A complex conveyor system threads its way through the plant. This system has a large number of 10-hp motors, and you replace one every few weeks. Your company's policy is not to send "throw away" motors out to your motor shop for a post-mortem.

Today, yet another motor failed. You noticed a burnt smell. What's a compelling reason to send this motor out for a post-mortem despite the policy, and what should you look for while it's being examined?

Before miners had gas meters to monitor oxygen levels, they took a caged canary into the mine with them. If the canary passed out, they knew the air was unsafe.

A rash of small motor failures is like that canary. The same root cause that is killing them is also putting large motors, such as those for plant air, at risk. You might not have a canary situation, but how do you know?

A competent post-mortem can indicate whether you have a localized problem (e.g., the motor was trying to drive too much load) or a systemic one (e.g., excessive harmonics).

The company policy regarding small motors makes sense only if those failures are rare. But in this situation, they aren't. Consequently, any money "saved" by not doing the post-mortem is lost through continued motor replacement and production interruptions. And there's that canary effect — what will burn up next?

Make sure this latest casualty gets an autopsy. While you're waiting for the results, do the following:

  • Check the gearbox of every motor that was replaced. You may have systemic problems with lubrication and/or alignment.
  • Put a power analyzer on the supply of a motor that has been replaced. Collect data long enough to cover shift changes and other routine stops and starts. Look for excess harmonics, high current, voltage imbalance, low voltage, and waveform distortion.
  • Obtain thermographic images of the locations where motors have been replaced and a few locations where they haven't. See if you can spot differences and anomalies.