Effect of sensor position on the measurement of acoustic wave produced by partial discharges.

This paper presents the finite element method (FEM) simulation of the propagation, measurement and evaluation of the time of arrival (TOA) of the acoustic wave created by a partial discharge (PD) in a transformer model using COMSOL multiphysics software. This model is a flat tank filled with an insulating liquid. In addition, 8 acoustic probes placed on one of the outer faces of the tank provide information on acoustic pressure levels for specific values of angles of incidence of the acoustic signal. The addition of signal transmission zones for each of the probes makes it possible to define precise paths for the acoustic signal, enabling the TOA of the acoustic wave to be evaluated for each path. The results of this study show that for angular values less than 40°, the error on the TOA is practically zero, but for values greater than 40° this error increases exponentially with the angle. This means that for an angle of 40.41° the error is 6µs, corresponding to 1.7%, and for an angle of 71.70° the error is 332µs, corresponding to 40.3%. This highlights the optimal nature of the choice of sensor position for locating partial discharge.

Effect of the relaxation time of mineral oil and monoesters on the fractal dimension and mutual information of creeping discharges propagating along a pressboard.

This paper presents a new method for analysing creeping discharges based on information theory as it applies to medical imaging. The analysis of information surface data is used to determine the impact of relaxation time on the characteristic parameters of creeping discharges. The same information is used to make a comparative study of the morphology of discharges propagating in palm kernel oil methyl ester (PKOME) and in mineral oil (MO). Other comparative methods based on fractal analysis and normality hypothesis tests associated with Anderson Darling (AD), Kolmogorov-Smirnoff (KS) and Shapiro-Wilk (SW) statistics are used. The results show that very short relaxation times increase the error on the measurement of the fractal dimension and the maximum extension of the discharges. A growth of the mutual information between 0 and 60% is observed for relaxation times varying between 60s and 420s respectively. For the same time interval, the P-value increases from 0.027 to 0.821 according to the AD statistic, from 0.01 to more than 0.150 according to KS and from 0.083 to more than 0.1 according to SW. This result indicates that the data are from a normal distribution. After 420s of relaxation, the error on the maximum extension measurement is reduced by 94% in PKOME and 92% in MO. Similarly, the error on the mean fractal dimension in MO is reduced by 86.7% for a relaxation time between 301s and 420s, and by 84.6% in PKOME for a time between 180s and 420s. These different results imply that the impact of the discharge can be predicted when it is in its initial phase during which the number of discharge occurrences is reduced. On the other hand, the physicochemical characteristics of the insulating liquid used dictate the relaxation time to be allowed for the laboratory measurements.