Electric motors are some of the most efficient devices on the planet. Given 100% energy they can be upwards of 96% efficient.  Motors consume 60% - 90 % of the energy at industrial facilities and many facilities painstakingly conduct extensive precision maintenance practices  and testing to ensure maximum longevity of their motors. Some of the best programs that we have witnessed over the years share a common shortcoming, proper care of their spare motors. As powerful and efficient as motors are, they all ultimately fail.  When they fail an on-sight spare is generally used to replace the failed motor.

At this point let’s ask you 3 questions:

1. Was this motor tested before it was placed in inventory?
2. Was the shaft routinely rotated to prevent rotor sag and brinnelling?
3. Has the motor been stored in a temperature and possibly a humidity-controlled environment?

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, and your conveyor starts, 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. Spares also fall into the category, just because it's in the warehouse doesn’t mean it is good, and just because it just came off the truck from the motor shop doesn’t mean it is good 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 are a few steps you can take to make sure your motors are healthy when you need them.

• Store them indoors, in a clean environment. It sounds obvious but I’ve seen motors still strapped to pallets sitting outdoors on a loading dock. Obviously wrong, but more common than one might think. 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 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 regular intervals. 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. Shaft rotation also prevents rotor sag. Rotors are heavy and only suspended by the bearings. Long-term storage can lead to the rotor bowing or sagging and may result in a rotor to stator rub when placed in service.
• 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.

Many facilities have a vendor that provides for motor storage in environmentally controlled warehouses.  Some motor repair facilities offer this service, which includes shaft rotation and resistance to ground testing on a regular basis. When a motor is needed they prepare and deliver.  It is unfortunate, but- we have been to a few of these storage facilities to test a customer’s motors and have found them plastic-wrapped, shafts blocked, and all the motor leads disconnected.  These are at facilities where motors are supposed to have the shafts rotated and routine resistance to ground checks accomplished. Trust but verify!

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.

Ask us about Electric Motor Testing Training and Certification.