"Dr J R Stockton" wrote in message
nvalid...
In uk.transport.london message
om, Tue, 12 May 2009 20:33:14, Tony Polson
posted:
Dr J R Stockton wrote:

Wiki Electric locomotive indicates that ordinary engine powers are in
the 5 MW range. Therefore, significantly more than a ton of SCs would
be needed to approach ordinary performance levels And a ton of SCs
would give 0.03 MWh, corresponding to less than half a minute of 5MW.


Looking at those data another way, 5.0 tonnes of SCs (say) would provide
two and a half minutes of 5.0 MW. That's about 208 kWh.

All of that 208 kWh could come for free, from regenerative braking - in
other words saving about £20 each and every time it gets used.

But you have to add the cost of transporting that five tons, plus the
weight of the gear required to mount and use it - and you have to
compare it with regenerative braking by (in principle, it will not be
that simple) reversing the motors and putting the energy back into the
wires.

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Coupla things: 1) the amount of energy required to keep a train rolling,
given steel wheel - steel rail's low rolling resistance is that required to
overcome drag. Drag is not related to mass. Any energy storage system using
regenerative braking to charge, in essence uses its braking force to provide
acceleration. It's not a perpetual motion machine, so there are losses.
Efficiencies in the 80's% are cited. Assuming this is 85%, then basically
15% of the energy needs replacing at each acceleration cycle. Again,
assuming that maximum axleloads for 160km/h running are around 21t, and
current EMU motor cars, under crush passenger load weigh in the 60s of
tonnes, then there's scope for over 10t of storage media. Let's make it 5t.
A total unit mass of around 200t with a crush load of pax (200 ~ 15t in each
car). Then you'd need enough energy to accelerate 205t instead, that's 2.5%
more mass, total increase in consumption of 2.5% (assuming linearity). Now,
as you're regenerating 85% of it, your consumption (for acceleration) is
15.375% of non-regenerative energy usage, a saving of 84.635%. That's what
you pay for the extra hardware with. The cruising energy consumption is
unchanged. The auxilliary energy consumption is unchanged. The big amperage
part, that which strains the supply system, is cut by 84.635%. In essence,
stored energy equipped trains can be used to increase passenger capacity on
electrified routes much more cheaply simply because they do not increase the
instantaneous load on the power supply system. On non-electrified routes, a
major saving in fuel can follow. Indeed, the number of diesel engines needed
can be cut, or better still lighter gas-turbines used, running at constant
power. The lighter internal combustion plant mass allows for more energy
storage media, etc ... until the optimising point is found. I don't have
the formula.

Not all electrified sections can use regenerative braking output; depends on
the substations. Where it is possible, in some cases, it's limited to the
amount of traffic at the time - whether the regenerated energy can be used
by another train in the same electrical section. In other cases, surplus
current can be returned to the grid. All substations have limits on their
current handling. So, on board energy storage media would still have a
place, even when regeneration to the supply network is possible.

2) the following, extracted from
http://www.railwaygazette.com/news_v...tteries.ht ml

may be of interest ....

USA: GE Transportation has announced plans for a $100m plant to produce
batteries for hybrid locomotives and heavy-load applications in the marine,
mining, telecoms and utilities sectors. Production is planned to start by
mid-2011, with the capacity to produce 10 million cells a year, equivalent
to 900 MWh, or 1 000 hybrid locomotives.

GE has invested more than $150m developing battery technologies, including a
high energy density sodium-based battery. The first application will be the
Evolution Hybrid locomotive, which uses batteries to recover braking energy.
A demonstrator was unveiled in May 2007, and commercial production is
planned for 2010.

'Hybrid locomotives, and the battery technology on board, could be an
important part of how we ship goods by rail in the future', said Matthew K
Rose, Chairman, President & CEO of Burlington Northern Santa Fe Corp. 'The
ability to produce a battery pack designed for rail applications is a
significant milestone to producing a commercially available hybrid
locomotive that will further enhance rail's reputation as the most
environmentally sound mode for moving freight in America.'

end of quote

The US GE company should properly be regarded as a bastion of conservative
railway/railroad engineering. They wouldn't be moving in this direction just
to get a few headlines.

Cheers

David down under