The basic types of transformers are three-phase and single-phase.
Three-phase 7-wire transformers, three-phase 3-winding transformers, and transformers for both motive and illumination power are examples of transformers that obtain power and electric light from a single unit.
Replacing two transformers, one three-phase and one single-phase, with one transformer saves space.

(1)A three-phase 3-winding transformer is a transformer that can supply power to a three-phase load (power) and a single-phase load (electric light) or a three-phase load (power) and a three-phase load (power) simultaneously with a single three-phase transformer.
(2)A three-phase 3-winding transformer is one in which the primary, secondary, and tertiary windings are isolated.

Transformers need to be selected according to the primary-side power receiving environment and the secondary-side load conditions, as well as the wiring and number of phases.

For details, please refer to the video.

2023.2.17：FAQ What is three-phase 7-wire transformer for low-voltage power receiving and distribution?