(1) Power Transformer

At present, representative products currently in operation in the system 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; DC transmission ± 500KV, 400MV · A converter transformer. Power transformers are mainly oil immersed, with two types of product structures: core and shell. Core production accounts for 95%, while shell production only accounts for 5%. There is no overwhelming advantage between core and shell, but the core process is relatively simple and is therefore adopted by most enterprises; The shell structure and process are more complex, and only traditional factories adopt them. Shell type is particularly suitable for high voltage and large capacity, with advantages in insulation, mechanical and heat dissipation, and is suitable for transportation of hydropower stations in mountainous areas. [3]

(2) Distribution Transformer

The capacity of foreign distribution transformers can reach 2500KV · A, with circular and elliptical iron core forms. The majority of them are circular, while the elliptical ones have a smaller M0 (spacing between iron core columns), which allows for a reduction in material usage. The corresponding coils are elliptical. Low voltage coils are available in both wound and foil types, while fuel tanks come in a few with heat dissipation pipes and most with corrugated ones. [3]

(3) Dry-type transformer

In recent years, dry-type transformers have developed rapidly in China. In major cities such as Beijing, Shanghai, and Shenzhen, dry-type transformers have accounted for 50%, while in other large and medium-sized cities, they have also accounted for 20%. There are four types of structures for drying: epoxy resin casting, filler casting, wrapping, and impregnation. At present, open ventilation H-class dry-type transformers are widely used in Europe and America, which is a new type of H-class dry-type transformer developed by absorbing the characteristics of the wrapped structure on the basis of immersion and using Nomex paper. Due to its high price, it has not yet been promoted in China. At present, the dry-type distribution transformer with the largest short-circuit test capacity in China is 2500KV · A and 10/0.4KV; The dry-type power transformer with the highest capacity through short-circuit testing is 16000KV · A and 35/10KV. [3]

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