Journal Articles

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Author: search.filters.author.Mishra, DeepakSubject: search.filters.subject.Power transformer insulation

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    Prediction of insulation sensitive parameters of power transformer using detrended fluctuation analysis based method
    (IEEE, 2022-06) Dutta, Saurabh; Dey, Jagriti; Mishra, Deepak; Baral, Arijit; Chakravorti, Sivaji
    Utilities prefer to perform a condition-based assessment of power transformer insulation in the least possible shutdown time. It is essential to estimate the values of various insulation condition sensitive performance parameters with higher accuracy. In the present work, a technique for the estimation of performance parameters, moisture content of paper, dissipation factor of the entire oil-paper insulation, paper conductivity, and activation energy is proposed. The evaluation of these parameters using reported techniques requires complete measurement of polarization and depolarization current profile, which requires around 20000 s of measurement time. The present method uses a forecasted polarization current profile obtained from 600 s of measured polarization current data. Detrended Fluctuation Analysis is applied to the forecasted polarization current data obtained from various in-service power transformers to obtain a suitable parameter. It is shown that this parameter maintains well-defined relationships with parameters; moisture content of paper, dissipation factor of oil-paper insulation, paper conductivity, and activation energy. The proposed technique is beneficial for utilities as it eliminates the requirement of measuring depolarization current and return voltage measurement for estimating activation energy.
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    Estimation of de-trapped charge for diagnosis of transformer insulation using short-duration polarisation current employing detrended fluctuation analysis
    (The Institution of Engineering and Technology, 2020-10-01) Dutta, Saurabh; Mishra, Deepak; Baral, Arijit; Chakravorti, Sivaji
    Researchers have shown that the value of charge carriers, de-trapped from the oil–paper interface of power transformer insulation, is useful in carrying out the diagnosis. However, the evaluation of the de-trapped charge requires the analysis of polarisation–depolarisation currents. Being an off-line time-consuming process, the measurement and analysis of polarisation and depolarisation current (PDC) data are not practically advantageous. The study presents a detrended fluctuation analysis-based technique to estimate the magnitude of normalised de-trapped charge using the polarisation current measured for a short duration. Using the proposed technique, the requirement of measuring the complete PDC data, for diagnosis purposes, can be eliminated. Further, the technique also eliminates the requirement of depolarisation current which in turn facilitates a reduction in equipment shutdown time. The applicability of the proposed technique is tested on the data obtained from several real-life power transformers.
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    Investigation related to performance parameter estimation of power transformer insulation using interfacial charge
    (IEEE, 2020-08-04) Mishra, Deepak; Verma, R.; Baral, Arijit; Chakravorti, Sivaji
    In the present paper, geometric capacitance is used as a normalization factor instead of DC insulation resistance. The results suggest geometric capacitance is more efficient in reducing geometry effect on the DC-trapped charge. The influence of normalizing deep charge using DC insulation resistance and geometric capacitance and their effect on estimating various insulation sensitive parameters are compared in this paper.
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    Reduction of time domain insulation response measurement duration for fast and effective diagnosis of power transformer
    (IEEE, 2018-10-05) Mishra, Deepak; Pradhan, A. K.; Baral, Arijit; Chakravorti, Sivaji
    Aging sensitive parameters like dissipation factor, oil and paper conductivity and paper moisture can be estimated from insulation model parameterized using polarization current to assess the condition of transformer insulation. However, polarization current measurement is a time-consuming offline technique. During measurement, variation of environmental conditions (especially temperature) affects the monotonically decreasing nature of recorded data. Analysis of such affected data lead to incorrect conclusion regarding insulation condition. Power transformer being a crucial equipment, utility prefer to reduce its shut down time to minimum amount. In this paper a technique is discussed through which the polarization current measurement time can be reduced significantly. Several transformer data are used for verification of developed method. Presented results show that measurement data corresponding to only 10 minutes is sufficient to estimate the remaining data through the application of discussed method.