Browsing by Author "Punekar, G.S."

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A comparative study of field computation methods: Charge simulation method and method of moments
(Institute of Electrical and Electronics Engineers Inc., 2018) Devarajan, D.; Punekar, G.S.
Numerical methods plays a vital role in computation of electric fields for the design of high voltage systems. For electric fields studies related to high voltage applications, the preferred numerical methods are charge simulation method (CSM) and method of moments (MoM). In the present study, the performance of these two numerical methods are analyzed by simulating sphere-plane gap arrangement (which has an analytical solution to compare). Through this example, CSM is found to be more accurate compared to MoM. Further, the effect of change in sphere-plane gap geometry on the electric field computed is reported and discussed. Â© 2018 IEEE.
A Search for Suitable Mother Wavelet in Discrete Wavelet Transform Based Analysis of Acoustic Emission Partial Discharge Signals
(University of Kragujevac Faculty of Technical Sciences in Cacak, 2024) Vippala, S.R.; Punekar, G.S.; Chemmangat, K.; Tangella, B.
Signal processing helps monitor the condition of power equipment. Partial discharge (PD) signals used in condition-based maintenance give crucial information in the diagnosis of degradation of insulation. The acoustic emission technique (AET) is one of the most widely used techniques in PD signal analysis due to its inherent advantages. Analyzing acoustic emission partial discharge (AEPD) signals in the wavelet-domain provides critical insights into the location and type of the sources of PD. Selection of the most suitable mother wavelet in applying discrete wavelet transform (DWT) on AEPD signals is important as it will directly impact the outcome. For this selection, 36 wavelets belonging to the Daubechies, Symlets, Coiflets, and Bi-orthogonal families are investigated. For this purpose, five experimentally collected AEPD test signals are used. The selection is based on the “accuracy of wavelet decomposition results” in this work, probably for the first time. One mother wavelet from each family is individually shortlisted for all three performances, namely (a) reconstruction, (b) denoising, and (c) compression, by computing and comparing their commonly used metrics. Further, based on percentage energy criteria, the most suitable mother wavelets are identified as coif3, coif4, and coif5, respectively, for the three performances. © 2024, University of Kragujevac Faculty of Technical Sciences in Cacak. All rights reserved.
Acoustic emission signal analysis of On-Load Tap Changer (OLTC)
(2013) Shanker, T.B.; Nagamani, H.N.; Punekar, G.S.
On-Load Tap Changer (OLTC) forms a vital part of a transformer. Acoustic emission signals have been acquired from OLTC of 230 kV 3 phase power transformers for signature analysis. The acoustic emission signals have been analyzed to characterize the signals with reference to energy and frequency using Discrete Wavelet Transform. Case studies of AE signals obtained from healthy OLTCs have been presented in the paper for probable consideration as reference signals for healthy and normally operating OLTCs. � 2013 IEEE.
Acoustic emission signal analysis of On-Load Tap Changer (OLTC)
(IEEE Computer Society, 2013) Shanker, T.B.; Nagamani, H.N.; Punekar, G.S.
On-Load Tap Changer (OLTC) forms a vital part of a transformer. Acoustic emission signals have been acquired from OLTC of 230 kV 3 phase power transformers for signature analysis. The acoustic emission signals have been analyzed to characterize the signals with reference to energy and frequency using Discrete Wavelet Transform. Case studies of AE signals obtained from healthy OLTCs have been presented in the paper for probable consideration as reference signals for healthy and normally operating OLTCs. Â© 2013 IEEE.
Affect of height of HV sphere above the ground in HV measuring sphere gap
(2007) Kishore, N.K.; Punekar, G.S.; Shastry, H.S.Y.
Sphere gaps are the standard gaps used for measurement of peak value of high voltages. Standards specify a minimum and maximum height of the spheres above the horizontal ground plane is specified as a function of its diameter 'D'. This height 'A' of the sparking point has to be within limits according to the guidelines of these standards. In the present work, both simulation and experimental results to see the affect of the height 'A' on breakdown voltage is presented. These results are presented for the worst case deviation from the guidelines by placing the ground sphere on the ground plane and the upper sphere above the ground sphere with gap separation S?D/2 units (considering commonly used vertical arrangement). The distance of the nearest grounded object is kept 'B' units away as specified in the standards. In continuation, in order to study the nearby grounded object a hemi-spherically tipped rod (needle) is brought near, radially, towards the gap axis. This needle is placed vertically on the ground plane maintained at ground potential. Experimental results are obtained with the radial distance of the needle to the gap axis as the parameter. The results are reported for both positive and negative polarity voltages. The simulation is carried out by developing charge simulation model (CSM). Some of the results (even with out the grounded needle in the vicinity) indicate that variation in 'A' modifies the surface electric fields of both the spheres. As the height 'A' is decreased the surface field intensity of upper sphere increases and that of the lower sphere decreases. The correlation between the experimental breakdown results and the simulation results is attempted. These results may help, the users, who have some constraints in actual practice in the laboratory to strictly follow the guidelines given in the standards. �2007 IEEE.
