In August 2020 I wrote an article for TheRamReview on the benefits surrounding Electrical Signature Analysis and it’s capabilities in viewing the entire system at one time (Regarding Reliability of Electric Motors: What Makes Electrical Signature Analysis Different? | THE RAM REVIEW ). In the past the discussion surrounding MCSA and ESA were such that very little time or attention was given. The primary reason has been that researchers and marketers focused on the technology’s ability to positively identify rotor faults, a challenge with other technologies such as vibration analysis.
When reviewing the complete Haynes and Eissenberg Oak Ridge National Labs patent 4,965,513 issued on October 23, 1990, there is very little mention of fault detection of an electric motor rotor. The patent, “Motor Current Signature Analysis Method for Diagnosing Motor Operated Valves,” specifically identifies that the method is used for evaluating lubrication, gear wear, bearing faults, and other electrical and mechanical conditions: “In addition to the fundamental frequency content, harmonic and sideband components are also observed. Those are indicators of a variety of mechanical modulations associated with time-dependent degradation including gear tooth wear, shaft eccentricity, and bearing noise which may change as the MOV suffers aging and wear due to operation and/or maintenance actions.”
“Motor current noise includes the sum of all of the mechanical load changes which refer back to the electric motor drive. The relative magnitude of the electric noise signal generated by a particular mechanical noise source will depend on its absolute magnitude and on its mechanical linkage to the motor which remains a fixed relationship for a given device. The motor itself acts as a transducer changing the mechanical load variations into electrical noise.”
At the Vibration Institute Annual Conference in Arlington, Texas, 2021, was the first time I’ve observed an almost equal number of topics presented related to ESA/MCSA as vibration and other technologies. There were several international papers including one from Egypt specifically on the identification of the number of bars broken in an induction motor – an application of a prior theory related to pole pass frequency amplitude – that was outstanding.
During the research into my present drafting of a new book on ESA I’ve also noted that the trend of one or two papers a year in IEEE has escalated to dozens per year and that since 2010 the number of engineering doctoral dissertations on MCSA, and a few properly titled ESA, has also escalated. Although they range in the low frequency to focus primarily on late stage faults and rotor bars, a few technologies have thrown their hats in the ring to use the term MCSA. However, a few power quality meters have claimed to be ESA/MCSA that are purely harmonic meters and do not present FFTs other than multiples of fundamental frequency required to properly analyze an electric machine and driven equipment.
Unfortunately, the lack of understanding of those attempting to enter the market, including little understanding of the history surrounding MCSA/ESA, continues to lead to the self-imposed limitations that the purpose of the technology is to evaluate the electric machine only, which is properly the transducer for the system – basically the same as suggesting that vibration analyzers are limited to testing the accelerometer. The true power of ESA is the ability to look well beyond the electric machine airgap magnetic field (the transducer) both upstream to the supply and downstream to the driven equipment and process.
The EMPATH system definitively conducts electrical and mechanical condition upstream and downstream from the point of test and provides detailed answers based on condition. Furthermore, it is not load or speed dependent for analysis and trending. The continuous monitoring system also provides an outstanding method for reviewing a complete system without mounting sensors on machines throughout the plant – the original proposition by ORNL.
We’ll cover more in this blog.