15 kV AC railway electrification

A pylon of a single-phase AC 110 kV power line near Bartholomä in Germany. Lines of this type are used in Germany to supply electric railways with single-phase AC at 16.7 hertz. In the substations of the railway, transformers are used to step it down to 15 kV.

Railway electrification using alternating current (AC) at 15 kilovolts (kV) and 16.7 hertz (Hz) are used on transport railways in Germany, Austria, Switzerland, Sweden, and Norway. The high voltage enables high power transmission with the lower frequency reducing the losses of the traction motors that were available at the beginning of the 20th century. Railway electrification in late 20th century tends to use 25 kV, 50 Hz AC systems which has become the preferred standard for new railway electrifications but extensions of the existing 15 kV networks are not completely unlikely. In particular, the Gotthard Base Tunnel (opened on 1 June 2016) still uses 15 kV, 16.7 Hz electrification.

Due to high conversion costs, it is unlikely that existing 15 kV, 16.7 Hz systems will be converted to 25 kV, 50 Hz despite the fact that this would reduce the weight of the on-board step-down transformers to one third that of the present devices.