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Charge relaxation on surfaces of polymeric insulating materials for outdoor applications

Sjöstedt H., Montano R., Serdyuk Y., Gubanski S. M.

Materials Science Poland

2009

Vol. 27, No. 4/2

1129--1137

The studies have been presented on spatial and temporal distributions of surface charge on samples of ethylene propylene diene monomer (EPDM) and silicon rubber (SIR). The charge was deposited from a positive impulse corona source located at 1 mm above the polymeric surfaces. During the experiments, the number of pulses and their voltage level were varied. It was observed that the spread of the charge over the surface of the samples as well as its magnitude were both increasing with increasing number of impulses applied. EPDM accumulated charge easier and had a longer relaxation time than SIR. A common feature frequently observed in both cases was that the resulting charge distributions had a saddle-like pattern. Performed computer simulations showed that this feature can be attributed to peculiarities of the corona charging in the considered system, which took place in a form of a burst corona, and the dynamics of the deposited charges could be related to burst corona pulses.

Dielectric spectroscopy measurements on oil impregnated paper / pressboard samples

Ekanayake C., Graczkowski A., Walczak K., Gubanski S. M.

Prace Naukowe Instytutu Podstaw Elektrotechniki i Elektrotechnologii Politechniki Wrocławskiej. Konferencje

2004

Vol. 40, nr 15

113-120

Dielectric response analyses of oil-paper/pressboard insulation in power equipment have been introduced for condition monitoring. This paper presents results of a laboratory study where dielectric spectroscopy measurements in frequency domain were performed on oil impregnated pressboard samples containing different amount of moisture (0.6% - 4%). Such data are necessary for correct interpretation of the diagnostic measurements. The measurements were earned out in the frequency range of 0.1 mHz - 1 MHz at temperatures between 20 °C and 80 °C. The measured dielectric response data were used for obtaining information on the change of activation energy and dc conductivity of pressboard with moisture content. The responses obtained were used to derive master curves. Furthermore, the influences of the non-linear behaviour and oil layers on the total dielectric response were discussed.