Tom Bishop
Technical Support Specialist
Electrical Apparatus Service Association
St. Louis, MO
The paper "Repair/Replace: What to Do When the Decision Is to Replace" by Tom Bishop, presented at the EASA Convention 2007, addresses the considerations and steps involved when the decision is made to replace an electric motor rather than repair it. This comprehensive guide covers selecting the right motor for the application, dealing with usual and unusual electrical and mechanical conditions, preventing problems by recognizing the causes of the original motor failure, and adding value by providing additional features and services to increase the reliability of the replacement motor.
The paper begins by emphasizing the importance of evaluating both the application and motor characteristics to ensure the replacement motor is suitably matched to the application. Key factors include environmental conditions, load inertia, speed versus torque, starting methods, and mechanical coupling and mounting. The author provides a detailed list of questions to ask to better assure proper motor selection, such as obtaining complete nameplate information, understanding the driven equipment, and knowing the motor's past history and operating environment.
Next, the paper discusses dealing with usual and unusual service conditions as defined by NEMA MG1 standards. Usual conditions include ambient temperature ranges, altitude, rigid mounting surfaces, and operation within specified voltage and frequency tolerances. Unusual conditions encompass exposure to hazardous materials, abnormal mechanical loads, and operation in extreme environments. Recognizing these conditions helps in selecting or modifying the replacement motor to fit the specific application needs.
Preventing problems by recognizing the causes of the original motor failure is another critical aspect covered in the paper. The author highlights the importance of root cause failure analysis, which involves inspecting and evaluating all motor components to determine the primary cause of failure. Common failure modes for stator windings, rotors, bearings, shafts, and cooling systems are discussed, along with diagnostic methods to identify and address these issues.
Finally, the paper explores adding value by providing additional features and services to enhance the reliability of the replacement motor. These include equipping motors with bearing and winding temperature sensing, surge protection, shaft seals, and insulated bearings. The author also suggests offering value-added services such as predictive maintenance (PdM), preventive maintenance (PM), and motor management to help end users maintain their motor inventory and prevent future failures.
Key Points Covered:
- Selecting the right motor for the application
- Dealing with usual and unusual service conditions
- Preventing problems by recognizing the causes of original motor failure
- Adding value by providing additional features and services
Key Takeaways:
- Proper motor selection involves evaluating both application and motor characteristics.
- Recognizing usual and unusual service conditions helps in selecting or modifying the replacement motor.
- Root cause failure analysis is essential to prevent premature failure of the replacement motor.
- Providing additional features and services can significantly enhance the reliability and lifespan of the replacement motor.
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