Original scientific paper
ELECTRICAL CONDUCTIVITY OF PRESSBOARD AND THE INFLUENCE OF MOISTURE CONTENT
T. Judendorfer
; Graz University of Technology, Inffeldgasse 18, 8010 Graz, Austria
R. Woschitz
; Graz University of Technology, Inffeldgasse 18, 8010 Graz, Austria
M. Muhr
; Graz University of Technology, Inffeldgasse 18, 8010 Graz, Austria
W. Exner
; WEIDMANN Electrical Technology AG, Neue Jonastraße 60, 8640 Rapperswil, Switzerland
S. Jaufer
Abstract
The electrical conductivity σ is an important parameter for material condition evaluation at AC
applications and is responsible for electrical field distribution in DC equipment. With a focus on HVDC
equipment design, the influence of moisture content in oil-impregnated pressboard is determined in this
preliminary investigation. The electrical conductivity of pressboard samples, which have been wetted
artificially in the laboratory, is investigated within this work. Moisture contents between <0,3% and 5,5%
could be achieved artificially through increasing pressboard moisture content levels in a climate chamber.
The electrical conductivity was determined by voltage-current measurements at 20°C in the style of
IEC 60093 with measurement times up to and longer than 24 hours. For these investigations, the
pressboard samples with a thickness of 1 mm have been placed in an (mineral) oil-filled test vessel and
stressed by a DC field with E = 3 kV/mm.
It could be demonstrated that the moisture content of pressboard has a strong influence onto the
electrical conductivity: An increase of electrical conductivity by a factor of around 10 for each percentage
point of moisture increase up to moisture levels of around 3,5% was observed. At higher moisture
contents (>5%), other mechanisms seem to govern the electrical current and the conductivity
respectively, which is also discussed within the work.
Keywords
Electrical conductivity; pressboard; moisture content; artificial moistening; HVDC equipment
Hrčak ID:
198825
URI
Publication date:
15.7.2017.
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