Included in this are melt filtration, in-line metal separation, and use of a closed system and a clean room. He defined contamination categories as oxidized polyethylene, metal, fiber, and others. S. Boggs asked if Bostrom thought the compound could be used by the manufacturer without requiring cleaning on-site. The answer was yes, that they have two 400 kV cables that have been made without this requirement. Boggs described water treeing as an electro-oxidation process.
Water treeing can be electromechanical or elechemical in nature.
At very high fields, such as can exist at the tip of the water needles, water treeing is largely electrochemical in nature with little electro-oxidation taking place relative to what occurs in cables in service. Under service conditions, water trees are primarily electrochemical in nature, with electro-oxidation having taken place. When the chemical potential is greater than about 1 ev, electro-oxidation occurs. It is at intermediate water conductivities that the chemical potential becomes maximized. The relative contributions of reduced hydrophobicity and increased water conductivity to the water tree resistance of EPR is not clear.