The electric insulation bearing adopts the special spraying process, and the high-quality coating is sprayed on the outer surface of the bearing. The bonding force of the coating and the substrate is strong, and the insulation performance is good, which can avoid the electro-erosion effect of the induced current on the bearing and prevent the current from acting on the grease and the rolling element. Damage caused by the raceway to improve the service life of the bearing. The process is continuously improved. In insulated bearings, there is a 100μm thick coating on the outer or inner ring surface that can withstand voltages up to 1000 V DC. The special spraying process creates a uniform coating with a very uniform adhesion and further treatment to protect it from moisture and humidity.
Inspection of insulation of insulated bearings
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 of the bearing, the shaft voltage and the shaft current. The purpose of measuring the motor shaft voltage is to understand the current 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 motor powered by the variable frequency power supply with the frame number 280 and above and the ordinary large and medium high voltage motor. Therefore, this test is generally only carried out during the initial design of these types of motors, or for individual motors that have a significant impact on the bearings due to shaft currents.
2. Measurement of insulation resistance of insulated bearings
When measuring, the bearing can be carried out separately, but it is preferable to carry out the bearing after it is mounted on the rotating shaft. Generally, an insulation resistance meter of 250V specification is used. Connect the E end of the meter to the rotating shaft; the insulating part of the bearing (such as the outer ring) is covered with aluminum foil, then the aluminum foil is fixed by the bare copper wire, and then connected to the L end of the meter; or the insulating bearing is installed in the bearing seat or the motor end. In the cover bearing chamber, the insulation resistance between the rotating shaft and the bearing housing or the motor end cover is measured in a state where the bearing housing or the motor end cover has no electrical path to the rotating shaft on which the insulating bearing is mounted. The measurement operation is exactly the same as measuring the insulation resistance of the motor and winding to ground.
3. Method for measuring bearing current
For motors using rolling bearings, the shaft current is measured as shown below. An insulating ring is placed between the bearing at the non-axial end of the motor and the casing (a dry insulating sheet is placed between the bearing and the rotating shaft) or an insulating bearing is used to ensure good insulation of the motor bearing.
Connect the ammeter to the metal piece that is in contact with both sides of the bearing insulation layer, run at no load at the rated voltage and rated frequency, and measure the current value, that is, the shaft current.
For motors using plain bearings and rolling bearings, if the measurement cannot be made as described above, the shaft current can be measured by placing a current transformer on the shaft.
Product Categories
Electrically insulated deep groove ball bearings
Electrically insulated angular contact ball bearings
Electrically insulated cylindrical roller bearing
Inner or outer ring insulated bearing 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 range: 18mm ~ 62mm
2, electrically insulated angular contact ball bearings
Inner diameter size range: 40mm ~ 140mm
Outer diameter size range: 80mm ~ 300mm
Width 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
advantage
Electrically insulated bearings can avoid damage caused by electrical corrosion, so they can be used in motors to ensure more reliable operation than ordinary bearings. It is more cost effective and reliable than other insulation methods such as shaft or housing insulation. Insulated bearings have the same dimensions and basic technical features as non-insulated bearings and are therefore 100% interchangeable. Applicable to motors, generators, especially variable frequency motors for a wider range of applications.
1. Causes and hazards of motor shaft voltage and bearing current formation
In the operation of the machine, any imbalance in the phase currents in the stator or rotor magnetic circuit or around the shaft can produce a rotating system flux linkage. When the shaft rotates, these flux chains can create a potential difference across the shaft. This potential difference is called the shaft voltage. The shaft voltage can excite a circulating current through a loop formed by the two ends of the bearing in the shaft and the casing (closed circuit), which is called the shaft current. As shown below.
Further, the rotor core has a large amount of remanence. For the wound rotor motor, if the winding is short-circuited to the rotor core or the rotating shaft at two or more points, the shaft voltage and the shaft current are generated.
The magnitude of the bearing current is related to the structure of the motor, the power of the motor, the magnitude of the drive voltage, the rise time of the pulse, and the length of the cable. The larger the power of the motor, the higher the driving voltage, the steeper the rising edge of the driving voltage, and the shorter the cable, the larger the bearing current.
2, measures to block the shaft current - use insulated bearings
In order to avoid damage to the bearing caused by the shaft current, effective measures should be taken to isolate the shaft current.
For large motors with separate bearing blocks at both ends, spacers made of insulating material can be placed between the bearing housing and the metal base. For a motor in which an ordinary bearing and a casing are assembled, an insulating bearing is generally used at one end thereof (often arranged at a non-spindle end), and for a high demand, an insulating bearing is installed at both ends. The insulating bearing used is generally a method of attaching (generally coating) the insulating layer to the outer ring. In some cases, the inner and outer rings are also provided with an insulating layer.