On Thu, 17 Jan 2008 22:22:08 -0000, "Chris Read"
wrote:


"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'.

The problem seems to be with the type of loading that 313s cause on
the DC supplies. In the early 1960s parts of the DC line had a 2 - 2.5
minute headway (back of envelope calculation gives about 2 Bakerloo
trains and 4 6-coach BR/LMS trains taking power) and the substations
coped with that but when cl501s were replaced with 313s they were
unable to run as 6-coach as they tripped out the sub-stations when
moving off.