Insulating cardboard can be classified by density or by cardboard forming process. It is suitable for oil-immersed transformers in transformers.
The insulating paperboard is made of pure sulphate wood pulp. It only uses pure fiber without any additives. It can be thoroughly dried, degassed and oiled. It can be used for the horizontal spacers of the cake winding and the axial stay of the winding. In the main insulation, partitions, paper tubes, oil gap stays, lead iron yoke insulation, end insulation, winding pressure plates, etc. Its thickness is 0.5mm, 1.0mm, 1.5mm, 2.0mm, 3.0mm, 4.0mm, 5.0mm, 6.0mm, 8.0mm and 10.0mm. The thickness of insulating paperboard commonly used in transformers is 1.0mm, 1.5mm, 2mm, 3mm, 4mm, 6mm.
Classification of insulating paperboard
Insulation paperboard is divided according to density: low density board, medium density board and high density board.
According to the cardboard forming process: hot-pressed cardboard and calendered cardboard.
(1) The density of low-density board is 0.75~0.9g/cm3, and its strength is low. It is used to make stretched parts after bending or wetting, such as forming corner rings, ring parts, soft paper tubes, etc. Low-density boards have high oil absorption and good formability, but poor mechanical properties.
(2) The density of the medium density board is 0.95~1.15g/cm3, which is used for insulating paper tubes, stays, cushions, etc. (that is, general parts and laminated products).
(3) The density of the high-density board is 1.15~1.3g/cm3, which is used to manufacture parts with high mechanical strength and no bending, such as insulating press plates, end insulation, spacers, etc.
(1) T4 extra hard cardboard has high tightness, low oil absorption, poor formability and good mechanical properties. Used to make large-scale transformer insulation press plates, end insulation, spacers and laminates and other insulating parts with high mechanical performance requirements
(2) T1 cardboard has higher tightness, lower oil absorption, poor formability, and better mechanical properties. Used to make hard paper tube spacers and insulating pressing plates and other insulating parts with high electrical and mechanical performance requirements
(3) T3 soft cardboard has small tightness, high oil absorption, good formability, and poor mechanical properties. It is used to make soft paper tubes, laminated boards, laminated pads, bending moldings and other insulating parts with high electrical performance requirements but low mechanical performance requirements.