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Electric Power Utility Motor Case Study

Electric Power Utility Motor Case Study. Diagnostics & Resolution Power utility contracted to perform off-line circuit and insulation testing of critical motors during major planned outage. Tests included MCA, IR & overvoltage hipot and impulse.

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Electric Power Utility Motor Case Study

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  1. Electric Power Utility Motor Case Study • Diagnostics & Resolution • Power utility contracted to perform off-line circuit and insulation testing of critical motors during major planned outage. Tests included MCA, IR & overvoltage hipot and impulse. • New 4 kV motors are impulse tested to 11.4 kVpk (IEEE). Recommended maintenance test is 9 kVpk. Impulse test discovered a 4 kV pump motor with phase insulation breakdown voltage of 7.2 kVpk. No indication of problem during MCA, IR and hipot tests. • Utility opted to start the motor repeatedly to study failure of weak motor insulation system. Insulation failed catastrophically on fifth startup. • Motor was rewound during planned shutdown • Cost of Diagnostics to Utility: <$10,000 including travel • Savings to Utility • No lost production: Potentially $100Ks • No emergency repair costs: $10Ks

  2. Common Off Line Electrical PdM Motor Tests { Under Voltage { Over Voltage

  3. Electric Power Utility Motor Case Study • Diagnostics & Resolution • Power utility contracted to perform off-line circuit and insulation testing of critical motors during major planned outage. Tests included MCA, IR & overvoltage hipot and impulse. • New 4 kV motors are impulse tested to 11.4 kVpk (IEEE). Recommended maintenance test is 9 kVpk. Impulse test discovered a 4 kV pump motor with phase insulation breakdown voltage of 7.2 kVpk. No indication of problem during MCA, IR and hipot tests. • Utility opted to start the motor repeatedly to study failure of weak motor insulation system. Insulation failed catastrophically on fifth startup. • Motor was rewound during planned shutdown • Cost of Diagnostics to Utility: <$10,000 including travel • Savings to Utility • No lost production: Potentially $100Ks • No emergency repair costs: $10Ks

  4. High Voltage Surge or Impulse • IEEE 522 & EASA • Simulates the transients on power lines which can cause insulation failure. Rise time = 0.1 µsec • Impulse test of turn and phase insulation where test voltage is incrementally increased in a stepped mode from 0V voltage to target test voltage looking for change in response frequency • Final impulse test voltage typically at 2 x line voltage + 1000 V (peak) • Only test capable of complete predictive testing of turn and phase insulation

  5. Steps of Degrading Insulation Electrical Failure • New insulation has high break down voltage • Motor insulation experiences aging • Thermal aging • Chemical or moisture contamination • Mechanical wear • Corona/Partial Discharge • Turn, phase or ground insulation break down voltage degrades resulting in arcing due to transients, start up coil movement, etc

  6. Steps of Degrading Insulation Electrical Failure • Induced arcs cause insulation to deteriorate much faster • Turn to turn or ground insulation breakdown voltage drops below operating voltage effectively causing a short between turns or a short to ground. • Shorted turns transformer action causes a large induced current in the short which creates a hot spot • Heat causes rapid insulation failure (typically minutes to hours)

  7. Breakdown Voltage Degradation v. Time

  8. Electric Power Utility Motor Case Study • Diagnostics & Resolution • Power utility contracted to perform off-line circuit and insulation testing of critical motors during major planned outage. Tests included MCA, IR & overvoltage hipot and impulse. • New 4 kV motors are impulse tested to 11.4 kVpk (IEEE). Recommended maintenance test is 9 kVpk. Impulse test discovered a 4 kV pump motor with phase insulation breakdown voltage of 7.2 kVpk. No indication of problem during MCA, IR and hipot tests. • Utility opted to start the motor repeatedly to study failure of weak motor insulation system. Insulation failed catastrophically on fifth startup. • Motor was rewound during planned shutdown • Cost of Diagnostics to Utility: <$10,000 including travel • Savings to Utility • No lost production: Potentially $100Ks • No emergency repair costs: $10Ks

  9. Contact Info:Torq EngineeringRandy Keenercell: 970-412-9337randy.keener@teamtorq.comField ServicesTrainingData Analysis

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