Electric motors have always fascinated me. One year for a science fair I made a simple motor using a battery, two sewing needles, some wire and a magnet. I think that was during the 4th grade, I got a third-place ribbon for it. I was disappointed, but not bad for half an hour of work. Once I started my maintenance and testing career, I saw motors in use and while I understood how they worked, I didn’t learn about how to properly test and maintain them until I made the leap into Condition Monitoring. I had no idea there was so much to know. One aspect of owning motors in a facility that is often overlooked is how to care for them while they’re stored, waiting to be put into service.
Sadly, motors are much like other electrical apparatus in that as long as they seem to function when called upon, they’re largely forgotten. Push a button, your conveyor starts, yay. Motor works. How healthy is it, though? As discussed in numerous tips and blogs we’ve posted, just because it turns when you start it doesn’t mean it’s defect free. For that matter, just because it came off the truck from the motor shop doesn’t mean that either. For the purposes of this discussion though, let’s assume you received a perfect motor, and it went into storage. How do you keep it healthy while it’s waiting? Here’s a few steps you can take to make sure your motors are healthy when you need them.
- Store them indoors, in a clean environment. You’d think I wouldn’t have to say this, but I do.I’ve seen motors still strapped to pallets sitting outdoors on a loading dock. This is just wrong. Being exposed to the elements isn’t good for a stored motor, even one that might end up being used outdoors.Additionally, storage should be away from high traffic areas to avoid ambient vibration as much as is possible.Excessive vibration during storage can lead to false brinelling in the motor bearing.
- Don’t allow exposure to the atmosphere. If you have surface rust, you probably have rust elsewhere. Coat a motor for corrosion protection. That might mean the motor has to be cleaned before entering service, but that’s better than if it fails because it was not protected.
- Avoid ambient temperature swings in storage. This can lead to condensation forming in the motor’s interior. There’s a lot of mass in an electric motor, so it will change temperature at a slower rate than the air where it’s stored. If it swings hot, then cold, then back again, winding damage can occur from moisture.
- Rotate the shaft at a regular interval. If you store motors vertically this isn’t as large an issue, but almost no one does it. A good rule of thumb is to rotate the shaft once a week for motors above 1000HP, and once a month for motors below this size. To be on the safe side, I’d rotate the shaft once a week on every motor you’ve got stored. This is to reduce the chance of false brinelling, which occurs when there’s weight on a spot on the bearing where the shaft rests. Rotating the shaft adjusts the position of the shaft relative to the bearing so it’s not in the same spot for days and weeks on end.
- Fully grease the bearings. Fill the bearing cavities completely so moisture and contaminants have nowhere to go. If the grease becomes contaminated with moisture or debris, clean it and replace it. If possible, it’s also a good idea to turn over bearings periodically so the grease doesn’t settle to one side.
It’s also worth mentioning that incoming motors be tested de-energized upon receipt, and again before installation, making sure the data matches from one test to the next, and again after installation but before energizing. If you’re not doing that, at least do the above-mentioned things while you pull together a good motor acceptance procedure.