Field motor testing: limiting risk

There are a number of insulation tests that can be applied to an AC winding, which, if applied in a systematic and thoughtful manner, can provide useful information about the condition of a motor´s insulation system. The nondestructive tests should always be performed first, followed by go/no-go testing if provision can be made for nondisruptive repair scheduling. While generally nondestructive, misdiagnosis of motor vibration will make it impossible to correct the responsible component. Very often, elevated vibration levels serve as early warnings of a more serious condition. With proper understanding of motor fundamentals and correct test procedures, the service life of a motor can be maximized with the least amount of incurred risk, and, therefore, at minimal cost. The following tests are discussed in this paper: insulation resistance testing, partial discharge testing, DC high potential tests, AC high potential tests, and vibration tests and analysis