Traction motors & drives

The traction motor converts electrical energy from the inverter into mechanical torque at the wheel or axle of European rolling stock, and reverses the conversion during braking to return energy to the traction circuit.

Three motor technologies coexist in the European fleet. DC series-wound commutator motors remain in service on older rolling stock, including some pre-1990 fleets in southern and eastern Europe, but are no longer specified for new vehicles.

AC three-phase induction motors (asynchronous motors) became standard from the 1980s, are mechanically robust, require no brush gear, and achieve conversion efficiencies of 91–94%.

Permanent magnet synchronous motors (PMSMs) are now specified for new high-speed and suburban rolling stock where energy efficiency is a priority: the absence of rotor copper losses gives PMSMs efficiencies of 96–98% and allows a 30% reduction in size and weight compared with an induction motor of equivalent power.

The efficiency gap between induction and PMSM becomes significant at scale. On a train drawing 5 MW continuously, a 3–5 percentage point efficiency gain represents 150–250 kW of avoided losses — equivalent to the full hotel power load of a 12-car intercity set.

Drive arrangement

Traction motors on modern European rolling stock are mounted on the bogie frame in one of two configurations: axle-hung, where the motor is bolted directly to the axle with a nose suspension on the bogie frame, or fully suspended, where the motor drives the axle through a cardan shaft and gearbox.

Fully suspended arrangements reduce unsprung mass and track forces; axle-hung arrangements are simpler and less costly. Some PMSM designs omit the intermediate gearbox entirely, using direct drive at the wheel.

Materials and supply chain considerations

PMSMs use neodymium-iron-boron (NdFeB) permanent magnets containing rare earth elements. China accounts for roughly 60–70% of global rare earth ore extraction, but a much larger 85–90% share of rare earth magnet processing and manufacturing — the more relevant chokepoint for traction motor supply chains.

This concentration is acknowledged as a strategic risk in both EU Critical Raw Materials Act policy and individual operator procurement decisions. Induction motors carry no such dependency, which maintains their relevance in procurement contexts where supply-chain resilience is a stated requirement.

Standards

IEC 60349-2 defines test methods for AC motors used in rail traction. EN 50155 and EN 61287-1 govern the electronics of the drive system. Traction system design must satisfy the electromagnetic compatibility limits of EN 50121-3-2 for rolling stock apparatus.