Comparison of Test Setups for High Field Conductivity of HVDC Insulation Materials

Abstract

Electrical conductivity is considered to be a key property for HVDC insulation. For cable insulation the conductivity level has to be sufficiently low in order to avoid a large leakage current that could cause heat generation in the insulation and contribute to additional transmission losses. The distribution of conductivity in the radial direction of the cable insulation dictates the distribution of electric field and space charge at steady state. It is therefore of interest to know the conductivity characteristics of insulation materials intended for HVDC cables.
This paper presents a test method and procedure for evaluating the high field electrical conductivity of HVDC insulating materials and crosslinked polyethylene in particular. The results presented in this paper are generated from two nearly identical measurement setups using the same sample geometry, but installed in two different test facilities (ABB and Borealis). The results reveal that differences in conductivity can be seen; even between test setups with only minor differences and that the influence of sample preparation is crucial to obtain reproducibility. However, the decay of the measured current was observed to be relatively different between the measurement set-ups.