Electrical windings shorts due to surges and transients tend to occur towards the motor lead connections in the winding. Degradation due to winding contamination, core problems or other defects will most often occur well into the motor windings. Motor circuit analysis is one of the technologies used to detect and trend degradation of insulation effecting the first few turns in the winding and is one of the few modern technologies that can detect and trend winding shorts deep into the motor windings (including DC fields), as well as across air gaps into wound rotor motors and synchronous fields that are missed with older high voltage technologies.
(References: EPRI AEMPM Study, May 2003; 2003 IEEE Electrical Insulation Conference Papers – “Inspection/Test Impact on Maintenance of Generators,” Clyde Maughan, PE; “Which Road Will You Take,” Dave Humphrey, Allison Transmission; “Estimating Motor Life Using Motor Circuit Analysis Predictive Measurements,” Howard W Penrose, Ph.D.; and, “Risk in Surge Testing of Turn Insulation in Windings of Rotating Machines,” Bal Gupta, AOK Technologies).
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