Sensing the Thermal Aging of Rotating Machine Insulation Using a Unique Parameter Extracted From Dielectric Spectroscopy Measurement

Accurate sensing of stator bar insulation condition is vital for the reliable operation of rotating machines, i.e., large ac generators and motors. In this context, dielectric response analysis is one of the popular techniques widely used for condition assessment of stator bar insulation. However, extraction of meaningful insulation-sensitive parameters from dielectric spectroscopy measurement in the case of stator bar insulation is a challenging task due to their complex nature of aging. Considering the aforesaid fact, in the present work, an attempt has been made to accurately estimate the extent of thermal aging in stator bar insulation through polarization-depolarization current (PDC) measurements. From the observed current response, it was observed that the lower time constants of depolarization current are sensitive to thermal aging. The recorded time domain dielectric response was subsequently converted to frequency domain using Hamon approximation. From the frequency domain response, a new parameter, i.e., mid value frequency has been proposed as an aging-sensitive parameter. To understand the effect of temperature on the developed methodology, the PDC measurements were conducted at two different temperatures, i.e., 30 degrees C and 50 degrees C. Experimental investigations revealed that the proposed mid value frequency parameter can be used to sense the thermal aging of stator bar insulation.