(1) Power Transformers
Representative products currently in operation include: 1150 kV/1200 MVA; 735–765 kV/800 MVA; 400–500 kV (3-phase 750 MVA or single-phase 550 MVA); 220 kV (3-phase 1300 MVA); and ±500 kV/400 MVA converter transformers for DC transmission. Power transformers are primarily oil-immersed and come in two structural types: core-type and shell-type. Core-type units account for 95% of production, while shell-type units account for only 5%. Neither type holds an overwhelming advantage over the other; the core-type is adopted by most manufacturers due to its relatively simpler production process, whereas the shell-type-which involves more complex structures and manufacturing techniques-is utilized primarily by traditional manufacturers. The shell-type is particularly well-suited for high-voltage, large-capacity applications, offering advantages in insulation, mechanical strength, and heat dissipation, as well as facilitating transport to mountainous hydroelectric power stations.
(2) Distribution Transformers
Distribution transformers abroad can reach capacities of 2500 kVA and feature either circular or elliptical cores. Circular cores are the most common; elliptical cores allow for material savings due to a smaller M0 (spacing between core limbs) and utilize corresponding elliptical coils. Low-voltage coils are available in wire-wound and foil-wound designs, while tank types include those with cooling tubes (a minority) and corrugated tanks (the majority).
(3) Dry-type Transformers
In recent years, dry-type transformers have seen rapid development in China. They account for 50% of the market in major cities such as Beijing, Shanghai, and Shenzhen, and 20% in other large and medium-sized cities. There are four structural types: epoxy resin cast, filled-resin cast, wrapped (resin-encapsulated), and impregnated. Currently, open-ventilated Class H dry-type transformers are widely used in Europe and the United States. These represent a new type of Class H dry-type transformer developed by incorporating features of the wrapped-coil structure into the impregnated-coil design and utilizing Nomex paper; however, due to their high cost, they have not yet been widely adopted in China. At present, the largest dry-type distribution transformer in China to have passed short-circuit testing is rated at 2,500 kVA (10/0.4 kV), while the largest dry-type power transformer to have passed such testing is rated at 16,000 kVA (35/10 kV).
(4) Amorphous alloy transformers
Although amorphous alloy transformers suffer from poor short-circuit withstand capability and high noise levels, their energy-saving qualities give them promising prospects for future development. Currently, China's largest manufacturer of amorphous alloy transformer cores has an annual production capacity of 3,000 to 4,000 tons. Production technology for the cores and transformers themselves is not the critical factor limiting their adoption; rather, a breakthrough in amorphous alloy strip material technology is required to achieve a qualitative leap in the product.
(5) Wound-core transformers
At present, the production of wound-core transformers in China is primarily concentrated in the 10 kV class, with capacities generally below 800 kVA. While 1,600 kVA units have been produced on a trial basis, the majority of purchases by power utilities are for units with capacities of 315 kVA or less, making them suitable for rural power grids. There are over 200 manufacturers of wound-core transformers in China, with approximately 20% operating at a significant scale. China's production capacity for wound-core transformers is approximately 16 million kVA, though actual output remains relatively low.