What can be done to reduce bearing failure?

What can be done to reduce the likelihood of premature bearing failure? Corrective measures fall into two main categories, which for simplicity’s sake I will call electrical and mechanical, and they each present advantages and disadvantages. Some common ones are as follows:

Electrical:

• Drive output filtering: Most commonly used are referred to as dV/dt filters, dV/dt representing the rate of rise of the voltage pulse with respect to time. This is basically an inductive impedance introduced to slow the rate of rise of the voltage pulse. By reducing voltage stresses imposed on the motor, effective dV/dt filters have been shown to reduce common mode currents by up to 30%. And common mode currents are one of the primary causes of bearing damage.

Mechanical:

• Insulated bearings: a non-conductive material is used to isolate the bearings. Due to expense and to the relatively lower probability of bearing problems on small motors, insulated bearings are normally used on IEC frame 315/NEMA frame 500 or larger motors. Insulated non-drive end (NDE) bearings are often standard, with insulated drive end (DE) bearings typically optional.
• Grounding brushes: a conductive brush is mounted between the shaft and grounded frame to provide a low-impedance path to ground. The brush is typically metallic and spring-loaded to maintain contact with the shaft.
• Shaft grounding ring: A ring with conductive micro-fibers is installed around the motor shaft and bonded to ground, bypassing the bearings.

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