Interfacial diffusion method to improve the breakdown strength of XLPE power cable joints

To further compact EHV XLPE power cables and joints has been a very important requirement among utility companies and so we developed a new method to improve the breakdown strength at the semicon-interface in a mold-type cable joint in order to fulfil the requirements. The method was named “interfacial diffusion method” and is based on an additive mixed into the semicon layer of an XLPE power cable joint. We found that the additive, conventional surfactant, diffused into the insulation layer during the heating process at the cable jointing. The additive improves the lamellar orientation at the interface and forms a diffusion layer near the interface, and consequently increases the breakdown strength at the interface. The method was applied to XLPE power cable joint models with insulation thickness up to 9 mm and the model passed a voltage endurance test for 154 kV cable joint. This paper describes some experimental results in terms of the breakdown strength and material analysis of XLPE insulation at the interface in the model with a transmission electron microscope (TEM). TEM analysis showed that the lamellar orientation in the XLPE insulation at the interface is improved as well as that in the XLPE insulation in the cable part