Journal Articles

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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.
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.
Analysis of Vibration characteristics and buckling behaviour of rotating Fiber-Graphene-Reinforced Composite Pre-twisted Shells
(Transactions of the Canadian Society for Mechanical Engineering, 2025-02-10) Battina, N Malleswararao
This study presents a novel approach to analyze the vibration and buckling behaviour of pre-twisted fiber-reinforced polymer composite shells reinforced with graphene inclusions. A key novelty lies in incorporating graphene's size-dependent mechanical properties are derived from nanoscopic empirical equations into the analysis. This allows for a more accurate prediction of the overall mechanical response of the composite, particularly at the nanoscale. The Halpin-Tsai model is employed to determine the equivalent elastic constants of the graphene-reinforced matrix, and a finite element formulation based on curved shear deformable shell theory is developed. The model's accuracy is validated against existing experimental or numerical results. Also, this study provides a comprehensive parametric analysis, investigating the influence of key factors such as graphene volume fraction, twist angle, aspect ratio, hub radius, and rotation speed on the vibration frequency and buckling load of the pre-twisted shells. These findings offer valuable insights for the design and optimization of lightweight and high-performance composite structures utilized in aerospace, automotive, and other engineering applications.
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.
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.
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.
Development of wire arc additive manufactured Cu-Si alloy: study of microstructure and wear behavior
(Springer Nature, 2023-02-21) Kazmi, Kashif Hasan; Sharma, Sumit K.; Das, Alok Kumar; Mandal, Amitava; Shukla, Amarish Kumar
Wire arc additive manufacturing (WAAM) is an approach to develop unique and sophisticated design products in comparison to other traditional techniques. In the present study, the components of Cu-Si alloy have been developed using WAAM with a robotic gas metal arc welding technique. In this process, the current and voltage varied from 70 to 110 A and 17 to 19 V, respectively. The effect of process parameters on the microstructure, hardness, and wear behavior of components have been studied in details. The results show that the surface roughness of the components reduced with the increase in current and voltage. The microstructure of the uppermost surface of WAAM components shows columnar followed by dendritic with equiaxed morphology. The process parameter also affects the mechanical and wear resistance properties of WAAM components. The results show that the microhardness (from 100.03 to 160.03 HV) and wear resistance of the Cu-Si alloy component increase with the increases in current and voltage.
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).
Enhancement of heat transfer of laminar flow of viscous oil through a circular tube having integral axial rib roughness and fitted with helical screw-tape inserts
(Begell House Inc., 2012-01-01) Saha, Sujoy
The experimental friction factor and Nusselt number data for laminar flow through a circular duct having integral axial rib roughness and fitted with helical screw-tape inserts have been presented. Predictive friction factor and Nusselt number correlations have also been presented. The thermohydraulic performance has been evaluated. The major findings of this experimental investigation are that the helical screw-tape inserts in combination with integral axial rib roughness perform better than the individual enhancement technique acting alone for laminar flow through a circular duct up to a certain value of the fin parameter.
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.
Estimation of paper conductivity from short duration polarisation–depolarisation current for diagnosis of power transformer
(The Institution of Engineering and Technology, 2019-07-12) Mishra, Deepak; Haque, Nasirul; Baral, Arijit; Chakravorti, Sivaji
The value of paper conductivity provides quantitative evaluation of transformer insulation health. However, proper identification of paper conductivity requires complete profile of polarisation–depolarisation current (PDC). PDC measurement being a time-consuming offline process generally takes several hours to complete. Furthermore, magnitude of PDC becomes very low at larger value of time, which makes it sensitive to changes in environmental conditions and field noise. Hence, accuracy of paper conductivity identification can be ensured by conducting multiple measurements. This in-turn prolongs shutdown time of equipment and become less advantageous to utilities. Here, a method is proposed which is capable of estimating paper conductivity using PDC data recorded for only 800 s. The proposed technique is tested on data collected from several real-life in-service transformers. In order to illustrate the accuracy of the proposed technique, paper conductivities (calculated from short duration PDC) were compared with those computed using PDC measured for 10,000 s.
