Why do the trains on the NLL switch over to 25Kv AC at Hackney Wick
and then switch back to DC at Dalston when the 3rd rail is continuous
along that section anyway? Why not just stay on DC and save the wear
and tear on the pantograph?

B2003

Boltar wrote:
Why do the trains on the NLL switch over to 25Kv AC at Hackney Wick
and then switch back to DC at Dalston when the 3rd rail is continuous
along that section anyway? Why not just stay on DC and save the wear
and tear on the pantograph?


Mainly because the Class 313s work better on AC than on DC. They were
originally designed as an AC unit with the DC only for the short
section from Drayton Park - Moorgate and reliability suffered when
they first transferred to the North London Line. Of course, from next
year when the new platforms open at Stratford, they will run on AC all
the way from Stratford to Dalston.

"Andy" wrote in message
...
Boltar wrote:
Why do the trains on the NLL switch over to 25Kv AC at Hackney Wick
and then switch back to DC at Dalston when the 3rd rail is continuous
along that section anyway? Why not just stay on DC and save the wear
and tear on the pantograph?


Mainly because the Class 313s work better on AC than on DC. They were
originally designed as an AC unit with the DC only for the short
section from Drayton Park - Moorgate and reliability suffered when
they first transferred to the North London Line. Of course, from next
year when the new platforms open at Stratford, they will run on AC all
the way from Stratford to Dalston.

and when ELLX gets to Highbury & Islington the NLL tracks will be AC between
Dalston and Camden Road, and the new NLL trains will run on AC all the way
from Stratford to Acton.

Peter

On 17 Jan, 16:31, "Peter Masson" wrote:
"Andy" wrote in message

...

Boltar wrote:
Why do the trains on the NLL switch over to 25Kv AC at Hackney Wick
and then switch back to DC at Dalston when the 3rd rail is continuous
along that section anyway? Why not just stay on DC and save the wear
and tear on the pantograph?

Mainly because the Class 313s work better on AC than on DC. They were
originally designed as an AC unit with the DC only for the short
section from Drayton Park - Moorgate and reliability suffered when
they first transferred to the North London Line. Of course, from next
year when the new platforms open at Stratford, they will run on AC all
the way from Stratford to Dalston.

and when ELLX gets to Highbury & Islington the NLL tracks will be AC between
Dalston and Camden Road, and the new NLL trains will run on AC all the way
from Stratford to Acton.

Will the 3rd rail be lifted then?

B2003

"Boltar" wrote

and when ELLX gets to Highbury & Islington the NLL tracks will be AC
between
Dalston and Camden Road, and the new NLL trains will run on AC all the
way
from Stratford to Acton.

Will the 3rd rail be lifted then?

The whole lot will probably have to be relaid anyway, to provide 4 platforms
at Canonbury and Highbury, and 4 tracks on the current 3-track section. I
can't see the juice rail surviving all that (except on the ELLX lines
between Dalston Junction and Highbury & Islington, as the ELLX will be an
entirely DC operation, and its trains, though in other respects essentially
the same as the new trains for the NLL, will be DC only).

Peter

On 17 Jan, 16:44, "Peter Masson" wrote:
"Boltar" wrote

and when ELLX gets to Highbury & Islington the NLL tracks will be AC
between
Dalston and Camden Road, and the new NLL trains will run on AC all the
way
from Stratford to Acton.

Will the 3rd rail be lifted then?

The whole lot will probably have to be relaid anyway, to provide 4 platforms
at Canonbury and Highbury, and 4 tracks on the current 3-track section. I
can't see the juice rail surviving all that (except on the ELLX lines
between Dalston Junction and Highbury & Islington, as the ELLX will be an
entirely DC operation, and its trains, though in other respects essentially
the same as the new trains for the NLL, will be DC only).

Peter

Obviously under the arrangement for the ELLX up to Highbury &
Islington that has become apparent lately there's no need for the ELLX
rolling stock to have AC equipment, but I was under the impression
that all the new class 378 Electrostar trains for London Overground
were all ordered as dual system (i.e. AC & DC) stock - am I wrong in
thinking this, or has the order subsequently been amended?

"Boltar" wrote:

Why do the trains on the NLL switch over to 25Kv AC at Hackney Wick
and then switch back to DC at Dalston when the 3rd rail is continuous
along that section anyway? Why not just stay on DC and save the wear
and tear on the pantograph?

Because the DC supply in that area is somewhat constrained, and only allows
a limited number of simultaneous train movements.*

No time to check, but I believe the NLL timetable is more intensive than
when that section was first used by the 2-EPBs.

Chris

* So says Mr Rob Curling on Video 125's 'North London Line Drivers Eye
View'.

various snipped out

I don't know what the current limit relays were set at on 501s but
being 4 motors per unit would be likely to draw more than a two motor
2EPB.

Published ''spotting book'' values of a 2EPB are 2x250 hp and 501
4x185 hp so that makes a 501 in round figures 50% more powerful than a
2EPB - but I'd caution those numbers with similar comments I have made
before about DC EMU in that the current limit relay setting needs to
be known to understand peak current draw.

As regards another part of the thread, I thought 2x313 operation was
killed by platform length limits. 501 units were on 57 foot frames
and platforms that could take 6cars laid out for that length - but
could not take standard 6car sliding door trains with 20 m bodies.

And I can't see why a 6car 313 would draw siginficantly more power
than a 6car 501 to trip traction supplies. Again using ''spotting
book'' values, without current limit values, a 313 has 8x82 kW motors
that in round figures is 880 hp per unit - while a 501 is 740 hp.

I would have expected the LNWR DC supply to have been a bit more
robust than that as the overall load increase taking all traffic is
not 20% from a simple 313 and 501 comparison - but is Bakerloo+501
c.f. Bakerloo+313 with the Bakerloo load unchanged.

Must admit never thought about this aspect before, I might be wrong,
its not a route thats easy to obtain gen on the traction supplies.

--
Nick

Does anyone know how many, if any. of the original LNWR sub-stations
are still in use? There are various large buildings adjacent to the
NLL/Euston DC Lines which seem to foor the bill but others have
disappeared. The one visible on the NLL from the Met/Jubilee Lines has
gone, as has another large structure which stood near East Putney on
the EN side. Is the large building on the WCML side in the Kenton/
Northwick Park area a former LNWR sub?

On Fri, 18 Jan 2008 04:19:29 -0800 (PST), wrote:

Does anyone know how many, if any. of the original LNWR sub-stations
are still in use? There are various large buildings adjacent to the
NLL/Euston DC Lines which seem to foor the bill but others have
disappeared. The one visible on the NLL from the Met/Jubilee Lines has
gone, as has another large structure which stood near East Putney on
the EN side.

Eh? This sounds like the LSWR, not LNWR!

Is the large building on the WCML side in the Kenton/
Northwick Park area a former LNWR sub?

Yes. AFAIK it is the only one still in use,; all the rest were taken
out of use in the 1940s, new rectifiers etc. being installed in
smaller buildings nearby. The buildings survive at Willesdan
Junction (derelict and rail-locked), South Acton and Headstone Lane
(both heavily adapted for other uses.) Dunno about Dalston
Junction.

There is a similar looking building at Harrow and W but this was not a
railway one.

The original Broad Street sub-station was beneath the viaduct somwhere
near Great Eastern Street; does anyone knowthe exact location please?


--
Peter Lawrence