Motors fail. It’s a fact of life that’s almost as certain as death and taxes.
With average electric rates increasing more than 17% over the past 10 years, the repair vs. replace business case often justifies replacing older, pre-Energy Policy Act (EPAct) motors with Premium Efficiency ones. However, if the failed motor is an energy-efficient or premium-efficiency motor, then the business case may recommend repairing that motor.
Yet, repairing a motor has the potential to degrade its efficiency: Several published studies assert that motor efficiency drops 1 – 5% on first repair and more with repeated rewinds. [i],[ii],[iii],[iv],[v] Even MotorMaster+ and Motors@Work assume that efficiency drops 0.5% per repair. Yet, studies by Advanced Energy and EASA show that it is possible for repaired motors to operate above its rated nameplate efficiency by as much as 1%—but only if the repair shop follows certain best practices.[vi],[vii]
If you’re interested in retaining or improving your motors’ efficiency during repair, ask yourself—and your preferred motor repair shop—these four questions:
- Is the shop EASA accredited?
EASA’s accreditation program assures that repairs performed at accredited facilities conform with the industry standards identified in ANSI/EASA AR100, including retaining motor efficiency and reliability. This program evaluates motor repair shops for evidence of compliance with industry best practices on over 70 elements in 23 categories covering both mechanical repairs and electrical rewinds. The independent, third-party audits required for accreditation include testing repaired and rewound motors to assess the shop’s proficiency with these prescribed practices.
If you think your preferred repair shop may be EASA-accredited already, check the EASA website or just look at the last motor you had repaired: Motors repaired at EASA-accredited shops are required to have the shop’s name, logo, internal reference number, and the EASA-accreditation logo permanently affixed to the machine for future reference.
- Does the shop provide you with their diagnosis for why the motor failed?
Receiving a diagnosis of why your motor failed is important for two reasons: First, there are certain motors that shouldn’t be repaired due to defects or physical damage that occurred to the motor during failure. Second, evidence collected during this post-mortem inspection—such as signs of overheating, mechanical abrasion, or inappropriate lubrication—indicate the need to check your facility’s power quality, assess the load or duty cycle on this motor, and/or change your facility’s motor maintenance practices. EASA-accredited shops are required to record this information on the motor’s service record and report it to their client.
- Does the repaired motor weigh the same as the damaged motor that left your facility?
Motors are simple electromechanical devices comprised of copper windings and iron and aluminum cores, rotors, and frames. When a motor is rewound, the shop burns out the old copper in a furnace at a temperature of 680°F – 700°F, then rewinds the stator, rotor, and in DC motors, the armature. According to the ANSI/EASA standard, the wire’s gauge and length should match—or exceed— the original manufacturer’s specification “in all aspects of performance and application” [p. 12]. If your rewound motor is considerably lighter than when it left your facility, this may indicate that the shop failed to pack the same amount of copper into the windings.
- Does the shop ask your preferences on open vs. enclosed bearings and grease type?
Many new motors now come with enclosed bearings that don’t require greasing, eliminating that maintenance requirement. Some motors that originally used open bearings can be converted to enclosed bearings during repair, so the shop should ask your preference.
For open bearings, the ANSI/EASA standard specifies greasing the bearing to one-third full; overfilling a bearing increases the mechanical friction—and decreases the efficiency—of your motor. Furthermore, the shop should ask for your facility’s preferred grease in order to eliminate the risk that you’ll grease with an incompatible product, which could cause bearing—and ultimately motor—failure.
If you’ve just discovered that your preferred repair shop doesn’t follow these best practices, it may be time to find a new provider. You can find your closest ANSI/EASA accredited repair shop on EASA’s website. To automate calculations of repair vs. replace decisions, and find out how to reduce your motor-related energy expenses by up to 30%, check out www.motorsatwork.com or email me.
Nicole Dyess is the Director of Client Solutions for Motors@Work, which provides cloud-based energy management solutions for maintaining and operating motors and motor-driven systems at their peak efficiency and lowest cost.
[i] WU McGovern, “High efficiency motor for upgrading plant performance,” Electric Forum 10.2 (1984): pp. 14-18.
[ii] RS Colby & DL Flora, Measured efficiency of high efficiency and standard induction motors, (North Carolina State University: 1990).
[iii] DH Dederer, “Rewound motor efficiency,” Ontario Hydro Technology Profile (Ontario Hydro: 1991).
[iv] Zeller, “Rewound high-efficiency motor performance,” Guides to energy management (BC Hydro: 1992).
[v] Ontario Hydro, Rewound motor efficiency, TP-91-125 (1991).
[vi] Z Kellum, “The effect of rewinding on induction motor losses and efficiency,” Energy efficiency in motor-driven systems: Proceedings of the third EEMODS conference held in Treviso, Italy, 18-20 September 2002 (Springer: 2003): pp. 196-201.
[vii] Electrical Apparatus Service Association, Inc., & the (UK) Association of Electrical & Mechanical Trades, The effect of repair/rewinding on motor efficiency (2003).