If a transformer is connected using 4 wires, what type of configuration is it?

When a transformer is connected using four wires, it indicates a Wye (or Star) configuration. In this setup, three phases of the transformer windings are connected at a central point, which is the neutral point. The four wires consist of the three phase conductors and one neutral conductor that allows for a return path for unbalanced loads, improving the system's stability and functionality.

The Wye configuration is particularly advantageous because it can accommodate both three-phase loads and single-phase loads. It allows for varying voltage levels: phase-to-neutral voltage is lower, which is useful for supplying single-phase loads, while phase-to-phase voltage is higher, suitable for three-phase loads. This versatility makes the Wye connection widely used in power distribution systems.

Other configurations, such as Delta, involve three conductors without a neutral and are typically used in different circumstances where phase balancing is not as critical. Series and parallel connections do not apply to transformer configurations in the context of three-phase systems, as they describe different ways of connecting electrical components rather than how transformers are interconnected in power systems.