Study of the behavior of metal particles in insulation oil under a non-uniform electric field

Insulation oil and copper particles were put into a petri dish made of epoxy resin, and a non-uniform electric field was applied to them. When the nonuniform electric field was applied, the copper particles were observed to form straight lines in the electric field direction with some branching. Moreover, repeated vibrations of the copper particles were also observed around the electrode. The behavior of the arrangement of copper particles can be explained by dielectrophoretic force, which acts on a particle whose relative permittivity differs from that of the surrounding medium. In addition, a partial discharge was detected and an acetylene gas was generated. When this behavior was allowed to continue for an extended period of time, the color of the epoxy resin was observed to turn brown. From the results of an energy dispersive X-ray fluorescence analysis, it was concluded that the changing color of the epoxy resin occurred as a result of fine copper particles a few μm in diameter and a thin copper layer adhering to the epoxy surface.