In our last post, we described how VFDs cause electrical bearing damage.  So, how do you protect motors from this damage?

Capacitive EDM currents are caused by electrons’ need to go through the bearings to travel between the shaft and ground.  So to prevent EDM currents, you only need to provide an alternative, low-resistance path from shaft to ground.  AEGIS® Bearing Protection Rings provide such a path, channeling these currents away from bearings and safely to ground.

For low-voltage motors (up to 100 HP), the best practice is to install an AEGIS® SGR Bearing Protection Ring – either internally or externally – on either the drive end or non-drive end of the motor to discharge capacitively induced shaft voltage.

For motors greater than 100 HP, capacitive EDM currents will still be present, but now high-frequency circulating currents will occur as well.  The best way to prevent HF circulating currents is to interrupt them with insulation or isolation of the bearing at the opposite end from the AEGIS® Ring.  For motors between 100 and 500 HP, install an AEGIS® SGR Ring on the drive end, and isolate the bearing housing on the non-drive end with an insulating sleeve or coating, or an insulated ceramic or hybrid bearing to disrupt circulating currents.

For low-voltage motors greater than 500 HP or medium-voltage motors, use an AEGIS® PRO Ring instead of an SGR Ring.

For all motors with both bearings insulated, install the correct AEGIS® Ring (SGR or PRO) on the drive end (either externally or internally) to protect the bearings in attached equipment.

Regardless of the type of AEGIS® Ring or where you install it, be sure to apply AEGIS® Colloidal Silver to motor shaft circumference in the area where the ring’s microfiber brushes will contact it.