1. Purpose and scope of inspection
In order to ensure the insulation performance, it is necessary to measure the insulation of the insulated bearing, including the insulation resistance, shaft voltage and shaft current of the bearing. The purpose of measuring the motor shaft voltage is to understand the size of the motor shaft current; The purpose of measuring motor shaft current is to get the value of current flowing through motor bearing directly.
Because the damage of shaft current mainly occurs in the motor with the frame size of 280 and above variable frequency power supply and ordinary large and medium high voltage motor. Therefore, this check is generally only carried out for these types of motors in the initial trial production or in the improvement of the design of the motor for which the shaft current is found to have a serious impact on the bearing.
2. Measurement of insulation resistance of insulated bearings
When measuring, the bearing can be carried out separately, but it is best to install the bearing on the rotating shaft. Generally, 250V insulation resistance meter is selected. Connect the E end of the instrument with the rotating shaft; After the insulating part of the bearing (such as the outer ring) is covered with aluminum foil, the aluminum foil is fixed with bare copper wire binding, and then connected with the L end of the instrument; Or the insulation bearing into the bearing seat or motor end cover bearing chamber, in the state of bearing seat or motor end cover and installed insulation bearing shaft without electrical access, measuring the insulation resistance between the shaft and the bearing seat or motor end cover. The measuring operation is exactly the same as measuring the insulation resistance of the motor and winding to the ground.
3. Determination method of bearing current
For a motor that uses rolling bearings, an insulating ring (dry insulating sheet is inserted between the bearing and the rotating shaft) or an insulating bearing should be installed between the bearing and the casing at the non-shaft extension end of the motor to ensure that the motor bearing is well insulated.
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