Evaluation of response characteristics using sensitivity analysis and TLBO technique of powder mixed wire EDM of Ti6Al4V alloy
(Elsevier, 2023-11-29) Chakraborty, Sadananda
The development of Powder Mixed Wire Electric Discharge Machining (PMWEDM) aims to enhance both precise dimension and surface quality, making it a more efficient method for the cost-effective production of precise dies and tools compared to conventional Wire Electric Discharge Machining (WEDM. This approach effectively eliminates the need for secondary operations. The present study is focused on the parametric influence of surfactant with powder mixed WEDM process parameters during die corner cutting on Ti6Al4V material in the presence of surfactant and powder with dielectric. A sensitivity analysis was conducted to determine the significant influence of machining parameters and powder properties in conjunction with the dielectric. To empirically explore these variables, a central composite full factorial design based on response surface methodology was utilized. The design involved varying the pulse on-time (Ton) within the range of 30–90 µs, pulse off-time (Toff) within 3–11 µs, gap voltage (GV) within 40–80 V, and powder concentration (PC) within 2–10 g/L. The mathematical model was developed to predict the responses such as corner inaccuracy (CI) and surface roughness (SR) using RSM. The results conclude that the sensitiveness of powder concentration is highest. Apart from this, positive sensitiveness towards surface roughness is determined for three inputs: pulse on time, pulse off time, and powder concentration. In comparison, powder concentration shows positive sensitiveness towards corner inaccuracy. An artificial intelligence technique namely, Teaching learning-based optimization (TLBO) algorithm has been used to determine the best output. The minimum output for both responses, i.e. corner inaccuracy of 12982.67 µm2 and surface roughness of 1.199 µm, was obtained using TLBO technique. Further improvement for surface finish and corner accuracy in addition powder (3 g/L) with dielectric in WEDM process is found to be a value of 50.77% and 23.01%, respectively, compared with conventional WEDM process. SEM was employed to observe and analyze the topographical changes that occurred during powder mixed and without powder mixed in WEDM process.
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.
Improvement of lubrication and cooling in grinding
(Taylor & Francis, 2017-08-10) Chakraborty, Samik
The presence of air boundary layer around a grinding wheel impedes the proper entry of cutting fluid into grinding zone and thereby lubrication and cooling are hampered. It leads to the thermal damage to the workpiece and rapid wheel wear. This experimental work is aimed at increasing the lubrication and cooling effects in grinding by a novel method of using scraper board. The experiments are conducted, using the scraper board, to find the critical region where the air pressure is zero. The coolant jet has then impinged into the grinding zone which is maintained within the critical region. The requirement of specific energy, surface texture, and mechanical properties of the ground surface are analyzed and compared with the traditional grinding and the grinding at various positions of scraper board. Results show that the grinding ratio improved by 35.6and 119%, surface roughness decreased by 36 and 54.2%, while the requirement of specific energy is reduced by 50.8 and 57.3% when scraper board is positioned at the critical distance in comparison to the 57.5° position and no scraper board, respectively. The results indicate that the introduction of fluid in the present method can improve the process efficiency and the product quality effectively.
