Classification And Requirements Of Power Transformer Oil Type
The insulation of power transformer oil type can be divided into inner insulation and outer insulation. Internal insulation can be divided into main insulation and longitudinal insulation. The main insulation is the insulation between the windings and the grounded part and between the windings. In oil-immersed transformers, the oil-paper barrier insulation structure is commonly used as the main insulation. Main insulation can be divided into graded insulation and full insulation. Graded insulation means that the main insulation level of the transformer winding near the neutral point is lower than the insulation level at the end of the winding. Conversely, if the insulation level of the transformer head and tail is the same, it is called full insulation. Longitudinal insulation is the insulation between parts of the same winding, such as insulation between different turns, turns and turns.
Power transformer oil type can withstand overvoltage and normal working voltage during operation. Withstands short-circuit current, overcurrent and normal operating current during operation. Moisture and aging will not affect the normal operation of the transformer. The main insulating materials inside the transformer are transformer oil, insulating cardboard, telephone paper, cable paper, and crepe paper. Insulating paperboard is mainly made of unbleached sulfate fibers, and there are many pores between fibers, so it has strong air permeability, oil absorption, water absorption, etc. If polyamide fiber paper with higher heat resistance is used, its life is greatly improved. For example, used as cable paper for insulating paper tubes, struts, spacers, partitions, angle rings, etc. As a kind of insulating paper, kraft pulp is used as raw material, and the transformer adopts DL2-08, DL2-12 type cable paper, the thickness is 0.08mm and 0.12mm respectively. The oil-immersed transformer is mainly used for the coating insulation of the outer surface of the wire, the interlayer insulation of the coil, the lead coating insulation, etc. It is one of the main insulating materials of the oil-immersed transformer. Telephone paper is made of kraft pulp and is mainly used for coil wire insulation and coil end insulation. Crepe paper is also an insulating paper, which is reprocessed from cable paper made from kraft pulp. It has good electrical properties in oil, such as high average breakdown voltage and small dielectric loss tangent. Crepe paper is mainly used to wrap the transformer outlet.
It can be seen that the field strength in the oil gap is much stronger than that of the cardboard, so the oil gap becomes the weak link of the oil-paper insulation. When the dielectric coefficients between them are close, the size of the power transformer oil type insulation structure may be reduced, so new paperboards with low dielectric coefficients are the current research and development direction.
