In this article we restrict ourselves to squirrel cage induction motors. There are only a few simple rules for the maintenance of these motors:
- Maintain high insulation resistance at all time and measure the insulation resistance by megger regularly.
- Keep the bearings lubricated properly and change the bearings at the recommended intervals.
- Maintain a uniform air gap.
- Keep the motor clean and dry always. Protect it from moisture.
If these simple rules are followed, your motor will run indefinitely and never give you any trouble. For the motors, cleaning is the most important maintenance that can be done. Regular cleaning must be done both on the outside and the inside of the motor. The winding should be cleaned with chemical agents like electro-solve and dried. In case insulation readings are low, then the windings can be dried by heating with an electric heater or by supplying an small intensity current through the windings, then followed by varnishing the windings.
In case compressed air is used for blowing the dust away, make sure that it is dry and has been passed through the dehumidifier. However prudent engineers do not use compressed air as the pressure of the air forced the dust and the contaminants inside the windings. It is better to use a long handle dog leg brush for the cleaning. Alternatively a vacuum cleaned can be used.
The motors become dirty from the outside in industries and then the overzealous staff paint them bright before the inspections. However it must be remembered that each additional layer of paint is reducing the heat transfer of the motor casing and fins. Years of painting lead to the overheating and the failure of the insulation and eventual burning of the motor. In case you find that the motor have become dirty it is a better option to clean them with a heavy duty cleaner than re painting.
In case you find that a motor is very hot when all the other parameters including the current drawn are normal, then a simple procedure of removing all the old layers of paint by a scraper will bring immediate relief.
Contamination of the windings due to the grease escaping from the ball bearings also contaminates the windings. In the bearings where a bearing covers are not available sealed ZZ type of bearings should be used. In the sealed bearings optimum quantity of grease is put and the same grease melts, lubricates and again gels.
Some engineers remove the shielding of the ZZ type of bearings to put additional grease. This action does uncountable damage to the bearings as well as the windings. In case there is evidence that the winding has been subjected to the onslaught of grease and oils, the same should be washed with cleaning agents like electrosolve and electraclean, etc.