Dielectric Papers Insulation Materials for Oil-immersed Transformers
Insulating paper (including insulating paperboard) is made of unbleached sulphate fibers. The molecular structure of cellulose (C6H10O5)n is chain-like, contains hydroxyl groups, and is resistant to oil and infusibility. The macrostructure fibers are tubular, and the fibers are porous, so they have gas permeability, water absorption and oil absorption. The breakdown electric field strength, mechanical strength and heat resistance are not high, but the electrical properties are good after impregnating the transformer oil. The smaller the gas permeability, the higher the breakdown electric field strength. It must be pointed out that a small gas permeability does not mean that the impregnation property is poor, and the two are different properties.
Insulation paper and paperboard are available in capacitor paper, cable paper,
telephone paper, wound paper, impregnated paper, insulating paperboard and steel paper (plates and tubes). Steel paper is treated with zinc chloride and cannot be used in high-pressure oil-immersed transformers; plastic paperboard (or cylinder) contains impurities such as free phenol, and is not suitable for high-voltage transformers. For high-voltage power transformers, there are mainly cable paper, telephone paper and insulating cardboard and cylinder.