Perhaps you should consider the case for the reduced heat generation
by considering the average total power used by the whole opperational
fleet; not just one train. When a train is regenerating it is
effectively drawing negative energy.

On Jul 25, 6:49*am, gunsmith wrote:
Perhaps you should consider the case for the reduced heat generation
by considering the average total power used by the whole opperational
fleet; not just one train. When a train is regenerating it is
effectively drawing negative energy.

Let's take a step back.

If Nick is right, then the new trains will, on aggregate, use twice as
much energy as the old trains.

Given 40 years of electrical efficiency improvements, and that the new
trains do more or less the same thing as the old trains, that can't be
right can it?

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

On Jul 25, 4:38*am, Andy wrote:


A more powerful modern traction system doesn't
necessarily generate twice as much heat just because it has twice as
much power at its disposal.


I^2*R still applies.

Power (w) = Volts (V) x Amps (A)

Same 630 V voltage applied, double the power = double the current.

Double the current and the heating effect in all conductors goes up 4
times.

That is one of the laws of electricity.

Either you are continuing to suggest - as I have already commented -
the laws of phyiscs are suspended or you just plain do not understand
it.


I give up.

--
Nick

On Sat, 25 Jul 2009 03:30:18 -0700 (PDT), John B
wrote:

Given 40 years of electrical efficiency improvements, and that the new
trains do more or less the same thing as the old trains, that can't be
right can it?

Yes, if they also carry additional load (e.g. aircon) and use AC
traction, which is more lossy than DC traction.

Guy
--
http://www.chapmancentral.co.uk

"Just zis Guy, you know?" wrote in message

On Sat, 25 Jul 2009 03:30:18 -0700 (PDT), John B
wrote:

Given 40 years of electrical efficiency improvements, and that the
new trains do more or less the same thing as the old trains, that
can't be right can it?

Yes, if they also carry additional load (e.g. aircon) and use AC
traction, which is more lossy than DC traction.

But they are NOT air-conditioned. And what's the advantage of using AC
traction if it's less efficient than DC?

On Jul 25, 11:36*am, "Just zis Guy, you know?"
wrote:
On Sat, 25 Jul 2009 03:30:18 -0700 (PDT), John B
wrote:

Given 40 years of electrical efficiency improvements, and that the new
trains do more or less the same thing as the old trains, that can't be
right can it?

Yes, if they also carry additional load (e.g. aircon) and use AC
traction, which is more lossy than DC traction.

But they don't carry aircon - and if AC traction wastes more energy
than DC traction, then why has it become the standard in all new
trains?

IANAelectrical engineer, but I just don't understand why it it would
make economic sense to switch to traction types that are inherently
less efficient.

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

On Jul 25, 11:36*am, D7666 wrote:
On Jul 25, 4:38*am, Andy wrote:

*A more powerful modern traction system doesn't
necessarily generate twice as much heat just because it has twice as
much power at its disposal.

I^2*R still applies.

Power (w) = Volts (V) x Amps (A)

Same 630 V voltage applied, double the power = double the current.

Double the current and the heating effect in all conductors goes up 4
times.

That is one of the laws of electricity.

Either you are continuing to suggest - as I have already commented -
the laws of phyiscs are suspended or you just plain do not understand
it.

No, you're missing the point, as far as I can make out.

If my excellent new power system gives me the *possibility* of using
1MW of power, when the previous power system only gave me the option
of 0.5MW, that says *absolutely nothing* about how much power (-
heat) I'm actually going to use.

And if the 1MW of power allows me to go from 0-90km/h in 20 seconds
instead of 40 seconds, then obviously the new train will be drawing
more power than the old train for the first 20 seconds... but then
it'll be in cruise instead of acceleration for the next 20 seconds,
and hence will be drawing much less power than the old train would, so
the total energy used won't be much different.

The actual *use of energy* will increase to match the higher rating of
the power system only if the power upgrade solely caters for increased
car weight, worse traction motor efficiency, more ancillary services,
etc, and doesn't actually improve acceleration.

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

On Sat, 25 Jul 2009, D7666 wrote:

On Jul 25, 4:38*am, Andy wrote:

A more powerful modern traction system doesn't necessarily generate
twice as much heat just because it has twice as much power at its
disposal.

I^2*R still applies.

