Electrical degradation interactions-kinetic and thermodynamic aspects of chain scission for water treeing

Water treeing consists of two basic processes: charge diffusion and irreversible chain scission reaction. Kinetic and thermodynamic aspects of electrical induced chain scission degradation are discussed. Thermodynamics sets the conditions for water treeing to occur, while kinetics determines how fast it will occur and propagate. The rate equation based on two primary reactants, charges and polymeric chains, are derived. The extent of chain scission degradation exhibits an exponential function, strongly influenced by the charge diffusion process. An electro-chemical potential, derived from thermodynamics, determines whether such electric induced degradation occurs or not. It also strongly depends on conductivity. Thermodynamic conditions for vented and bow-tie trees are the same. An analogy to the “fire triangle”, the interaction of dielectric insulators, conductive species, and electro-chemical potential, is proposed. When the electro-chemical potential reaches the bond energy, main-chain scission occurs and generates free radicals, which result in a loss of the local resistivity in the dielectric insulator. Such degradation does not require the presence of oxygen. However, with the presence of oxygen, electrical and oxidative degradation is interconnected through free radical chain reactions