Browsing by Author "Mishra, Deepak"

Now showing 1 - 20 of 39

A fast and effective method for assessing insulation condition based on time domain spectroscopy data
(IEEE, 2022-01-21) Mishra, Deepak; Pandey, Sandeep; Baral, Arijit
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 method to predict degree of polymerization value of oil-paper insulation using interfacial charge
(IEEE, 2029-12-20) Singh, Vijeta; Mishra, Deepak; Baral, Arijit; Chakravorti, Sivaji
Analysis based on Degree of Polymerization (DP) value is assumed to provide reliable regarding insulation condition. However, due to the invasive nature of testing, DP value based-analysis is not feasible in practical cases as it requires a paper sample from the in-service unit. Here, an attempt is made to develop a methodology to predict DP value based on non-invasive testing of oil-paper insulation. In this paper, it is found that DP value maintains a well-known relation with interfacial charge (estimated using Polarization Depolarization Current data) as both these parameters are related to the cellulosic condition. The proposed method successfully applied on various laboratory prepared samples containing different moisture content.
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.
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.
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.
A novel method to predict severity of thermal aging and degree of polymerization for reliable diagnosis of dry-type insulation
(IEEE, 2022-04) Mishra, Shalini; Baral, Arijit; Mishra, Deepak; Chakravorti, Sivaji
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.
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.
Analysis of thermal behaviour of a microprocessor using simulation and experiment
(Indian Maritime University, Kolkata Campus, 2023-07) M, Naveen; Das, Nachiketa; Mondal, Sabyasachi; Mishra, Deepak
Thermal management of microprocessor is considered as an important factor in computer appliances. Several analysis and methods have been discussed regarding the scope of heat sink and microprocessor. The shape, size, material of heat sink and velocity and direction of air from the CPU fan plays an important role for thermal management of microprocessor while running the CPU. In this research a numerical and experimental analysis is done for the heat sink and microprocessor in order to understand the thermal response. Numerical analysis is done using software ANSYS 2023 STUDENT R1 version and an infrared thermographic study has been done as part of experimental analysis on the CPU model HP COMPAQ ELITE 8300 SFF. Microprocessor used in this experiment is Intel core i7 chips and exact dimension of CPU chassis have been taken for the numerical part. The thermal images are captured with Fluke Ti 450 camera. The device offers high spectral resolution while taking the thermal image. Analysis shows there are small deviations between the numerical and experimental part. Using nanofluids, a method is also been discussed for thermal management of microprocessor as a substitute for heat sink, for future scope of the project.
Assessment of interfacial charge accumulation in oil-paper interface in transformer insulation from polarization-depolarization current measurements
(IEEE, 2017-06-03) Mishra, Deepak; Haque, Nasirul; Baral, Arijit; Chakravorti, Sivaji
Accumulation of interfacial space charge in oil-paper interface is a critical issue in insulation diagnostics of transformers. This interfacial charge mainly accumulates due to the conductivity difference of oil and paper. Accumulation of interfacial charge leads to localized field enhancement, which further leads to partial discharges and acceleration in the aging of insulation. Therefore, from the point of view of transformer insulation diagnostics, assessment of interfacial charge is very important. However, it is not easy to estimate interfacial space charge behavior from the transformer diagnostics methods currently in use. In case of Polarization-Depolarization Current (PDC) measurement, a well known method for transformer condition monitoring, the effect of interfacial charge is reflected in the non-linearity of current response during polarization and de-polarization. During de-polarization process, a part of the interfacial charge accumulated during polarization period is absorbed by the electrodes producing a current, which is difficult to separate using conventional linear dielectric theory. In this paper, an attempt has been made to separate this current component from de-polarization current through considering charge de-trapping mechanism. Terming this current component as de-trapping current, its relationship with other parameters of transformer insulation is discussed. The developed methodology has been applied on several practical transformers. It was observed that the time constant of de-trapping current is related to the paper conductivity, oil conductivity, dissipation factor and age of the insulation.
Compensating the effect of residual dipole energy on dielectric response for effective diagnosis of power transformer insulation
(The Institution of Engineering and Technology, 2017-11-28) Mishra, Deepak; Baral, Arijit; Chakravorti, Sivaji
Analysis of relaxation current is a widely accepted method for diagnosis of power transformer insulation. The accuracy of such diagnostic tool is dependent on insulation model parameters which are formulated using relaxation current. This implies that the accuracy and hence the reliability of existing insulation diagnosis methods indirectly depends on the accuracy of the recorded polarisation depolarisation current. Sometimes during field measurement relaxation current measurement equipment fails to record proper current, even after application of dc charging voltage. As per utilities, this primarily happens due to improper/loose connections (this cannot be avoided entirely due to the involvement of human factors) and such situation is usually followed by checking and rectifying improper connection. The analysis presented in this study shows that the polarisation current recorded immediately after rectifying the correction is inaccurate and leads to the erroneous diagnosis. Furthermore, it is observed that in these cases, the measured and calculated (using insulation model) values of performance parameters like dissipation factor, polarisation index, and paper-moisture differ by a large extent. This work is aimed at removing the effect of this residual dipole energy introduced during the improper connection phase.
