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Electrical Troubleshooting Quiz — December 5, 2023

Dec. 5, 2023
How would you determine the cause behind a plant's high motor failure rate?

On your second day on the job as the new plant electrical engineer, your boss (the plant engineer) hands you a task. He says the high rate of motor failure is one reason your job was created. He shows you the stats, and they are alarming.

He goes on to tell you it’s nearly all bearing failure, so he checked the CMMS and found all the motors are being lubricated on schedule, so he has thus ruled out a lubrication problem. “I think it’s some kind of power fluctuation, and I read about circulating currents,” he believes. This is where he wants you to focus. He wants you detect and identify the undesired current flow and then develop a way to stop it.

What should be your first steps?

Answer to Quiz. Don’t be so quick to rule out lubrication problems. An appliance plant in Tennessee had this same problem. Motors were failing at high rates, mostly with bearings spun or practically eaten away. But in this case, it was a new plant engineer. He was an IE, not an ME or EE. He had done the same first step of looking for a lack of lubrication.

The problem got set aside due to other things, and he picked it back up shortly after hiring an EET as the plant electrical engineer. Here is where things got interesting. There were two lubrication techs, and they were very junior in the maintenance department. The plant engineer had always wondered why such a critical job would be assigned to people so junior.

The EET asked them how much grease they used. The one tech said a single shot from the grease gun, another said two shots. This raised the question of how much is a shot? And with which grease gun? If Tech A used two shots on a motor in February and Tech B used one shot on that same motor in August, was it overlubricated once, underlubricated once, or underlubricated both times? He shared these thoughts with the plant engineer and added that the whole shot thing was misdirection. They decided to watch each tech lubricate a motor.

The first thing the EET noticed was there was no designated grease gun or grease type specified in the PM documentation. The techs thought all grease was basically the same, so they grabbed whatever was handy. They had mixed incompatible greases, an action that in many cases was akin to pouring sand into the motor.

He then noticed each tech would walk right up to the motor, put the nozzle onto the zirc, and give the grease gun a pump or two. By not cleaning the zirc first, they were injecting dirt into the bearing space. He also noticed neither tech opened the drain plug. Upon questioning them, he found they didn’t know there was a drain plug. There were other mistakes they made, too.

So, even though the CMMS showed when the motors were lubricated, it did not show how they were lubricated, which was destroying the motors.

These motors also received no insulation resistance testing, no vibration monitoring, and no winding temperature monitoring. The only saving grace was that each of the motors was properly bonded, which at first was surprising. But the motors were installed by contractors, not by the maintenance personnel.

If the situation had been one motor with high rates of failure, then systemic failure in the motor lubrication program would not have been under consideration. Perhaps, as in the case in another area of the same plant, it was the gearbox. In that area, a gearbox driven by a “high failure rate motor” had oil but not gear oil (as evidenced by no sulphur smell in the case, and it was maybe 40 weight oil). That gearbox ran so hot, so personnel could not safely touch it. Once the gearbox had been cleaned out and properly lubricated (correct amount and type of gear oil), it was at 2° above ambient after running for an hour; four hours later, it showed the same 2° differential. The motor no longer needed to work so hard or heat its windings so much to drive its gearbox.

When faced with high failure rates, you need to thoroughly examine all of the potential causes. Lubrication deficiency is a major cause of motor failure. Lubrication isn’t a simple task to be given to the lowest guy on the totem pole. It’s a responsibility with serious consequences when done poorly.

About the Author

Mark Lamendola

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