Pan up or pan down on the move

[Ken H]

With increasing number of Bi-modes coming, I was wondering if raising or lowering the pantograph on the move is possible/allowed/a good idea. And is it possible at 100mph +

For example...
If Northern decide to use Cl769's on Barrow -Manc Airport trains, they would get to the up platform at carnforth, which last time I went there wasnt wired.

So would the train have to do carnforth - Lancaster on diesel under the wires, or could it get on the electrified line, then raise its pan and shut down the diesel?

Would that potentially damage the pan or the overhead. Would you need specially strengthened overhead to allow this? How would the driver know if a possible 2nd unit was under the overhead? Would the train circuit breaker have to be tripped while this happened to stop an arc forming?

Will pan up/down be used as a temporary measure at Steventon on GWR until the bridge is rebuilt?

Does anything do pan up/down on the move currently? Actually the only pan up/down in service I know of currently is Thameslink and at Drayton Pk, and I suppose the IEP's now, but I think thats all done at stations - but I may be wrong.

 

[LNW-GW Joint]

800s can switch on the fly (eg at Didcot East if heading for Oxford on the Didcot avoiding line).
I believe all new-build bi-modes will be specified to do this.
Class 373 Eurostars could switch from DC to AC on the move at Dollonds Moor.
But the 319s, and other AC/DC dual-voltage pre-privatisation EMUs, were designed to switch while stationary.
I think some recent dual voltage stock can switch on the move, eg 350/1 on the West London line.
We'll have to see about 769s, but I suspect they will only switch while stationary.

 

[rebmcr]

Does anything do pan up/down on the move currently?

Yes, I believe the Southern service to Milton Keynes does this somewhere between Clapham and Willesden.

 

[westcoaster]

Southern do not do it on the move, but the overground 378's do.

 

[baz962]

Southern do not do it on the move, but the overground 378's do.

Correct , and the wires are strengthened to allow it.

 

[lewisf]

Southern do not do it on the move, but the overground 378's do.

Not only to Southern switch over while stationary, the rear unit of an 8 car train is still off the third rail when it pans down and is dragged dead until Shepherds Bush

I only have anecdotal evidence to back this up however

 

[Steve Harris]

Yes, I believe the Southern service to Milton Keynes does this somewhere between Clapham and Willesden.

Traction current change overs always used to happen at Mitre Bridge Junction (a little way south of North Pole).

 

[Prestige15]

The 800 can do it at top speed

@ 16:14 and watch the rear pan

 

[philthetube]

Yes, I believe the Southern service to Milton Keynes does this somewhere between Clapham and Willesden.

I seem to recall that when stock was introduced they did it on the move, I could be wrong though.

 

[87015]

I seem to recall that when stock was introduced they did it on the move, I could be wrong though.

Definitely did on occasion. More often with 319s - it was pretty regular for a while - all stopped when a 377 brought the lot down a few years ago.

 

[swt_passenger]

Not only to Southern switch over while stationary, the rear unit of an 8 car train is still off the third rail when it pans down and is dragged dead until Shepherds Bush

I only have anecdotal evidence to back this up however

The online version of the SA reckons the AC/DC overlap is 55 chains. Of course that doesn’t show signal positions, so i guess it is possible trains stop with the back end off the DC, but it does seem odd.

Traction current change overs always used to happen at Mitre Bridge Junction (a little way south of North Pole).

Going by the SA I’d say changeover position is somewhat south of Mitre Bridge Jn, more like alongside the North Pole depot connection. Mitre Bridge Jn is well north of the DC limit, however many other people have previously said that’s where changeover happens. Could it have been moved at some time?

 

[87015]

Going by the SA I’d say changeover position is somewhat south of Mitre Bridge Jn, more like alongside the North Pole depot connection. Mitre Bridge Jn is well north of the DC limit, however many other people have previously said that’s where changeover happens. Could it have been moved at some time?

It’s done at North Pole, AC at Mitre Bridge. Loco changes used to occur at Mitre Bridge so talk of there could be a hangover from that. I don’t think the third rail has been moved since it was put in.

 

[coppercapped]

Correct , and the wires are strengthened to allow it.

According to people working on the Western who post here and elsewhere the overhead is not specially strengthened, it's just that the changeover place is chosen to be on a length of contact wire at a point where there are no overlaps between tension runs or switch and crossing work. Also by always carrying out the changeover at the same place Network Rail can monitor the condition of the overhead more effectively.
At these points changeover can take place at up to line speed. Changeover can take place at any other location as long as the train speed is 20mph or less.

 

[baz962]

I was told by my dm it was strengthened , but hey ho. I had just driven the route and back an hour or so before posting here.

 

[aleggatta]

Generally, a 377 could change from AC to DC with no real issues, as it would just coast before the shoe ran up the third rail ramp as it normally would. DC to AC however would probably need more thought put into it (for anything not designed to do it on the move currently at least!).

