Reasons for using insulated bearings in motors and hazards of non-insulated bearings

Many maintenance technicians will know that the motor should use insulated bearings at the non-drive end to rotate, because when the motor does not use insulated bearings after a certain speed, shaft voltage and shaft current will be generated, and the bearing current will cause the bearing to generate high temperature, resulting in Severe damage to bearings . Many people don't understand this, so everyone will ask "why does the non-drive end of the motor use insulated bearings?"  BSSD will tell you the reasons for using insulated bearings and the inapplicability of insulated bearings based on a comprehensive understanding of bearing knowledge. What harm will it bring to the motor.

First of all, let's understand what an insulated bearing is . The so-called insulated bearing is a general term that can block the passage of current and the bearing itself has insulating properties. Electrically insulated bearings adopt a special spraying process to spray high-quality film on the outer surface of the bearing. The film has strong bonding force with the substrate and good insulation performance, which can avoid the electric corrosion effect of the induced current on the bearing and prevent the current from affecting the grease and rolling elements. , The damage caused by the raceway improves the service life of the bearing.

Reasons for using insulated bearings in motors:

1. First of all, for safety, at high frequency, the rotor induced current will be very large to prevent the motor shaft current.

2. If the electrically insulated bearing is not used, the current will flow through the bearing to form a circular current, and the bearing will easily heat up or be damaged due to electric splashes.

3. The most notable characteristic of the electric corrosion of bearings caused by high-frequency shaft current in the frequency conversion speed regulation system is the generation of dense washboard-like groove stripes on the inner and outer rings and balls of the motor bearings. Therefore, the motor must have an electrically insulated bearing at one end.

Consequences of unsuitable insulated bearings for motors:

1. Shaft current will be generated

When the motor is running, the potential difference between the two ends of the shaft or between the shaft and the bearing is called the shaft voltage. If the two ends of the shaft form a circuit through the motor frame, the shaft voltage forms the shaft current. The shaft current is generated by the shaft voltage through the motor shaft, bearing, stator frame or auxiliary device to form a closed loop.

2. The consequences of shaft current under normal conditions and high shaft voltage

Under normal circumstances, the shaft voltage of the motor is low, and the lubricating oil film in the bearing can play an insulating role, and no shaft current will be generated.

However, when the shaft voltage is high, or the oil film is not formed stably at the moment of motor startup, the shaft voltage will cause the lubricant film to discharge and break down to form a circuit to generate shaft current. The high temperature generated by the partial discharge energy release of the axial current can melt many tiny areas on the inner ring, outer ring or ball of the bearing, and form grooves, thereby generating noise and vibration. Great impact.

Benefits of using insulated bearings:

Electrically insulating bearings can improve reliability and increase machine uptime by essentially eliminating electrical corrosion by integrating insulating properties into the bearing.

Electrically insulated bearings typically have an aluminum oxide-coated outer ring OD face and end faces. Insulated bearings with a coated inner ring bore and end face, these bearings offer increased protection against high frequency currents due to the smaller coated surface area of the inner ring than the outer ring.