Can a Transformer Convert Single Phase to Three Phase?

Although single-phase power can be derived from a three-phase power source, a transformer cannot convert single-phase power to three-phase power. Converting single-phase power to three-phase power requires either a phase converter or a variable frequency drive.

Although a transformer does not function as a phase-changing device or transform single-phase input power into three-phase out, transformers can be designed for connection to other phase configurations besides single-phase and three-phase, including two-phase, six-phase, or even 24-phase for certain DC rectification transformers. Commonly, a single-phase component can be connected to only one of three phases of a three-phase power source. In addition to powering a large three-phase load, for instance, one leg of a three-phase transformer is often used to feed a low power single-phase load, such as a cooling fan.

Voltage into a three-phase application can be stepped up or down as required by either:

Connecting three single-phase transformers—having one coil and core each—
together, thus forming a “three-phase transformer bank,” or,
Using a single three-phase transformer—having three coils, one for each phase—
assembled onto a single laminated core.
To be compatible with a three-phase supply, three single-phase transformers can be connected together in a way that functions electrically like a three-phase transformer. That is, if the primary windings of three single-phase transformers are properly interconnected into a delta or wye configuration and the same is done with the secondary windings, they will operate much like a three-phase transformer, using three-phase power in to deliver three-phase power out.

The benefits of using a three-phase transformer compared to three single-phase transformers? The three-phase design utilizes windings, core, and available space more effectively, where using three single-phase transformers to accomplish the same electrical design objectives typically only increases labor, size, weight, and cost.