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Static Eccentricity Faults Using Electrical Signature Analysis

Bill Kruger
Bill Kruger | Training Technical Manager, ALL-TEST Pro

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

Bill Kruger
Bill Kruger Training Technical Manager, ALL-TEST Pro

William Kruger joined ALL-TEST Pro, LLC as the Technical Manager in 2005. Since joining ATP, Bill has traveled the world teaching the Theory and Application of Motor Diagnostics, helping Fortune 500 Companies implement Predictive Maintenance Programs. In 2010 Bill’s proven instructional techniques earned him the new title of Training Technical Manager.

Before joining ALL-TEST Pro, LLC Bill Kruger worked in many different aspects of the Engineering and Maintenance Fields. Bill worked as an Electrician in the US Navy Nuclear Submarine Program. He has completed the Journeyman Electrician Program and started one of the first Predictive Maintenance Programs in the Utility Industry. Bill Kruger holds a Bachelor of Science Degree from San Diego University.

With his combined work in the field as well as with ALL-TEST Pro, Bill has over 40 years of proven experience in the practical engineering and predictive maintenance field.