Faculty Publications
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Item Electric fields in the transition region of sphere-gaps to parallel-plane gaps(2004) Punekar, G.S.; Mishra, V.; Kishore, N.K.; Shastry, H.S.Y.The electrode gaps which results in to uniform electric fields are the most widely used gap configurations in assessing dielectric strength. In the present study simulation results of parallel plane electrode gap configurations with symmetrical and unsymmetrical supply are reported. When plane radius of plane electrode is reduced the plane electrode at Its extreme case forms a sphere resulting in to sphere gap arrangement Results in this transition region are reported. The Charge Simulation Method (CSM) is used to compute electric fields; with errors in simulation being less than 0.06% (in potential). Simulation results indicate that as the plane radius increases the field uniformity increases. Non uniformity for a given plane radius depends on the gap spacing. For given gap spacing when the plane radius of the electrode is more than the gap spacing, improvement In uniformity are not significant The unsymmetrical supply results in higher field non-uniformity in the gap. The height of high voltage (H.V.) electrode above the ground plane (designated as parameter "A" in IS 1876-1961 for sphere gaps with vertical electrode arrangement) has shown negligible influence on the electric field distribution in the gap. © 2004 IEEE.Item Study of GA assisted CSM models using optimally located point charges(2006) Punekar, G.S.; Kishore, N.K.; Shastry, H.S.Y.The Charge Simulation Method (CSM) due to its favorable characteristics is very commonly used technique for electric field analysis in High voltage engineering. In the conventional CSM location of these fictitious charges are predetermined by the programmer. In the present work charges are located optimally to increase accuracy. CSM models being case specific even while optimizing the model, the optimization parameters chosen play an important role. Here in the present work the models of high voltage sphere above the ground plane with and without another sphere below it are discussed. The study is done with optimally located symmetrically placed set of point charges. The infinite plane is simulated using image sphere(s). The paper compares the accuracies of the optimized CSM models and is an effort to evolve guide lines for CSM modeling which is a 'user experience specific' field computation method. The Genetic Algorithm (GA) is used as the tool for optimization. Numerical experiments on the simulated models indicate that, even with optimized charge locations errors in simulating a ground potential (or lower potential) sphere in the vicinity of a high voltage sphere is always high. Also, if higher is the potential of the second sphere, lower is the CSM error. On reaching this limiting accuracy the options to improve the models accuracy further lie in selectively freeing the charges in optimization process (increasing the degree of freedom in optimization). ©2006 IEEE.Item Simulation of electric fields using symmetrically placed charges(2006) Punekar, G.S.; Kishore, N.K.; Shastry, H.S.Y.The electric fields associated with sphere-plane gap geometry is simulated using charge simulation method (CSM). In the present study simulation results with symmetrical placed 6 and 14 point charges are reported. The errors in Charge Simulation Method (CSM) of sphere surface potentials are analyzed by optimally placing the charges. The optimal location of point charges used in simulation are identified using Genetic Algorithm (GA). The GA makes use of maximum-potential-error on the surface of the sphere electrode as the objective function in identifying optimal charge locations. A large number of numerical experiments are conducted and surface error plots are reported. The effort here has been to see the effect of optimally and symmetrically placed charges on simulation error. Results indicate that percentage maximum potential errors in simulation on the surface got reduced from 3.86e-004 to 1.30e-005 when the number of charges is increased from 6 to 14, respectively (with optimal locations). It is known from the literature that increasing the number of charges improves results of simulation in CSM. Application of GA in conjunction with CSM have been some of the recent efforts and the present work brings out the point that non optimally located increased number of charges may not yield results with improvement in accuracy.Item Optimized charge simulation models of horizontal sphere gaps(2006) Kishore, N.K.; Punekar, G.S.; Shastry, H.S.Y.The horizontal sphere gap is modeled using six point charges per electrode as a test case. Two intuitively felt Optimized Charge Simulation Method (OCSM) models of horizontal sphere gap arrangement are set up by selectively changing degree of freedom to understand its effect on the simulation errors. The optimal location of charges is obtained using Genetic Algorithm (GA). A large number of numerical experiments are conducted by varying potential assigned to the low potential sphere, height of the spheres above the ground plane and gap separation. Lower potential sphere always shows higher error. For a typical case, the maximum surface potential error with increased freedom in locating charges reduced to 4% from its earlier value of 9.5%. The simulations with symmetrical supply show maximum surface potential error of 1.0% on both the spheres. On the other hand simulating a ground potential electrode near a high voltage electrode involves more errors and hence more effort. The Charge Simulation Method being semi analytical technique, the shape of the geometry and symmetry (if any) plays a major role and setting up accurate OCSM model still requires user experience. © 2006 IEEE.Item 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.Item 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.Item Sparkover in sphere gaps with alternating voltages and perturbed electric fields(2009) Kishore, N.K.; Punekar, G.S.; Shastry, H.S.Y.Quasi uniform field gaps, namely sphere gaps are quite often used in high voltage laboratories. In the present work, both simulation and experimental results to see the electric stress distribution on breakdown voltage are presented. 