Pantographs - leading or trailing?

[Alex TM]

Hi everyone,

 

Having been on the ECML a number of times in the last couple of months I have noticed the following practice concerning which pantographs are used on their Hitachi units:

 

LNER - trailing
TransPenine - leading

 

Does anyone know if there is any particular reason for the differing practices regarding the Hitachi units?

 

Thanks and regards,

 

Alex.

[St. Simon]

1 hour ago, Alex TM said:

Hi everyone,

 

Having been on the ECML a number of times in the last couple of months I have noticed the following practice concerning which pantographs are used on their Hitachi units:

 

LNER - trailing
TransPenine - leading

 

Does anyone know if there is any particular reason for the differing practices regarding the Hitachi units?

 

Thanks and regards,

 

Alex.

Hi Alex,

 

There’s no technical reason for choosing one pantograph over the other, it is simply a company policy.

 

The argument for the trailing pan to be raised is if it gets snagged in the OLE it won’t fall on the rest of the roof of a train and get tangled in the roof equipment. Not quite sure what the argument for the leading pan is.

 

Great Western use the Leading Pan on single units and the Outer Pans on multi-units. This could indicate a DfT decision.

 

Simon

[Michael Hodgson]

On the Woodhead route the locos used both pantographs.  I think the reason was that to get the same power from 1500vDC as from 25kV AC you draw a much higher current.

[DY444]

12 hours ago, St. Simon said:

Hi Alex,

 

There’s no technical reason for choosing one pantograph over the other, it is simply a company policy.

 

The argument for the trailing pan to be raised is if it gets snagged in the OLE it won’t fall on the rest of the roof of a train and get tangled in the roof equipment. Not quite sure what the argument for the leading pan is.

 

Great Western use the Leading Pan on single units and the Outer Pans on multi-units. This could indicate a DfT decision.

 

Simon

 

The use of the outer pans on 2 x 5 80X is to maximise the distance between them for operation at higher speeds so that the disturbance to the contact wire caused by the leading pan doesn't affect the operation of the trailing pan.  If one or both of the inner pans are being used the train has to run at restricted speeds (off the top of my head it's something like 110mph max if one inner in use and 80mph max if both inners are in use - that sort of order anyway).  I think it is an NR requirement to protect the ole. 

Edited September 21, 2021 by DY444

[DY444]

8 hours ago, Michael Hodgson said:

On the Woodhead route the locos used both pantographs.  I think the reason was that to get the same power from 1500vDC as from 25kV AC you draw a much higher current.

 

In the modern day, Thameslink Class 700s use both pans as, despite being a single unit, electrically they are two separate units (700/0 2 x 4 car, 700/1 2 x 6 car) permanently coupled with no HT connection between them.  Class 373 also use both pans, again as there is no HT connection down the train.

[Michael Hodgson]

I think I heard of some safety edict about not connecting HT between vehicles at least on new stock - presumably to reduce risk of electrocution should the vehicles become separated in an accident?

[Wheatley]

Certainly there has been at least one near miss on maintenance where fitters working on one unit believed it to be electrically dead whilst the one coupled to it still had the pan up and the 25KV jumper connected.  I can't remember the details but it was 2x 308s and I don't believe they started off connected. 

[keefer]

Unless it was only control voltages involved as none of the Mk1 EMUs had 25kV power jumpers between units.

It was also the reason why the full APT-P formations had 2 power cars in the middle, as BR didn't want line voltage going through the train (unlike the TGV).

That said, don't the Pendolinos have a 25kV line, IIRC they only use one pan at a time?

Edited September 21, 2021 by keefer

[hexagon789]

37 minutes ago, keefer said:

That said, don't the Pendolinos have a 25kV line, IIRC they only use one pan at a time?

Yes, it's on the roof - it doesn't pass through the passenger accommodation.

[45125]

7 hours ago, hexagon789 said:

Yes, it's on the roof - it doesn't pass through the passenger accommodation.

As does the HT line on IEP. That what the curly pig tail is between vehicles.

[MarkC]

22 hours ago, Michael Hodgson said:

On the Woodhead route the locos used both pantographs.  I think the reason was that to get the same power from 1500vDC as from 25kV AC you draw a much higher current.

Yes, the current draw on 1500V is much higher than that on 25kV - Power = Volts x Amps, in simple terms.

[phil-b259]

On 20/09/2021 at 20:46, St. Simon said:

 

Great Western use the Leading Pan on single units and the Outer Pans on multi-units. This could indicate a DfT decision.

 

Simon

 

Don't forget that to provide good electrical contact pantographs lift the contact wire ever so slightly as they pass. This causes the wire to oscillate and if a second pantograph is subjected to these oscillations then it can either start to lose electrical connectivity with the wire causing arcing or end up getting snagged and ripping the wires down!

 

This can be compensated to a degree by:-

• Making the overhead lines stiffer (hence a move away from the flimsy headspan design favoured by British rail from the 1970s which is inherently pretty flexible to the stiff Swiss designed stuff used on the GWML) thus reducing the oscillations
• Moving the pantographs further apart so the oscillations have more time to subside between pantograph passes
• Lowering the speed of trains as the pantographs of slower trains produce less of an uplift on the contact wire and smaller oscillations which die out more quickly.

 

On the GWML the use of a more robust OLE system plus the use of the outermost pantographs on coupled units means that the oscillations set up by the leading pan do not affect the rearmost one even at 140mph (the eventual goal once ECTS is installed).

 

By contrast I believe such a configuration would not be suitable for large chunks of the ECML due to the use of headspans and large mast spacing distances.

 

 

[phil-b259]

15 hours ago, Michael Hodgson said:

I think I heard of some safety edict about not connecting HT between vehicles at least on new stock - presumably to reduce risk of electrocution should the vehicles become separated in an accident?