Power (w) = Volts (V) x Amps (A)

Same 630 V voltage applied, double the power = double the current.

Double the current and the heating effect in all conductors goes up 4
times.

That is one of the laws of electricity.

Either you are continuing to suggest - as I have already commented -
the laws of phyiscs are suspended or you just plain do not understand
it.

I give up.

Not yet, i want a go!

So the new trains have twice as much power as the old trains (where
'twice' means 2.12 times as much or whatever). When both trains are
accelerating at full tilt, the new ones will draw twice as much power.
Presumably, though, the new trains will thus accelerate faster, and so
reach their top speed sooner - and then stop accelerating, and stop
drawing power. Doesn't that mean that the mean power consumption over a
whole start - cruise - stop cycle will be less than the peak power would
lead you to think? Do we have figures for the whole-cycle power
consumption? Or is that what the figures that are being bandied about are?

tom

--
Rapid oxidation is the new black. -- some Mike

On Fri, 24 Jul 2009, Recliner wrote:

"Tom Anderson" wrote in message
th.li
On Thu, 23 Jul 2009, Recliner wrote:

"Tom Anderson" wrote in message
rth.li
On Thu, 23 Jul 2009, Peter Masson wrote:

"Tom Barry" wrote

If they'd only had aircon...

Among the problems with aircon on the tube lines is - where do you
dump the heat?

You'd have to install a fake open air. By which i mean some point on
the line where trains could stop and offload their heat - some
apparatus they sit inside which blows a gale of super-cooled damp air
(or even water) into their heat exchangers, and sucks the warmed
exhaust out again. You wouldn't want to do it in passenger service,
but if you could build ten minutes into the schedule at one end, it
could be done during turn-around. Admittedly, this would involve
changing the Victoria operating principle quite a bit, but at least
it's technically feasible. Ish.

I think it makes a lot more sense to just take more heat out of the
stations and maybe the tunnels as well. That means more surface
ventilation fans running (which is think is already happening) and
some sort of additional cooling, such as the plan to use heat
exchangers with the cold ground water being pumped out. That way,
the passengers in the stations benefit as well, and you don't need
to complicate the already cramped trains any more than they are
already.

But you don't cool the interiors of the trains as much as you would
with on-board AC.

I'd say that cooling the stations is a pre-requsite to air-conditioning
the trains, given how hot the Victoria Line tunnels already are. It's
less of an issue with the other Tube lines, as the trains pump a lot of
fresh air in already at the portals.

I absolutely agree that you can't put aircon on the trains until you have
a higher-capacity thermal egress from the tunnels. What i was wondering is
if there is a way to do this other than air conditioning the stations - a
way that would provide dedicated high-capacity cooling directly to the
trains. Like my suggested combination underground train-wash and cooling
shower using groundwater.

tom

--
Miscellaneous Terrorists: Ducks | Bird Flu | Avian flu | Jimbo Wales |
Backstreet Boys | The Al Queda Network | Tesco -- Uncyclopedia

On Fri, 24 Jul 2009, Peter Masson wrote:

"D7666" wrote

There is a substantial uplift in heating effect from the new trains.
Unless my sums are seriously flawed, there'd have to be some seriously
hefty cooling gear to cool stations. Gear that itself draws power ...
maybe more than the entire train regenerated power is taken up by air-
con ?

Add to that the congestion relief works at Victoria and the more frequent
service, there'll be more passengers pumping kilowatts into the system.

Perhaps the Victoria Line needs to be extended into the open air, at least so
the piston effect of trains can add ventilation into the tunnels, and ideally
so that the next generation (49 stock) can have aircon that takes heat out of
the system and dumps it in the open air.

How about putting in some crossovers at Finsbury Park and running some
trains from Cockfosters into the Vic core? It's probably too far from the
Picc portal to Finsbury Park for this to really help.

Could you get a piston effect with some more ventilation shafts with
valves attached? Shafts would come in pairs, with a one-way valve on each,
so passing trains would push up one and suck it down the other. Integrate
some of the shafts with the Lea and New River for water-cooling of the
incoming air.

tom

--
Miscellaneous Terrorists: Ducks | Bird Flu | Avian flu | Jimbo Wales |
Backstreet Boys | The Al Queda Network | Tesco -- Uncyclopedia