A Novel Method to Predict Severity of Thermal Aging and Degree of Polymerization for Reliable Diagnosis of Dry-Type Insulation

The effect of thermal aging on Nomex-paper-based vacuum pressure impregnation (VPI) insulation is reported in this article. The frequency-dependent dielectric loss of Nomex-paper-based VPI dry insulation is affected after significant thermal aging. This variation in dielectric loss of the insulation maintains a good correlation with the duration of thermal aging. A new parameter sensitive to the severity of thermal aging is also introduced. To identify the parameter, the excitation voltage waveform and the corresponding insulation response at a given frequency are required. Determining the parameter does not require denoising of recorded waveforms, reducing the overall computational burden. Based on the newly introduced parameter, a cost-effective method is proposed to predict the dielectric loss and degree of polymerization (DP) in a thermally aged VPI-type dry insulation. The proposed method employs the intermediate frequency range and hence does not require time-consuming low-frequency measurements.