 

Up until the Pendalinos were built our gold plaiting and bureaucratic safety experts in Whitehall banned BR from having a 25KV connection running between vehicles carrying passengers. I suspect they were worried that a train becoming divided could somehow end up with a 25KV cable ending up dangling in a place where a traveller might be able to touch it even though there are plenty of engineering solutions to address that problem.

 

This was despite many European nations showing it to be a perfectly safe practice - including the French TGV which ran faster than any UK train did.

 

This edict meant that a full length ATP - which needed two power cars but could only have a single Pantograph raised at any one time due to the lightweight OLE system that BR was forced to use by Government spending restrictions had a problem and could it could only be solved by putting the two power cars in the middle of the train and preventing passenger movement through them.

 

It took privatisation for 'the men from the ministry' to see sense - and now the provision of a 25KV feeder cable (within one unit only) on the likes of the IETs is considered the norm

 

 

Edited September 22, 2021 by phil-b259

[SRman]

20 hours ago, DY444 said:

 

The use of the outer pans on 2 x 5 80X is to maximise the distance between them for operation at higher speeds so that the disturbance to the contact wire caused by the leading pan doesn't affect the operation of the trailing pan.  If one or both of the inner pans are being used the train has to run at restricted speeds (off the top of my head it's something like 110mph max if one inner in use and 80mph max if both inners are in use - that sort of order anyway).  I think it is an NR requirement to protect the ole. 

That's almost certainly the case. Back in the 1970s, Victorian Railways here in Australia bought some Hitachi suburban trains, initially run as 4 +2 car units with three driving motors. These all had the pans at the leading ends, which was fine while they were spaced along the trains. Then they reformed them into 2 x 3-car units with driving motors at the outer ends of each three car set. This meant that now the two inner DMs had pantographs with much less than one carriage length between them, they soon found that the extra strain on the overhead lines was causing the droppers to let go, even at our usual slow suburban speeds (VR considered 40 mph points to be "high speed"!). 

The trains were still being delivered at that time, so an amendment was made to only the last 10 or 20 DMs to have their pan at the rear of the coach. That was too late to save the problem, so strengthening works had to be implemented, adding extra dropper wires to the OHLE. 

Our trains run on 1500V DC, but suburban trains don't have quite the power draw that the freight locomotives would have that required two pans to be up to feed the one unit, but most Melbourne suburban trains have run with one pantograph for each motored coach, with the exception being the current X'trapolis units, which have one pan for a 3-car unit.

From all this, one can see just how much of an effect two pantographs on a high-speed train could have on the OHLE, especially if they are too close together.

[Fat Controller]

11 hours ago, MarkC said:

Yes, the current draw on 1500V is much higher than that on 25kV - Power = Volts x Amps, in simple terms.

When French 'bi-courant' locos start a train on 1.5 kV, they often use their 25kV pantograph, as well as their DC one, until the train is rolling.

[Fat Controller]

20 hours ago, keefer said:

Unless it was only control voltages involved as none of the Mk1 EMUs had 25kV power jumpers between units.

It was also the reason why the full APT-P formations had 2 power cars in the middle, as BR didn't want line voltage going through the train (unlike the TGV).

That said, don't the Pendolinos have a 25kV line, IIRC they only use one pan at a time?

Even TGVs only have the 25kV line within the rake; when working in multiple, one pantograph is used on each unit.

Could the incident with the UK EMUs be down to an induced voltage from an adjacent live line? I know of at least one instance of this happening, resulting in one fatality,  and the person who tried to rescue him suffering very serious burns.

[Steadfast]

I'm surprised about the variety in pan usage on the Hitachi units by different operators.

I guess running with the front pan reduces the risk of a driver raising the rear pan on the front set in a 2x5 car formation by mistake, but comes with the risk of damaging the roof and rear pan in a dewirement.

 

Jo

[Ken.W]

On the IETs, in single unit formation then front / rear pans basically company policy.

 

When in 2 x 5 car formation, due to the oscillation effect in the OHL its;

Both outer pans raised 125mph

One set outer pan and other set inner pan 100mph

Both inner pans 80mph

 

They do have a 25kv line along the roof and connected between coaches within each set, which supplies OHL power to the Main Transformers located on each Driving Trailer, and on 9 car sets one of the two intermediate Trailers

[rodent279]

On 22/09/2021 at 10:03, Fat Controller said:

When French 'bi-courant' locos start a train on 1.5 kV, they often use their 25kV pantograph, as well as their DC one, until the train is rolling.

The straight 1500v DC CC6500's were impressive. With around 6000kW installed, hard acceleration usually resulted in heavy sparking, sometimes almost flames, coming from the pan.

[rodent279]

Slightly OT, here's a gap in the wires deliberately engineered in.

 

 

Edited October 27, 2021 by rodent279

[GordonC]

is that a gap in the overhead but the pantograph stays raised across it???

 

[Titan]

44 minutes ago, GordonC said:

is that a gap in the overhead but the pantograph stays raised across it???

 

 

Think so, I have seen similar near Amsterdam, where there are a lot of swing bridges over rivers/canals. Saves coming up with a complex solution for wiring the bridge.  Would be no good for low bridges, there would be a pile of ripped off pantographs beside the bridge before long!

[GordonC]

13 minutes ago, Titan said:

 

Think so, I have seen similar near Amsterdam, where there are a lot of swing bridges over rivers/canals. Saves coming up with a complex solution for wiring the bridge.  Would be no good for low bridges, there would be a pile of ripped off pantographs beside the bridge before long!

 

thats what I thought, they must be really careful to avoid ripping the pantograph off on returning to the overhead

[Bittern]

So long as the contact wire starts above the maximum pan height and slopes down gently enough, it should be OK.