They are transformers covered under vacuum with OG coils and epoxy cast resin; AG coils are transformers in which both cast resin and resin-absorbed prepreg.
They are produced with the power range of 160 – 25000 kVA up to 36 kV voltage level with the option of natural air-cooled (AN) or fan-cooled (AF). (Power increase up to 50% is provided by using cooling furnace.)