Why Do UK Trains Generally Have Single Arm Pantographs?

[whhistle]

As in, not like many European designs like this:

Is it just the diamond version is just an old design?

 

[Bletchleyite]

Is it just the diamond version is just an old design?

In short...yes!

 

[TRAX]

European designs have given up on diamond designs long ago too. Diamond pantographs are a thing of the past everywhere.
The Z pantograph enables a better current pickup at higher speeds.

 

[pdeaves]

Many British electric trains had the 'diamond' type when new in, ooh, 19-'long time ago'.

 

[Railperf]

Latest Italian E464 locos still sport diamond pantographs..

 

[AlistairCowell]

EM1 and EM2 1500v DC locomotives (later Class 76 and 77) used on the Woodhead route had them, as well as the Class 506 units used on Manchester to Glossop and Hadfield line.

Class 306 and 307 also had them when GEML was electrified at 1500v DC until 1960, when both the units and the route were converted to standard 25kV AC.

 

[edwin_m]

Many British electric trains had the 'diamond' type when new in, ooh, 19-'long time ago'.

Most of them were replaced by the Brecknell Willis high speed design, which I believe was mandatory for 110mph operation on the WCML so replaced the original type on Class 87 (a sort of diamond but the lower struts crossed over) and found its way onto various other locos and units too. This is a single-arm design.

 

[Railperf]

Diamond pantographs seem to be used on trains running on DC networks at speeds less than 200km/h (124mph) . Maybe there is something inherent in that design that suits DC operation. Or the operators sticking to a tried and tested product?

 

[TRAX]

All DC pantographs in France are Z pantographs.

 

[duesselmartin]

Italy had diamond pantos up to the 1990s including the ETR 500 HST's

 

[AM9]

Most of them were replaced by the Brecknell Willis high speed design, which I believe was mandatory for 110mph operation on the WCML so replaced the original type on Class 87 (a sort of diamond but the lower struts crossed over) and found its way onto various other locos and units too. This is a single-arm design.

The trains that were converted from 1500VDC to 25kVac (and 6.25kVac) were fitted with Stone-Faiveley AMBR single arm pantographs. These pantographs are heavy and complex with their upwards force being provided by mechanical springing. Although some of their contemporary EMUs and locos that were ac from introduction, were also fitted with the Stone-Faiveley type and could run at service speeds up to 100mph (mainly EMU class 309 and loco classes 80-86), they have now been retired. The other MKI EMUs (classes 300-305 & 308,) were 75mph designs. Later classes of MKII classes (310, 311, and 312), 'PEP' derivatives (classes 313-315) and some MKIII EMUs (classes 317-322) were fitted with AMBRs but where the trains were expected to run a large part of their diagrams at higher speeds (90-100mph) under modern lightweight auto tensioned OLE, the Brecknell-Willis with it's pneumatic suspension, secondary suspension and better aerodynamics has been the preferred type. This design has been developed for speeds up to 140mph when suitably tuned with adjustable aerofoils.
There was an experimental cross-arm design developed by GEC-AEI that was used on some class 86 & 87 locos, but those fitted were replaced with Brecknell-Willlis types after a while.

 

[Ken H]

The trains that were converted from 1500VDC to 25kVac (and 6.25kVac) were fitted with Stone-Faiveley AMBR single arm pantographs. These pantographs are heavy and complex with their upwards force being provided by mechanical springing. Although some of their contemporary EMUs and locos that were ac from introduction, were also fitted with the Stone-Faiveley type and could run at service speeds up to 100mph (mainly EMU class 309 and loco classes 80-86), they have now been retired. The other MKI EMUs (classes 300-305 & 308,) were 75mph designs. Later classes of MKII classes (310, 311, and 312), 'PEP' derivatives (classes 313-315) and some MKIII EMUs (classes 317-322) were fitted with AMBRs but where the trains were expected to run a large part of their diagrams at higher speeds (90-100mph) under modern lightweight auto tensioned OLE, the Brecknell-Willis with it's pneumatic suspension, secondary suspension and better aerodynamics has been the preferred type. This design has been developed for speeds up to 140mph when suitably tuned with adjustable aerofoils.
There was an experimental cross-arm design developed by GEC-AEI that was used on some class 86 & 87 locos, but those fitted were replaced with Brecknell-Willlis types after a while.

