Shaft Grounding Devices | Shaft Earthing Devices

Shaft grounding devices minimize the shaft voltage and prevent bearings damage caused by the circulating current. There are numerous reasons for developing shaft voltage in the motor. The main reasons for developing shaft voltage are as follows.

  1. Leakage
  2. Induction
  3. High frequency circulating currents caused by VFD

How does Shaft Earthing prevent bearing damage?

The shaft voltage developed due to any reason may cause severe damage to motor parts. Therefore, we use shaft grounding devices to redirect electrical circulating current from the shaft to the ground. This way no current flows from the motor shaft to the motor parts.

generator shaft earthing

Carbon brush technology provides a suitable solution for shaft voltage. The carbon brush technology does not prevent the shaft voltage, but it provides the lowest resistance path for the current caused by the shaft voltage. Carbon brush has silver graphite material for better conductivity and least wear out.

Benefits of Shaft Grounding Systems

The circulating current flows from the motor shaft to vulnerable parts of the motor. The electrical current always flows through the least resistance path until it is grounded. In most motors, bearings offer the least resistance path, and the current causes arcs across them, creating fluting, pitting, or other types of bearing damage. Therefore, bearings are more susceptible to the current flowing through them.

motor shaft grounding

The magnitude of the circulating current is even more with variable frequency drive. The shaft grounding devices hinder the path of the circulating current through the bearings, and they divert the current to the ground. Thus, the motor remains protected with shaft grounding.

Once motor bearings’ surfaces got rough due to arcing current, bearings with rough surfaces can’t perform as well as bearings with smooth surfaces. It causes excess vibration and noise which affects the functioning of other equipment connected to the motor. 

A shaft grounding system provides the electrical current a more ideal path to reach the ground. Thus the current gets diverted from the motor’s internal parts and it eliminates the possibility of bearings damage. The carbon brush leads the current away from the motor bearings and allows the electricity to leave the motor in a controlled fashion. Shaft grounding systems keep the equipment safe and save money in terms of parts replacements and lost production time.

  1. Why Insulated Bearing is used for VFD-driven Motor?
  2. Why is armature of alternator connected in Star not in Delta?
  3. Difference between Earthing, Grounding and Neutral

Leave a Comment