You were recently promoted to plant electrical engineer. In your previous position, you were one of four electrical supervisors who each had teams in one of the plant’s four buildings. Mike, the electrical supervisor over Building No. 3, stopped in your office and told you about a problem your predecessor failed to address. A couple of motors had an excessive failure rate. Over the past five years, one of them was replaced three times and the other four times.
There are plenty of other motors in Building No. 3, so Mike says it’s not voltage imbalance or some other power quality issue. He doesn’t have any motor experts on his team, and he’s asked for you to either identify the cause or bring in someone who can. Before he left, Mike smiled and said, “What I just did is called managing up. How am I doing?”
Don’t rule out power quality yet
Mike is doing great at managing up. Bringing a problem to your supervisor when you are out of your depth is always a good thing to do. And not only because of the cost, such as all those wasted motors. It’s also good for your career. Leaving a problem to fester because you’re afraid to look less than capable also means you are likely going to be blamed for that problem at some point. Eliminate the problem and you eliminate the chance of blame. Punting it up the ladder has a similar effect.
On the technical side of this, don’t rule out power quality just yet. Power quality problems can be localized. So, at the motor, conduct the basic checks for power factor, excess harmonics, and waveform distortion. Some other things to check on each of those failed motors:
- Motor forensics. If there’s any chance to get a forensics report from a qualified expert (e.g., a motor rewind shop), get it. Knowing the failure mode will help you isolate the problem. If, for example, what causes bearings to fail may differ from what causes windings to fail. Note that something like incorrect lubrication can cause windings or bearings to fail, though the means differs. Windings will fail due to overgreasing that shorts them out. Bearings will fail due to incompatible greases, which will grind them up. Incompatible greases don’t cause windings to fail; that’s a bearing failure cause.
- Noise signature. Conduct an ultrasonic inspection of the motor bearings, gearbox, and related items. If the testing predicts failure, you know to look very closely for the causes. For example, if the motor bearings are already damaged, you likely have undesired current flowing through the motor bearings due to improper bonding.
- Vibration. Use a handheld vibration meter to see if the motor might be out of alignment or have other issues that show in the form of excess vibration. Once those are addressed, install vibration monitoring on the motor.
- Drive issues. If the motor has an electronic drive, ensure it is set up correctly for that motor and that application. For example, an incorrect soft start setting can cause the motor to run hot. The soft start reduces the inrush current, thus allowing the motor to accumulate less heat when starting. If there’s any doubt, contact the drive manufacturer.
- Load. Does the gearbox turn freely? A bad bearing in a gearbox can cause the motor to run hot. Check the gearbox oil; if it doesn’t stink of sulfur, replace it with the correct viscosity but use a full synthetic oil. Perform a visual inspection on the entire load side of the motor; sometimes what it reveals is surprising.
- Motor vs. application. Is this motor of the correct NEMA design, horsepower, temperature rating, etc., for this application? How do you know that?
- Motor lubrication. Since other motors are not failing, it would seem this issue is unlikely here. But if a single tech is lubricating these motors and not the others, that tech’s lubrication methods could be the cause of the motor failures. Another consideration is these two motors might require X lubricant while the others require Y lubricant. So, sometimes those failing motors get Y. But X and Y are incompatible greases, with the result the motor bearings get ground up. If different lubricants are required, color code the motors and the lubricant containers.
- Voltage drop. What is the voltage at the motor terminals? If you have excess voltage drop, you’ll need to update your power distribution to fix that. This can be expensive and require a capital request. Obtain from operations the downtime costs from these failures.
- Ventilation. Is there enough air circulating around these motors? Do they have vents? If so, are those vents clear of debris? If they do not have vents, why is that? Conduct a thermographic exam on each of these motors to see if excess heat is an issue. If it is, you have many ways to address that include ducted air.
- Operator error. Determine exactly how these motors are being used. Have someone watch, and have a discussion with the operators. For example, an operator who is frequently stopping and starting the motor is loading it up with heat. Excess heat is the No. 1 killer of motors.
Next steps
If you check all these things and still cannot identify the cause, try these two tactics:
- Reach out to the motor manufacturer. They may have some insight, but they will need you to collect and provide a significant amount of information.
- Schedule a mid-life motor shop inspection. Before the motor fails, replace it with a new one and send it to a motor shop for a detailed examination. This should reveal the “fingerprints” of whatever is causing the failure. You can then follow up on the findings to identify and correct the specific cause(s).
As you go through this process, be sure to include Mike. And once you solve the problem, be sure you acknowledge him for bringing it to your attention and aiding you in resolving it. That’s a good way to manage down the chain, just as Mike managed up. Have a talk with each of the other supervisors, including the one who replaced you, about problems they feel need attention.
