Partial discharge tests are used to evaluate the condition of the electrical insulation in motor and generator stator windings rated 6 kV or more. It has been generally believed that such testing for stator windings rated 4 kV or lower is not worthwhile. This paper presents results that indicate that some 4 kV motors do not have partial discharges when tested at rated voltage. However, if the motor stator insulation is significantly degraded, partial discharges are measured at operating voltage. Preliminary observation suggests that only a few months warning may be given to indicate that the stator winding may be close to failure. Therefore, it appears that partial discharge tests on 4 kV motors at the rated line-to-ground voltage of 2.3 kV can be useful for identifying stator windings close to failure. Identifying these stator windings enables 4 kV motor user's to remove motors from operation before catastrophic failure occurs.
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