Research Publications

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Author: search.filters.author.Mishra, Deepak

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Now showing 1 - 10 of 36
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    A time-efficient and innovative method to determine the dp value of power transformer insulation /
    (IEEE, 2024-11-22) Mishra, Deepak; Parveen, Shabnam
    The DP value is a robust and reliable parameter for estimating the state of cellulose-based insulation in power transformers. However, its practical application is limited due to the invasive nature of testing. Hence, a methodology is reported in the present work to predict DP value using Polarization Depolarization recorded for a short duration. Reported results later in this paper suggest that the initial rate of measured polarization current can be used to forecast the DP value. The suggested method was successfully tested on several specimens (having different amounts of moisture percentages) prepared in the laboratory.
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    Reliable sensing of insulation sensitive performance parameters using time domain-based measurement at different temperatures /
    (IEEE, 2023-09-05) Mishra, Deepak; Parveen, Shabnam
    The amount of moisture and conductivity are the two crucial parameters that signify the condition of oil–paper insulation (OPI). The reliable sensing of moisture and conductivity of solid insulation requires a fully measured profile of polarization–depolarization current (PDC) data, which is monotonically decaying in nature. The measured PDC data are significantly influenced by measuring temperature. Hence, sensed values of insulation sensitive parameters may provide ambiguous information related to insulation state due to temperature variation. In the present work, an efficient method is suggested, which can be used for sensing crucial performance parameters (such as paper moisture and paper conductivity) using the dielectric response measured at various temperatures. The proposed methodology provides an easy way to sense paper moisture and paper conductivity that will be independent of the measured temperature. In order to test the capability of suggested method, the analysis is performed on the data collected from in-service power transformer insulation. Research findings show that the proposed technique can be applied to data collected from in-service power transformers for sensing insulation condition-sensitive parameters.
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    A nonlinear regression-based approach to assess transformer insulation condition using dielectric response recorded for short duration /
    (IEEE, 2023-01-01) Mishra, Deepak
    Analysis of polarization current data is generally done to assess power transformer insulation condition. Due to considerable measurement time and low magnitude, noise and other environmental factors often affect the recorded dielectric response data. The influence of these factors cannot be avoided during field measurement. Once the recorded data are affected by external factors, it becomes difficult to analyze the data. Available literature has reported some techniques to reduce the testing time. However, these reported methods are ineffective in addressing the practical issues experienced during field measurement. This present article proposes a nonlinear regression-based approach to reduce insulation response measurement time significantly. Data collected from various in situ transformers have been analyzed to test the effectiveness of the proposed method.
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    Importance of depolarization current in the diagnosis of oil-paper insulation of power transformer /
    (IEEE, 2023-01-01) Mishra, Deepak
    Recently, Polarization Depolarization current (PDC) measurement is widely accepted time domain spectroscopy-based method for assessing the insulation condition. Various performance parameters like Dissipation factor (%tan δ ), Paper Moisture (%pm), Dielectric Adsorption Ratio (DAR), Polarization index (PI) etc. can be estimated by analyzing the PDC data. During field measurement various factors influences the recorded PDC data. As per existing literature, presence of low frequency noise, effect of temperature variation and influence of residual charge are common during field measurement. These factors significantly affect recorded polarization current and hence estimated performance parameters. Hence, analysis using recorded polarization current data may provide misleading information regarding insulation condition. Under such practical situation where polarization current is affected by above mentioned factors that generally observed during field measurement, depolarization current should be used for analysis of insulation condition. The depolarization current does not influence by such external factors. The present work shows the importance of depolarization current where polarization current is influenced by external low frequency noise and residual charge. The analysis firstly applied on sample prepared in the laboratory and then on data collected from real life in-situ transformers. The results obtained from the analysis shows that the data obtained from depolarization current is more reliable.
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    Sensorless field oriented control of ac induction motor using pi, pd & pid controllers /
    (IEEE, 2022-11-20) Antony, Nikhil John; Mishra, Deepak; Parveen, Shabnam
    With the Field-Oriented Control (FOC) vector approach, the control of the induction motor behaves similar to that of a separately excited dc motor. The torque and flux components in the d-q rotating reference frame can be independently controlled with the help of unit vectors. The main focus of the present work is to show the effective utilization and feasibility of field-oriented control of AC induction motors using PI, PD, and PID controllers without using any physical sensors and using observers. The speed, torque, and position in this scheme are estimated, analyzed, and simulated with the help of a motor control block-set in MATLAB/Simulink for a (10HP, squirrel cage induction motor) to a VSI using the SVPWM for effective modulation.
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    A novel and fast approach for sensing activation energy for reliable health assessment of power transformer /
    (IEEE, 2022-09-13) Mishra, Deepak
    Activation energy represents the average rate of interaction between aging by-products and cellulose. Activation energy is a crucial parameter that can be used to identify the remaining life of insulation in high voltage (HV) equipment. Existing noninvasive methods take a significantly longer time to sense activation energy for given insulation. This is primarily due to the volume of data required for such analysis, which generally takes significant time to measure. This work reports a noninvasive and effective approach to predict activation energy of oil–paper insulation using a dielectric response that is recorded for a very short span of time. The proposed method requires polarization current data sensed for a few seconds (15–20 s) to operate. The initial decay rate (DR) of the sensed data is found to be sensitive to the activation energy. This feature of the initial DR is utilized to sense the value of activation energy within a short duration. The proposed technique utilizes the current sensor (present within an electrometer) more efficiently. This facilitates the measurement of a highly accurate polarization profile and ensures reliable activation energy estimation. The proposed methodology has been successfully applied to data collected from a few real-life transformers. Reported results show that the suggested method provides satisfactory results with good accuracy.
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    Prediction of insulation sensitive parameters of power transformer using detrended fluctuation analysis based method /
    (IEEE, 2021-08-04) Mishra, Deepak
    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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    Reliable Assessment of Oil-Paper Insulation Used in Power Transformer Using Concise Dielectric Response Measurement
    (IEEE, 2023-03-24) Mishra, Deepak
    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 the diagnosis of solid insulation requires a complete profile of polarization current, which is time-consuming. Hence, utilities always prefer noninvasive and rapid techniques to predict insulation conditions and minimize shutdown time. The proposed technique is based on short-duration polarization current data. The present manuscript suggested a method that uses the initial decay rate (IDR) 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.