On Jul 24, 6:19*pm, D7666 wrote:
On Jul 23, 4:57*pm, Andy wrote:

And the regenerative braking on the new 2009 stock will also mean less
heat released into the stations and tunnels in the first place.

Ummm thats not strictly true. Overall you might be generating less
heat directly from braking, true, but the type of train, with AC
motors, will itself create more heat to be released, including
indirectly from braking.

Ok, so how much more heat would be generated if the trains were not
regenerating?


Go back to the NR southern third rail zone power upgrade for Mk.1
stock replacement. What was that all about. All the new trains coming
in had AC motors, replacing DC motors under the Mk.1s. The big issue
was heating effect.


And how much of the extra power requirement came from the trains being
heavier.

AC motor characterisitics are such that it draws a higher constant
current - this means the heating effect in lineside traction equipment
is much increased - because heat dissipated is I^2*R [I-squared-R].
When the trains are regenerating, the heating effect in lineside eqpt
is still I^2*R, it still is still being heated, it does not cool
because it is reversed, and it does not cool because t gets no respite
(like it does when a friction brake train brakes). A non regen braked
train using friction brakes disspates the heat transformed from
mechanical energy at the brake shoes/pads - wheel rim/disc interface.
A regen braked train convert mechanical energy to electrical, which
while contributing a useful energy saving does nonetheless heats
lineside gear in doing so.

But much of the regenerated energy should be going into powering other
trains, sure you need hefty lineside kit in case everything all brakes
at the same time, but the Victoria line should be ideal for reusing
the energy. Also isn't the peak current draw less with AC than DC. The
AC motors will be warming up fairly constantly during the whole of the
acceleration (and deccelaration) phases and so their heat production
will be spread out. The old DC motors will warm up much more quickly
at the start as that is the point of peak current draw and, of course,
this is will be in the stations.


1967 stock Crompton/Brush LT115 DC traction motors are 53 kW cont.
rating.
2009 stock Bombardier Mitrac AC traction motors are 75 kW cont.
rating.

1967 stock 8-car trains are MTTMMTTM - 16 motors per train = 16 x 53
kW = 848 kW per train
2009 stock 8-car train are MTMMMMTM - 24 motors per train = 24 x 75
kW = 1800 kW per train

All those motrs and traction packs get hot.


Piers Connor (in his series The Underground Electric Train in
Underground News, June 2007) say the following:

"In order to make use of the additional throughput capability of the
new signalling, the
2009 Stock has a higher performance than the current stock. The
existing 1967
Tube Stock draws about 2,700 amps maximum, while the 2009 Tube Stock
will draw
3,500 and is capable of drawing up to 4,500 amps."

This looks like well under double the peak current draw.


A 2009 stock train draws over twice the traction load of 1967 stock,
and thats before you look at DC v. AC, and before you look at
auxiliary loads. All this air-con draws a load that was not there with
1967. Thats never put back into regen braking.

Further, the service frequency will be increased, and there are more
trains in service at any one time. True they will all regenerate, but
there are more of them to accelerate in the first place, and
accelerating at a higher rate.

It all adds up - I bet one would not be far wrong to say current draw
on the whole line with full TPH with 2009 stock may well be 3 times
that of 1967 stock at the same voltage. Offset this by *increasing
from 630 V to 750 V which is a 30% current drop, so overall load
doubled.

All that heat has to go somehwere. And Peter is quite right, there is
nowhere to dump the air-con load.


Lineside equipment will be MUCH easier to cool, as it is in fixed
locations which should already be ventilated.

NR southern zone has trackside power distrbution cables everywhere, LU
does not, so at east not heating tunels that way.

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 ?


Just to be clear, I wasn't arguing for air conditioning to be fitted,
but I still think you are mis-estimating the effect of regeneration on
the total energy consumption and heating for the new trains. The whole
point of regeneration is to reuse the energy which used to be 'wasted'
in resistor banks on the trains (with the original rheostatic train
brakes). My understanding is that little of the recovered energy goes
back to the lineside equipment, if the current rails are not
receptive, then the spare energy goes to resistors, like in older
stock. The extra big lineside equipment is purely because more current
is needed in the first place.