A combined transformer is a transformer that integrates a step-up transformer body, switching equipment, fuses, tap changers, and corresponding auxiliary devices. The high-voltage switches and fuses are all installed inside the oil tank, resulting in relatively small overall dimensions. Its structural form is similar to the pad-mounted transformers introduced from the United States in the 1990s. According to the product structure and component configuration, it can be divided into two types: one is a fully insulated compartmentalized product, and the other is a common-box product with high-voltage bushings for the outgoing lines.

• The combined transformer is divided into three parts: the high-voltage room, the low-voltage room, and the transformer, arranged in an "L" shape or a triangular layout;
• In the combined transformer, only oil-immersed transformers can be used, and dry-type transformers are not allowed;
• The combined transformer body and heat dissipation fins are fully exposed and open on the exterior of the enclosure, ensuring excellent heat dissipation. All other live compartments are sealed within independent isolation rooms, with each room separated by partitions to form isolated sections. A manhole is also provided inside the enclosure for convenient installation and maintenance;
• The box body is made of cold-rolled steel plate or stainless steel plate, with smooth and flat internal and external surfaces free from rust, coating peeling, or impact damage. The paint layer is firmly and evenly applied, without noticeable contrast or reflective glare;
• The top cover of the box is equipped with a weatherproof sealing cover and a rain guard, while the double-layer structure of the top cover prevents thermal radiation;