Electrical signature analysis utilizes voltage and current Time Domain conversions to Frequency Domains, in other words a Fast Fourier Transform, to provide a wealth of spectral data. This signal processing technology can be extremely effective in identifying electrical and mechanical anomalies within the power circuit, the motor and the driven load. Many problems provide unique signatures that are readily identifiable as particular problems. Other issues are more difficult to diagnose.
Identifying spectral frequency origins can be useful in localizing a potential problem. Every frequency peak in a spectrum has an origin. In order to determine if it is a significant problem, it must be isolated to the source.
In Figure 2, many spectral peaks are present with four being marked to show frequencies that may be indicative of rotor static eccentricity. Many other peaks are also present. Where do they originate? Are they a problem? What caused them to occur? Answering these questions can be difficult. The first thing we need to do is determine the fundamental origin. This can be accomplished utilizing a simultaneous capture of voltage and current with conversion to an FFT format.
With the spectral data overlaid and accounting for differing noise levels, the frequencies that are present in both current and voltage should be observed for which peak is dominant.
Voltage Dominant – Source is electrical and upstream of your circuit connection points.
Current Dominant – Source is electrical and downstream of your circuit connection points.
Peak in Current Only – Source is mechanical and downstream of your circuit connection points.
With the source localized it is now a process of elimination. For more information on fault localization and electric motor testing, contact the Snell Group and schedule one of our comprehensive training courses. Don’t forget to ask about our new De-Energized Electric Motor Data Analysis Wall Chart. A 36” x 48” laminated chart that is a wealth of information. Order Now.