Effects of condition of water blocking tape on the buffer layer failures of high voltage XLPE cables in electric field and temperature field

Abstract

In recent years, buffer layer failure of high voltage crosslinked polyethylene (XLPE) cables have occurred many times. The typical feature is the appearance of holes surrounded by white powders on the surface of water blocking tape. Although the generation of white powders is possibly related to the moisture of water blocking tape, the failure mechanism of buffer layer is not yet clear. In this paper, the effects of moisture content on the amount of white powders and volume resistivity, relative permittivity as well as thermal conductivity of the tape were studied through experiments. Moreover, based on the test results mentioned above, the electric and temperature field distribution of the buffer layer were calculated by finite element simulation. It has shown that water blocking powders become spherical after absorbing water, which is an important feature to indicate the tape getting wet. Moreover, volume resistivity of the tape also rised with increasing powders. With the increase of white powders, volume resistivity of water blocking tape increases and both relative permittivity as well as thermal conductivity decreases. Additionally, the cause of buffer layer failure is that the precipitation of white powders causes the increasing volume resistivity and decreasing relative permittivity of water blocking tape, which finally leads to the partial discharge between the tape and aluminum sheath.