FS Class E.431

Class E.431
Italian 3-phase locomotive FS Class E.431 at the railway museum in Savigliano, Italy
Type and origin Power type electric Builder Tecnomasio Italiano-Brown-Boveri and Ansaldo Build date 1922-1925 Total produced 37
Specifications Configuration: ​  • AAR 1-D-1  • UIC 1'D1' Gauge 1,435 mm (4 ft 8 1⁄2 in) standard gauge Driver dia. 1630 mm Loco weight 91 tonnes Electric system/s Three-phase overhead line 3.6 kV, 16.7 Hz
Performance figures Maximum speed 100 km/h Power output 2,000 kW
Career Operators FS Disposition Two preserved

The FS Class E.431 was a class of three-phase AC electric locomotives of the Italian State Railways (FS).

The E.431 was a class of 37 locomotives, built between 1922 and 1925 by Tecnomasio Italiano-Brown-Boveri (TIBB), divided into three batches, the last in collaboration with Ansaldo. The locomotives were designed and constructed to be suitable for hauling heavy trains at 100 km / h which, at the time, was considered the limit for the three-phase system. The extension of the electrified network with the three-phase system had come to involve the regions of Piedmont, Liguria and part of Lombardy. This included the cities of Turin, Genoa and indirectly Milan. With associated lines, international transits were possible. These lines were used by fast and important international trains with heavy loads (up to 20 carriages) hence the need for machines suitable for this type of service.

In practice, the E.431 did not live up to expectations. In particular, the cascade connection of the motors at the lower speeds gave insufficient tractive effort, affecting performance during starting and uphill travel. They were not, therefore, used on the Frejus and Brenner lines, while on the remaining climbs, in particular on those that lead from the Ligurian coast to the hinterland, they were always used in multiple. These problems were solved, even if not definitively, with Class E.432 which had different control systems. On the flat, the E.431s could show off their speed, hauling the trains for which they were designed, but even here they sometimes worked in multiple. Some attempts to improve performance when running in cascade mode were made during the early years of service but they were not very successful.

With the conversion of the three-phase lines to direct current operation, the E.431s were progressively withdrawn but some locomotives remained in service on local trains until the end of the three-phase system occurred in 1976.