Technology

Classification of insulated bearings and their application in motors

The electrical insulating bearing adopts a special spraying technique, and thus the outer surface of the bearing is sprayed with a high-quality coating. The coating has sturdy bonding force with the substrate and good insulation performance. , The injury caused by the raceway can increase the service lifespan of the bearing. 

The process is systematically being improved. In insulated bearings, there is there is coating on the outer or inner ring surface, which could arise to voltages up to at least one thousand V DC. A special spraying technique creates a coating of uniform thickness and really sturdy adhesion, that’s further treated to create it ladder-proof to status and status.

 Inspection of insulation of insulated bearings

1. the aim and scope of the scrutiny

In order to create certain the insulation performance, it’s a necessity to measure the insulation of the insulated bearing, that has the insulation resistance, shaft voltage and shaft current of the bearing. the aim of measuring the motor shaft voltage is to understand the magnitude of the motor shaft current; the aim of measuring the motor shaft current is to directly acquire the value of this flowing through the motor bearing.

Because the injury of shaft current mainly happens in motors supercharged by variable frequency power give with frame size of 280 and better than and customary big and medium-sized high-voltage motors. Therefore, this scrutiny is typically exclusively administered for these forms of motors throughout the initial trial production or for individual motors that unit found to possess a big impact on the bearing owing to shaft current throughout use.

2. activity of insulation resistance of insulated bearings

When measuring, the bearing area unit usually administered alone, but it is best to carry out the activity once the bearing is place in on the rod. Generally, the insulation resistance meter of 250V specification is chosen. 

Connect the E end of the instrument to the rotating shaft; once covering the insulating a district of the bearing (such as a result of the outer ring) with tin foil, bind the tin foil with clean copper wire to fix it, therefore connect it to the L end of the instrument; or install the insulating bearing into the bearing seat or motor end at intervals the bearing chamber of the quilt, live the insulation resistance between the rod and thus the bearing seat or the motor end cowl once there is not any electrical path between the bearing seat or the motor end cowl and thus the rod thereon the insulating bearing is place in. 

The activity operation is exactly constant as measuring the motor and winding insulation resistance to ground.

3. activity technique of bearing current

For motors exploitation rolling bearings, the shaft current is measured as shown in Figure one. Install associate insulating ring between the bearing of the non-shaft extension end of the motor and thus the

casing (a dry insulating sheet is placed between the bearing and thus the rotating shaft) or use associate insulating bearing to create certain that the motor bearing is well insulated.

Connect the meter nonparallel to the metal elements up-to-date with the two sides of the bearing insulating layer, run below no-load at rated voltage and rated frequency, and live this price, that is, the shaft current.

For motors exploitation slippery  bearings and rolling bearings, if the upper than technique cannot be measured, the shaft current area unit usually measured by golf stroke a current device on the shaft.

Insulated bearing product classification

Electrically insulated deep groove ball bearings

Electrically insulated angular contact ball bearings

Electrically Insulated Cylindrical Roller Bearings

Inner or outer ring insulated bearings with compound coating

Hybrid bearings with electrically insulating ceramic rolling components

Advantages of insulated bearings

Electrically insulated bearings can avoid injury caused by electrical corrosion, so they’re usually used in motors to create certain further reliable operation than customary bearings. it’s less costly and reliable than various insulation ways in which, like shaft or housing insulation. The outer dimensions and basic technical characteristics of insulated bearings unit constant as those of non-insulated bearings, so they unit 100% interchangeable. it’s applicable for motors, generators, notably variable frequency motors, that unit further wide used.

Application of Insulated Bearings in Motors

1. Causes and hazards of the formation of motor shaft voltage and bearing current

During motor operation, any imbalance at intervals the computer and rotor magnetic circuits, or at intervals the half currents around the shaft, can manufacture a rotating system flux linkage. once the shaft rotates, these flux linkages can generate a potential distinction across the shaft, that’s named the shaft voltage. The shaft voltage can excite a current current at intervals the loop (closed circuit) intentional by the shaft and thus the casing through the bearings at every ends, that’s named the shaft current.

In addition, the rotor core options a heap of residual magnetism. For a wound rotor motor, if a pair of or further windings unit short-circuited to the rotor core or the rod, shaft voltage and shaft current are going to be generated.

The magnitude of the bearing current is claimed to the structure of the motor, the power of the motor, the amplitude of the driving voltage, the rise time of the heartbeat, and thus the length of the cable. the larger the power of the motor, the higher the drive voltage, the vessel the rising fringe of the drive voltage, and thus the shorter the cable, the larger the bearing current.

2. Measures to dam shaft current – use insulated bearings

In order to avoid the burn injury to the bearing caused by the shaft current, effective measures need to be taken to isolate the shaft current.

For large motors with freelance bearing housings at every ends, a spacer made of insulation area unit usually placed between the bearing housing and thus the metal base. 

For a motor with a standard bearing and a casing assembled into one body, associate insulating bearing is typically used at one end (often organized at the non-spindle extension end), and for occasions with higher wants, associate insulating bearing is place in at every ends. 

The insulating bearing used is typically the strategy of attaching (usually coating) associate insulating layer to the outer ring.

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