How to Reduce Damage to Electric Motor Bearings

Electric motors are the lifeblood of countless businesses across dozens of industries. Nearly 70% of the energy consumed today is used to power electric motors for business. To reduce operational energy usage, many larger electric motors utilize a Variable Speed Drive (VSD) to reduce energy consumption and long-term operating costs.

Unfortunately, without proper grounding, VSDs can create a condition known as common-mode voltage, which can lead to bearing damage or premature motor failure. Improper grounding creates an imbalance in the three-phase electrical load. This imbalance induces a voltage on the motor’s shaft, discharging via the path of least resistance, typically the motor bearings.

Electrical arcing in the bearings can quickly damage the bearing surface or raceway. As the damaged material breaks free, it can cause pitting, fluting, grinding, noise, and excessive vibration.

Electric Motor Grounding Options

The good news is that, depending on your use and application, several methods exist to protect essential motor bearings from electrical damage, which we’ve outlined below.

Shaft-Grounding Device

This generic term describes various devices used for connecting the motor’s rotor to the earth’s ground via the motor frame, creating a low-resistance path to safely disperse the shaft voltage away from the motor bearings.

Carbon-Grounding Brushes

These brushes connect the stationary and rotating elements of the motor’s electrical system. This prevents common-mode voltage from building up and discharging through the bearings.

Ceramic Bearings

As the name implies, the ceramic-coated balls prevent shaft voltage from flowing through the bearing assemblies when discharged from the motor.

Ground-Bearing Isolators

This grounding assembly combines a metallic rotor, an isolated conductive filament ring, and a non-contact isolation shield to divert shaft currents from the bearings. These units eliminate contamination and lubrication loss and can replace standard bearing isolators and seals for improved efficiency.

Shaft-Grounding Rings

This option uses a stationary ring of conductive fibers positioned around the motor shaft. As the shaft spins, the fibers work as a brush to provide a shaft voltage discharge path away from the bearings. This option is ideal for wash-down motor requirements, as the unit can be installed inside the motor housing. Electro Static Technology’s AEGIS® Shaft Grounding Rings are used in millions of motors across the globe to prevent bearing damage and failure.

The Hi-Speed team can be reached at 1-800-713-0103 and via email, so don’t hesitate to ask if you have any questions about proper grounding for your electric motors.

As part of our commitment to keeping you up and running, let’s examine two other options for reducing damage to your electric motor bearings.

Electric Motor Bearing Lubrication

Unlike oil, grease is a semi-solid lubricant designed to remain in place to protect bearings and motor shafts against friction, corrosion, and excessive wear. Most horizontal shaft motors typically use NLGI 2-grade grease, while NLGI 3-grade grease is the industry standard for vertical shaft arrangements.

Bearing grease is available in various formulas formulated for specific applications and use cases.

Lithium
Moly
Silicone
Dielectric
Marine
Polyurea

Unlike oil, grease does not protect against heat buildup in rotating equipment. To ensure maximum bearing protection and longevity, always check the manufacturer’s recommendation for your electric motors’ correct grease formula, including any required additives.

The next option for reducing bearing damage is to create and follow a specific maintenance plan. Regular inspections and maintenance can dramatically improve the lifespan of electric motors and internal components, such as shafts and bearings.

Preventive Electric Motor Maintenance Plan

With a preventive maintenance plan, regularly scheduled equipment inspections and maintenance services can help you postpone or avoid an electric motor failure. Depending on the motor size and specific application, these schedules typically follow the manufacturer’s recommendation in either calendar days or usage.

The goal is to replace components before they adversely affect performance, reach the end of their lifecycle, or fail without warning. This can reduce unplanned downtime and emergency repair costs.

For example, once a bearing has reached a predetermined number of hours of usage, it gets replaced. Or, after X number of operational hours, the motor must be rewound.

Predictive Electric Motor Maintenance

This maintenance option typically utilizes sensors throughout the system to continually monitor the electric motor while in service. In addition to sensors that collect real-time data, dynamic tests such as thermal imaging and vibration analysis can be analyzed against past performance levels. This helps you to identify and determine which components will require servicing or replacement soon.

While both options can reduce downtime and repair costs, your maintenance strategy should center on how you use your electric motors. Always follow the manufacturer’s maintenance and inspection schedules to comply with warranty requirements.

That wraps up our overview of reducing damage to electric motor bearings. If you still have questions about bearing protection, maintenance, or the correct lubrication for your electric motors, call us at 800-713-0103 or email us.