By Tom Bishop, P.E.
Senior Technical Support Specialist
Electrical Apparatus Service Association, Inc.
St. Louis, MO
The paper "AC Motor Assembly and Testing" presented by Tom Bishop at the EASA Convention 2010 provides a comprehensive overview of the procedures and considerations involved in the assembly and testing of AC motors. The document covers various aspects of motor assembly, including electrical and mechanical inspection, static and run testing, and the handling of different types of bearings such as ball, roller, and sleeve bearings. Bishop emphasizes the importance of proper diagnostic testing to ensure the motor's integrity and performance. He discusses several testing methods, including surge tests, high-potential tests, and megohmmeter tests, which are crucial for evaluating the insulation and overall condition of the motor windings.
The surge test involves applying high voltage across motor phases and analyzing the resonance patterns to detect insulation issues. The high-potential test checks the insulation system's integrity by applying high voltage between motor leads and the frame, measuring leakage current to identify weak points. The megohmmeter test assesses the winding ground insulation condition, providing valuable data on insulation resistance and polarization index.
Mechanical inspection is critical for identifying the root cause of motor failures. Bishop outlines procedures for inspecting exterior parts, attachments, and shaft surfaces for signs of wear, cracks, and other damage. He highlights the importance of checking shaft runout and ensuring the motor feet are coplanar to avoid soft-foot conditions that can lead to vibration and mechanical stress.
The assembly process involves meticulous preparation, including verifying repairs, balancing the rotor, and ensuring all parts are received and in good condition. Proper bearing installation is crucial, with methods such as heating/shrink fitting, press fitting, and light impact fitting discussed in detail. Bishop stresses the importance of maintaining correct oil levels and inspecting grease fittings to ensure proper lubrication.
During test runs, monitoring bearing temperature and vibration levels is essential to detect issues early. Bishop explains the significance of marking the magnetic center and checking end float to ensure the motor operates smoothly without axial hunting. He also addresses the importance of blocking motor shafts during shipping to prevent damage.
Overall, the paper provides a thorough guide to AC motor assembly and testing, emphasizing the need for careful inspection, proper testing, and meticulous assembly procedures to ensure reliable motor performance.
Key Points Covered:
- Electrical and mechanical inspection procedures
- Surge test, high-potential test, and megohmmeter test
- Importance of proper diagnostic testing
- Mechanical inspection for identifying root causes of failures
- Procedures for inspecting exterior parts, attachments, and shaft surfaces
- Importance of checking shaft runout and motor feet coplanarity
- Detailed assembly process and preparation steps
- Bearing installation methods and lubrication practices
- Monitoring bearing temperature and vibration during test runs
- Marking magnetic center and checking end float
- Blocking motor shafts during shipping
Key Takeaways:
- Proper diagnostic testing is crucial for motor integrity.
- Mechanical inspection helps identify failure causes.
- Correct bearing installation and lubrication are essential for motor performance.
- Monitoring during test runs can prevent damage.
- Blocking shafts during shipping protects the motor.
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