Class 76 and 77 dual pantographs

[The Stationmaster]

 

 

BR Research did many studies into the mechanics of current collection and a spin off form this was the development of the sophisticated Brecknell-Willis pantographs that were pretty much standard for BR. These use aerofoils to help control the upward contact force which tends to rise as speed increases. The continental approach was to accept that the force would increase with speed and stiffen up the overhead accordingly. Hence when spare eurostars were used on ECML duties they had to be fitted with a BR pantograph so that they did not bring down the OHLE.

 

 

Not correct as far as the comment about Eurostars is concerned.  It is true that the original pans for UK use were 'problematic' (to say the least) with, in particular, the Mk3 catenary on the ECML, and the design of the 'BR' pan resulted in the trains being limited to 110mph maximum speed.  However on tests it was considered too dangerous to run with the rear pan raised at speeds of c.100mph, let alone higher, because of the amount of movement taking place in the contact wire.

 

Accordingly a set was despatched to France for extensive testing at even higher speeds in order to study the behaviour of the pantographs and to try to establish a way of alloing trains to operate on the ECML with both pans raised and without severely limiting their maximum speed.  It was establlshed that the problem was mainly a result of excessive (for cheapo BR catenary) uplift force and the pans were modified to reduce that force with - I believe - a redesigned head and possibly some other changes.

[Grovenor]

The Heysham arrangement, as you describe it is not 'regeneration' as no power is being fed back from the train, the battery would charge up from the line during the low load periods.

The automatic regeneration feature of 3-phase systems was one of their inherent features along with a constant speed controlled by the frequency of the supply, made it good for mountainous areas. Now we have electronic control nice simple 3-phase motors with their automatic regen are becoming the norm as the 3 phase is produced on board the train  and with a variable frequency to control the speed.

Keith

[Poor Old Bruce]

The OLE on the DC is I think about 2 square inches in area in total against less than 1 sq inch for AC due to the lowere currents and voltage losses.

 

That sound like a lot of copper to me. Have you got your unit right?

[Titan]

I didn't say it was bulshit, If you find out what bulshit bingo actually means then you will understand my post.

Posts 2 & 3 were a quite adequate explanation for the vast majority of us on the forum, there is no need for willy waving.

When you have, I will expect removal of the disagree icons and an apology to me.

 

Mike.

 From the Urban Dictionary:

 

1.

 

bingo

A game that can be played in large meetings. The players write down management-nonsense word like "Out-of-the-box-thinking", "Synergy", "Content streamlining" etc. in a 5 by 5 square bingo card.

 

There were no management-nonsense words in the post to which you were reffering to, indeed no nonsense at all albeit it may have been hard to understand, but being hard to understand and using technical words is not , bingo or otherwise. The disagrees were well earned, appropriate and justified, and your request for an appology ridiculous!!!

[Titan]

That sound like a lot of copper to me. Have you got your unit right?

 

I believe that the old DC contact wires were about 150mm²  which compared to the standard 107mm² of the Mk1-Mk3 range. New installations are tending to use 120mm²

[Poor Old Bruce]

I believe that the old DC contact wires were about 150mm²  which compared to the standard 107mm² of the Mk1-Mk3 range. New installations are tending to use 120mm²

 

Thanks Titan, that makes a bit more sense. My sums tell me that 150 sq mm is about 14mm diameter while 2sq in would be about 40mm diameter!

[jamie92208]

That sound like a lot of copper to me. Have you got your unit right?

Sorry about that, my mistake. I knew that they were quite a lot thicker I realise now that I was thinking of the very heavily reinforced overhead on the French 1500 DC lines.  This was very rigid with I think 2 square contact wires in parallel and several larger catenary and intermediate wires above and my rough estimate looking at them from the platform was between 1 and 2 sq. inches.   They did have to cope with such beasts as the 6500 series locos though.

 

Jamie

[Dave Scott]

I didn't say it was bulshit, If you find out what bulshit bingo actually means then you will understand my post.

Posts 2 & 3 were a quite adequate explanation for the vast majority of us on the forum, there is no need for willy waving.

When you have, I will expect removal of the disagree icons and an apology to me.

 

Mike.

As an electrical engineer of 42 years standing, now retired, I seriously object to technical explanations being willy waving. The explanations on this forum are the Janet and John version ( childrens reading primers). The full technical explanations are considerably more complicated.

 

It saddens me that your attitude is far too common when issues get technical. What made GB great was enterprising engineers and scientists. Financiers may have fouled it up but is the engineers who are putting the country back together again.  

[roythebus]

It's broke, they're fixing it!

[Edwin_m]

As a matter of interest after the posts about the second pan on AL6s being considered unnecessary, Pendolinos carry two pans and normally run with the rear one raised.  The logic for using the rear one is, I believe, that if the rear one is damaged by hitting something (and it doesn't bring the wires down) then the front one has already passed under the damaged area and can be raised instead. 

