(1) Power Transformers
Currently, representative products already in operation include: 1150KV, 1200MV·A; 735～765KV, 800MV·A; 400～500KV, 3-phase 750MV·A or single-phase 550MV·A; 220KV, 3-phase 1300MV·A power transformers; and ±500KV, 400MV·A DC transmission converter transformers. Power transformers are mainly oil-immersed, with two main structural types: core-type and shell-type. Core-type transformers account for 95% of production, while shell-type transformers account for only 5%. There is no overwhelming advantage between core-type and shell-type transformers; however, core-type transformers have a simpler manufacturing process and are therefore adopted by most companies. Shell-type transformers have a more complex structure and manufacturing process and are only used by traditional factories. Shell-type transformers are particularly suitable for high voltage and large capacity applications, offering advantages in insulation, mechanics, and heat dissipation, and are suitable for transportation in mountainous hydropower stations.
(2) Distribution Transformers
Foreign distribution transformers can reach capacities of 2500 kVA, and come in circular and elliptical core forms. Circular cores are the most common, while elliptical cores, due to their smaller M0 (spacing between core columns), require less material, and their corresponding coils are elliptical. Low-voltage coils are either wire-wound or foil-wound, and oil tanks are available with cooling pipes (a minority) or corrugated (the majority).
(3) Dry-Type
Transformers Recently, dry-type transformers have seen rapid development in China. In major cities like Beijing, Shanghai, and Shenzhen, dry-type transformers account for 50%, and in other large and medium-sized cities, they account for 20%. Dry-type transformers have four structures: epoxy resin casting, filler casting, wrapped, and impregnated. Currently, open-ventilated H-class dry-type transformers are widely used in Europe and America. These are new H-class dry-type transformers developed based on the impregnated type, incorporating the characteristics of the wrapped structure and using Nomex paper. Due to their high price, they have not yet been widely adopted in my country. Currently, the dry-type distribution transformer with the largest short-circuit test capacity in China is 2500 kV·A, 10/0.4 kV; the dry-type power transformer with the largest short-circuit test capacity is 16000 kV·A, 35/10 kV.
(4) Amorphous Alloy Transformers
Although amorphous alloy transformers have poor short-circuit resistance and high noise, they are energy-saving, thus their future development prospects are promising. Currently, China's largest amorphous alloy transformer core manufacturer has an annual core production capacity of 3000-4000 tons. The core and transformer production technology is not the key factor restricting the promotion of amorphous alloy core transformers; breakthroughs in amorphous alloy strip materials are needed to achieve a qualitative leap in product quality.
(5) Winded Core Transformers
Currently, the production of wound core transformers is mainly concentrated in the 10 kV class, with capacities generally less than 800 kV·A. A 1600 kV·A transformer has also been trial-produced, but power departments mostly purchase transformers with capacities below 315 kV·A, suitable for rural power grids. There are currently more than 200 manufacturers of wound-core transformers in China, with about 20% of them being of a certain scale. China's production capacity for wound-core transformers is approximately 16 million kVA, but the actual output is relatively low.