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The following insulation deterioration mechanisms are detected by predictive maintenance testing so that appropriate measures can be taken on a planned, and not a crash-action, crisis basis.
Thermal Conditions
Poor cooling is a common cause of insulation overtemperature failure. Inadequate cooling is caused by plugged cooling ducts or accumulated dust on windings. Keeping the motor clean promotes heat dissipation and prolongs insulation life. Depending on its specific chemical composition, elevated temperatures can cause insulation to become brittle and/or shrink. Shrinkage can allow the winding to vibrate, eventually allowing the copper winding to contact the steel core of the motor.
If the insulation is subjected to shrinkage, wedges might loosen or be lost entirely, or the coil side packing might allow too much movement of the coils. Once...