BSEE-NOV21-PG28-29NEW.qxp_Layout 1 25/10/2021 11:31 Page 29
ELECTRICAL SERVICES
Motors that utilise re-greaseable bearings should be regreased on average every year or so when in storage, to help prolong bearing life and ensure that the motor is fit for service when needed.
Any moisture or dampness in the air will eventually find its way into a motor and speed up the oil oxidation process. So, as well as minimising corrosion, a dry environment is advisable for storing motors to prolong the effective life of their lubrication. The AEMT advises that before putting an oil-lubricated motor into storage, it is a good idea to first drain the oil, flush it through and replace it with fresh oil. In operational motors, the oil helps ensure that any debris or particles are held in suspension while the motor is running. But, when stationary, the debris held by the oil will sink to the bottom of the motor sump. Then, when the motor is finally started up again, all the debris will be quickly pulled through the motor.
Ensuring that stored motors are filled with the correct quantity of clean oil, and making sure that it is sealed correctly, will slow down the inevitable oil oxidisation process. In reality, however, all stored motors will be subject to some degree of temperature fluctuation, and this will cause the seals to expand and contract, allowing moisture to enter the motor. Because the oil in a stored
Ensuring availability
AEMT members have frequently reported stored motors being used as a source of unofficial spares for operational motors – most often, they are found to be missing parts such as terminal box lids and fan cowls. Obviously, this practise should be discouraged. While it is often only the intention to ‘borrow’ a part, too often, the part does not get replaced, which means that the spare motor will not be operation ready. If this absolutely has to happen, it should be recorded in a spares inventory or similar, and the implications of not having the doner motor available as a spare assessed.
Conclusion
motor will degrade over time, it is advisable, as part of the maintenance schedule, to regularly check the oil in stored motors, and it is good practice to change the oil before starting a motor after a long period of inactivity.
Testing stored motors
Before putting a motor into storage, it is also advisable 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 is in resisting the flow of electrical current. Before putting a motor back into service, repeat this test to ensure that any decreases in insulation effectiveness that may have occurred during storage can be addressed. After installation, vibration levels should be recorded to evaluate the spectra on motors with rolling element bearings for any signs of bearing fault frequencies. A vibration analysis should be performed during start-up with uncoupled baseline vibration levels documented.
Minimising downtime is critical in many sectors, with the cost of interrupted production or operations often having significant bottom-line implications. Therefore, being able to quickly and effectively respond to issues with plant and equipment is essential. If kept in the right environment and properly maintained, motors can be safely stored for many years without encountering any problems when they are put back into service. But to ensure this is the case, a planned approach to motor storage is crucial.
BSEE
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BUILDING SERVICES & ENVIRONMENTAL ENGINEER NOVEMBER 2021 29
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