Austin Bonnett
Education and Technology Consultant
Electrical Apparatus Service Association, Inc.
Gallatin, MO
In his paper presented at the EASA Convention 2005, Austin Bonnett explores the reliability differences between premium efficient motors, EPAct motors, and pre-EPAct motors. The study aims to determine whether premium motors offer greater reliability by analyzing design differences and their impact on motor failures. Reliability is measured in terms of mean time between failures (MTBF), with a focus on excluding failures caused by misapplication, mishandling, or misuse.
Bonnett begins by highlighting the importance of conducting a comprehensive root cause failure analysis to accurately compare the reliability of different motor generations. He notes that bearing failures are the leading cause of motor failure, accounting for over 50% of all failures. Other common causes include winding failures and mechanical part failures. The study focuses on horizontal TEFC motors and examines design differences among major motor manufacturers.
The findings reveal that there are no significant changes in bearing systems, winding insulation systems, or mechanical parts across the three motor generations. All three generations use similar bearing sizes and systems, class F or better insulation systems, and have comparable winding operating temperatures. As a result, the thermal life and service factor capability remain unchanged, and there is no significant impact on reliability.
Bonnett concludes that there is no significant difference in reliability between premium efficient, EPAct, and pre-EPAct motors. This conclusion is based on the fact that the leading causes of motor failures—bearing systems and winding temperatures—remain unchanged across the three generations. He emphasizes that TEFC frames rely on heat transfer between the inside frame surface and the outside ribs, and newer designs with more ribs improve heat transfer. However, if the ribs are coated with an insulating material, it can hinder heat radiation and lead to overheating.
The paper also discusses the economic benefits of using premium efficient motors, such as energy cost savings and environmental benefits. Bonnett encourages service centers to "upsell" premium efficient motors to help customers save money, add value to business relationships, and reduce emissions. He provides formulas for calculating annual savings and simple payback, highlighting the long-term energy savings associated with premium motors.
In summary, Austin Bonnett's paper provides a thorough analysis of motor reliability, concluding that premium efficient motors do not offer significant reliability advantages over EPAct and pre-EPAct motors. The study emphasizes the importance of understanding design differences and their impact on motor failures, while also highlighting the economic benefits of premium efficient motors.
Key Points Covered:
- Comparison of reliability between premium efficient, EPAct, and pre-EPAct motors
- Importance of root cause failure analysis
- Leading causes of motor failures: bearing systems and winding temperatures
- Design similarities across motor generations
- Economic benefits of premium efficient motors
Key Takeaways:
- There is no significant difference in reliability between premium efficient, EPAct, and pre-EPAct motors
- Bearing systems and winding temperatures are the primary factors influencing motor reliability
- Premium efficient motors offer economic benefits through energy cost savings and environmental impact
- Service centers should consider upselling premium efficient motors to enhance customer relationships and profitability
- Understanding design differences is crucial for accurate reliability comparisons
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