal.
The air inlet of the ventilation and cooling system shall be unobstructed, the air inlet shall be clean, the ventilation pipe shall be free of air leakage, and the inner wall of the pipe shall be free of dirt.
3. Motor overload is too fast
The motor is loaded too fast, especially the newly installed motor is loaded too fast, which is easy to cause the phenomenon of uneven temperature. Because the coil in the motor is made of copper and is equipped with steel parts at the same time, the expansion coefficient of copper and steel is not the same, and the heating speed is not the same, so the sudden temperature rise and uneven temperature will cause insulation damage and other accidents.
At the same time, the mechanical bearings and moving parts also need to buy gradually running in. Therefore, the loading process of the newly installed compressor should be gradual, and the method of sudden load rise and pressure rise should be avoided.
4. Abnormal heat caused by electrical reasons
When the following conditions occur, abnormal heating of the motor will be caused;
The line voltage is higher or lower than the voltage specified by the motor nameplate;
The air temperature around the working environment of the motor is too high;
Motor wire turn short circuit;
Incorrect pole coil connection;
The contact between the brush and the soft wire is poor, the cross section of the wire is too small, etc.
There are two methods to measure the motor temperature:
(1) Thermometer detection: for the motor assembled as a whole, use a thermometer attached to the surface that can be reached to measure its temperature. At this time, the thermometer can indicate the surface temperature of the place where it is placed.
For example, use glass putty to adhere the thermometer to the temperature measuring surface or insert it into the screw hole of the motor lifting ring to measure the temperature.
(2) Internal temperature detector of motor: the resistance thermometer or thermocouple and other temperature measuring instruments are pre installed inside the motor. This method can measure the internal temperature of the hottest point.
The stator of large compressor synchronous motor is usually equipped with a multi-point internal thermometer, and the preset temperature value of each point can be found on the dashboard of the operating platform.