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Class 455 EMUs state of the art traction upgrade

Part of a £40m investment in South West Trains’ Class 455 EMUs


Vehicle Class

Number of Cars






Scope of Work




Porterbrook Leasing Company contracted GRT to upgrade the traction system on their fleet of 91 Class 455 EMUs, Sub Classes 455/7, 455/8 and 455/9 with modern three-phase AC traction motors and Insulated-Gate Bipolar Transistor (IGBT) technology traction.

Scope of work

As part of a £40m investment in South West Trains’ Class 455 EMUs, the Class 455 EMUs are one of the first EMU fleets in the UK to benefit from a state of the art traction upgrade.

Work carried out

This new technology transforms older units into modern trains and delivers an economical solution to the most pressing business
needs, including increasing passenger demand. The cost for leasing and maintaining this fleet will be substantially lower than investing in new trains.

Kiepe Electric in Düsseldorf were responsible for the manufacture and delivery of the integrated solid-state traction equipment whilst GRT based in Birmingham provided the Turnkey Project responsibility for the design and integration engineering, approvals, installation and testing of the equipment.

  • The work started on the trial Class 455 Unit at Wimbledon depot in June 2014, on-track testing commenced in March 2015 and the Unit entered into service in April 2016.
  • The second trial unit was also modified at Wimbledon depot with the production EMUs being re-tractioned at Eastleigh depot.
  • The project included the re-tractioning of the two motor bogies in each of the Class 455 Units Motor Second Open (MSO) vehicles where the existing 2 off DC Motors bogie are replaced with 2 off new, lighter, axle-hung nose suspended three-phase AC traction motors that offer greater energy-saving efficiencies.
  • The new AC traction motors were designed to be direct replacements for the DC machines. The work also included the replacement of the 750V DC camshaft control system on each EMU with an AC three phase Variable Voltage Variable Frequency (VVVF) inverter.

Key benefits

  • The new AC traction motors achieve a weight saving of 500 kg per motored axle compared to the original design which makes the wheel sets more track friendly. There will also be reduced maintenance, service and repair costs as AC traction motors have a smaller number of moving and wearing parts compared to the original DC traction motors.
  • The new IGBT Traction System provides a regenerative braking facility that uses the traction motors as generators when the train is braking. The electrical energy generated is fed back into the 750 V third rail DC supply and offsets the electrical demands of other trains on the network.
  • Tests have shown that the energy consumption can be reduced by between 10 per cent and 30 per cent, depending on conditions. With the increasing cost of energy, regenerative braking has a massive positive cost impact on the long-term operation of these trains. If the supply is non-receptive, the generated power is dissipated by the rheostatic brake.
  • The project included a replacement of the brake control equipment with a modern Knorr Bremse EP98 brake control system. This system provides the necessary brake blending between this new electric or dynamic braking on the MSO and the existing conventional friction braking system across the unit to maximise the savings that can be made.
  • The Wheel Slide Protection (WSP) system is operable on all four vehicles of the unit and is upgraded to improve stopping distances, reduce the occurrences of wheel flats and other wheel tread faults in low adhesion conditions when compared to the existing system. The new braking system with WSP has another major benefit of reducing friction brake and wheel set maintenance.


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