Concept of motor case resistance
Motor case resistance refers to the resistance value between the motor case and ground (or zero). The measurement of shell resistance is one of the tests for the insulation condition of the motor, and it is also one of the important parameters for judging motor failure. By measuring the resistance of the motor case, you can understand the state of the motor insulation and determine whether replacement or maintenance is needed.
Normal range of motor case resistance
The size of the motor case resistance is generally affected by the following factors: motor power, rated voltage, insulation material, etc. Under normal circumstances, the value of the motor case resistance should be between 2 and 100 megohms. Specifically, when the motor power is relatively small (such as less than 0.75kW), the shell resistance value should be greater than 2 megaohms; and when the power of the motor is relatively large (such as more than 200kW), the shell resistance value should be between 10 and between 100 megohms. In short, the specific normal range of motor case resistance should be judged based on the specific conditions of different motors to ensure its normal operation and service life.
Reasons for the sudden change in the resistance value of the motor case
During the operation of the motor, the shell resistance value of the motor sometimes changes suddenly. Common causes of this mutation are as follows:
1. The motor insulation is aged or damaged.
2. The insulation material used in the motor is not good enough
3. The motor ground wire is in poor contact
4. Motor winding short circuit
Conclusion
The motor case resistance is one of the important parameters to measure the insulation condition and operating status of the motor. For the measurement of motor case resistance, we need to understand the motor's power, rated voltage, insulation material and other factors, and make judgments based on the actual situation. When the resistance value of the motor case changes suddenly, possible fault points need to be carefully checked and repaired in time to ensure the normal operation of the motor.
