Scott-T transformer

Nikola Tesla's original polyphase power system was based on simple-to-build two-phase four-wire components.

However if a two-phase load is not balanced (more power drawn from one phase than the other), no arrangement of transformers (including the Scott-T transformers) can restore balance: Unbalanced current on the two-phase side causes unbalanced current on the three-phase side.

Since the typical two-phase load was a motor, the current in the two phases was presumed inherently equal during the Scott-T development.

In modern times people have tried to revive the Scott connection as a way to power single-phase electric railways from three-phase Utility supplies.

The customary maximum capacity of such a distribution transformer is 333 kVA (a third of a megawatt at unity power factor).