[Titan]

I am pretty sure the reason for the early AC electrics having two pans was that it was believed that the pan performed better with the knuckle leading, thus each pan would be used in turn depending on direction. I don't think they ever ran with two pans up. (waits for someone to produce obscure photographic evidence... )  In practice it was discovered that it did not make much difference, and as there were maintenance savings to be had by only having one pan, then the extra one was removed.

 

With the class 92's it was about having redundancy in case one pan was damaged, particularly as they were to run through the channel tunnel. This was something that Brush strongly resisted. With such a crowded loco - basically two locos in one as the traction package is completely duplicated apart from just having one transformer, they wanted to have only the one pantograph well and build the rest of the roof full height to gain space. However the specification called for two pans and so that is what they had to provide.

[jamie92208]

As a matter of interest after the posts about the second pan on AL6s being considered unnecessary, Pendolinos carry two pans and normally run with the rear one raised.  The logic for using the rear one is, I believe, that if the rear one is damaged by hitting something (and it doesn't bring the wires down) then the front one has already passed under the damaged area and can be raised instead. 

I Think that it's also to allow the driver more time to drop the pan if they see some damaged OLE and more time to slow down as well as the reason given above.

 

Jamie

[david.hill64]

Not correct as far as the comment about Eurostars is concerned.  It is true that the original pans for UK use were 'problematic' (to say the least) with, in particular, the Mk3 catenary on the ECML, and the design of the 'BR' pan resulted in the trains being limited to 110mph maximum speed.  However on tests it was considered too dangerous to run with the rear pan raised at speeds of c.100mph, let alone higher, because of the amount of movement taking place in the contact wire.

 

Accordingly a set was despatched to France for extensive testing at even higher speeds in order to study the behaviour of the pantographs and to try to establish a way of alloing trains to operate on the ECML with both pans raised and without severely limiting their maximum speed.  It was establlshed that the problem was mainly a result of excessive (for cheapo BR catenary) uplift force and the pans were modified to reduce that force with - I believe - a redesigned head and possibly some other changes.

Are you sure? Brecknell Willis' literature shows the Eurostars as a reference for pantograph fitment. I know that they are fitted with Faiveley pans now (and originally).

[chaz]

I didn't say it was bulshit, If you find out what bulshit bingo actually means then you will understand my post.

Posts 2 & 3 were a quite adequate explanation for the vast majority of us on the forum, there is no need for willy waving.

When you have, I will expect removal of the disagree icons and an apology to me.

 

Mike.

 

On the subject of pantographs and the differences between AC and DC I have nothing to say BUT I do think it a shame if postings are rude or provocative. Acrimony has no place on this forum and we all should be polite and reasonable. We also need to be aware of how easily jokey asides can be misinterpreted.

 

When someone has "inside knowledge" of a topic it is worth them adding their expertise. I would much rather see properly informed information and if some of it goes over my head it's not a problem.

 

Chaz

[The Stationmaster]

Are you sure? Brecknell Willis' literature shows the Eurostars as a reference for pantograph fitment. I know that they are fitted with Faiveley pans now (and originally).

Yes, I'm sure.  As far as I'm aware Brecknell Willis didn't just make pans to their own design and there were of course published pics of a Regional Eurostar set in GNER livery in France taken while it was there for the pantograph trials and tests.

[Joseph_Pestell]

ISTR Dutch locos on their system (1500v dc) would have both pantographs raised during acceleration from station stops and then drop one when the current had dropped within the capability of a single one..............not sure if that still happens, it used to when they had proper locos over there - 11's, 12's, 13's, 15's................

 

French operating practice under 1500v was the same.

 

Edit: Sorry. See that Jamie has already said this.

[Joseph_Pestell]

I believe that the old DC contact wires were about 150mm²  which compared to the standard 107mm² of the Mk1-Mk3 range. New installations are tending to use 120mm²

 

Most DC wiring is compound catenary. So in addition to the diameter of the contact wire, there is a second heavy cable carrying current above it. I don't know the respective total dimensions but the difference must be considerable given the current to be carried. Note also the size of conductor rail needed for thirdrail at 600 - 750V even when using small light trains such as DLR.

 

On any long-distance railway, the extra infrastructure costs (catenary and sub-stations) of DC soon outweigh the extra cost of AC locomotives/EMUs. On a busy urban service with frequent trains, DC may still be the best answer although modern technology for regenerating current on AC moves the goalposts in that calculation.

[Joseph_Pestell]

I have always struggled a bit with 3-phase. But, as I understand it, you would not regenerate as such. Each train would be drawing current from one of the positive phases and then returning current into another phase which would be the one used by the following train. So long as 33% of your train fleet is drawing from each of the three phases, everything should work nicely. It's not regeneration "as we know it, