Fault Zone Analysis AIR GAP

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Fault Zone AnalysisAIR GAP

• Luis Leon
• PdMA Corporation
• Motor Reliability Technical Conference
• May 15-17, 2007 St. Petersburg, FL

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Objectives

• Discuss Air Gap Fault Mechanisms
• Compare Lap Wound vs. Concentric
• Analysis Techniques

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Fault Mechanisms

• Static Eccentricity
• Soft foot
• Misaligned end bell
• Cocked bearing
• Oil bath bearing

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Fault Mechanisms

• Dynamic Eccentricity
• Loose bearing
• Warped shaft

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Fault Mechanisms

• Five Basic Types
• Rotor O. D. is eccentric to axis of rotation
• Stator bore is eccentric
• Rotor and stator are round but do not have the
  same axis of rotation
• Rotor and shaft are round but do not have the
  same axis
• Any combination of the above

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Fault Mechanisms

• Uneven Magnetic Pull
• Increased Vibration
• Possible Pull-Over During Start Up
• Rotor/Stator Rub

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Analysis

• MCE
• Rotor Influence Check (RIC)
• EMAX
• Eccentricity test

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MCE RIC Analysis
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Alignment
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Software Alert

• Does the motor have Lap or Concentric wound
  windings?
• How does this affect RIC results?

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Lap Wound Stator
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Concentric Wound Stator
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Concentric Wound Analysis
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Concentric Wound Analysis
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Concentric Wound Analysis
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Concentric Wound Analysis
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EMAX Eccentricity Analysis
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EMAX Air Gap Evaluation

• Evaluation of the spectrum depends on a number of
  variables
• Line Frequency
• Number of Rotor Bars
• Motor Speed

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Eccentricity Frequency

• fEcc B (fShaft)
• Where fEcc Eccentricity Frequency
• B Number of Rotor Bars
• fShaft Shaft frequency (RPM/60)

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Eccentricity Indications

• Look for at least 4 peaks (typically located
  between 600-2500 Hz)
• Not harmonics of line frequency
• Separated by two times line frequency
• gt 20 dB above noise level

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Caution and Alarm

• PdMA Corporation
• Average Noise level 15dB Caution
• Average Noise level 20dB Alarm

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Eccentricity Test

• Software Features
• Harmonics markers
• Manual eccentricity markers
• Estimate number of rotor bars
• When using the software features for manual
  eccentricity markers or the estimate bars, the
  vertical marker on the spectrum is placed on the
  first sideband to the left of the expected
  eccentricity frequency.

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VFD Application
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VFD Application
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VFD Application
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VFD Application
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VFD Application
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RIC vs. Eccentricity
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Helpful Hints

• Rotor Influence Check
• Might require an additional pole face
• Use the balance of inductance to determine if a
  longer test is required
• Eccentricity Test
• For VFD powered motors, strobe/tach speed
• The X16 scale will fit 4 peaks

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Summary

• Correlate Test Data
• Investigate All Possible External Causes
• Use data to make better decisions