Faculty Publications
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Item Thermal effects on acoustic emission based PD in transformer oil: A study(2012) Bhavani Shanker, T.; Nagamani, H.N.; Punekar, G.S.Transformers operate at different service conditions in the field resulting in operating temperatures of oil and winding, much above ambient temperature. Acoustic emissions due to partial discharge activity in transformer insulation system, including transformer oil, have been investigated by a few researchers at temperatures ranging from 25°C to 40°C. It is more realistic to consider the study at service temperature which could be around 50°C to 70°C; depending on the service conditions and type of insulation employed. The paper deals with acoustic partial discharge behaviour in transformer oil at temperatures ranging from 30°C to 75°C along with some of the properties of transformer oil. © 2012 IEEE.Item Some aspects of location identification of PD source using AE signals by an iterative method(2012) Punekar, G.S.; Jadhav, P.; Bhavani, S.T.; Nagamani, H.N.An acoustic Partial Discharge (PD) location problem modeled mathematically, gives system of sphere equations, which are non-linear. These equations are formed with known acoustic emission (AE) sensors co-ordinates, with PD locations co-ordinates as unknowns. Newton's method is implemented to locate the PD activity using the AE signals. This is an iterative method and the convergence depends on the initial guess. Different aspects such as initial guess, location of sensors (sensor co-ordinates) and tank orientation in space are studied in this paper by numerical experiments on the algorithm implemented using the experimental data published (available) in a literature. The published data considered for the study here uses 8 number of sensors (4 on the front and 4 on the back wall of the transformer tank; laboratory model). The method of locating acoustic emission partial discharge (AEPD) requires at most 4 sensors (three to identify the coordinates of the location and one for arrival time of AE signal). Hence, results of such 70 combinations (i.e. 8C4) are studied using the algorithm implemented. The numerical test runs indicate that some combinations either do not lead to convergence or yield results with high errors. At least such 10 combinations (out of 70) are identified and analyzed. © 2012 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 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. © 2013 IEEE.Item 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. © 2017 IEEE.Item Inrush Current Parameters Associated with Back-to-Back Switching of Capacitors in a Bank(Taylor and Francis Inc. 325 Chestnut St, Suite 800 Philadelphia PA 19106, 2017) Ramesh, M.; Nagamani, H.N.; Vaidhyanathan, V.; Punekar, G.S.Back-to-back switching of 50 kVAr capacitors, in a capacitor bank of 200 kVAr is investigated experimentally. The switching inrush currents in a three-phase, 200 kVAr, 415 V Automatic Power Factor Correction panel at power frequency are captured in the laboratory. The characterizing features of inrush current are reported and analyzed. The commercially available two makes of switches (contactors) are used to compare the inrush currents with and without their pre-insertion resistors (PIR). The inrush current scenario of the experimental setup is modeled in EMTDC/PSCAD to ascertain the results. The ratio Ipeak/IN for both the contactors without PIR exceeded the limit mentioned in IEC 60831-1 Ed 3.0 : 2014. © 2017, Copyright © Taylor & Francis Group, LLC.Item Effects of transformer-oil temperature on amplitude and peak frequency of partial discharge acoustic signals(Institute of Electrical and Electronics Engineers Inc., 2018) Shanker, T.B.; Nagamani, H.N.; Antony, D.; Punekar, G.S.The behavior of partial discharge (PD) acoustic emission (AE) signals in the transformer oil for a temperature range of 30-75 °C is studied via laboratory experiments. The AE signals are analyzed using the fast Fourier transform (FFT) to obtain the peak frequency and the AE amplitude. A peculiar behavior of reduction in the peak frequency and the AE amplitude observed above 65 °C is reported. An attempt is made to explain the reduction in the AE amplitude after a certain temperature by correlating it with the properties of the transformer oil such as the viscosity and the breakdown voltage. This AE signal analysis is perhaps an important advancement in the PD diagnosis and the PD spectrum analysis at different temperatures in the transformer oil. © 1986-2012 IEEE.