Testing to assure reliable operation of electric motors

Several field test procedures that can be used as part of a motor maintenance program are discussed, and failure mechanisms in motor insulation systems are considered. It is suggested that motor windings fail due to a few simple mechanisms. The magnetic forces which turn the rotor also cause motion in the windings. The motion causes wear between the wires, abrading the insulations. The thin turn-to-turn insulation is least able to sustain this wear; thus turn-to-turn shorting often occurs before the thicker ground wall insulation is affected. If turn-to-turn shorting is a major factor in causing motor winding failure, it stands to reason that a test for impaired turn insulation is a good periodic test for motors. The surge test has been used for a generation as a quality control tool in motor manufacturing plants. Development of portable field test instruments has allowed the test to be adopted as a tool which can be incorporated in plant maintenance programs. Experimental and practical test data have shown this conclusion to be accurate