🚀 go-pugleaf

The railway technical pages at www.trainweb.org will give you some answers:

"DC, on the other hand was the preferred option for shorter lines, urban
systems and tramways.  However, it was also used on a number of main line
railway systems, and still is in some parts of continental Europe, for
example.   Apart from only requiring a simple control system for the motors,
the smaller size of urban operations meant that trains were usually lighter
and needed less power. Of course, it needed a heavier transmission medium, a
third rail or a thick wire, to carry the power and it lost a fair amount of
voltage as the distance between supply connections increased.  This was
overcome by placing substations at close intervals - every three or four
kilometres at first, nowadays two or three on a 750 volt system - compared
with every 20 kilometres or so for a 25 kV AC line".

Generally voltages were low on old systems because electrical gear was heavy
and bulky if needed to reduce voltages for the DC motors, designed to
operate at around 600 volts.    1920s London tube stock for example had
about a third of each motor carriage devoted to the control gear, if you had
to reduce voltage from the line supply with the technology then available
you would have lost considerably more revenue space.

Regards

David Bennetts

Yn erthygl <MPbf9.3193$Sr6.110768@ozemail.com.au>, sgrifennodd David 
Winter <winterdspamtrapper@icespamtrapnet.com.au.invalid>
>Also, what's the range of nominal voltages used with guarded types of side
>contact 3rd rail systems (eg Docklands).

Docklands is not side contact but bottom contact, and the rest of the 
rail is covered by an insulated shroud. It is nominally 750 volts, but I 
don't know the tolerances, sorry.

-- 
John Sullivan

How does one find the railway technical pages from the trainweb home page?

DW

"David Bennetts" <davibee@hotmail.com> wrote in message
news:oVdf9.3227$Sr6.111820@ozemail.com.au...
: The railway technical pages at www.trainweb.org will give you some
answers:
:
: "DC, on the other hand was the preferred option for shorter lines, urban
: systems and tramways.  However, it was also used on a number of main line
: railway systems, and still is in some parts of continental Europe, for
: example.   Apart from only requiring a simple control system for the
motors,
: the smaller size of urban operations meant that trains were usually
lighter
: and needed less power. Of course, it needed a heavier transmission medium,
a
: third rail or a thick wire, to carry the power and it lost a fair amount
of
: voltage as the distance between supply connections increased.  This was
: overcome by placing substations at close intervals - every three or four
: kilometres at first, nowadays two or three on a 750 volt system - compared
: with every 20 kilometres or so for a 25 kV AC line".
:
: Generally voltages were low on old systems because electrical gear was
heavy
: and bulky if needed to reduce voltages for the DC motors, designed to
: operate at around 600 volts.    1920s London tube stock for example had
: about a third of each motor carriage devoted to the control gear, if you
had
: to reduce voltage from the line supply with the technology then available
: you would have lost considerably more revenue space.
:
: Regards
:
: David Bennetts
:
:
:
:
:
:
:
:

"David Winter" <winterdspamtrapper@icespamtrapnet.com.au.invalid> wrote in message news:<zthf9.3417$Sr6.113577@ozemail.com.au>

> How does one find the railway technical pages from the trainweb home page?

http://www.trainweb.org/railwaytechnical/index.html

--
| Nick Lawford
|
| read this backwards to contact me
|
| moc tod liamtoh ta drofwal erocsrednu kcin

David Winter asked:

> With 3rd rail systems, what is the spacing between substation (ie range of
> one substation).
> 
> This will vary with system and load.
> 
> My question is looking at 3 min frequency, 6-car full size single deck
> trains, with a 750v nominal supply with either medium (+/- 100v) or wide
> tolerance (+/- 200v).
> 
> I know there's some well versed electrical engineering types who lurk
> hereabouts - so some indicative figures would be helpful noting that each
> situation requires its own assessment.
> 
> Also, what's the range of nominal voltages used with guarded types of side
> contact 3rd rail systems (eg Docklands). I know that 1200v DC was used near
> Manchester - has any system been implemented with higher DC or AC voltages
> in a 3rd rail supply?
> 
Well David, there are many more variables that require assessment to
answer your question with certainty, these include:

The traction characteristics of the train(s) involved
The stopping pattern
Geographical and topological data including gradients, curvature,
tunnels etc.
Signalling system used
The conductivity of the conductor and running rails

and so on...........

In trying to answer your question, I will assume that:

a) It is a metro type system with a maximum speed of 100km/h
b) Accelleration rate of train is 0.8m/s/s Service braking rate is
also 0.8m/s/s
c) Weight of train is 200 tonnes tare, max line current is 3000A@750V
d.c
d) Station spacing is 3000m
e) No significant civil engineering features such as severe gradients,
curves or operation within tunnels
f) Regen braking is not used
g) Conventional 3 aspect signalling is used
h) Trains use three phase drive with broadly constant power
characteristic
i) Auxiliary load is 240kW per 6 car train
j) Running rails are UIC60, grade 600 (non hardened rails) =
35milliohms per km
k) Conductor rail is 74kg/m grade 600, = 27 milliohms per km.

