Do semicons affect space charge?

Ho, Y. F. F., Chen, G., Davies, A. E., Hampton, R. N., Swingler, S. G. and Sutton, Simon (2001) Do semicons affect space charge? pp. 105-8 .

Abstract

Cross-linked polyethylene (XLPE) and thermoplastic (TP) are now being used as the bulk insulation in power transmission cables. However, under certain high voltage operating conditions, trapped or low mobility electrically charged species within the bulk can give rise to space charge, resulting in localised electric stress enhancement which may lead to premature failure of the cable well below the anticipated and designed values.Over the past decade, significant advances in space charge measurements in polymers have resulted in a better understanding of charge dynamics and the effects of material selection and processing. However, little attention has been given to the effects of semiconducting screens on space charge formation in the bulk insulation. This paper reports on the space charge measurement of 1.5mm thick as-received and degassed XLPE and TP plaques with two different kinds of semiconducting electrodes (i.e. carbon loaded XLPE and carbon loaded thermoplastic). Samples were subjected to dc and 50Hz ac at electric stresses in the region of 25kV/mm (at room temperature). Measurements of charge profiles and stress distributions were made using the modified laser induced pressure propagation (LIPP) system. Emphasis has been placed on comparing the space charge characteristics of the two insulation systems with the different semicon? electrodes. The effects of sample treatment (i.e. degassing) on the space charge dynamics are also presented.

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