Abstract
This chapter discusses winding insulation and maintenance of electric motors. Different manufacturers adopt different practices of insulating the coil or the windings by simple impregnation in a recommended insulating varnish, normally synthetic or epoxy, followed by baking. For large motors, insulation is done with resin-rich glass and mica paper tapes. The latest standard practice is to have the stator vacuum pressure impregnated (VPI) in insulating resins, not only to meet the requirements of "powerhouse insulation," but to also develop a more simplified insulating process to cure and toughen the stator windings and to meet the severities of all operating conditions that a motor may have to encounter. The properties of an insulating material are greatly affected by moisture, temperature, repeat overvoltages, and chemical vapor. Care must be taken to avoid these harmful effects to achieve prolonged life of the machine. Whenever a motor is installed in a humid atmosphere and is switched on after a long shutdown, insulation resistance must be checked before energizing the motor. Monitoring the quality of insulation is necessary, irrespective of the class of an insulation system and its quality.
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