Effect of low temperature on electrical treeing of polypropylene with repetitive pulse voltage

Polypropylene (PP) has been considered as an alternation to cross-linked polyethylene (XLPE) using as the high voltage direct current (HVDC) cable insulation material due to its no crosslinking process and environment friendly characteristics. During the operation, repetitive pulse voltage may generate in HVDC cable system and the challenge of the low temperature environment may occur. This paper compares the tree characteristics of PP and XLPE with the pulse voltage of 12 kV and 400 Hz under low temperature. Furthermore, the influence of pulse amplitude and frequency on the electrical trees of PP under low temperature is investigated. The frequencies of pulse voltage were 400, 800 and 1200 Hz and the pulse amplitudes were 12 and 15 kV. The experimental temperature from 30 to -196 °C was applied in the test. The results show that compared with the XLPE, the electrical tree is more difficult to be generated in the PP. The growth rate and fractal dimension of tree in the PP are smaller than these in the XLPE with the same treeing time. The low temperature, pulse frequency and amplitude have an influence on the treeing process. It is obtained that the growth of electrical tree is resisted under the low temperature. The higher pulse frequency accelerates the tree propagation process. The higher amplitude accelerates the tree growth rate and fractal dimension at -30 and -196 °C. However, the tree propagation process is not accelerated by the higher amplitude at -90 °C.