Compensating the impact of residual energy on time domain dielectric response using time-varying model /
(IEEE, 2025-01-01) Mishra, Deepak
Compensating the impact of residual energy on time domain dielectric response using time-varying model /
(IEEE, 2025-01-01) Mishra, Deepak
Condition assessment of power transformer insulation using short-duration time-domain dielectric spectroscopy measurement data
(IEEE, 2019-10-14) Mishra, Deepak; Baral, Arijit; Haque, Nasirul; Chakravorti
Utilities prefer noninvasive methods for assessing the condition of power transformer insulation. Analysis of polarization-depolarization current (PDC) is one such popular method. One such analysis involves the estimation of trapped charge released from the interfacial region of oil-paper insulation. The literature shows that such charges can be reliably used for the diagnosis of transformer insulation. However, such analysis requires a complete profile of PDC. PDC measurement (an offline technique) takes a large amount of time (several hours) to complete. The magnitude of PDC data for a larger value of time is also sensitive to changes in environmental conditions and field noise as its magnitude is low. Hence, a reliable estimation of detrapped charge may require numerous PDC measurements. This situation is not convenient for utilities as it prolongs shut down time. In this article, a method has been proposed which is capable of estimating detrapping charge using PDC data measured for a short span of time. The proposed method is tested on data collected from several real-life in-service transformers.
Condition Monitoring of Lubricating Oil used in Marine Vessels
(Indian Maritime University, Kolkata Campus, 2025) Kumar, Ajay; Mishra, Deepak
The reliability and efficiency of marine propulsion systems heavily depend on the condition of lubricating oil, which serves as both a protective and functional medium for critical engine components. Over time, lubricating oil undergoes degradation due to thermal stress, oxidative reactions, contamination, and prolonged usage. Traditional oil condition monitoring techniques primarily focus on viscosity changes, spectroscopic analysis, and chemical composition assessments. However, in recent years, polarization current analysis has emerged as a promising diagnostic tool for evaluating the dielectric integrity and degradation behaviour of lubricating oils in marine applications. This study explores the application of polarization current measurement as an effective method for monitoring the deterioration of lubricating oil used in marine vessels. The research involves subjecting lubricating oil samples to controlled thermal aging at varying temperatures (40°C, 50°C, 60°C) over extended periods to simulate real operational stress conditions. By applying a 500 V DC voltage using an insulation tester, the resulting polarization current behaviour is recorded and analyse providing valuable insights into molecular breakdown and insulation capacity loss. Experimental findings indicate that as the thermal aging process progresses, the polarization current exhibits increasing magnitudes, signifying a reduction in the resistivity of the lubricating oil. This behaviour aligns with the formation of conductive degradation byproducts such as free radicals, oxidation compounds and polar contaminants, which alter the dielectric properties of the oil. Notably, samples exposed to higher temperatures (50°C and above) demonstrate significant fluctuations in polarization current, suggesting a higher degree of dielectric instability and lubricant deterioration.
De-noising of time-domain spectroscopy data for reliable assessment of power transformer insulation
(The Institution of Engineering and Technology, 2020-04-24) Mishra, Deepak; Baral, Arijit; Chakravorti, Sivaji
Polarisation–depolarisation current (PDC) measurement and its analysis is a popular technique for assessing the condition of transformer insulation. Owing to the low magnitude of PDC, recording noise-free PDC data from in-situ power transformers is a challenge. Once the relaxation current data get affected by noise, it becomes difficult to formulate insulation model (as recorded data loses its characteristic shape). This further makes the data difficult to analyse and predict insulation condition. In this study, two de-noising techniques are discussed (one is based on Wavelet Transform while the other is based on Stockwell Transform) for eliminating low-frequency non-stationary noise from recorded PDC data. Comparison between these two techniques suggests de-noising using Stockwell Transform is advantageous over wavelet analysis. The proposed methodology is first tested on data recorded from the sample prepared in the laboratory and then on data measured from real-life in-service power transformer.
