Water treeing retardant XLPE insulation grade with improved electrical endurance

Abstract

XLPE has been the dominant insulation material for medium voltage (MV) cables in Europe since end of the 1970's. The service experience over the years with these cables is excellent. Improved cable constructions (e.g. the use of tough MDPE jacketing) manufacturing processes (dry curing and triple extrusion) and quality control methods have ensured the high performance of the final cables. This means that within the standard formulation concept there is not much further room for practical improvements.However, physical damage caused by mishandling of the cable can allow water penetration into the insulation and may lead to water treeing. At present there is concern about the effect of water tieeing upon the life time of XLPEcables. This has called for efforts to develop improved materials and the paper will describe the development and testing of the resulting new water tree retardant (WTR) XLPE'insulation grade. The major points included are a description of a hypothesis relevant for the growth of water treeing, verification of the efficiency of the new material from laboratory to full scale compound manufacture, showing that it is possible to process the new grade on conventional cable production lines and finally the short and long term electrical properties of these cables.It is clearly shown that the resulting XLPE grade has significantly improved resistance to water treeing. This is achieved without sacrificing other important properties.

Influence of moisture on the electrical properties of XLPE insulation

“…In fact, Submarine insulated cables are immersed in water and underground ones are located in humid places [3,4]. Although their high safety designs, a physical damage caused by mishandling of the cables can allow water penetration into the insulation and may lead to water treeing [5,6]. Numerous studies have reported the possible mechanisms of moisture permeation and water absorption of insulating materials from the environment [3,7].…”