Affect of height of HV sphere above the ground in HV measuring sphere gap
(2007) Kishore, N.K.; Punekar, G.S.; Shastry, H.S.Y.
Sphere gaps are the standard gaps used for measurement of peak value of high voltages. Standards specify a minimum and maximum height of the spheres above the horizontal ground plane is specified as a function of its diameter 'D'. This height 'A' of the sparking point has to be within limits according to the guidelines of these standards. In the present work, both simulation and experimental results to see the affect of the height 'A' on breakdown voltage is presented. These results are presented for the worst case deviation from the guidelines by placing the ground sphere on the ground plane and the upper sphere above the ground sphere with gap separation Sâ‰¤D/2 units (considering commonly used vertical arrangement). The distance of the nearest grounded object is kept 'B' units away as specified in the standards. In continuation, in order to study the nearby grounded object a hemi-spherically tipped rod (needle) is brought near, radially, towards the gap axis. This needle is placed vertically on the ground plane maintained at ground potential. Experimental results are obtained with the radial distance of the needle to the gap axis as the parameter. The results are reported for both positive and negative polarity voltages. The simulation is carried out by developing charge simulation model (CSM). Some of the results (even with out the grounded needle in the vicinity) indicate that variation in 'A' modifies the surface electric fields of both the spheres. As the height 'A' is decreased the surface field intensity of upper sphere increases and that of the lower sphere decreases. The correlation between the experimental breakdown results and the simulation results is attempted. These results may help, the users, who have some constraints in actual practice in the laboratory to strictly follow the guidelines given in the standards. Â©2007 IEEE.
Cable dimension determination using Finite Element Method Magnetic (FEMM) for three-core belted and gas insulated cables
(Elsevier Ltd, 2024) Tefera, T.N.; Punekar, G.S.; Ibrahim, K.; Tuka, M.B.; Bajaj, M.
A numerical approach utilizing the Finite Element Method (FEM) based freeware Finite Element Method Magnetic (FEMM) is employed to optimize the insulation thickness to diameter ratio (‘T/d’) for a three-core belted cable, enclosed by a grounded sheath, as well as for a gas-insulated cable (GIC) with a common enclosure. The method analyzes the maximum electric field (E-field) within the cable. The minimum E-field magnitude across three critical regions where the E-field at its peak is calculated for different ‘T/d’ ratios, and the optimal ‘T/d’ is identified by selecting the maximum of these minimum values. Analogs to single-core coaxial cable, for a three-core belted cable with a radius of 1 per unit (p.u.), the best ‘T/d’ ratio is 0.80 when subjected to a 1 p.u. Peak potential. Additionally, the optimal conductor radius and conductor-to-cable center dimension for common-enclosure gas-insulated cables are verified to be 0.18 and 0.5, respectively. This study provides a first-time investigation of the best ‘T/d’ ratio for three-core belted cables and verifies CGIC cable parameters using FEMM, where no analytical solutions are available. The results are validated by comparing FEMM with analytical and Charge Simulation Method (CSM) outcomes. Hence, the FEMM provides low computational cost and reliable results compared to commercial software. Through these simulation efforts, the study re-examines the stress within the belted and gas-insulated cables and the parameters that influence it. The FEMM method allows for precise control of both conductor and sheath potentials, ensuring no potential discrepancies between the applied and calculated values across the entire range of T/d ratios. © 2024 The Author(s)
Case studies on transformer fault diagnosis using dissolved gas analysis
(2018) Shanker, T.B.; Nagamani, H.N.; Antony, D.; Punekar, G.S.
In this paper the results of dissolved gas analysis (DGA) along with details of the DGA data from in-service transformers are discussed. Two case studies are given of which, first case study deals with the detection of the partial discharge and the second case study deals with the detection of thermal fault in transformers at thermal power stations in India. The interpretation of DGA data are conducted using key gas method. The interpretations are validated by the application of gas ratio method. Gas ratio method included in this study are Rogers ratio and Doernenburg ratio. � 2017 IEEE.
