Depending on the transferred power, the transformers can be 3-phase or 1-phase and can have one or two valve windings per phase. The valve windings are exposed to AC and DC stress and therefore a special insulation design is necessary. Additionally, the load current contains a considerable amount of harmonic that leads to higher losses and higher noise. Above all, special bushings are necessary for the valve windings, where normally both ends are brought outside the transformer tank. Special DC and polarity reversal tests have to be performed to check these windings.

Besides the standard parameters of each transformer, special parameters must be known for the design of an HVDC transformer. These parameters are normally determined by the designer of the HVDC station in consultation with the transformer designer in order to reach a cost-effective design for both the transformer and the whole HVDC station.