Effects of Partial Discharge Echo in Motor-Insulation Systems of Transportation Power Devices

One of the mostly applied assessments of electrical insulation’s condition is based on the measurement of partial discharges (PDs). In addition to conventional PD measurements on motor insulation, a novel approach called PD echo (PDE) is described in this article. This can be applied to various excitation-voltage waveshapes [such as sinusoidal, pulse wave modulated (PWM), etc.] that form chopped sequences. The PDE methodology may extract information about the condition of the insulation—especially depicting its surface effects. Since it operates in the voltageless part of a chopped sequence, it is more immune to excitation-driven disturbances. This article presents the results that were obtained on twisted pair (TP) specimens that were the representative of electrical-machine insulation that is untreated and degraded by hot-air streaming. A comparison of the experimental results based on the PDE time constant revealed distinct echo patterns (especially the accelerated decay of the PDE pulse magnitude) in cases of deteriorated TP samples. The echo discharges were attributed to the mechanisms that occurred on the enameled wire surface in the air gap between the turns. The aim of this article was to provide quantitative insight into the winding interturn insulation in the form of PDE attributes. It also provides an attempt to extract additional insulation degradation-related information from phase-resolved PD images. The PDE phenomenon may open new opportunities for evaluating electrical insulation and providing directions toward potential diagnostic applications in motors.