Transformer design for dual-voltage applications

Multiple voltage levels often exist in a power transmission or distribution system. Additionally, existing systems may be changed from one voltage level to another. Purchasing transformers capable of operating at multiple voltage levels is an option that gives the user flexibility to install a transformer at multiple locations in the system, or readily adapt to anticipated system changes. The multiple voltages are achieved through changing winding connections inside the transformer, either through the use of an externally operated switch (or switches) or through internal terminal boards. Changes to internal connections may involve connecting windings or sections of windings in series or parallel or to buck or boost, and also windings or sections of windings may be tapped out of the circuit altogether. Special considerations must be made in the design and construction of such transformers because many factors, including the impedance, load losses, core losses, localized heating and short circuit forces, may be affected when changing from operation at one voltage level to another. The focus of this discussion will be to familiarize transformer users with some of the commonly used winding arrangements and to discuss the impact on the transformer´s design and construction