In article <aCoak.189010$9x.103925@newsfe05.ams2>, illia@blueyonder.co.uk
(Tom Barry) wrote:

> Batman55 wrote:
> > It seems odd that as LUL attempts to cool down the tube, it is 
> > introducing giant electric projectors at many stations, along 
> > with the illuminated moving panels on the escalators. The stories 
> > in Railway Herald this week, page 5 about cooling down, and page 
> > 6 about the heat producing equipment, seem to show a lack of 
> > joined up thinking!
> > 
> > What might be more sensible is for equipment at every sub surface 
> > station to be reviewed and every heat producing item examined to 
> > see how its heat output could be reduced or eliminated. Every 
> > little bit might help!
> 
> According to TfL, the heating effect arises because of the 
> incremental heating and cooling caused by each passing train's 
> energy consumption. The frequency of trains means the cooling of 
> the tunnel walls is that little bit less than the heating, so over 
> the years the ground heats up because it never gets a long enough 
> break between trains.  This is rather borne out by the original 
> Bakerloo Line claim that it was an nice, cool way to travel in the 
> heat of the summer - it was decades before the effect was realised. 
>  Presumably if you could shut the tube for a few years you could 
> reverse it, but I can spot a couple of problems with that idea.
> 
> I suspect, therefore, that things like lighting and electronics in 
> stations (which are better ventilated than the tunnels anyway) are 
> of minute benefit compared with reducing the heat produced in the 
> tunnels by each train by a little bit.  Indeed, one of the ideas 
> being looked at is blowing cold air over the brakes of trains 
> standing at stations, so they don't take the heat into the tunnel 
> when moving off.  Obviously this merely transfers it to the 
> station, whence it can be removed somewhere.  Regen braking has a 
> place here, too, if you can shove the heat from the necessary 
> resistors outside.

If it's regen braking, rather than rheostatic, the heat goes as energy to
other trains and not into resistors.

-- 
Colin Rosenstiel

On 1 Jul, 22:01, rosenst...@cix.co.uk (Colin Rosenstiel) wrote:
> > Regen braking has a
> > place here, too, if you can shove the heat from the necessary
> > resistors outside.
>
> If it's regen braking, rather than rheostatic, the heat goes as energy to
> other trains and not into resistors.

Ish. On AC, absolutely right; on DC, you need banks of resistors as
well because putting it back to the grid if there isn't a conveniently
placed train to take it is Too Bloody Hard. However, given the traffic
density on LUL, most of the time there'll be someone accelerating
while you're breaking so it should work out OK...

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

John B wrote:
> On 1 Jul, 22:01, rosenst...@cix.co.uk (Colin Rosenstiel) wrote:
>>> Regen braking has a
>>> place here, too, if you can shove the heat from the necessary
>>> resistors outside.
>> If it's regen braking, rather than rheostatic, the heat goes as energy to
>> other trains and not into resistors.
> 
> Ish. On AC, absolutely right; on DC, you need banks of resistors as
> well because putting it back to the grid if there isn't a conveniently
> placed train to take it is Too Bloody Hard. However, given the traffic
> density on LUL, most of the time there'll be someone accelerating
> while you're breaking so it should work out OK...
> 

Yes, that's what I was getting at.  In mitigation, I hadn't read Cap'n 
Deltic's latest screed in MR at that point, which suggests that 
receptivity in DC networks is higher than previously thought, so you 
might not need as much resistance capacity and associated cooling around 
the place.

What's the effect of the suggested upping of the voltage to 750v DC on 
some lines?  Being a concrete'n'steel type engineer (manqué) I don't 
understand electricity as well as I should.

Tom

On 1 Jul, 23:34, Tom Barry  wrote:
> John B wrote:
> > Ish. On AC, absolutely right; on DC, you need banks of resistors as
> > well because putting it back to the grid if there isn't a conveniently
> > placed train to take it is Too Bloody Hard. However, given the traffic
> > density on LUL, most of the time there'll be someone accelerating
> > while you're breaking so it should work out OK...

[hangs head in shame at 'braking' typo]

> Yes, that's what I was getting at.  In mitigation, I hadn't read Cap'n
> Deltic's latest screed in MR at that point, which suggests that
> receptivity in DC networks is higher than previously thought, so you
> might not need as much resistance capacity and associated cooling around
> the place.

My last bout of crazy-travelling-about-the-place ended just before the
latest edition came out, so I've only seen the preview email. Bring on
the next train voyage...

> What's the effect of the suggested upping of the voltage to 750v DC on
> some lines?  Being a concrete'n'steel type engineer (manqué) I don't
> understand electricity as well as I should.

transmission losses [hence, here, heat gains] = current^2 / resistance

Since resistance is ~constant and power delivered to the train =
current * voltage, increasing the voltage from 630V to 750V reduces
the current required to provide the same power by 16%, which reduces
transmission losses by 29%.

This ignores the effect of almost everything real-world (especially
the fact that you're dealing with two rails at  and -210 rather
than a single rail at ), but you get the idea.

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

On 2 Jul, 10:20, Roland Perry  wrote:
> wouldn't need a steady flow of current, and could simply absorb whatever
> was available from one second to the next. Then use the hydrogen to
> power those buses they have. Or did that experiment end now?

For it to be a proper experiment they need some published results.
Haven't seen any yet. More likely it was just green bandwagonning by
Ken.
I haven't seen the buses themselves for a while now but they weren't a
common site in the first place so they could still be bumbling about
somewhere.

B2003