Effect of charge accumulated at oil–paper interface on parameters considered for power transformer insulation diagnosis
(The Institution of Engineering and Technology, 2018-01-02) Mishra, Deepak; Haque, Nasirul; Baral, Arijit; Chakravorti, Sivaji
Polarisation and depolarisation current (PDC) measurement and analysis is one of the popular tools for effective diagnosis of power transformer insulation. Normally, it is assumed that polarisation current is the combination of the current due to dipole movement and conduction current. Similarly, the depolarisation current is only due to the relaxation of dipoles. However, it is found that after eliminating the effect of dc conduction from polarisation current the resulting current is not similar to that of measured depolarisation current. This shows some non-linearity is present in the system. This non-linearity occurs due to movement of trapped charge that resides in the interfacial region of oil–paper insulation. This study shows the effect of de-trapping charge on various performance parameters that are used for insulation diagnosis like paper moisture and dielectric dissipation factor (tanδ).
Effect of charge accumulated at oil-paper interface on zero of transfer function formulated using classical debye model parameters
(IEEE, 2017-11) Mishra, Deepak; Pradhan, Arpan Kumar; Baral, Arijit; Haque, Nasirul; Chakravorti, Sivaji
PDC measurement and analysis is one of widely used tool for reliable diagnosis of power transformer insulation. In different reported methods of analysis it is considered that polarization current is composed of the current due to dipole movement and conduction current. Similarly the depolarization current is assumed to be composed of relaxation of dipoles. However when the dc conduction effect is removed from polarization current it is found the resulting current is not similar to the measured depolarization current. This deviation in both the currents show the presence of nonlinearity in the system. This nonlinearity arises due to migration of trapped charges that reside at the interfacial region of oil-paper insulation. The present paper shows the effect of such free charge on some important performance parameters like paper moisture and zero of Transfer Function of Classical Debye Model.
Effect of interfacial charge on parameters considered for insulation diagnosis of power transformer
(IEEE, 2017-12-02) Mishra, Deepak; Baral, Arijit; Pradhan, Arpan Kumar; Haque, Nasirul; Chakravorti, Sivaji
Out of various analysis methods available Polarization Depolarization Current (PDC) measurement is extensively used for monitoring of oil-paper insulation health. In such case, Classical Debye Model (CDM) is used for analysis of recorded PDC data. CDM has limited capacity to simulate the effect of interfacial charge. Due to this interfacial charge, nonlinearity arises in the system which adversely affects the insulation. Conductivity difference between oil and paper is the main reason behind this interfacial charge which creates nonlinearity in system. In the present work, the effect of interfacial charge is analyzed on some of the performance parameters used for diagnosis of insulation like peak value of return voltage spectrum and paper conductivity.
Effect of measurement temperature of insulation poles used for assessment of oil-paper insulation
(IEEE, 2018-12-07) Verma, R.; Mishra, Deepak; Baral, Arijit; Chakravorti, Sivaji
Analysis of Polarization-depolarization current (PDC) data is a popular technique used for assessing condition of oil-paper insulation. Oil-paper insulation deteriorates with aging during the operational life of the power equipment. In order to get information regarding the insulation condition; different performance parameters are used which can be estimated from PDC data. These parameters include paper moisture (%pm), Dissipation factor (%tanδ) and paper conductivity (σ paper ). In addition to these parameters, insulation poles can also be used for insulation diagnosis. Recently, it has gained popularity in field of insulation diagnosis as it does not depend on physical geometry of insulation. In this paper, the effect of measurement temperature on insulation poles has been analysed. Also, an attempt has been made to establish a relation between insulation poles and other insulation sensitive parameters such as %pm, σ paper and %tan δ.
Effect of measurement temperature on interfacial charge freed from deep traps located at the interface of oil-paper insulation
(IEEE, 2018-12-07) Dey, Debangshu; Sarkar, A.; Pal, Sayantan; Kumar, A.; Mishra, Deepak; Baral, Arijit; Haque, Nasirul; Chakravorti, Sivaji
Accumulation of interfacial charge creates local field distortion during insulation response measurement. Furthermore, such localized field enhancement affects the interaction between polar compounds present within oil-paper insulation and in turn affects its aging process. By getting sufficient trap energy (normally by thermal oscillation) these trapped charges dislocate from their locations and contribute in depolarization current. These interfacial charges include charges dislocated from shallow and deep sites at interfacial region. The charge residing at deep locations takes more time to dislodge themselves compared to charge residing at shallow sites. As dipole present in cellulose has large relaxation time, there might be some relation between deep charge and paper insulation sensitive parameters. In this work, effects of temperature on deep traps are analyzed. Results reported in this paper shows that magnitude of charge freed from deep locations maintains a correlation with measurement temperature and paper conductivity.