Regal-Beloit was one of the many exhibitors at AHR 2018. Several of Regal’s brands feature AEGIS® Bearing Protection Rings to protect the motor bearings against electrical damage caused by VFD control. We talked with Chris Reid, Product Market Manager, about Marathon Motors in particular.
Marathon Motors “BCP” motors, equipped with internally mounted shaft grounding rings, ensure successful operation with Variable Frequency Drives without sustaining bearing damage due to inverter-sourced bearing current. Their “Bearing-to-Bearing” guarantee includes bearing replacement for the duration of the standard warranty period.
|BCP is available in the following standard stock product lines:
LEESON’s lines of Premium Stainless Steel motors and Extreme Duck motors, through 2 HP, now include motors with internally mounted AEGIS Shaft Grounding Rings. SGRs are needed in applications where motors are controlled by inverter drives, to eliminate the voltages that may damage the motor’s bearings.
EXTREME DUCK ULTRA IS ONE TOUGH DUCK: The revolutionary new design of this motor ensures that liquids won’t penetrate the motor in any mounting position, and made the motor a bronze winner in Plant Engineering’s Product of the Year. Plus it’s easier to install and connect because of unique non-wicking colored leads. Less corrosion, less operating costs. AEGIS Rings are available as an option for ½ to 2 HP.
Century Electric Motors are also available with factory-installed AEGIS Rings. If you plan on running your new Century motor on a VFD, be sure to request a factory-installed SGR.
Electric motors make the industrial world go around. Found in most manufacturing facilities, electric motors are responsible for 64% of all industrial electric power used in the United States.
Your electric motors represent a significant expense. When one fails, costs associated with that motor add up. Those costs include not only the price for repair or replacement of the failed motor but also the cost of lost production time or unplanned downtime. In fact, the cost due to lost production usually dwarfs the motor repair and replacement cost.
As vital as it is to get your motor back up and running, it is as important to find out why it failed in the first place. Discovering the cause of the failure allows you to prevent that problem from causing any future failures. Whether the investigation is done your own maintenance team or by a motor repair contractor, it is essential to learn from failures in order to improve your operations’ reliability.
Bearing failure accounts for over half of all electric motor breakdowns. So when you begin to look into why the motor failed, start by looking at the bearings.
When the motor arrives for repair, cut and inspect every bearing, especially if a VFD controlled it. Inspecting the bearings provides vital information helping make the best recommendation for repair. Knowing why the bearing failed and taking steps that prevent it from happening again improves the machine’s lifetime performance.
Bearing inspection is also required by AR100-2015, the recommended motor repair practices of the Electrical Apparatus Service Association (EASA). Section 2.2 on Bearings begins, “Bearings should be inspected for failure modes such as spalling, contamination, fretting, fluting, frosting, and scoring or other damage.”
We recommend the following procedure to inspect the bearings. These steps are available in the AEGIS® Handbook.
Please Note: Follow established safety precautions and use personal protective equipment including eye protection, hearing protection, face shield, gloves and protective clothing.
1. Inspect the outside and the inside of both bearings. Keep a sample of the lubricant to analyze. When examining the lubricant, look for:
2. Remove seals or shields first, then cut the outer race into halves.
3. Inspect the grease and look for any contamination in the bearing.
New bearing grease is available in many colors. The blue grease is Polyrex EM, commonly found in electric motor bearings.
4. Clean the bearing’s components using a degreaser or solvent.
5. Inspect for evidence of Electrical Discharge Machining (EDM). EDM damage is millions of microscopic electrical pits created when shaft voltage discharges through the motor’s bearings. The electrical voltage overcomes the dielectric of the bearing lubrication and instantaneously arcs through the inner race, through the rolling elements, and to the outer race. The individual pits are usually between 5 and 10 microns in diameter.
6. Frosting: Frosting appears to be a grey discolored line around all, or part, of the bearing race and evident in both the inner and outer race. Both mechanical wear and EDM causes that discoloration. Use a microscope to determine if the line is EDM or of a mechanical nature.
If the motor was operated by a VFD with no bearing protection installed, there is a high likelihood that the frosting is from EDM.
Fluting Damage: Identified by a distinctive washboard pattern. A distinctive washboard pattern identifies fluting damage, seen using the naked eye or with 10x magnification.
Take care to identify the correct electrical fluting damage using the observed damage. Sometimes, fluting gets confused with mechanical bearing damage such as brinelling or false brinelling.
Besides using these recommended practices, please refer to other bearing failure analysis experts to determine the root cause of the failure. Install new AEGIS Ring whenever replacing bearings on an inverter-driven motor.