So, let's work this through on a very rough basis:

Train accellerates at 0.8m/s/s (average) and thus takes 34 seconds to
reach 27.7m/s (100km/h). During this time, the train will draw 3000A
continuously.At 750V, this equates to 2.25MW. Drawing from my file of
traction characteristics, a very similar train to this then requires
0.9MW to balance the losses travelling at 27.7ms speed. This equates
to 1200A at 750V.  Likewise, the train's service braking rate is the
same and will take 34 seconds to decellerate to a stand at the next
station.

Ignoring the integration required to cater for the accelleration and
decelleration phases of the journey, and using approximation, the
journey time from station to station will take about 140 seconds of
which 106 seconds will be under power (34 at 3000A and 72 at 1200A).

Let's face it, no railway ever runs properly all of the time (least of
which the one I work for) and the electrification engineer would
design this metro type system to cater for trains operating one after
the other at the signal spacing, which I am assuming will be 1000m (3
block sections between stations).

So, with the railway operating for a period with trains backed up at
every signal, between two stations, we could have 2 trains
accellerating at their maximum rate for short periods, before they
have to brake for the next signal. This could lead to a peak current
of 6000A per road.

Again, drawing from my files, whilst it is allowable under Euronorm
standards to allow for the line voltage to drop to 450V d.c from the
nominal 750V, most current designs of train would suffer from losing
time and possibly some auxiliaries such as air conditioning, if they
didn't receive 550V, so we will use that as the lowest allowable
limit.

For each km of running and conductor rail, and assuming all 4 running
rails are bonded together in parallel, the loop resistance is
35.75milliohms.

Thus for a permissible voltage drop of 200V, at 6000A, the maximum
single end feeding resistance would be 33.3 milliohms (200/6000) or
about 930m. DC electrification systems feed from both ends, so this
distance would be doubled to 1860m. If a track parallelling hut were
introduced at the electrical mid point (it has the effect of
parallelling the positive feeds and thus reducing their apparent
resistance looking from the train), this could be stretched to 2200m.
Further allowances based on diversity, driving technique and also the
engineers asking the commercial people whether they really require
full train performance when the trains are approaching red signals
would all affect the spacing considerations.

So, the strictly correct answer to your question, based on the
gargantuan assumptions I state is 1860m. However, real life ain't like
that and other considerations such as differing train types, wear
allowances, availability of land for substations, allowable
performance under perturbed conditions, driving techniques, junctions,
permissive signalling and so on and so on, would affect the spacing
decisions. When the spacings get long, a trade off needs to be made
between the size and ratings of the equipment in the substations and
their spacing (.e. few large substations versus lots of small ones),
to get an economic solution.

No voltage above 1200V d.c. has been used for conductor rail
installations on any large scale within Europe. DB has an extensive
network of such lines around Hamburg and BR used to have this system
for Manchester to Bury. This voltage is no longer standard within
Europe. All 1200V d.c systems use insulated shrouds around the rail
and either side or bottom contact.

750V d.c. systems in the UK are not insulated with the exception of
the Docklands system.

Hope this answers your question.

Richard Catlow

In article <d3979d5f.0209101145.1a1d5a7f@posting.google.com>, Richard
Catlow <RBCatlow@aol.com> writes
>David Winter asked:
>
>> With 3rd rail systems, what is the spacing between substation (ie range of
>> one substation).
>> 
>> This will vary with system and load.
>> 
>> My question is looking at 3 min frequency, 6-car full size single deck
>> trains, with a 750v nominal supply with either medium (+/- 100v) or wide
>> tolerance (+/- 200v).
>> 
>> I know there's some well versed electrical engineering types who lurk
>> hereabouts - so some indicative figures would be helpful noting that each
>> situation requires its own assessment.
>> 
>> Also, what's the range of nominal voltages used with guarded types of side
>> contact 3rd rail systems (eg Docklands). I know that 1200v DC was used near
>> Manchester - has any system been implemented with higher DC or AC voltages
>> in a 3rd rail supply?
>> 
>Well David, there are many more variables that require assessment to
>answer your question with certainty, these include:
>
>The traction characteristics of the train(s) involved
>The stopping pattern
>Geographical and topological data including gradients, curvature,
>tunnels etc.

<snipped a bit>

Another very interesting bit of reading. Can you explain why the tunnel
would be significant please?. Is it to do with wind resistance perhaps.

