ナノコンポジットコーティングを効果を考慮した油/プレスボード界面における沿面放電挙動及び数値モデル解析

摘要

Electrical insulation has been described as the most important component of electrical equipment such as transformer, circuit breakers, vacuum interrupters and power cables. Above all, oil filled transformers are one of the basic elements of a power system. They are connected to a large number of customers via power transmission and distribution system. However, partial discharge and breakdown phenomenon by lightning surge has proved to be one of the major factors and weak point at the oil/pressboard (PB) interface. Besides, aged oil filled transformers are increasing trend, there is need for replacement of aged transformer. Especially, the life time of a transformer is mainly dependent on the life of solid insulation. To enhance competitiveness and cost reduction of transformer system, there is need for alternative conventional pressboard in terms of miniaturization and simplification of insulation structure in oil filled transformer. Besides, to improve of design electric field, dielectric strength as well as suppression of creepage discharge occurrence, there is necessary to improve the insulation performance to prevent discharge phenomena. In this reason, a lot of work has been recently devoted to improve the dielectric properties of insulation by adding specific functional additives in to the solid polymer, GIS spacer as well as liquid oil. However, recently few studies have been focused on modifications of the insulating paper using various specific functional additives to improve dielectric and mechanical properties; it is because streamer propagation in oil is greatly affected by the presence of pressboard. Above viewpoints, this research work suggest the new coating method on pressboard surface by thin solid layer coating such as epoxy resin, Teflon coating and silica/epoxy nanocomposite to study discharge phenomena and behavior in transformer composite insulation system. In experiment, five kinds of specimens are used with different coating materials using rod-plane and needle-bar electrode configuration. The creepage discharge properties of conventional pressboard in oil/pressboard composite insulation are compared with that of the solid layer coated pressboard newly in terms of discharge propagation length, discharge occurrence probability and dielectric properties. Besides, to clarify the effect of epoxy/silica nanocomposite, we investigated the creepage discharge behavior using epoxy/silica nanocomposite plate with different silica filler loading and different nano silica size. Additionally, we investigated the creepage discharge behavior using COMSOL Multiphysics 2D model for simulation. In simulation, to understand the creepage discharge phenomena in composite insulation system depending on solid insulation parameters such as work function and permittivity, creepage discharge modelling and simulation have been investigated. The simulation is based on a system of coupled general expression of governing equations that contain the physics to model streamer development based on the hydrodynamic diffusiondrift including ionization, dissociation, charge recombination and electron attachment, combined with Poisson’s equation in dielectric liquids. The governing equations for solid pressboard insulation are composed of Gauss’s Law. All the results are reported and discussed.