Case studies on transformer fault diagnosis using dissolved gas analysis
(IEEE Computer Society, 2017) Shanker, T.B.; Nagamani, H.N.; Antony, D.; Punekar, G.S.
In this paper the results of dissolved gas analysis (DGA) along with details of the DGA data from in-service transformers are discussed. Two case studies are given of which, first case study deals with the detection of the partial discharge and the second case study deals with the detection of thermal fault in transformers at thermal power stations in India. The interpretation of DGA data are conducted using key gas method. The interpretations are validated by the application of gas ratio method. Gas ratio method included in this study are Rogers ratio and Doernenburg ratio. Â© 2017 IEEE.
Comparative Analysis of 500 kV Double-Circuit Transmission Line Electric Field Intensity: Ethiopian Lines Compliance With ICNIRP
(Institute of Electrical and Electronics Engineers Inc., 2024) Tefera, T.N.; Punekar, G.S.; Ibrahim Yassin, K.; Tuka, M.
The high-intensity electric fields, which are in the vicinity of power transmission lines, have adverse effects on human and other living beings if they are not within the specified limits. The International Commission on Non-ionizing Radiation Protection (INCIRP) specifies guidelines for these E-fields from the perspective of public exposure at the ground level and sets it to 5 kV/m at 50 Hz. Thus, this study was aimed at analyzing and comparing the E-fields intensity of differently configured double-circuit 500 kV transmission lines at a height of 1 m above the ground plane. Charge Simulation Method (CSM) using MATLAB as a programming platform is used for this study. Among the tower configurations studied, a configuration that provided minimum E-fields with minimum ground clearance was identified. From the actual built transmission lines included in the study, vertical lines configuration produces a minimum E-fields intensity of 4.565 kV/m root mean square and fulfills the INCIRP requirement. However, triangular line configuration is the preferable configuration for 500 kV double circuit transmission lines giving the least E-fields at the ground with minimum ground clearance using optimized phase sequence arrangements irrespective of other comparative parameters. Additionally, an evaluation of these line configurations based on the distribution of the conductor surface E-fields was conducted. The study reveals that the E-fields on the surface of the transmission line conductors included in the study remains significantly below the intrinsic breakdown strength of atmospheric air. Therefore, it was anticipated that the designs will remain free from corona discharge under fair weather conditions. © 2013 IEEE.
A comparative study of field computation methods: Charge simulation method and method of moments
(2018) Harimurugan, D.; Punekar, G.S.
Numerical methods plays a vital role in computation of electric fields for the design of high voltage systems. For electric fields studies related to high voltage applications, the preferred numerical methods are charge simulation method (CSM) and method of moments (MoM). In the present study, the performance of these two numerical methods are analyzed by simulating sphere-plane gap arrangement (which has an analytical solution to compare). Through this example, CSM is found to be more accurate compared to MoM. Further, the effect of change in sphere-plane gap geometry on the electric field computed is reported and discussed. � 2018 IEEE.
Concerning channel base current functions for lightning studies
(Institute of Electrical and Electronics Engineers Inc., 2012) Shakthi Prasad, D.; Punekar, G.S.
Analysis of channel base current functions with specific reference to new channel base current (NCBC) function is reported. The main concern has been of adjusting the maximum time rate of change of lightning current (di/dt) max along with time to crest tm. A new ratio (maximum time rate of change of lightning current (di/dt)max by average time rate of change of lightning current (di/dt)avg) has been defined. The critical numerical value for this ratio is identified as 1.7 for NCBC function. The performance of NCBC function is compared with Heidler's function in the wave front region. © 1964-2012 IEEE.
Configuring voltage impulse generator using simplex search algorithm
(2019) Sonu, P.K.; Punekar, G.S.
This paper attempts to study the performance of simplex search method using an electrical engineering problem while configuring voltage impulse generator. Simplex search method is based on Nelder-Mead algorithm. Configuring the voltage impulse generator implies producing the standard waveshape characterized by their time-To-front (tf) and time-To-Tail (tt). To get the desired values of tfand tt for a given impulse generator (generator capacitance, Cg) and load capacitance (C1), the wave-shaping resistors (Rsand Rd) values are to be determined. The mathematical model of voltage impulse generator is transformed into a search problem (simplex search) to arrive at the best values of Rsand Rd, for a given Cg, C1, to achieve intended tfand tt. � 2019 IEEE.
Configuring voltage impulse generator using simplex search algorithm
(Institute of Electrical and Electronics Engineers Inc., 2019) Sonu, P.K.; Punekar, G.S.
