New developments in medium and high voltage cable with laminate sheaths as moisture barriers

Abstract

Introduction his paper will overview the evolution of moisture barrier cables and the data that support their use. T There has been extensive development of moisture barrier medium and high voltage cables as a countermeasure to water treeing. The moisture barrier can take traditional forms, including extruded or welded metallic tubes. The latest developments in moisture barrier cable design use laminate sheaths. This paper will discuss the traditional approaches and present an evolution of the laminate sheath. An overview of the various designs, under-jacket with foil or sheet, or oncore, will be given. Design considerations also will be discussed. Information on deployment in the field and standardization activities will complete the report.As the reader will discover, an immense amount of data and information on moisture barrier cable has emerged. In spite of this body of knowledge on the effectiveness of moisture barriers against treeing and the commercialization of moisture barrier cable, the treeing phenomena is still being extensively researched and studied. Well over a thousand papers have been presented on treeing related research. Great energy is still being expended to understand the mechanism and the material constraints. Yet the causes of treeing or its acceleration are well known. They are the presence of water and the presence of ions in an electric field concentration. The evidence is indisputable that if moisture and ions are kept out of the insulation, cable service life is assured. To this end, radial and longitudinal moisture barriers have been developed to the degree that practical, cost-efficient cable designs are available. In point of fact, there has been a proliferation of moisture barrier or water impervious cable designs in recent years. Field data on performance is starting to emerge and it is excellent.To set the stage, some background data on the use of jackets to increase moisture resistance will be presented, followed by general construction details with data on There is overwhelming evidence that the use of moisture barriers on medium and high voltage power cables will solve the problem of water treeing. the performance of moisture barrier sheaths. Details on the types of sheaths in use for both medium voltage and high voltage cable applications comprise the body of the report.

Water Diffusion in High Voltage Subsea Cable Outer Sheath Materials

“…The permeability coefficient P, is defined as P=DS (4) The temperature dependence of the coefficients is given by the Arrhenius relations over a relatively large temperature region…”

“…Barrier designs with layered polymeric materiais are good alternatives due to low cost and low weight [4]. The water migration properties of cables with such barriers can be calculated numerically if the water migration properties of the polymeric materials are known.…”