Vicki Warren, Iris Power
Mississauga, Ontario
Brian F. Moore, Georgia Power
Atlanta, Georgia
Surveys have shown that stator winding insulation failure account for about 40% of motor failures in motors rated 2300V and above. In addition, the work force in general is losing its technical experience. This impacts both the customers we serve and our own internal work force that fixes the equipment. Lastly, there seems to be a shift toward a more political type customer base that is less likely to own up to their contribution to motor failures. These reasons combine to force motor shops into better testing to know that a more reliable product is being shipped.
Several old and new test methods have recently gained popularity with AC induction motor maintenance specialists. This paper, presented at the 2013 EASA Convention, will examine Power Factor Tip-up and Partial discharge testing to assess stator winding conditions for motors rated 2300V and above. Both tests will be evaluated for: effectiveness; which windings/types of machines the test is effective; set-up; interpretation and limitations.
Topics discussed include:
- Brief review of stator winding failure mechanisms
- Brief review of power factor and power factor tip-up
- The theory/math behind it
- Georgia Power’s use as a sorting tool
- Partial discharge terms that apply to power factor and tip-up testing
- Inception and extinction voltage
- Magnitude
- Polarity
- Reading actual power factor and test data sheets
- Advantages and limitations of off-line tests
- Deciding if there is a problem or not
- Case studies: What to do next (if you suspect a problem)
- Partial discharge testing (brief theory and expected results)
- Dynamometer testing or full-load testing at the customer’s plant us
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EASA Technical Manual
More information on this topic can be found in EASA's Technical Manual- Section 2: AC Machines
- Section 7: Electrical Testing
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