Turn insulation capability of large ac motors: Volume 1, Main report: Final report
Technical Report
·
OSTI ID:6846315
Steep fronted transients such as switching surges can cause severe stress on motor turn insulation. Failure of many large ac motors in generating stations have been blamed on switching surges. The introduction of vacuum switchgear has caused particular concern since multiple surges can be generated in each switching operation. This project is aimed at determining the actual surge environment in typical power plants as well as the capability of modern turn insulation to withstand these surges. Laboratory work included studies of the surge distribution within the windings of eleven motor stators, the impulse strength measurements of fifty-three new coils and eighteen motor stators, and testing of vacuum interrupts from five manufacturers. Switching surges were measured on thirty-three motors in sixteen utility plants, covering over 700 normal switching operations. Analytical models for the motor supply system and the motor winding were developed, and validated against the measured results. Switching surges measured on the motors were significantly below the withstand strength of most utility motors. In normal motor switching operations, the risetimes and magnitudes of surges are similar for air-magnetic and vacuum breakers. Although deleterious surge levels cannot be totally ruled out for vacuum switchgear when interrupting motor starting current, it appears that voltage escalation is not a problem for modem vacuum devices applied as recommended by the breaker manufacturers. Practical guidelines are provided for improving motor reliability in new and existing motor installations and for analyzing premature motor failures.
- Research Organization:
- Electric Power Research Inst., Palo Alto, CA (USA); Ontario Hydro Research Div., Toronto (Canada); Rensselaer Polytechnic Inst., Troy, NY (USA)
- OSTI ID:
- 6846315
- Report Number(s):
- EPRI-EL-5862-Vol.1; ON: TI88015387
- Country of Publication:
- United States
- Language:
- English
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