Pan up or pan down on the move

[coppercapped]

Perhaps I can clarify a few matters.

AC/D.C. changeover happens in passenger service at 7 locations today:

Farringdon / City TL
Acton Central
Mitre Bridge*
Willesden New Lines* (but you’ll need to be up early or stay up late to see it)
Drayton Park
Ebbsfleet
Ashford International

All except * are at stations where all trains stop (or will for the voltage changeover, if not for passenger calls) and only at Mitre Bridge is it done on the move. Even then it is at slow speed (20mph IIRC) and only by London Overground Electrostars, as Southern (apparently) have a different approach to the risk assessment over such matters for their Electrostars and drivers. Nevertheless it hasn’t stopped a nice collection of dents on the Westway bridge.

With regards to bi-modes. Trains can drop their pans at any time without restriction. However raising pans at speed comes with issues. The force of raising a pan at speed is higher than when stationary, as the aerofoils on the pan itself generate uplift, and quite a bit of it at full tick (I forget the physics, but I think the force increases proportional to the cube of the speed). Now this isn’t necessarily a problem, and can be done on a occasional basis, eg if coasting is temporarily imposed on a section, of if the driver drops the pan and raises in an attempt to reset a truculent MCB (something I’ve seen first hand in the cab).

However, if it is done at the same place, repeatedly, for a long period it will cause fatigue in the OLE, and particularly in the small part steelwork which will be moving around a lot more than is usually expected. For this reason, OLE is normally strengthened in locations where pans are to be raised at high speed for a prolonged period. The strengthening can be by providing an extended overlap (essentially two contact wires per track), or higher tension contact wires, or shorter distances between OLE structures, or some combination of the three. AIUI this is what has been done on the GWML at Maidenhead and Steventon. I don’t know the area too well, so happy to be corrected.

Thank you for that, it's very informative.

 

[coppercapped]

As long as I don't lose my pan , I'm happy lol

Like it!

 

[heedfan]

Academic question because they won’t do 125 mph on diesel, only 110 mph isn’t it?

You’re probably right, I don’t know to be truthful. But read 110mph for 125mph there I guess, still seems quick for a pan shooting up?

 

[swt_passenger]

You’re probably right, I don’t know to be truthful. But read 110mph for 125mph there I guess, still seems quick for a pan shooting up?

There’s loads of discussion of this over in the GW electrification thread, but I believe their pans go up at line speed in certain defined changeover areas...

 

[clockend]

Ebbsfleet used to be on move when the Maidstone W starters didn’t call...

 

[alangla]

Whether they were designed to or not, Class 91s can raise or drop their pantographs while on the move. I remember when the wires came down on the ECML north of Retford in September 2016, all Class 91/Mk4 services had to take a run-up to the 'de-wired' section (it involved the services queueing at a signal a fair distance from the section), drop the pantograph to coast through, and raise it back up again once through the section.

Something similar happens when there’s icicles in High Street tunnel in Glasgow. Basically, leave Queen Street low level or High Street, accelerate as hard as possible to 30 mph, power off, pan(s) down, if it’s a 318 or 320 the lights go out apart from the emergency lights, then coast in the dark to the next station. Usually when stopped the pans go back up & the driver gets off to check them.