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 redistribution of electric stresses, experiments have been conducted by placing a hemi-spherically tipped rod (needle), near the gap axis. This rod is placed vertically on the ground plane being at ground potential. Experimental results are reported with the rod diameter of 3 mm and its height 10 cm as a function of sphere-gap separation. Experimental results reported are with power frequency alternating voltages. The simulations corresponding to these experimental conditions are reported to correlate the change in electric field distribution obtained by charge simulation models (CSM). Interpreting the experimental breakdown results in relation with simulation results of geometric electric field is attempted. The results with rod in the vicinity of sphere gap results in to a non axi-symmetric field. These are simulated to obtain the maximum stress on the electrodes. © 2009 IEEE.Item On electric fields in belted cables and 3-phase gas insulated cables(2011) Punekar, G.S.; Nafo, T.; Kishore, N.K.The electric field distribution in Belted Cables and 3-phase gas insulated cables (GIC) enclosed in a common ground enclosure is analyzed and presented in this paper. The electric fields in this type of GIC are analogous to those of 3-phase belted cables. Unlike 3-phase screened cables, the stress distribution in belted cables is not radial. With time varying voltages (power frequency voltage variations; quasi-static voltages) the stress distribution in the cable insulation changes, not being radial. The electric stress distribution is expected to show systematic, revolving effect. This revolving effect is important as the location of maximum stresses keep on shifting. Also, as a secondary effect, the revolving e-field results into electric-field-winds which can add to the particle movements in the gas insulated cables. The literature acknowledges that particle movements in the gas insulated system can have deleterious effect on the over all system insulation strength; which partly get impetus from e-field-winds. The stresses in such a cable are analyzed using open source software Finite Element Method Magnetics (FEMM). The results presented show that the field distribution over a cycle (of 50 Hz) at discrete time intervals are thought to be having a great educational value, giving a feel of electric field variation in (i) belted cables and (ii) GIC with common enclosure. The computed results of electric stress and potential distribution using FEMM are compared with available results based on CSM models to validate the present results where ever possible. © 2011 IEEE.Item Genetic algorithm in location identification of AEPD source: Some aspects(IEEE Computer Society, 2013) Punekar, G.S.; Antony, D.; Bhavanishanker, T.; Nagamani, H.N.; Kishore, N.K.Using the experimental data obtained from an Acoustic Emission Partial Discharge (AEPD) system, efforts are made to locate the source of Partial discharge (PD) with a transformer tank. The AEPD data with 8 sensors (available in the literature) is numerically experimented with a Genetic Algorithm, although minimum of 4 sensors only are necessary for identifying the location. With eight sensors, four sensors considered at a time, form 70 ( 8C4) combination of sensors. The effect, implication and usage of superfluous sensor data in identifying the location with GA is analyzed and reported. Results are compared with Newton's method. © 2013 IEEE.Item Effects of error in time-delay on AEPD source localization using Newton's method: Numerical experimentation(Institute of Electrical and Electronics Engineers Inc., 2017) Antony, D.; Punekar, G.S.; Kishore, N.K.Newton's method is one of the commonly used methods for acoustic emission partial discharge (AEPD) source localization in power transformers. The major problem in the AEPD source localization is the difficulty in accurately measuring the signal arrival time from the source to the multiple sensors. The exact instant at which the partial discharge (PD) occurs is not known. Therefore, instead of the absolute time, the time-delay in signal reception of each sensor with respect to the sensor nearest to the PD source is estimated. In the present study the effect of time-delay error on the accuracy of the PD source localization is analyzed through numerical experimentations. The solution of the Newtons's method in turn depends on the choice of the initial guess. Hence, different initial guesses are selected for Newton's method randomly. For a fixed set of coordinates for the four sensors and the PD source positions, the time-delays are theoretically calculated. The error is systematically increased in the calculated time-delay to form different groups of time-delays. The PD source is localized using each initial guess for all the groups of time-delays to analyze the effect of error in time-delay on accuracy of PD source localization. The error in time-delay greatly affects the AEPD source localization. Moreover, if Newton's method with a bad initial guess is used then the errors in AEPD source localizations are not systematic. © 2017 IEEE.