This is a research project jointly funded by the Electric Power Research Institute (EPRI) and the National Science Foundation (NSF). Since the 1960's, polyethylene-insulated cable rated for 15 to 35 KV service has been used extensively to provide underground service to residences. Polyethylene is inexpensive, is easily spliced and terminated and has very good dielectric properties. Such polyethylene-insulated cables often fail before the expected 40 year lifetime. Examination of insulation from failed underground cables frequently reveals the presence of diffuse bush- or fan-like structures which develop only in the presence of water. These structures, know as "water trees", are usually in the 0.1 to 1.0 mm size range, consist of a collection of voids and originate at the interface between the insulation and another material. Plasma polymerization refers to the formation of polymeric materials from the plasma state of a gas or monomer at low pressure (vacuum). The resulting materials are significantly different from most conventional polymers. Plasma polymerization is system dependent and a variety of polymeric materials including diamond, graphite, carbonaceous films, to polystyrene-like films can be prepared using plasma polymerization of styrene. The key factor which determines the properties of the material which results is the design of the plasma polymerization reactor. This research project is a fundamental investigation of the potential use of plasma polymerized films (plasma polymers) for the optimization of metal-polymer interfaces which are relevant to application in electric power cables. The study is focussed on three major objectives: (1) improvement of the moisture barrier characteristics of jackets and primary insulators, (2) improved corrosion protection of the center conductor and neutral, and (3) development of a triboelectrically graded interface to minimize breakdown due to charge injection. The work involves studies of the basic phenomena associated with the metal-polymer interface, such as adhesion, and water and/or electrical-treeing.
