Space charge characteristics of oil gap and pressboard mixed insulation based on the pulsed electro-acoustic measurement

There are many researches about the space charge behavior of solid insulation (oil immersed insulation paper/pressboard) in transformer based on the pulsed electro-acoustic (PEA) technique. However, no research on the space charge behavior of the oil-paper insulation system consisted by oil gap and oil immersed insulation pressboard was conducted. The space charge characteristics of the oil immersed insulation paper, the mixed insulation consisted of oil gap and pressboard were investigated using the PEA Measurement System. The space charge accumulation behaviors at the interface between oil gap and pressboard were analyzed. The distortion of the electrical field in the oil gap and pressboard was also analyzed. Results show that there are many charges injected into the oil and the pressboard. The charges accumulated at the interface between oil gap and pressboard increases with the electric filed applied. The electrical field distortion is obvious with the applied electric filed for the sample with 0.68% moisture content. While the charges accumulated in the mixed insulation system with 3.83% moisture content become less with the conductivity increased, as well as the electrical field distortion.