 

[Steve Harris]

The online version of the SA reckons the AC/DC overlap is 55 chains. Of course that doesn’t show signal positions, so i guess it is possible trains stop with the back end off the DC, but it does seem odd.


Going by the SA I’d say changeover position is somewhat south of Mitre Bridge Jn, more like alongside the North Pole depot connection. Mitre Bridge Jn is well north of the DC limit, however many other people have previously said that’s where changeover happens. Could it have been moved at some time?

Unfortunatly what you are thinking is Mitre Bridge Jcn and what i am thinking is, isn't the same.

Mitre Bridge Jcn is the set of crossovers (south of North Pole Depot), which are almost on top of the bridge over Mitre Way. Have a look on Google Earth.

(I dont have the SA to hand so it may be just plain Mitre Bridge rather than Jcn).

Haven't been down that way in a while but that's where the 313's used to changeover.

Edit. Just managed a look at a map. I apologise, it is in fact just Mitre Bridge, which is south of Mitre Bridge Jcn and North Pole.

 

[swt_passenger]

Unfortunatly what you are thinking is Mitre Bridge Jcn and what i am thinking is, isn't the same.

Mitre Bridge Jcn is the set of crossovers (south of North Pole Depot), which are almost on top of the bridge over Mitre Way. Have a look on Google Earth.

(I dont have the SA to hand so it may be just plain Mitre Bridge rather than Jcn).

Haven't been down that way in a while but that's where the 313's used to changeover.

Ah, possible explanation then is that the Kent/Sussex/Wessex SA I’m referring to has Mitre Bridge Jn immediately south of the level crossing, ie where the Wembley and Willesden routes split, but it doesn’t name those crossovers south of the depot.

Mitre Bridge seems to definitely be the canal bridge, the bridge nearest those crossovers is Mitre Way Bridge. So I’m still unsure of the name of those crossovers...

 

[Steve Harris]

Ah, possible explanation then is that the Kent/Sussex/Wessex SA I’m referring to has Mitre Bridge Jn immediately south of the level crossing, ie where the Wembley and Willesden routes split, but it doesn’t name those crossovers south of the depot.

Mitre Bridge seems to definitely be the canal bridge, the bridge nearest those crossovers is Mitre Way Bridge. So I’m still unsure of the name of those crossovers...

Im sure those crossovers is / are Mitre Bridge. There used to be a signal box there which im sure was of the same name.

The OHLE stops at the point where the A40 goes over the railway. In BR days that is where Cross Country services changed from electric to diesel traction (and vice versa).

When the Willesden Jcn High Level to Clapham Jcn service changed from DMU to EMU (Class 313) operation (when the DC was installed from Latchmere Jcn's to North Pole Depot). The AC to DC changeover happened in the same place.

I have now had chance to refer to my Quail map and it states that northbound AC/DC changover takes place at signals VC 813/815 (which are south of the crossovers) and the southbound changeover takes place at signals VC 816/818 which are north of North Pole Jcn.

So it seems we are both right, lol.

That is, if it hasn't changed since i last went down there!

 

[baz962]

Changeover is just after North pole signal straight after mitre bridge and before A40 bridge or you lose ya pan on the up. On the down it is a bit after A40 bridge , before mitre bridge on the down.

 

[baz962]

You start changeover at signal vc818 on the up. On the down if the pan isn't up in time we have to stop at vc813 .

 

[Steve Harris]

Changeover is just after North pole signal straight after mitre bridge and before A40 bridge or you lose ya pan on the up. On the down it is a bit after A40 bridge , before mitre bridge on the down.

Thanks baz.

Is Mitre Bridge the bridge which goes over the Great Western Mainline ??

 

[baz962]

Yea and the grand Union canal.

 

[Steve Harris]

Yea and the grand Union canal.

Thanx.

So, what was the signal box called that was sited near those crossovers ??

Is my memory playing tricks on me. As it was abolished a long while ago now.

 

[Silver Cobra]

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.

 

[baz962]

That I don't know sorry.

 

[heedfan]

Whilst the 800s are capable of pan up/down on the fly without loss of drive, I have heard talk that Network Rail are not particularly keen on pans going up at 125mph on the ECML which always seems to have more than its fair share of OHLE problems. Could easily just be mess room chat, however!

 

[swt_passenger]

Whilst the 800s are capable of pan up/down on the fly without loss of drive, I have heard talk that Network Rail are not particularly keen on pans going up at 125mph on the ECML which always seems to have more than its fair share of OHLE problems. Could easily just be mess room chat, however!

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

 

[coppercapped]

I was told by my dm it was strengthened , but hey ho. I had just driven the route and back an hour or so before posting here.

So...

...you pays your money and takes your choice!

 

[baz962]

So...

...you pays your money and takes your choice!

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

 

[Bald Rick]

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 square 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.

Edited to correct my own physics!