All these transformers are designed, manufactured and supplied against specific requirement of supply voltage for the equipment. e.g. Equipments imported from American Countries work on supply voltage of 110/120 V, 1-Ph or 200/220 V, 3-Ph. Depending upon the type of equipment, Step up/ step down transformers can be supplied in both auto wound type or isolated type.
Similarly step up or booster transformers are supplied for the areas, where the supply voltage is usually very low.