On Jul 24, 10:57*pm, D7666 wrote:
On Jul 24, 10:15*pm, Andy wrote:

"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.

You've missed the whole point.


No I've not, you've missed mine. You were the one mentioning 3 times
the current draw, when the numbers say less than twice the current
draw.

Its not the PEAK current thats the issue. This has been explained in
uk.railway several times before - and it seems to be a fundamental
issue that headline writers can't get right.

With DC motors the PEAK current is very large but drops off very
quickly and gets ever smaller as the train accelerates.

With AC motors it is a constant current, its not as high as the DC
peak, but it never tapers off, it is flat, across the whole train
speed. But at all times it is considerably higher than the DC motor
train at speed.

3500 A constant is much much more heating effect than 2700 A that
drops off rapidly. Thats how AC asynchronous and DC commutator motors
work, full stop.


But only constant current whilst the train is actually motoring, it
would be a very strange train which was drawing 3500A when stationary
or decelerating. I understand the workings of the different sorts of
motors, I was just trying to point out that your estimates seemed to
be in error.

It all amounts to much much more I^2*R heat to get rid of when trains
are motoring than from a DC motor train.


Yes and as the current is being drawn much more consistently, a large
proportion of the regained energy from the regeneration will be going
into powering other trains, rather than heating braking resistors as
it does at present. The current 1967 stock braking system will be
dumping a lot of heat straight into the stations, with 2009 stock
regeneration, a lot of that energy will instead be used.