A Construction, Performance and Reliability Comparison for Pre-EPAct, EPAct and Premium-Efficient Motors

The vast majority of totally enclosed fan cooled (TEFC) squirrel cage induction motors in the 1 to 200 hp range installed in the Petroleum and Chemical industries are NEMA "T" frames built prior to 1992, NEMA "T" frames built in accordance with the Energy Policy Act of 1992 (commonly referred to as EPAct motors) and the NEMA Premiumtrade motors, introduced after the year 2000, which exceed the EPAct efficiency standards. All three types are available in accordance with the IEEE 841 Recommended Practice and Standards. The most obvious difference in these three generations of motors is their efficiency levels. There has been some concern expressed by the users of these motors that in order to achieve the premium levels of efficiency it was necessary to compromise other performance characteristics and the motor reliability. This paper addresses these claims and shows that they are without basis. The paper provides a comparison of the key motor characteristics and construction features for each generation. A review of failure data does not indicate any shift in the reasons for failure. For all three generations, bearing failures account for approximately two-thirds of all failures. Winding failures is a distant second accounting for one-fifth of all failures. This paper will explain the reason why there has been no significant change in this distribution. The meantime between failure (MTBF) was also reviewed and found to have remained relatively constant. The issue of repair or replace is also discussed with criteria that can be used to assist in making a decision as to when to repair and when to replace with either the EPAct motor or the premium efficient motor