Brecknell Willis were the top guys on current collection. their hi-speed pantograph allowed 110mph operation. They put little aerofoils on the pantograph to even out the upward force - a V shaped pantograph pushes up more when running open end first.

were they not involved with the development of composite conductor rail, allowing longer distances between sub-stations due to the lower electrical resistance of aluminium? easier to handle due to lower weight.

 

[dubscottie]

Diamond pantographs seem to be used on trains running on DC networks at speeds less than 200km/h (124mph) . Maybe there is something inherent in that design that suits DC operation. Or the operators sticking to a tried and tested product?

I did read in one of my books that diamond pantos are more suited to DC use. Something to do with the high currents and heavier OHLE.

It may even have something to do with the fact that the wires on many DC systems were fixed and not tensioned with weights like AC wires.

The MSJ&A units had their diamond pantos replaced with single arm ones just before withdrawal.

The diamond ones could not be used under the lighter AC OHLE that was going up in stages during the conversion of the line from 1500v DC to 25kv AC.


Edit- Found the book there. Its is to do with the OHLE. Diamond pantos are useless under tensioned, variable height OHLE. They are slow to react to changes in wire height or wire bounce so the carbon strips get damaged easily from the wire smashing into them.

Single arm pantos are better at keeping contact with a bouncy wire!

Forgot how good that book was!

 

[hexagon789]

Most of them were replaced by the Brecknell Willis high speed design, which I believe was mandatory for 110mph operation on the WCML so replaced the original type on Class 87 (a sort of diamond but the lower struts crossed over) and found its way onto various other locos and units too. This is a single-arm design.

I wonder if the pantographs are a reason for the seemingly random restriction of some 87s to 100mph even in 1986, two years after 110mph operation on the WCML commenced.

 

[dubscottie]

I wonder if the pantographs are a reason for the seemingly random restriction of some 87s to 100mph even in 1986, two years after 110mph operation on the WCML commenced.

It was because they had not been equipped for one-man operation if I remember right. 87008/010 & 019 were the last to be equipped.

 

[hexagon789]

It was because they had not been equipped for one-man operation if I remember right. 87008/010 & 019 were the last to be equipped.

I thought double-manning was required for over 100mph operation into the 1990s? Or was that 110 which then eventually be vane 125.

 

[43096]

It was because they had not been equipped for one-man operation if I remember right. 87008/010 & 019 were the last to be equipped.

110mph operation on the West Coast required Brecknell Willis high-speed pantograph fitted locos. The 87s were progressively modified for the 110mph launch in 1984 - and it did take a while to do them. Anything not Brecknell Willis fitted was 100mph restricted.

Single manning mods may also have had an impact as you say, but pantographs were a critical factor.

 

[AM9]

The AMBR design of pantograph was top heavy and more liable to lateral oscillation. The Brecknell-Willis design however, not only had a lighter but overall stiffer construction, - it also could be supplied with a secondary suspension system. There are three sections to the arm:

1) the lower arm that is raised or lowered by a compressed air or hydraulic ram
2) the upper arm that is levered up by the angle of the lower arm
3) a short return arm on which the head is mounted. This arm is more compliantly sprung​

In operation, the overall height is adjusted by the two lower arms, but minor bumps and vibrations are taken up by the much lighter short arm which has a much quicker response time.

 

[dubscottie]

The 87s all had BW pantos by 1986 though and were all 110mph capable. BR abandoned 110mph running in effect in early 1986 as it was costing around £500,000 a year in manning & extra maintenance costs.
It was progressively reintroduced after single manning mods and union approval. HSTs north of Newcastle were restricted to 100mph so they could be single manned around the same time (again for cost reasons). Unions doing what unions do best!

 

[hexagon789]

110mph operation on the West Coast required Brecknell Willis high-speed pantograph fitted locos. The 87s were progressively modified for the 110mph launch in 1984 - and it did take a while to do them. Anything not Brecknell Willis fitted was 100mph restricted.

