Regenerative braking and Melbourne’s trains

This week Melbourne newspaper The Age ran an article about Melbourne’s aging railway infrastructure – in particular the power supply system. So how much truth is there to it?

Comeng passes the Campbellfield substation on an up Upfield service

The relevant portion of the article is this:

Metro’s five-year plan includes a target to cut power use by 10 per cent for each kilometre of train travel. It aims to achieve this through the use of regenerative braking technology, which uses a train’s motor and brakes to put power back into the overhead wiring to be used by other trains.

But little progress has been made in the two years since it put the power-saving proposal to government, with the high cost and practical difficulty of applying the technology to Melbourne’s rail system being blamed.

Metro said a computer simulation on the hilly Lilydale line had shown the energy regenerative braking technology would save electricity.

”This showed that once the technology is affordable, a business case can be made so that it’s commercially viable,” spokeswoman Larisa Tait said. ”The technology is in its infancy and is currently very expensive and we are waiting for the cost of the storage units to reduce.”

Additionally, many of the electrical substations that help power the network and which were built in the 1920s when Melbourne’s rail lines were first electrified are not equipped to handle regenerated electricity.

On the subject of regenerative braking, the spokesperson at Metro is poorly informed – the technology is well proven overseas and widely deployed, as this 2007 article from the Railway Gazette details how Japanese railways have taken advantage of it:

Regenerative braking became popular for normal service braking even in the DC traction era of the late-1960s, when field chopper control was introduced by many private railways. Metros followed in the 1970s when armature chopper control was introduced. In the 1980s, AC traction motors replaced DC motors for almost all EMUs and regenerative braking capability became inherent in the power control circuits. Except for special circumstances, dynamic braking where energy is dissipated in resistance grids was abandoned because of the additional weight, cost and potential danger of fire.

In addition Melbourne existing Siemens and XTrapolis train fleets are already equipped with regenerative braking, but unfortunately in Melbourne it isn’t used as intended – most of the time the energy captured from the stopping train is thrown away because no other trains are around to accept the current.

The Railway Gazette has more to say on the issues facing the reuse of energy:

In regenerative braking the current is returned to the overhead line or third rail. Until relatively recently, regenerative braking was mainly employed on DC electrified lines. However, braking is dependent on the ability of other trains on the same route to accept the current. This is known as receptivity and is affected by a number of variables, including location, traffic density and line voltage. On a busy suburban service at peak times receptivity can be as high as 15%. On a line with long sections between stations and low service frequency it can fall below 5%.

Early implementations of regenerative braking used large resistor grids in the substation to ‘burn off’ surplus power from the system as heat, which increased the receptivity of the overhead system, but with the side effect of letting the generated energy go to waste.

However, a solution to that problem is on the horizon, and this might be the ‘technology is in its infancy’ that the Metro spokesperson spoke of. Trials of batteries at substations for energy storage have been carried out in the USA, as have flywheel based systems onboard trains, and supercapacitors onboard trams.

So what about the comment from Tony Morton, president of the Public Transport Users Association?

We still operate a 1920s vintage power-supply system for our trains. Fifteen-hundred volts DC was state of the art when it was first put in, but virtually all of the other 1500-volt DC infrastructure around the world – or certainly in the developed world – has since been upgraded to the contemporary standard.

That is a half truth – three major users of the same 1500 volt DC system used in Melbourne are:

  • Shanghai Metro – the longest metro system in the world
  • Hong Kong’s Mass Transit Railway – the go to example of how to run a railway
  • Japan’s commuter railways – famous worldwide for on time trains

Stating that Melbourne’s choice of railway electrification system is holding us back makes as much sense as saying that traffic lights hold back our road network – both are technologies perfected decades ago, and both have limitations compared to the latest developments, but pretending they are the reason for Melbourne’s transport network being in the stone ages is a misinterpretation.

Footnote

Despite what I have written above – Melbourne’s rail network does rely on a clapped out power supply system – the following figures are from a 2007 report on the issues and challenges facing it:

Franchise renewals per year, as fractions of total:

  • AC circuit breakers: 3 out of 126 (2.4% pa)
  • Rectifier units: 2 out of 81 (2.4% pa)
  • DC circuit breakers: 10 out of 457(2.2% pa)
  • Signal transformers: 1 out of 67 (1.6% pa)
  • Frequency converter units: 0 out of 6 (0% pa)

If design life is 30 years then 3.3% pa is the benchmark.

And the problems caused by a lack of infrastructure renewal:

  • Increasing maintenance debt
  • Maintenance level does not account for increasing capacity
  • No augmentation to match future demands
  • Compounding factors: maintenance debt + no capacity increase = High level of deferred costs

Deferred maintenance of railway infrastructure – where have we heard that before?

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13 Responses to “Regenerative braking and Melbourne’s trains”

  1. Tom the first and best says:

    Can they not just put the electricity back into the grid?

    • Marcus Wong says:

      For 25 kV AC electrification systems feeding back into the grid is common, but for DC system like Melbourne it is a lot more complicated: you need to convert the DC power the train back to AC power as found on the grid, which requires additional equipment in the substations.

  2. Anonymous says:

    “same 1500 volt DC system used in Melbourne”

    Is there are reason you didn’t list Sydney?

    • Marcus Wong says:

      While Sydney is a large rail system that uses 1500 volt DC, I omitted it from my list because most people wouldn’t call it a world beating mass transit system!

  3. mich says:

    “Fifteen-hundred volts DC was state of the art when it was first put in, but virtually all of the other 1500-volt DC infrastructure around the world

  4. Daryl says:

    The VR L-class electric locomotives had dynamic braking which fed power back into the overhead. I heard it was very effective.
    These locos entered service in the early ’50s.

    The NSW 46-class (similar vintage) also had dynamic braking. Apparently they can balance the dynamic brake lever with the ‘throttle’ so that it acted as a cruise control. Don’t think it was meant to.

    The larger diesel locos have dynamic braking but the electricity is fed into a dummy load which I think was an air cooled brass grid.

    T413 is the only T-class which has dynamic braking, I used to fantasize about covering it with a thousand light globes which lit up when going downhill.

    • Marcus Wong says:

      Back in the 1980s a number of W class trams were covered with light bulbs for advertising purposes – I can only imagine T413 with the same setup!

  5. Myrtonos says:

    Another thing to do would be to somehow use regerative braking to power accessories, particularly the air-conditioners. In fact regerative braking has been around for a very long time. Its first use in Australasia was on a hilly line just west of the Sydney metropolitan area.

  6. David Mason says:

    Marcus thanks. Is there a published link you know of to how much electricity Melbourne’s network actually uses; and perhaps to what their supply contracts are? Interested in what potential there is for specifying a percentage to come from renewable energy sources as the Dutch are reported to have done.

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