(1) Power transformers
Power transformers are mainly oil-immersed, with two product structures: core and shell. Core-type production accounts for 95%, while shell-type production accounts for only 5%. There is no overwhelming advantage between the core and shell types. The core type is simply simpler in process, so it is adopted by most companies; while the shell type is more complex in structure and process, so it is only adopted by traditional factories. The shell type is particularly suitable for high voltage and large capacity. It has advantages in insulation, mechanical and heat dissipation, and is suitable for transportation to hydropower stations in mountainous areas.
(2) Distribution transformers
Foreign distribution transformers have a capacity of up to 2500 kV·A and are available in round and elliptical core forms. The round type accounts for the vast majority. The elliptical type has a small M0 (the spacing between the core columns), so the material consumption can be reduced, and the corresponding coil is elliptical. Low-voltage coils are wire-wound and foil-type, and the oil tanks are available with heat pipes (a minority) and corrugated (the majority).
(3) Dry-type transformers
Recently, dry-type transformers have been rapidly developed in China. In major cities such as Beijing, Shanghai and Shenzhen, dry-type transformers have accounted for 50%, and in other large and medium-sized cities, they have accounted for 20%. There are four types of dry-type transformers: epoxy resin casting, filler casting, wrapping and impregnation.
(4) Amorphous alloy transformers
Although amorphous alloy transformers have poor short-circuit resistance and high noise, they are energy-saving and therefore have promising future development prospects. At present, China's largest amorphous alloy transformer core manufacturer has an annual core production capacity of 3,000 to 4,000 tons. The production technology of cores and transformers is not the key factor restricting the promotion of amorphous alloy core transformers. Only breakthroughs in amorphous alloy strips can promote a leap in product quality.
(5) Wound core transformers
Currently, the production of wound core transformers is mainly concentrated in the 10KV level, with a capacity generally less than 800KV·A. 1600KV·A has also been trial-produced, but the power sector mostly purchases capacity below 315KV·A, which is suitable for use in rural power grids.