The insulation resistance of a motor is a key parameter for evaluating its insulation performance, which is directly related to the safe operation of the motor. Due to the different types and voltage levels of motors, the minimum standards for insulation resistance are also different.
Insulation resistance of low-voltage motors
For low-voltage motors with voltage levels of 400V and below, the minimum standards for insulation resistance are as follows:
Newly laid lines: The insulation resistance between lines and between lines and ground should not be less than 0.5 megohms.
Equipment and lines in operation: The insulation resistance should not be less than 1 megohm/kilovolt, or equivalent to 1 kiloohm/volt.
Insulation resistance of small and medium-sized motors
For general small and medium-sized motors, the minimum standard for insulation resistance is also not less than 0.5 megohms. This standard applies to equipment and lines in operation, and the insulation resistance should not be less than 1MΩ/kV.
Insulation resistance of high-voltage electric motors
The insulation resistance requirements for high-voltage motors are more stringent. The specific standards are as follows:
Stator insulation resistance: At operating temperature, the insulation resistance should not be less than 1 megohm per kilovolt.
Rotor insulation resistance: Its insulation resistance should not be less than 0.5 megohms per kilovolt.
Measurement of motor insulation resistance
When actually measuring the insulation resistance of a motor, there may be certain differences due to the reference of different standards and the influence of factors such as temperature and absorption ratio. Especially when the insulation resistance value and absorption ratio are close to the critical value, the test results of different operators may be different. Therefore, when measuring, the relevant regulations should be strictly followed, the appropriate instrument should be selected, and the different limit requirements for cold and hot states should be distinguished.
In summary, the minimum insulation resistance standard of the motor depends on its voltage level and type. The insulation resistance of low-voltage motors and small and medium-sized motors/ medium voltage induction motor is usually required to be no less than 0.5 megohms, while the insulation resistance of high-voltage motors should not be less than 1 megohm per kilovolt. These standards are intended to ensure that the motor will not cause safety accidents due to insufficient insulation during operation.