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Static Eccentricity Faults Using Electrical Signature Analysis

Mark Koch | Technical Support Manager, ALL-TEST Pro, LLC

Static Eccentricity Faults Using Electrical Signature Analysis

Static Eccentricity (air gap) is a fault that is created when the rotor is not in the magnetic center of the stator. Static eccentricity can cause an increase in operating current, overheating, energy losses, and overloading of bearings. Electrical Signature Analysis (ESA) evaluates the current and voltage spectrums using a Fast Fourier Transform (FFT), which converts the time waveforms to a frequency spectrum. The FFT highlights amplitudes and frequencies identify faults such as static eccentricity.

When there are peaks at the same frequency in the current and voltage high-frequency spectrums, they are related to the incoming power. When there are peaks only in the current and not the voltage, then the fault is coming from either the motor or the driven load. In the ESA example above, a Static Eccentricity problem is indicated by Line Frequency (50Hz) and twice Line Frequency sidebands of running speed multiplied by the number of rotor bars. The red arrows identify static eccentricity frequency peaks in the current spectrum and not in the voltage.

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About the Author

Mark Koch Technical Support Manager, ALL-TEST Pro, LLC

Mark Koch is a member of the Technical Support team at ALL-TEST Pro, LLC (ATP), where he has provided professional support worldwide for users of ATP equipment since 2014. He has 17 years of electrical and reliability maintenance experience. In 2001, he started his career as a construction electrician. During this time, he worked his way up from shop floor apprentice to a foreman in charge of starting and completing remodel and new construction projects. In 2010, he began working at the Metropolitan Sewer District (MSD) of Greater Cincinnati, Ohio, USA, where he learned electrical maintenance best practice and helped implement a predictive maintenance program (PdM). During his service at MSD, his team was the recipient of both the Uptime Magazine’s Best Emerging Maintenance Reliability Program Award and the Uptime Magazine’s Best Asset Condition Management Program Award. At MSD, he learned and provided routine PdM services such as thermography, vibration, lubrication, visual inspection, motor testing, and ultra-sonics.


Education and Certifications:

2001-2006- International Brotherhood of Electrical Workers (IBEW) Apprenticeship Program and the National Electrical Contractors Association (NECA) Inside Wireman Certification.

2013- PdM Visual Testing Level 2 Certification & Level 1 Thermographer Certification; 2014- Vibration Analysis Level 1T Certification.