Soumya Chatterjee

Electric field computation in presence of water droplets on a polymeric insulating surface

In this paper electric field enhancement factor has been computed due to presence of different volumes of single as well as multiple water droplets on a polymeric insulating surface. Outdoor polymeric insulators are exposed to different environmental conditions like rain, fog, salted fog etc. Hence the formation of discrete water droplets on the surface are very common. These water droplets cause the electric field enhancements at the triple points (interfacial point of three dielectric mediums i.e. solid, liquid and air) which may lead to external partial discharge or even flashover. Hence, in this contribution, the electric field computation has been performed due to presence of discrete water droplets using Finite Element Method under tangential AC electric field. To overcome the singularity problem of calculating electric field at the triple points, a different method of field calculation have been presented in this contribution which may provide better understanding of the electric field distribution in presence of water droplets on a insulating surface.

Estimation of damping resistor in mechanically switched capacitor with damping network at different tuning frequencies during switching

Mechanically switched capacitor with damping network (MSCDN) is a low cost economical device used in power systems to serve the dual purpose of supplying reactive power at the fundamental frequency as well as to eliminate the unwanted harmonics when tuned at the desired harmonic frequency. However, during switching in a high voltage A.C grid, various elements of an MSCDN plant are subjected to transient electrical stresses which may be vulnerable for the insulation. Proper designing of the damping network is therefore key to mitigate the switching transients. Hence, in this contribution transient analysis is performed on an exemplary MSCDN model for various values of damping resistor at different tuning frequencies. Finally, an optimum range of damping resistor values have been proposed for designing a MSCDN plant tuned to different harmonic frequencies.

Identification of salt and salinity level of 11kV contaminated porcelian disc insulator using STD-MRA analysis of leakage current

In the present work, a scheme has been developed based on standard deviation of multi resolution analysis (STD-MRA) plot of surface leakage current of a 11kV porcelain disc insulator artificially contaminated with NaCl and KCl. Leakage current analysis is perhaps the most efficient method to analyze the condition of insulator surface. For this purpose, a 11kV porcelain disc insulator is artificially contaminated in the laboratory by applying two soluble salts NaCl and KCl using solid layer method. Two salinity levels 0.5 and 1.5 indicating two different pollution levels are achieved by mixing NaCl and KCl individually with kaolin in distilled water and the leakage current is measured at three voltage levels of 5kV, 15kV and 30kV. The measured leakage currents are decomposed using wavelet transform and the standard deviation of the details are computed for each mentioned salinity levels at 5kV, 15kV and 30kV, respectively. From the above analysis, it is possible to identify the salinity level as well as the type of soluble salt (NaCl or KCl) deposition on the insulator surface which may be useful for condition monitoring of outdoor insulators.

Transient analysis of mechanically switched capacitors with and without damping network connected to A.C grid

Mechanically switched capacitors (MSC) are very well known reactive power compensation devices which are extensively in use in power transmission systems. However, during switching of MSC in a high voltage grid, significant transients are found to appear across the capacitor bank bus as well as different elements of MSC which may lead to insulation degradation affecting the long term performance of the capacitor banks. An improved version of the MSC is MSCDN where a damping network is employed with the capacitor banks to damp out the transient oscillations. However, during switching of a MSCDN plant significant transients are observed across its different elements. Considering the afore-said fact, in this contribution, a comparative study of transient behavior of mechanically switched capacitors with and without damping network is presented during switching in a 400 kV A.C grid. Transient simulations are performed on an exemplary MSC and MSCDN model using PSCAD/EMTDC software. It has been observed that there is a significant reduction in transient overvoltage and inrush current in switching a MSCDN plant when compared to a mere MSC switching. Moreover, the percentage reduction in transient overvoltage and inrush current during switching a MSCDN plant is found to depend on the design of damping network which may be important to analyze the transient behavior during switching in a high voltage A.C grid.

Electric stress analysis of a contaminated polymeric insulating surface in presence of dry bands

In this contribution, influence of dry bands on electric field distribution on a polymeric insulating surface has been carried out using Finite Element Method. Formation of dry bands on insulating surfaces result in electric field enhancement leading to surface discharges, dry-band arcing etc. which in turn affects the long term performance of the insulators. Hence, in the present work, a polymeric insulating surface is modeled as sheath model using Comsol Multiphysics software. Electric stress analysis is performed in presence of dry bands of different length and at different locations on a contaminated insulating surface. Moreover, the effect of different contamination levels on electric field distribution in presence of dry bands have also been investigated.

Cross-correlation based feature extraction from EMG signals for classification of neuro-muscular diseases

In this contribution, classification of two main neuromuscular diseases namely Myopathy and Neuropathy and Healthy signals is performed using cross-correlation based feature extraction technique. For this purpose, cross-correlation of Healthy, Myopathy and Neuropathy disease EMG signal is done with a reference Healthy signal. Selective features like Hjorth, Adaptive Autoregressive and statistical features comprising mean, standard deviation and power are extracted from the cross-correlated signals. Support Vector Machine(SVM) and k-Nearest Neighbor(kNN) are the two classifiers used for this work. Highest classification accuracy of 100% is obtainedby SVM using Gaussian Radial Basis Function (RBF) as the kernel function with AAR and all combined features as the feature set. For kNN, k=4 yields best result of 100% accuracy using the combined feature set.