How do you ensure that stored electric motors are properly maintained to ensure they are ready to run when needed?

Most commercial and industrial operations will rely on electric motors, and for many organizations it is standard practice to store working spare parts so that in the event of a motor failure, downtime can be minimized by replacing the failed motor with working spare parts.

For this reason, stored motors must be kept in an operationally ready condition, which does require correct management and regular maintenance.

First, it is important to protect stored motors from vibration and extremes of temperature and weather, so outdoor storage is not recommended. Ideally, electric motors should be stored indoors in a clean, dry environment.

While a climate-controlled environment is the best option for storing electric motors, in some cases, this may not be possible. In this case, the motor may need to be stacked outdoors. If this is the only option, the motor should be loosely covered with a waterproof cover to ensure air circulation to help reduce condensation. It is also important to try to protect low IP motors from pests.

Make sure all openings – cable entries, vents, grease tubes, etc. – are properly covered or sealed during storage.

Exposed surface areas may also be coated with corrosion inhibitors, which will need to be removed before the motor can be put back into service.

Protect bearings

To prevent indoor vibration, it's also a good idea to store the motor away from any areas of environmental vibration.

Bearings in storage motors are known to fail due to fretting wear caused by environmental vibrations or erroneous Brinell indentations, which cause small movements in the bearings. Over time, even the smallest environmental vibration can cause motor bearings to wear out. Therefore, it is a good practice to store your motor on a material that helps absorb vibration.

Regular shaft rotation also helps reduce bearing wear at any point on the bearing, helping to extend its service life. AEMT recommends that the shaft be rotated at least once a month, with larger motors having the shaft rotated more frequently.

While it is generally accepted that shaft turning is necessary for storage equipment, AEMT members report that in practice, this task is rarely performed regularly. Therefore, someone should be responsible for rotating the axles regularly as part of the shop's maintenance plan.

Ensure adequate lubrication

For grease-lubricated motors, the shelf life of the grease in the bearings should be considered. If the motor has sealed bearings, if it is not run for a long time (say two years), the grease in the bearing is likely to separate and not function optimally when it needs to start turning again. Motors using relubricable bearings should be re-lubricated on average once a year or so while in storage to help extend bearing life and ensure the motor is suitable for use when needed.

Any moisture in the air will eventually get into the motor and speed up the oil oxidation process. Therefore, in addition to minimizing corrosion, it is also recommended to store the motor in a dry environment to extend the effective life of its lubrication.

It is recommended that before putting the oil-lubricated motor into storage, it is best to drain the oil, rinse it clean, and then replace it with new oil. In a running motor, oil helps ensure that any debris or particles remain suspended while the motor is running. However, when stationary, debris in the oil will sink to the bottom of the engine sump. Then when the motor finally starts up again, all the debris will be pulled quickly through the motor.

Ensuring that the motor is stored with the correct amount of clean oil, and that it is properly sealed, will slow down the inevitable oil oxidation process. However, virtually all stored motors are subject to some degree of temperature fluctuations, which can cause seals to expand and contract, allowing moisture to enter the motor. Because the oil in a stored motor will degrade over time, it is recommended that the oil in a stored motor be checked regularly as part of a maintenance schedule, and it is good practice to change the oil before starting the motor after extended use.

Test stored motors

Before placing a motor into storage, it is also recommended to perform an insulation resistance (IR) test, which measures the total resistance between any two points separated by electrical insulation. This test determines how effective the insulation material is in resisting the flow of electrical current. Before placing the motor back into service, repeat this test to ensure that any degradation in insulation effectiveness that may have occurred during storage can be addressed.

After installation, vibration levels should be recorded to evaluate the frequency spectrum of motors with rolling bearings for any indication of bearing failure frequency. Vibration analysis should be performed during startup and uncoupled baseline vibration levels recorded.

in conclusion

In many industries, minimizing downtime is critical, as the cost of production or operational disruption often has a significant impact on the bottom line. Therefore, being able to respond quickly and efficiently to plant and equipment issues is critical. If kept in the right environment and properly maintained, motors can be stored safely for many years without any problems when put back into service. But to ensure this, a planned approach to motor storage is crucial.