Journal Articles

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Start date: 2020Subject: search.filters.subject.Power transformer

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Now showing 1 - 5 of 5
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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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    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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    Importance of depolarization current in the diagnosis of oil-paper insulation of power transformer
    (IEEE, 2023-06-07) Kumar, Alok; Mishra, Deepak; Baral, Arijit
    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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    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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    A novel and fast approach for sensing activation energy for reliable health assessment of power transformer
    (IEEE, 2022-09-13) Mishra, Deepak; Baral, Arijit; Chakravorti, Sivaji
    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.