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Product Abstract

Improved Motors for Utility Applications, Volume 1: Industry Assessment Study: Update and Analysis

Product ID:EL-4286-V1
Date Published:01-Oct-1985
Sector Name:Generation
Document Type:Technical Results
Price:No Charge

This Product is publicly available

   5.26 MB - Adobe PDF (.pdf)

This comprehensive analysis of power plant motor failures, which updates an earlier data base, relates failure rates to operating and maintenance practices, as well as application and manufacture. Using the expanded analytic methodology, utilities can analyze the data for other factors significant to improving motor reliability.


This study is part of a larger project addressing the need to improve reliability and efficiency in power plant auxiliary systems. From an evaluation of the present reliability of powerhouse motors, the aim is to develop recommendations for improving motor components and application technologies. An industry survey performed in the initial phase of the project yielded failure data from 56 utilities on 4785 powerhouse motors used in 132 generating units (EPRI report EL-2678). After publication of that report in 1982, further data were collected.


To update the industry assessment study published in 1982 by including failure data from an additional 1527 motors.


The new data from 11 utilities, 9 of which were not participants in the original analysis, concerned 36 generating units and 1527 motors. Thus, the combined data base contained material from a total of 65 utilities on 168 generating units and 6312 motors. Use of the constant-hazard-rate model to represent time to first failure in motors enabled investigators to analyze the effects on reliability of such factors as application and manufacturer.


The updated data base represented a total of 1052 failed motors and 1474 recorded failures. Of the recorded failures, 422 occurred on motors that had failed before. In addition to summarizing the motor failure data, the report presents a methodology for analyzing those data. The analysis of the overall motor population and failure characteristics examines the occurrence of multiple failures and discusses failure rates with respect to such key parameters as generating unit, operating utility, application, and manufacturer. The methodology and data are available in the report for additional analysis.

EPRI Perspective

The updated analysis closely resembled the initial survey in the distribution of identified failures by components and in the distribution of identified reasons for the failures. In the updated survey, 41 percent of the failures were related to bearings; 36 percent, to stators; 9 percent, to rotors; and 14 percent, to other components. The reasons were related to poor design in 39 percent of the failures, to poor workmanship in 26.6 percent of the failures, to misoperation in 21.5 percent of the failures, and to misapplication in 12.9 percent of the failures. Beyond these similarities, however, this study expanded the initial methodology -- based on analysis of first failures -- to include subsequent failures. Moreover, it used the new methodology to analyze the relationships of failures to the individual generating units and operating utility, as well as to the motor application. Some applications, it found, have significantly higher than average failure rates. Overall, the information presented in this report should prove useful in industry efforts to improve the reliability of utility motors. Other volumes in this report will focus on specific areas of motor technology and application improvement.

Program 71   Combustion and Coal Quality Impacts
  • Motors
  • Electric Generators
  • Failures
  • Reliability
  • Availability
  • Statistical Analysis

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