There must be some insulative gap and heat dissipation channel (oil passage) between high voltage winding and low voltage winding, and between low voltage winding and core column, and insulated with cardboard tube. The size of the insulation distance depends on the voltage level of the winding and the clearance required for the heat dissipation channel. When the low voltage winding is placed near the core column, because the insulation distance between it and the core column is relatively small, the size of the winding can be reduced, and the size of the whole transformer will also shrink at the same time.
The transformer winding is set on the core column of the transformer, the low voltage winding is in the inner layer, and the high voltage winding is set in the outer layer of the low voltage winding to facilitate the insulation. It is easy to be insulated from iron core. The iron core is a grounding electrode, and the iron core stack is capacitive grounding.
The arrangement of the three windings in the inner and outer layers of the core column should consider both the convenience of the insulative treatment and the direction of the power transferring. Considering from insulation, the high-voltage winding should not be placed on the core and should be placed in the outer layer.
When the three winding transformer is used in the boost stage of the generator, the direction of the power transferring is transferred from the low voltage winding to the middle and high voltage side. The low voltage winding is placed in the middle, and the middle voltage winding is arranged in the inner layer. When used for pressure reduction, the direction of power transmission is transferred from the middle side and the low side of the high voltage side. The middle voltage winding is placed in the middle, and the low voltage winding is arranged in the inner layer.