Combined transformer substation (American type transformer substation), widely used in wind power and solar power stations, is a transformer substation that combines the step-up transformer, switch equipment, fuse, tap changer and corresponding auxiliary equipment. The high-voltage switch and fuse of this kind of products are all installed in the oil tank; the overall size is small; the transformer has no separate shell, and the heat dissipation effect is good. It can be divided into two types according to product structure and component configuration. One is fully insulating product with separate compartments; and another is common compartment product in which the high-voltage adopts dry-type busing outgoing line. Combined transformer substation used for photo-voltaic power generation is mainly divided into two kinds: double winding and axial direction double split. Among them, high voltage of axial direction double split is wrapped in axial section and low voltage is wrapped in copper foil. The two branches of low-voltage can operate separately and they can also operate at the same tine or in parallel. This kind of product is widely used in photo-voltaic power generation.