Power transformers can be classified in several ways. By function: step up, step down, auto transformer, phase shifting and regulating transformers. By winding configuration: two winding, three winding, and auto connected types. By phase: single phase and three phase units. By cooling: oil immersed and dry type with many subcategories. By application: generator step up, transmission, distribution, furnace, traction or converter transformers. Although lists differ, in practice engineers focus on function, voltage level, cooling and winding arrangement when specifying the particular type needed for a project.