Feel the power

Source: Rail Technology Magazine Apr/May 2012

A £22m project that started in 2008 to fit more than 200 trains in the South West Trains fleet with regenerative braking is now complete. RTM spoke to the operator’s engineering director Christian Roth.

Investing in regenerative braking is one of those business decisions that can be safely labelled as a no-brainer. With energy saving costs in the 20% region, and even higher in high-traffic parts of the network, the associated environmental benefits, and a return on investment in under a year, it’s no wonder South West Trains chose to convert much of its fleet.

The project began in 2008, when its 30 Class 458s were upgraded to enable regenerative braking, where the energy ‘created’ by braking is returned to the third rail for use by other trains, instead of being wasted.

From 2010-2011, testing and upgrading began on the operators’ 172 Desiros too (Classes 444 and 450), so now trains in the London suburban area and out to Guildford, Alton, Portsmouth, Reading, Southampton and Weymouth are all fitted with the energy-saving technology.

Winning approval

South West Trains engineering director Christian Roth told RTM: “It took about a year to fit all the Desiros and get them all up to speed.

“Modern electric trains have been braking electrically for many years, but the electric braking energy went into a braking resistor, instead of back to the conductor rail as now. The friction braking on the train remains as it is and was in the past.

“The biggest issue was not really the change on the train side; it was actually the approvals, and issues to do with interference with signalling systems, and the interface with London Underground.”

As Roth says, the complexity was not in the technological upgrade – this is fairly standard, and the principle is decades old. “The complexity was really in managing all the different parties involved; so on the 458s, there was Alstom as a supplier, for the Desiros we had Siemens, then Network Rail on the power and signalling side, then London Underground with their specific requirements in the London area.

“It was all quite time-consuming, so the approvals process took longer than anticipated, especially because of the London Underground issues. The technical element was less of a challenge than getting all the approvals and paperwork needed!”

Virtuous circle

Receptivity can be a problem for regenerative braking systems – getting other trains on the network to ‘accept’ the returned current.

There have been no such issues with this project, although the actual regenerative rates achieved do vary starkly based on the service frequency in the area.

In the London area, rates can be in the 20s and 30s percent region, while in more remote areas in the South West, such as between Southampton and Weymouth, it is more like 8%, he said.

Twenty units have been equipped with metering equipment to monitor the regenerative braking rates and thus energy savings, which can be compared with a baseline established before the system was ‘switched on’.

Roth said: “We have quite a good understanding of the mechanism and the different rules and service patterns. You can only get that through energy metering.”

Saving energy

In all, the operator estimates that the switch will save 50 million kWh of electricity annually – enough to power more than 11,500 homes for a year.

The project was not mandated by anyone else, Roth said. “It was a South West Trains decision to do this. There is a very good business case – a return on investment in less than a year – so there was a strong argument to do this, on top of the environmental benefits.”

He was full of praise for Siemens and their excellent working relationship with the company, saying: “It would not have been possible to coordinate and implement such an ambitious programme without the support and excellent working relationship with our Desiro maintainer Siemens.”

The modifications to the Desiros were carried out by Siemens technicians during the nightshift and at weekends to minimise disruption to the service.

South West Trains is a subsidiary of Stagecoach Group, which is investing £11m across its group in sustainability measures.

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