Keeping an extra motor on hand is done for one primary purpose: to reduce downtime when a motor in production fails. So it’s critically important that motors in storage are maintained as well as motors in production.
There are two key problems that can arise when motors are stored for extended periods of time. Both problems are the result of condensation collecting in the motor that damages the winding and bearings. Condensation that collects on the stator coils will result in deterioration of the insulation system. This will eventually lower the motor’s resistance to ground. The motor bearings can be damaged when condensation contaminates the bearing grease. This can result in oil leaching out of the grease, causing the grease to harden and lose its ability to lubricate. It can also result in stationary brinelling of the bearing race.
Motors keep in inventory are an asset that customers cannot afford not to maintain. Simple maintenance on motors in storage can reduce the potential for these two problems and protect your investment.
1. Store motors in a clean, dry, low-humidity (60% or less) environment with a temperature range of 50F to 120F. This environment will help prevent condensation on the windings and bearings.
2. Motors that are equipped with space heaters on the windings should be energized whenever the storage ambient conditions reach the dew point or at least 48 hour prior to the motor going into service. Motors stored in high humidity environments should have space heaters energized.
3. Shock or vibration in the environment must not exceed 2 mils maximum at 60 Hz to prevent the bearings from brinelling.
4. All motor drains are to be fully operable while in storage and/or the drain plugs removed. The motors must be stored so that the drain is at the lowest point. All breathers and automatic “T” drains must be operable to allow breathing and draining at points other than through the bearings around the shaft.
1. Oil-lubricated motor bearings must be filled with oil when the motor enters storage since they are shipped dry from the factory.
2. Grease-lubricated motor bearings require relubrication every six months during extended storage. The motor will have a nameplate indicating the grease to be used. If using a different grease, make sure it is compatible with the nameplate grease.
3. The motor shaft should be rotated monthly. This distributes lubricant to machined surfaces and prevents false brinelling damage.
1. During extended storage, all motors should have their insulation resistance checked and recorded at periodic intervals.
2. A 50% drop in the resistance-to-ground from the initial reading indicates moisture in windings and requires electrical or mechanical drying before the motor can be placed in service.
When a motor is removed from storage, it must be in good operating condition and ready for service. Performing a few, relatively simple maintenance steps during storage will help ensure a motor operates properly when installed.