This paper attempts to study the performance of simplex search method using an electrical engineering problem while configuring voltage impulse generator. Simplex search method is based on Nelder-Mead algorithm. Configuring the voltage impulse generator implies producing the standard waveshape characterized by their time-To-front (tf) and time-To-Tail (tt). To get the desired values of tfand tt for a given impulse generator (generator capacitance, Cg) and load capacitance (C1), the wave-shaping resistors (Rsand Rd) values are to be determined. The mathematical model of voltage impulse generator is transformed into a search problem (simplex search) to arrive at the best values of Rsand Rd, for a given Cg, C1, to achieve intended tfand tt. Â© 2019 IEEE.
Design of an HV capacitor using the inherent advantage of charge simulation method and experimentations
(Institution of Engineering and Technology journals@theiet.org, 2018) Devarajan, H.; Punekar, G.S.; Kishore, N.K.
Standard capacitors form an important component of the measurement and instrumentation in the electrical laboratory. A high-voltage (HV) standard capacitor of 100 pF, 12 kV (rms) is designed using the charge simulation method (CSM). CSM is a semi-analytical method and it provides inherent advantage in designing a capacitor from the first principle. The capacitance is obtained from the magnitude of the simulating charges of the CSM-based model and the corresponding potential. The design details of HV standard capacitor are discussed along with the analysis of the potential and the electric stress distribution. The electric stress everywhere in the capacitor, which is designed, is assured to be <5 kV/cm, which was set as the limiting (maximum permissible) stress. The capacitance of the fabricated unit is measured in the HV laboratory. The CSM-based result of the capacitance of the designed HV capacitor agree well with the results of the laboratory experimental measurement. The inherent advantage of CSM in designing a capacitor is confirmed by comparing with the results of method of moments (MoM). © The Institution of Engineering and Technology.
Disruptive discharge voltages in sphere gaps with perturbed electric fields
(2008) Punekar, G.S.; Kishore, N.K.; Shastry, H.S.Y.
Quasi uniform field gaps, namely sphere gaps are quite often used in high voltage laboratories. They exhibit very little polarity effect when subjected to direct high voltages. But if their electric field is disturbed by a near by earthed object they tend to show polarity effect. In the present work, both simulation and experimental results to see the electric stress distribution on breakdown voltage are studied. Considering commonly used vertical arrangement of sphere gaps disruptive discharge voltages are measured experimentally. These experiments are with one sphere grounded. In order to study the polarity effect on redistribution of electric stresses, experiments have been conducted by bringing a hemi-spherically tipped rod (needle), radially, towards the gap axis (of varying rod dimensions). This rod is placed vertically on the ground plane being at ground potential. Experimental results with both positive and negative polarity dc voltages are reported. The simulations corresponding to these experimental conditions have been reported to correlate the change in electric field distribution using charge simulation models (CSM). The video of spark channel formation under positive and negative polarity with field perturbing rod will be shown during presentation. With rod in the vicinity, electric field gets redistributed and affects the disruptive discharge process. Under negative polarity voltage applied to the upper sphere with rod at the ground potential (along with the ground sphere), the spark is drawn towards the rod. Depending on the vicinity of the rod the spark channel is between the upper sphere and the rod. On the contrary, with the positive potential applied to the upper sphere, the spark channel is drawn towards the rod; (having got disturbed and not being along the sphere gap axis) but strikes the lower sphere and not the needle. Authors feel this research effort is likely to help better understand many aspects related to lightning rods and discharges.
Disruptive discharge voltages in sphere gaps with perturbed electric fields
(2008) Punekar, G.S.; Kishore, N.K.; Shastry, H.S.Y.
Quasi uniform field gaps, namely sphere gaps are quite often used in high voltage laboratories. They exhibit very little polarity effect when subjected to direct high voltages. But if their electric field is disturbed by a near by earthed object they tend to show polarity effect. In the present work, both simulation and experimental results to see the electric stress distribution on breakdown voltage are studied. Considering commonly used vertical arrangement of sphere gaps disruptive discharge voltages are measured experimentally. These experiments are with one sphere grounded. In order to study the polarity effect on redistribution of electric stresses, experiments have been conducted by bringing a hemi-spherically tipped rod (needle), radially, towards the gap axis (of varying rod dimensions). This rod is placed vertically on the ground plane being at ground potential. Experimental results with both positive and negative polarity dc voltages are reported. The simulations corresponding to these experimental conditions have been reported to correlate the change in electric field distribution using charge simulation models (CSM). The video of spark channel formation under positive and negative polarity with field perturbing rod will be shown during presentation. With rod in the vicinity, electric field gets redistributed and affects the disruptive discharge process. Under negative polarity voltage applied to the upper sphere with rod at the ground potential (along with the ground sphere), the spark is drawn towards the rod. Depending on the vicinity of the rod the spark channel is between the upper sphere and the rod. On the contrary, with the positive potential applied to the upper sphere, the spark channel is drawn towards the rod; (having got disturbed and not being along the sphere gap axis) but strikes the lower sphere and not the needle. Authors feel this research effort is likely to help better understand many aspects related to lightning rods and discharges.
