Quality control of XLPE cables by means of impulse voltage test

High voltage cable lines are rated among the most expensive investments in the electric energy supply system. Due to economic and operational requirements these lines are to live up to the highest expectations as far as reliability and adequate life time are concerned. Therefore it is recommended to undertake impulse voltage tests with increased level apart from tests as provided in the relevant standards. Thanks to these examinations impurities in the insulation and in the interface between insulation and semi conductive layers can be recognized fast and easily for they cause lower levels of the impulse strength. Particularly so-called protrusions in the interface between insulation and semi conductive layers or inadequate adhesion of the semi conductive layers to the insulation, both defects that can occur during the production of the cable, are subjected to the test. During operation these impurities can cause increased local electrical field strength in the insulation as well as water trees and electrical trees. Additionally they speed up the aging process in the insulation of the cable and this can lead to early faults respectively a shorter life time. These production related defects are not detectable by standard tests as partial discharge measurement or voltage tests with power frequency. Due to our investigations and good experience in the field of quality control of XLPE cables we carry out this test for all Austrian and some German utilities.