Increase of breakdown strength by morphological improvement at semicon interfaces in XLPE power cables and joints

A new method to improve the breakdown strength at a semicon-interface in XLPE power cables and mould-type cable joints was developed. The method was named “Interface Diffusion Method” and is based on the modification of the semicon-layer material with an additive. It was determined that the additive improves the morphology in the XLPE insulation, the lamellar orientation at the interface and forms a diffusion layer near the interface. The modification results in the increase of the breakdown strength at the interface. The method was applied to XLPE power cables and joint model specimens with insulation thickness up to 9 mm. The specimens passed a voltage endurance test as 154 kV cable system components. This paper describes the breakdown strength and the material change (morphological change) of XLPE insulation at the interface in the specimens. The material change was analyzed with a transmission electron microscope (TEM)