Home >> Science & Nature >> Science

Transformer Connection Types

Three-phase transformers have three low voltage and three high-voltage windings. Each winding has two end points that can be connected in various ways. Depending on whether the winding ends are connected to each other or to a common ground, the transformer connection type is a combination of wye and delta connections. Power-grid designers use these different transformer connection types for stepping voltages up or down and the different types have various advantages and disadvantages.

Delta-Delta
- The delta transformer connection type involves connecting the ends of the three high-voltage and three low-voltage windings end-to-end to form two triangles. Each winding is powered by two of the phases of the electric grid and sees the phase-to-phase voltage. A winding on the high-voltage side, forming one leg of the high-voltage triangle, induces the lower voltage in one winding on the low-voltage side. This connection type has the advantage that maintenance or repair technicians can remove one pair of high- and low-voltage windings and the transformer will still be able to carry a reduced load.
Wye-Wye
- A wye connection involves connecting the three ends of one side of the high-voltage windings together and to ground. The other three ends are connected to the three power grid phases to form a star or Y-shaped configuration. The transformer has the same connections for the low-voltage side. Each high-voltage winding induces the low voltage directly in the corresponding low-voltage winding. Utilities use wye-wye transformers in their distribution networks because of their simple design and low cost.
Wye-Delta
- Wye-delta transformers have their primary windings connected in the wye configuration and the secondary windings in delta. This connection type is common for step-down transformers because the wye-connected high-voltage windings only see the lower phase-to-ground voltage instead of phase-to-phase voltages. This reduces insulation costs in the high-voltage windings. For the lower voltages of the low-voltage winding, the insulation costs are not as high.
Delta-Wye
- Delta-wye transformers have their primary and secondary windings connected in the delta and wye configurations, respectively. Similarly to the wye-delta type, utilities use this type of transformer for step-up transformers to save on insulation costs in the secondary, high-voltage windings. In addition, since only the wye side windings have a ground connection, both the delta-wye and wye-delta tranformers isolate the delta side systems from ground faults occurring on the wye side.

Science