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. This will not result in balanced current on the three-phase of being equal. The instantaneous difference in loading on the two sections will be seen as an imbalance in the three-phase supply; there is no way to smooth it out with transformers. Back to back arrangement The Scott-T transformer connection may also be used in a back-to-back T-to-T arrangement for a three-phase to three-phase connection. This is a cost-saving in the lower-power transformers due to the two-coil T connected to a secondary two-coil T instead of the traditional three-coil primary to three-coil secondary transformer. In this arrangement the X0 neutral tap is part way up on the secondary teaser transformer (see right). The voltage stability of this T-to-T arrangement as compared to the traditional three-coil primary to three-coil secondary transformer is questioned, as the "per unit" impedance of the two windings (primary and secondary, respectively) are not the same in a T-to-T configuration, whereas the three windings (primary and secondary, respectively) are the same in a three transformer configuration, if the three transformers are identical. Three-phase to three-phase (also called "T-connected") distribution transformers are seeing increasing applications. The primary must be delta-connected (Δ), but the secondary may be either delta or "wye"-connected (Y), at the customer's option, with X0 providing the neutral for the "wye" case. Taps for either case are usually provided. The customary maximum capacity of such a distribution transformer is 333 kVA (a third of a megawatt at unity power factor). See also Alternating current Polyphase coil Symmetrical components High-leg delta References Electric transformers AC power fr:Transformateur électrique#Transformateur diphasé-triphasé