Estimation of the Zero Sequence Voltage on the D-Side of a DY Transformer by Using One Voltage Transformer on the D-Side

The usual practice to measure the zero sequence voltage on the D-side of a transformer is to use three voltage transformers (VT), each of them connected between each phase and earth on the primary side and broken-delta connected on the secondary side. In this paper a method is presented for the estimation of the zero sequence voltage on the D-side of a Dy transformer by the use of only one VT connected between one phase and earth on the D-side and three VTs and current transformers (CT) on the y-side. The method is first introduced theoretically. Results from simulations and laboratory tests are then presented. The method proved to be accurate with an observed maximum error around 7% of nominal phase-to-earth voltage during transformer energization and below 1% in all other cases.