Insulation inspection of insulated bearings
1. Purpose and scope of inspection
In order to ensure the insulation performance, the insulation of the insulated bearing needs to be measured, which includes 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 the motor shaft current is to directly obtain the value of the current flowing through the motor bearing.
Because the damage of the shaft current mainly occurs in the motors and ordinary large and medium-sized high-voltage motors powered by the frequency conversion power supply of the frame size 280 and above. Therefore, this inspection is generally only carried out when improving the design of these types of motors during the initial trial production or for individual motors that have found that the shaft current has a serious impact on the bearings.
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. Insulation resistance meter with 250V specification is generally selected. Connect the E end of the instrument to the rotating shaft; after the insulating part of the bearing (such as the outer ring) is covered with aluminum foil, fix the aluminum foil with bare copper wire and then connect it to the L end of the instrument; or install the insulated bearing into the bearing seat or motor end In the cover bearing room, the insulation resistance between the rotating shaft and the bearing housing or the motor end cover is measured in a state where there is no electrical path between the bearing housing or the motor end cover and the rotating shaft where the insulated bearing is installed. The measurement operation is exactly the same as measuring the insulation resistance of the motor and windings to ground. [1]
3. Measuring method of bearing current
For motors with rolling bearings, the shaft current is measured as shown below. Install an insulating ring between the bearing at the non-shaft-extending end of the motor and the casing (dry insulating sheets are inserted between the bearing and the rotating shaft) or use an insulated bearing to ensure good insulation of the motor bearing.
Bearing current measurement method Bearing current measurement method
Connect the ammeter to the metal parts that are in contact with the bearing insulation on both sides, run at no load at the rated voltage and rated frequency, and measure the current value, that is, the shaft current.
For motors using sliding bearings and rolling bearings, if the above method cannot be measured, the method of placing a current transformer on the shaft can be used to measure the shaft current. [2]
product category
Electrically insulated deep groove ball bearings
Electrically insulated angular contact ball bearings
Electrically insulated cylindrical roller bearings
Insulated bearing with inner or outer ring with oxide coating
Hybrid bearing with electrically insulating ceramic rolling elements
Size range
1. Electrically insulated deep groove ball bearings
Inner diameter size range: 40mm～140mm
Outer diameter size range: 80mm～300mm
Width size range: 18mm～62mm
2. Electrically insulated angular contact ball bearings
Inner diameter size range: 40mm～140mm
Outer diameter size range: 80mm～300mm
Width size range: 18mm～62mm
3. Electrically insulated cylindrical roller bearings
Inner diameter size range: 45mm～140mm
Outer diameter size range: 100mm～300mm
Width size range: 25mm～62mm