In Search of a Linkage Between Personality Traits and Interpersonal Behaviour During the COVID-19 Pandemic: A Case Study on Indian Marine Engineers Using Structural Equation Modelling
(Galenos Publishing House, 2024) Mitra, Toorban
Building and maintaining social and interpersonal relationships are crucial for mental health. However, due to the unique characteristics of jobs, building and maintaining such interpersonal relationships with colleagues as well as others may not be as similar to off-shore employees like shorebased ones. On the contrary, preference towards exhibiting interpersonal relationship behaviour is another area that needs attention in the maritime sector. Such preferences may be unique while individuals pass through uncertain situations like the coronavirus disease-2019 (COVID-19) pandemic. Against the backdrop of the COVID-19 pandemic, this study investigates the linkages between personality traits and interpersonal relationship behaviours among Indian marine engineers. Data was gathered through snowball sampling from 385 marine engineers utilising the Big Five Inventory and the Fundamental Interpersonal Relationship Orientation-Behavior™ framework after necessary adaptations of these instruments. Results show that conscientiousness is linked to expressed inclusion and wanted control. Extraversion is linked with all behaviours except wanted control, while agreeableness is associated with expressed control. Neuroticism shows linkages with wanted inclusion, expressed control, and wanted control. This study fills critical research gaps by examining the missing links between personality traits and interpersonal relationships in a high-stress environment like the maritime sector and that too during the COVID-19 pandemic. These insights emphasise the need for effective communication and teamwork in high-stress maritime environments.
Influence of temperature on interfacial charge of power transformer insulation
(The Institution of Engineering and Technology, 2019-06-21) Dutta, Saurabh; Mishra, Deepak; Haque, Nasirul; Pradhan, Arpan Kumar; Baral, Arijit; Chakravorti, Sivaji
One of the popular methods for insulation diagnosis is measurement and analysis of polarisation–depolarisation current (PDC). During normal operation, charges get confined at the interface of oil–paper insulation. A part of these accumulated charges get absorbed in depolarisation current and contribute to the overall PDC data. The process through which charges are released from their confinement is known as charge de-trapping, which is highly influenced by thermal energy content of the insulation and hence by measurement temperature. In the current work, an effort has been made to investigate the effect of measurement temperature on de-trapped charge. Two samples are prepared and analysed in the laboratory at different temperatures for this purpose. This is followed by analysis of data collected from several real-life power transformers. Related analysis presented here suggests that measurement temperature of the system plays an important role in determining the amount of de-trapped interfacial charge during PDC measurement.
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.
Linkage of job ranks and personality traits with augmented stress: a study on Indian marine engineers in the context of the COVID-19 pandemic
(International Maritime Health, 2023-05-04) Mitra, Toorban
Background: Marine engineering is a profession that affects a high level of physical and psychological stress. Such a high level of stress was further aggravated during the coronavirus disease 2019 (COVID-19) pandemic. On the other hand, personality traits and perceived stress are linked with each other, while job ranks also influence stress levels among employees. However, very few clinical studies are available on this mechanism in seafarers. This study explores the hidden area through the collection of cross-sectional data. Materials and methods: Big Five personality traits instrument, along with a stress augmentation questionnaire, were administered among 280 Indian marine engineers across job ranks who have sailed prior to and during the COVID-19 pandemic. The collected data were analysed using Kruskal-Wallis test and structural equation modelling. Results and Conclusions: The analysis reveals significant differences among Indian marine engineers across their job ranks towards their perception of augmented stress levels. It also indicates that, except for extraversion, personality traits have linkages with levels of augmented stress among Indian marine engineers during the pandemic.
Linking Logistics Service Quality, Customer Satisfaction and Customer Loyalty: An Indian Perspective
(MANTHAN: Journal of Commerce and Management, 2025-06-15) Mitra, Toorban
In e-commerce, the customers and the sellers are distant and can’t interact face to face regarding their likings and dislikings about the product, delivery quality, buying experience, etc. This results in an absolute need for e-commerce companies to measure customer satisfaction and loyalty to grow and sustain performance in the competitive business world. The available pieces of literature fail to sufficiently explain the relationship between e-commerce logistics service quality, customer satisfaction and customer loyalty, especially in the Indian context. This study aims to explain the same through a Structural Equation Model encompassing different factors connected with e-commerce logistic service quality. The finding shows the significant effects of logistics service quality factors like order accuracy and order discrepancy handling on customer satisfaction. This study also indicates a significant impact of customer satisfaction on customer loyalty.