Which must be why certain 87s are not marked as 110mph in 1986.

The 87s all had BW pantos by 1986 though and were all 110mph capable. BR abandoned 110mph running in effect in early 1986 as it was costing around £500,000 a year in manning & extra maintenance costs.
It was progressively reintroduced after single manning mods and union approval. HSTs north of Newcastle were restricted to 100mph so they could be single manned around the same time (again for cost reasons). Unions doing what unions do best!

I don't doubt this but I've never heard of this policy before. So in effect the WCML reverted to 100mph running from early 1986 until presumably around the time push-pull came in? With the ECML being 125 only as far as Newcastle until presumably around electrification then?

 

[Railperf]

Italy had diamond pantos up to the 1990s including the ETR 500 HST's

The original ETR500 power cars - now reclassified as E414 locos and marshalled each end of a rake of UIC loco hauled stock still have diamond pantographs fitted. So do ETR460/463/485 Pendolinos.

 

[Kneedown]

The original ETR500 power cars - now reclassified as E414 locos and marshalled each end of a rake of UIC loco hauled stock still have diamond pantographs fitted. So do ETR460/463/485 Pendolinos.

Not too much knowledge of Italian loco classes, but the majority I saw this last week, passing while we were on the beach at Taormina, Sicily, seemed to have diamond pan's.

 

[Taunton]

An associated point is that 1960s locomotives had two single arm pantographs, which is why the pantograph well goes for much of the length of the loco. One arm faced each way, normally the rear one on the loco was used, with the "knuckle" halfway up at the forward end. There must have been some reason for this, possibly aerodynamic.

The Woodhead locos also had two diamond pantographs, and ran with both raised, I gather that at only 1,500v DC the current is far more substantial and both were needed for an adequate current path.

It was progressively reintroduced after single manning mods and union approval. HSTs north of Newcastle were restricted to 100mph so they could be single manned around the same time (again for cost reasons). Unions doing what unions do best!

Well of course, they had AWS. But then someone decided (without risk assessment) they could run without AWS, if it had failed. Someone else decided (also without risk assessment) they could run single manned, without thinking of the AWS failure possibility in combination. Someone else (no you-know-what) put up OHLE on the GW main which ended the old ability on this exceptionally straight line of always being able to see one or two signals ahead. The civils chimed in putting in single lead ladders without the previous double-crossover ability to set the flanking crossover move as protection, which had hitherto always been interlocked (guess what they didn't do). And finally someone different again decided (still no risk assessment) that the old priority given to expresses was no longer relevant in privatisation, so it could readily be pulled up to allow a freight to cross in front of it. Then there was Southall....

 

[driver_m]

AFAIK. All the 319s have now lost their AMBR pans. (Not sure about the 769 conversions but some of the Northern ones had theirs replaced just before going out of service). Apart from PEP/317/318s and a few 86’s, there aren’t any others left now are there?

Incidentally. Who supplies the pans now fitted to new units & those on the 350’s?

 

[jopsuk]

Incidentally. Who supplies the pans now fitted to new units & those on the 350’s?

Pretty much universally Brecknell Willis isn't it?

 

[AlexNL]

Diamond pantographs seem to be used on trains running on DC networks at speeds less than 200km/h (124mph) . Maybe there is something inherent in that design that suits DC operation. Or the operators sticking to a tried and tested product?

Here in the Netherlands (1500 V DC everywhere*), you'll only find diamond pantographs on heritage rolling stock. The fleets used for squadron service all have Z-shaped pantos.

* Except for the High Speed Line Amsterdam - Belgium, and the Betuweroute from Rotterdam to Germany (25 kV)

 

[Skutter]

I did read in one of my books that diamond pantos are more suited to DC use. Something to do with the high currents and heavier OHLE.

Edit- Found the book there. Its is to do with the OHLE. Diamond pantos are useless under tensioned, variable height OHLE. They are slow to react to changes in wire height or wire bounce so the carbon strips get damaged easily from the wire smashing into them.

Sounds interesting - which book is this please?