Electrical insulation paper is used to insulate transformers and motors because pure cellulose has outstanding electrical properties. During development, manufacturers of insulation paper need to test their products in order to ensure a consistent level of quality. The power transformer, an important piece of power transmission equipment, is the core component of the power system. Currently, most transformers are oil-immersed transformers, and their insulation is composed of the insulation oil and insulation paper. Insulation paper, which is widely used in oil-immersed transformers, is made of natural cellulose. Although its use began in the 1890s, natural cellulose insulation paper is still widely used in oil-immersed power transformers, although insulation materials have made significant changes and progress. Insulation paper is composed of cellulose, which is linked by hydrogen bonds. There are a large number of gaps in the interior of insulation paper; when the insulation paper is immersed in insulation oil, those gaps are filled with the insulation oil. Under an electric field, the breakdown first occurs in the weakest part. Because the electric field strength distribution of each part of composite insulation has an inverse correlation with relative permittivity, the relative permittivity of cellulose is higher than that of insulation oil and the breakdown strength of insulation oil is lower than that of cellulose. Therefore, those gaps that are filled with insulation oil in the interior of the oil-impregnated insulation paper are broken down first.