E-field computation in 765 kV substation using CSM with reference to occupational exposure
(Institution of Engineering and Technology journals@theiet.org, 2018) Devarajan, D.; Punekar, G.S.; Bhatt, N.S.
With the increase in transmission voltage level, and the guidelines of the International Commission on Non-Ionising Radiation Protection (ICNIRP), the effects of non-ionising radiation on biological elements at high-voltage substations have gained significant importance. The electric field (E-field) distribution in an upcoming 765 kV substation in the Indian subcontinent is computed using the charge simulation method (CSM). CSM is used to model the 765 kV bays, transmission lines, buses, and ground wires in the substation. The three-dimensional (3D) E-field is calculated through the superimposition of E-fields obtained in two orthogonal planes using infinite-line charges. This proposed method of using infinite-line charges gives realistic results. The simplistic model using infinite-line charges greatly reduces the complexity of the CSM-based model (due to the reduced number of charges) apart from increasing the CSM-based model accuracies. This fact has been demonstrated by comparing these results with those of CSM-3D-model of a detailed bay model (including major equipment and associated support structures). The complex-charge-based CSM helps in computing the root mean square value of the E-field at a point, directly, as per ICNIRP guidelines. This RMS value of the E-field is compared with the occupational exposure reference value prescribed in the ICNIRP guidelines. © The Institution of Engineering and Technology 2017.
E-fields inside 765 kV substation: Influence of conductor & bay arrangements
(2017) Singh, S.K.; Punekar, G.S.
Increasing voltage level in generation and transmission system have become inevitable. The threats of non-ionizing radiation and their biological effects at substations have increased. As per International Commission for Non-Ionizing Radiation and Protection (ICNIRP) guidelines suggest maximum limits for electric and magnetic field exposure is 10 kV/m and 1 mT for occupational and 5 kV/m and 250 ?T for public exposure. Keeping this in view results of a case study of electric field distribution in an upcoming 765 kV substation in India are computed and discussed in this paper. Using the existing layout of this substation, the E-fields at 2 m height above the ground plane are computed using FEMM (a free ware). Results show that Bays which are at a height of 14 m from ground are dominant and contributing more to the E-fields. The paper further computes and compares E-field strength due to (i) a single conductor (a phase of bay alone), (ii) single bay (iii) and with all the bays of substation with buses, overhead headlines and ground wires. The effect of bay height (around 14 m) on the E-field is also reported. The average E-field in substation arena is well within the ICNIPR suggested limit of 10 kV/m, whereas E-field at some places exceeds this value. � 2016 IEEE.
E-fields inside 765 kV substation: Influence of conductor & bay arrangements
(Institute of Electrical and Electronics Engineers Inc., 2017) Singh, S.K.; Punekar, G.S.
Increasing voltage level in generation and transmission system have become inevitable. The threats of non-ionizing radiation and their biological effects at substations have increased. As per International Commission for Non-Ionizing Radiation and Protection (ICNIRP) guidelines suggest maximum limits for electric and magnetic field exposure is 10 kV/m and 1 mT for occupational and 5 kV/m and 250 Î¼T for public exposure. Keeping this in view results of a case study of electric field distribution in an upcoming 765 kV substation in India are computed and discussed in this paper. Using the existing layout of this substation, the E-fields at 2 m height above the ground plane are computed using FEMM (a free ware). Results show that Bays which are at a height of 14 m from ground are dominant and contributing more to the E-fields. The paper further computes and compares E-field strength due to (i) a single conductor (a phase of bay alone), (ii) single bay (iii) and with all the bays of substation with buses, overhead headlines and ground wires. The effect of bay height (around 14 m) on the E-field is also reported. The average E-field in substation arena is well within the ICNIPR suggested limit of 10 kV/m, whereas E-field at some places exceeds this value. Â© 2016 IEEE.