الفهرس Only 14 pages are availabe for public view
 |  | from | 175 |  |  |
| | | from | 175 | | |
Abstract
In medium voltage and high voltage polymeric insulated power cables, operating
in a wet environment, a degradation process known as water treeing may occur. Water
treeing phenomenon causes the creation of structures called water trees, which are
dielectrically weakened areas, in polymer insulation. This phenomenon was first
detected in 1969. Research on understanding the mechanism of formation of water trees
and means of preventing treeing was initiated worldwide. In spite of the vast amount of
literature on this subject, the phenomenon remains unexplained.
Presently, water treeing is considered responsible for the majority of failures in
underground distribution cables. Water treeing occurs at moderate fields and needs the
presence of at least moisture and electric field. Because of the formation and growth of
water trees the breakdown strength of the cable insulation is reduced below the rated
service voltage. Although many cable manufacturers reduce this problem by a proper
cable design, e.g. water tight shields, the uncertainty in the cable lifetime prediction
remains.