On Aug 12, 10:36*am, wrote:
On Wed, 12 Aug 2009 10:26:30 +0100

"Recliner" wrote:
True, but the new Victoria line trains are longer, faster and more
frequent, so that may account for some of the extra power.

I suppose.

I don't see why trains shouldn't also get significantly more efficient,
more comfortable and more reliable over time (though, of course,

I don't know about reliability but there does seem to be a trend of every
new electric train in this country using more power than its predecessor.
In the case of the 377s significantly more. This is in stark contrast to
cars which despite getting heavier year on year are still using less fuel
with each generation. Whatever the train builders are concentrating on in
their designs, energy efficiency doesn't seem to be it.

No, you're missing the point here. Power isn't the same thing as
energy. Power rating is a peak; energy consumption is an average.

New trains have more efficient motors than older trains [thanks to the
move from DC traction to AC traction], and the weight of the 09 stock
is no higher than the weight of the 1967 stock - but instead of a peak
power rating of 848kW, it has a peak power rating of 1800kW.

That means it accelerates to line speed faster, hence putting more
load on the infrastructure, hence (alongside the regenerative braking
already discussed) the need for the power upgrade.

But it also means that it'll spend less time drawing the peak power
rating, and more time cruising - hence overall energy consumption
won't be higher (OK, there'll slight extra air resistance and friction
from the fact that the train spends more time going faster, but this
will be small, and more than offset by the impact of regen).

With the Mk1 replacements on the Southern, it's a bit more
complicated, as the new trains were heavier and had power doors,
aircon, etc - but again, a lot of the difference was higher peak draw
not higher overall energy consumption.

--
John Band
john at johnband dot org
www.johnband.org