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Increasing need of cost effective identical sensors for partial discharge (PD) location prompted us to take up this research study. Four high-frequency current transformers (HFCT) were assembled and its performances with a used commercial sensor were compared with the known type of PD signals. In this paper, the responses due to surface, oil corona and air corona are analyzed. PD occurrence in 20 ms period and the shape of single PD with more sampled data points are characterized using seven techniques. The study indicates that HFCT with biflar winding is more sensitive in identifying different types of known PD. The number of turns and gauge of the used wire in HFCT play a role in increasing the sensitivity of PD detection. Index Terms--Cluster analysis, condition monitoring, HFCT, partial discharge, phase distribution, signal processing, time-frequency transformation, wave shape of single PD, weibull distribution.

This paper presents the measured and analyzed responses of the partial discharge (PD) when it propagates in a power network from its origin to the measuring nodes. On and offline measurements are done in a power network consisting of a 16.5-kV/250-MVA-rated power generator, busbar, and step-up transformer. The simultaneously measured PD at two ends of the busbar indicated that the intensity of PD decreased as it traveled a longer distance and the time interval of its occurrence had a finite delay indicating the dominant mode of PD propagation as a transmission line. Frequency-domain analysis indicated the presence of characteristic resonance frequencies and the number increased as the measuring node moved away from the PD origin. The offline measurement by injecting an exponential PD signal at the neutral indicated that the signal will be absorbed in the generator, and the signal at the measuring node will be attenuated by 50 times and will be distorted. Pspice simulation is used to develop the network model for the propagation path. The Pspice analysis indicated that the distributed models of generator, busbar, and lumped parameter models of a transformer can be used to match the offline measurement. The model showed that each model can have the characteristic resonant peaks depending on the selected parameters and it can distort the simultaneously observed PD at two different nodes. Index Terms--Busbar, generator, partial discharge (PD), propagation, simulation, transfer function, transformer.

Locating partial discharge (PD) using single-pulse analysis is considered in this research. The studied network is a generator connected to a transformer through the busbar. Since the stator winding of a generator consists of a finite number of wound coils and finite length busbar, an analysis based on a simple ladder transmission-line model with a finite number of sections has been carried out. A simulation study using the SIMULINK package on the model produces network frequency responses under varied line parameters, and a varied number of sections and termination conditions. The investigation shows that the results of simultaneous PD measurements at different locations can be reproduced satisfactorily using the network model in terms of predicting its resonant frequencies and the time-domain envelope profile of the PD. The proposed method enables one to discriminate PD pulses originating from different locations of the generator winding, as it is observed that the PD magnitude attenuates during propagation. Index Terms--Busbar and transformer, partial-discharge (PD) models of generator, PD propagation, transfer function.

This paper describes a method of studying and modeling the dielectric relaxation for stationary power apparatus in an interconnected network to get the necessary aging indicators. The polarization phenomenon was studied using Recovery Voltage (RVM) and Polarization Current (PCM) Measurements on individual power apparatus and on network with other connected apparatus. Because of dielectric absorption in composite insulation, all RVM responses showed a single peak response and the response was linear with charging voltage. PCM decreased monotonically with a sudden drop in the initial period and after 100 s, it decreased very slowly and the response was linear with charging voltage. The responses were analyzed by modeling the dielectric function as an exponential function and as two-time dependent fractional power law function to determine suitable aging parameters. Exponential function model was found to fit both responses to get an equivalent electrical circuit of the system. Interrelation of RVM and PCM was established in most of the cases. Predicted dielectric response function for generator was more linear with time than for transformers and cable. In the frequency plane, it was found to have distinct regions of relaxation spectrum. Studies indicated that the parameters of fit for RVM response with each charging period differed from all RVM responses. Index Terms--Polarization current, recovery voltage, dielectric relaxation, Network dielectric response, universal fractional power law, extended Debye law.

A simple numerical technique to identify the parameters of metal-oxide attester models is described. Using measured arrester voltage obtained under impulse test conditions the arrester parameters are determined using an optimization technique. The validity and the accuracy of the model are then assessed by comparing the predicted against the measured values of arrester energy, initial slope, residual voltage, and the overall deviation. Application of the arrester model on network system studies is illustrated. Index Terms--Insulation coordination, metal-oxide surge arrester, optimization method, parameter identification.

This paper proposes a theoretical model to analyze the movement of a small conducting sphere stressed with alternating voltage in transformer oil. The model is verified by comparing it with the experimental observations of a metal particle of radius 0.5 mm in an electrode gap of 8 mm stressed with ac voltage. The model suggests that for practically existing micrometer-sized particles (approximately equal to 50 microns m diameter), the opposing viscous force is the most significant component. The viscous force is dissipated in the medium as fluid drag both along and perpendicular to the direction of movement. A theoretical analysis of the contribution of multiple particles to viscous drag is presented, and is shown to provide a possible explanation for the experimentally observed particle cloud formation at lower ac stresses and dispersion at higher ac stresses.

Locating partial discharge (PD) using single-pulse analysis is considered in this research. The studied network is a generator connected to a transformer through the busbar. Since the stator winding of a generator consists of a finite number of wound coils and finite length busbar, an analysis based on a simple ladder transmission-line model with a finite number of sections has been carried out. A simulation study using the SIMULINK package on the model produces network frequency responses under varied line parameters, and a varied number of sections and termination conditions. The investigation shows that the results of simultaneous PD measurements at different locations can be reproduced satisfactorily using the network model in terms of predicting its resonant frequencies and the time-domain envelope profile of the PD. The proposed method enables one to discriminate PD pulses originating from different locations of the generator winding, as it is observed that the PD magnitude attenuates during propagation. [ABSTRACT FROM AUTHOR]