Browsing by Author "Mishra, D."

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A fast and effective method for assessing insulation condition based on time domain spectroscopy data /
(IEEE, 2022-01-21) Mishra, D.
A novel methodology is suggested to predict the condition of Oil-paper Insulation (OPI), popularly used in power transformers. The proposed method is based on transient measurement of polarization current data from laboratory samples. Initially, complete polarization current profile is used to formulate an insulation model and then find the rise time of the system. After that, a relation is provided between rise time and measured performance parameters like moisture content(%pm). Further, another relation is suggested between rise time and the initial decay rate of recorded data. Hence, just by knowing the value of the initial decay rate, the value of crucial parameters like %pm can be evaluated using the proposed relationship.
A novel method to predict severity of thermal aging and degree of polymerization for reliable diagnosis of dry-type insulation /
(IEEE, 2022-01-01) Mishra, D.
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.
Reliable Assessment of Oil-Paper Insulation Used in Power Transformer Using Concise Dielectric Response Measurement
(IEEE, 2023-03-26) Mishra, D.
Oil-impregnated paper is usually the preferred choice of insulation in power transformers. The working life of any transformer depends on its insulation condition. The paper conductivity, moisture content and dissipation factor of solid insulation are a few crucial parameters used to determine the insulation condition. The reliable estimation of such parameters for diagnosis of solid insulation requires a complete profile of polarization current which is time-consuming. Hence, utilities always prefer non-invasive and rapid techniques to predict insulation conditions and minimize shutdown time. The proposed technique is based on a short-duration polarization current data. The present manuscript suggested a method that uses the initial decay rate of recorded polarization current data to predict various performance parameters related to paper insulation. In order to show the effectiveness of the proposed method, the analysis is performed on the data measured from various in-situ transformers.