Very surprised that the rail resistance is so low as you quoted, still
never actually measured a bit.....
-- 

 Tony Sayer

tony sayer wrote:

> In article <d3979d5f.0209101145.1a1d5a7f@posting.google.com>, Richard
> Catlow <RBCatlow@aol.com> writes
> >David Winter asked:
> >
> >> With 3rd rail systems, what is the spacing between substation (ie range of
> >> one substation).
> >>
> >> This will vary with system and load.
> >>
> >> My question is looking at 3 min frequency, 6-car full size single deck
> >> trains, with a 750v nominal supply with either medium (+/- 100v) or wide
> >> tolerance (+/- 200v).
> >>
> >> I know there's some well versed electrical engineering types who lurk
> >> hereabouts - so some indicative figures would be helpful noting that each
> >> situation requires its own assessment.
> >>
> >> Also, what's the range of nominal voltages used with guarded types of side
> >> contact 3rd rail systems (eg Docklands). I know that 1200v DC was used near
> >> Manchester - has any system been implemented with higher DC or AC voltages
> >> in a 3rd rail supply?
> >>
> >Well David, there are many more variables that require assessment to
> >answer your question with certainty, these include:
> >
> >The traction characteristics of the train(s) involved
> >The stopping pattern
> >Geographical and topological data including gradients, curvature,
> >tunnels etc.
>
> <snipped a bit>
>
> Another very interesting bit of reading. Can you explain why the tunnel
> would be significant please?. Is it to do with wind resistance perhaps.
>
> Very surprised that the rail resistance is so low as you quoted, still
> never actually measured a bit.....

I seem to remember that those installed on the Jubilee Line were aluminium (it's
pretty easy to see), which has a greatly reduced resistance - about 30 times lower
than steel I think.  Are these rails solid aluminium alloy, or are they steel with
an aluminium outer layer?

Angus

Angus Bryant <atb23@cam.ac.uk> wrote in message
news:3D7F0C83.CFB890A2@cam.ac.uk...

> I seem to remember that those installed on the Jubilee Line were aluminium
(it's
> pretty easy to see), which has a greatly reduced resistance - about 30
times lower
> than steel I think.  Are these rails solid aluminium alloy, or are they
steel with
> an aluminium outer layer?

I imagine that they are aluminium (alloy), with a steel contact strip.

Tony Sayer asked
> 
> Another very interesting bit of reading. Can you explain why the tunnel
> would be significant please?. Is it to do with wind resistance perhaps.
> 
The rolling resistance of a vehicle is governed by a number of factors
called Davies coefficients in the form a+bv+cv^2

Where a= static resistance of train to motion i.e. stiction
b= rotary intertia
c= aerodynamic drag
v= velocity

Thus a train in a tunnel has a higher c element of the equation as the
turbulent air flow of the train interacts with the tunnel. The actual
drag in a tunnel depends upon bore size, whether there is oncoming
traffic in the same bore, speed, uniformity and smoothness of the
tunnel bore surface, tunnel length, whether there are vents and their
physical location etc. It all makes an interesting computational fluid
dynamics problem, even more so if you have to control smoke flows as
well. I spent a little time working for the CFD guru who looked at
these problems for the Channel Tunnel - very absorbing it was too.

Richard Catlow

In article <d3979d5f.0209111108.4634cd7@posting.google.com>, Richard
Catlow <RBCatlow@aol.com> writes
>Tony Sayer asked
>> 
>> Another very interesting bit of reading. Can you explain why the tunnel
>> would be significant please?. Is it to do with wind resistance perhaps.
>> 
>The rolling resistance of a vehicle is governed by a number of factors
>called Davies coefficients in the form a+bv+cv^2
>
>Where a= static resistance of train to motion i.e. stiction
>b= rotary intertia
>c= aerodynamic drag
>v= velocity
>
>Thus a train in a tunnel has a higher c element of the equation as the
>turbulent air flow of the train interacts with the tunnel. The actual
>drag in a tunnel depends upon bore size, whether there is oncoming
>traffic in the same bore, speed, uniformity and smoothness of the
>tunnel bore surface, tunnel length, whether there are vents and their
>physical location etc. It all makes an interesting computational fluid
>dynamics problem, even more so if you have to control smoke flows as
>well. I spent a little time working for the CFD guru who looked at
>these problems for the Channel Tunnel - very absorbing it was too.
>
>Richard Catlow

Thanks for that!....
-- 

 Tony Sayer

"Richard Catlow" <RBCatlow@aol.com> wrote in message
news:d3979d5f.0209111108.4634cd7@posting.google.com...
> Tony Sayer asked
> >
> > Another very interesting bit of reading. Can you explain why the tunnel
> > would be significant please?. Is it to do with wind resistance perhaps.
> >
> The rolling resistance of a vehicle is governed by a number of factors
> called Davies coefficients in the form a+bv+cv^2
>
> Where a= static resistance of train to motion i.e. stiction
> b= rotary intertia
> c= aerodynamic drag
> v= velocity
>
> Thus a train in a tunnel has a higher c element of the equation as the
> turbulent air flow of the train interacts with the tunnel. The actual
> drag in a tunnel depends upon bore size, whether there is oncoming
> traffic in the same bore, speed, uniformity and smoothness of the
> tunnel bore surface, tunnel length, whether there are vents and their
> physical location etc. It all makes an interesting computational fluid
> dynamics problem, even more so if you have to control smoke flows as
> well. I spent a little time working for the CFD guru who looked at
> these problems for the Channel Tunnel - very absorbing it was too.

I know it's nothing to do with 3rd rail, but does any modern stock (air-con,
post-privatisation) have valves to shut off the pressure when the train goes
into a tunnel?  I seem to remember that Eurostar does, but does anything
like the Pendolino/Voyager/etc?

Angus