My Motor Failed. Now What?

This sleeve bearing motor, with a drive-end bearing failure and bent shaft, arrived at a service center without its sheave, and with very little information. Bearing wear was presumed to be the cause of failure. After the motor was returned to service with a new shaft and new sleeve bearings, it failed in less than an hour. A simple photo of the motor following the initial failure would have correctly identified the cause—excessive overhung load for the sleeve bearing—and a motor with rolling-element bearings could have been installed to prevent a second failure.

 By Mike Howell, Electrical Apparatus Service Association (EASA)

PROCESS DOWNTIME is expensive—even more so when it’s unexpected. So, when an electric motor fails, we tend to pull, repair, or replace it, and move on as quickly as possible. In doing so, however, we may miss an opportunity to capture basic information that could help improve the reliability of the application. With a little planning, these data can be gathered with no delay in startup.

Collect initial data. Develop a simple, standard procedure that a “trained” operator can use to jot down or check off some basic information about the process at the time of failure. In special applications or cases of chronic failure, photos could be extremely helpful.

Don’t destroy two motors. Startup procedures vary widely, depending on factors such as application and equipment size. Have appropriate measures in place so that, following a failure, you can rule out problems with the power supply or starting equipment before attempting to start a replacement motor.

This sleeve bearing motor, with a drive-end bearing failure and bent shaft, arrived at a service center without its sheave, and with very little information. Bearing wear was presumed to be the cause of failure. After the motor was returned to service with a new shaft and new sleeve bearings, it failed in less than an hour. A simple photo of the motor following the initial failure would have correctly identified the cause—excessive overhung load for the sleeve bearing—and a motor with rolling-element bearings could have been installed to prevent a second failure.

Help your service center. Sometimes, the cause of failure seems so obvious that, with too little information, we jump to the wrong conclusion. Furthermore, we may only discover our error when the repaired motor or its replacement quickly fails. The more application and failure details that you can share with service-center personnel, the easier it will be for them to help identify and eliminate the actual problem and provide a reliable repair for the application. With most applications, much of the documentation can be done long before a failure occurs. Such details can make all the difference when the service center performs causal analysis. Examples of data that can be recorded in advance include:

• Complete motor nameplate information
• Power supply information: sinewave/non-sinewave power (ASD/VFD), known transients, voltage variation, voltage unbalance, starting method
• Environment: indoors/outdoors, ambient temperature, humidity, contamination
• Mounting and coupling: direct coupled, belt drive, integral mounted, overhung load, mounted vertically
• Application information: pump, blower, conveyor, crusher, inertia/starting torque requirements, acceleration time, duty cycle, typical loading.

Once a failure occurs, combine this general information about the application with specifics about the failure event, including any available photos. This approach will get your service center off to a good start in accurately determining the cause of your motor’s failure and preventing another one. MT

Mike Howell is a technical support specialist at the Electrical Apparatus Service Association (EASA), St. Louis. For more information, visit www.easa.com.