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Metros & Urban Rail

A Q&A with Stephen Goh, Technical Director – Traction Power Systems

Stephen Goh

Stephem Goh has 28 years in-depth railway traction power expertise, electrification infrastructure experience and rolling stock expertise, coupled with an awareness of risk and environmental issues and solutions. 

He has breadth of management experience in all aspects of railway electrical engineering and has worked as the design manager/lead engineer of traction power design teams globally with experience working in client offices in the UK, Sweden, Singapore, Taiwan, South Africa and Australia.

Stephen has in-depth knowledge of current and emerging technologies and their practical applications; such as light rails, suburban commuter trains, high speed trains, freight trains and innovative solutions (energy, cost, regenerative braking & recycling of braking energy) for 750V DC, 1500V DC, 25kV AC (RR & BT) and 25-0-25kV autotransformer (AT) electrification systems. 

He has also designed systems catering beyond the short term operational needs so as to provide the future expanded capacity which integrates with existing systems. He has a PhD Electrical Engineering (Power Systems and Power Electronics Systems) from Staffordshire University (UK). 

In this article, Stephen shares a few of his thoughts on traction power systems technology and future developments.

Passenger RailWhat are the most important considerations when selecting traction power systems for passenger rail compared to light rail or metros systems?

When selecting optimal traction power systems for either passenger rail or light rail or metro systems, there are a number of key considerations to assess:

  • Capacity, e.g. service level, number of passengers per train, number of cars;
  • Types of trains, e.g. EMU, Power car or Locomotive driven;
  • Maximum power demand of each train. This will affect the top speed of the trains; 
  • Journey time;
  • Availability of High Voltage (HV) supply connection points for DC Substations/ AC Feeder Stations along the route;
  • Availability of land for installing the DC Substations/AC Feeder Stations.

Take passenger rail for example. Customers invariably expect a high level of service – in terms of capacity, frequency, availability – throughout morning and evening peak commuting periods. More so than light rail or metro systems, passenger rail needs to be fast, reliable and sustainable for high capacity – and importantly – consistent volumes of commuters.

As such, passenger rail services demand significantly more power that its rail counterparts. To put it in perspective, a 1500V DC power system will require a large number of substations to support such a service and the availability of supply connections is a crucial requirement. 

On the other hand, a 25kV or 2x25kV AC system will require a small number of 25kV Feeder Stations and may be easier to find HV supply connection points. For a new built passenger line, the obvious choice of traction power system is a classic 25kV AC or 2x25kV AC autotransformer system. 

Of course, the optimal solution is very individual to any given project so there definitely isn't a 'one size fits all' approach.

What have been the most important developments in traction power for light rail systems in recent years?

There have been a number of major developments in the last few years, notably regenerative braking and wireless/wire-free traction power systems.

Regenerative braking is a particularly efficient, sustainable solution by which expended braking energy is converted from kinetic energy to electrical energy and being recycled to other accelerating trains on the network, thereby saving energy consumption. 

Another crucial development has been the introduction of “wireless” or “wire-free” traction power systems for the historical areas or CBD areas where the overhead wires are considered visually unattractive. 

Thanks to the battery and/or super capacitor technologies developed by a growing number of international manufacturers, wireless systems are now a reality. Cities like Nanjing (China), Seville (Spain), Kaohsiung (Taiwan), Bordeaux (France), and Guangzhou (China) are fantastic examples of major urban areas which have modernised with wireless tram or light rail systems. 

Ralph Moulang, Aurecon’s Principal Overhead Wiring Engineer based in Melbourne, Australia, recently wrote an excellent article exploring these developments in further detail. You can read it here

Encouragingly, I see “green” developments in traction power systems on the horizon for urban transit systems around the world, perhaps including a development towards less overhead wires around CBD areas.

What have been the most exciting traction power project(s) you have worked on in the last five years?

The most exciting traction power projects I have worked on in the last 5 years are:

  • Crossrail project (London, UK). I designed this 2x25kV AC AT system. I believe it is the world’s first 2x25kV AC AT system for metro trains. It can save up to 30% energy through recycling of train braking energy.
  • Gold Coast Light Rail project (QLD, Australia)
  • Dockland Light Rail project (London, UK)
  • City Rail Link (CRL) extension project (Auckland, NZ)
  • Adelaide Electrification project (Adelaide, Australia)
  • Edinburgh Tram project (UK)

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