Gene Vogel
Pump & Vibration Specialist
Electrical Apparatus Service Association, Inc.
St. Louis, MO
The paper "Vibration Testing in the Service Center" by Gene Vogel, presented at the EASA Convention 2010, provides a comprehensive overview of the importance, methods, and challenges of vibration testing for electric motors and generators in service centers. Vibration testing is crucial for assessing the condition of machines before and after repair, diagnosing vibration-related issues, and ensuring proper operation post-repair. The paper emphasizes the need for a solid understanding of vibration fundamentals, adequate instrumentation, documented acceptance criteria, proper mounting methods, and awareness of advanced analysis techniques.
Vogel explains that the most common standard for electric motor vibration is the NEMA Standard MG1, Part 7, which specifies maximum allowable vibration levels. Vibration amplitude and frequency are key parameters, with amplitude measured in displacement, velocity, or acceleration units, and frequency measured in cycles per minute (cpm), Hertz (Hz), or orders (multiples of rotating speed). Proper mounting methods, such as resilient mounts, flush mounts, and bolted test-bed mounts, are critical for accurate vibration testing.
The paper discusses the practical aspects of machine mountings and the impact of mounting methods on vibration levels. Resilient mounts, which use durometer pads, are preferred for isolating motor vibration from external effects. Flush mounting and bolted test-bed mounting are also acceptable, with specific considerations for each method. Vertical motors and various pumps present unique challenges for test runs, requiring careful handling to avoid damage and ensure accurate vibration measurements.
Vogel delves into vibration fundamentals, explaining the importance of amplitude, frequency, and phase in vibration analysis. He highlights the need for appropriate instrumentation, such as spectrum analyzers and oscilloscopes, to measure and analyze vibration data. The paper outlines various vibration analysis techniques, including high-resolution spectrum analysis, synchronous-time averaging, and phase analysis, to identify the sources of vibration and distinguish between mechanical and electrical forces.
The paper also addresses common vibration issues, such as unbalance, resonance, and mechanical looseness. Unbalance is characterized by steady amplitude and phase at 1x rpm and is often caused by factors like empty keyways or auxiliary fans. Resonance occurs when the machine mount is tuned to the rotating speed, amplifying vibration levels. Mechanical looseness can result from improper mounting or frame distortion.
Vogel concludes with practical advice for diagnosing and correcting vibration problems, emphasizing the importance of careful analysis and knowledge of available techniques. He notes that while most vibration issues can be resolved through precision balancing, more complex problems may require advanced analysis and troubleshooting.
Key Points Covered:
- Importance of vibration testing in service centers
- NEMA Standard MG1 for electric motor vibration
- Vibration amplitude and frequency parameters
- Proper mounting methods for accurate testing
- Vibration fundamentals: amplitude, frequency, phase
- Instrumentation for vibration measurement and analysis
- Vibration analysis techniques: spectrum analysis, synchronous-time averaging, phase analysis
- Common vibration issues: unbalance, resonance, mechanical looseness
Key Takeaways:
- Vibration testing is essential for assessing machine condition and ensuring proper operation post-repair.
- Understanding vibration fundamentals and using appropriate instrumentation are crucial for accurate testing and analysis.
- Proper mounting methods significantly impact vibration levels and testing accuracy.
- Advanced analysis techniques are necessary for diagnosing and resolving complex vibration problems.
- Regular vibration testing and careful analysis can prevent machine failures and extend equipment life.
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