As an important part of rural power grid distribution, oil immersed transformers are also a common type. They use transformer oil as insulation and cooling medium, which has the advantages of durability, waterproofing, and low cost. They are mainly composed of iron core, winding, oil tank, oil pillow, insulation sleeve, tap changer, and gas relay.

Oil immersed transformers have also gone through several versions of standards. The old S7 and S9 have been phased out, while the commonly used S11 and S13 on utility poles, as well as the new national standards S20 and S22, and the amorphous iron core SH15, SH21, and SH25, have been replaced. In addition, there are various specialized transformers for specific purposes. For example, high-voltage transformers used in experiments, transformers used in electric furnaces, transformers used in welding, and transformers used in thyristor circuits.