Dual voltage transformer is defined as a transformer that consists of two separate windings which can be connected in series to handle a specified voltage and kVA, or in parallel to handle the same kVA at one half the series connected voltage. The voltage is changed by operating a dual voltage switch.

A dual voltage distribution transformer is protected by an internally installed, multi-rated surge arrester which is selectively connected with plural primary windings by a dual voltage switch such as to establish a high surge voltage protection level when the primary windings are connected in series by the switch and a correspondingly lower surge voltage protection level when the primary windings are connected in parallel by the switch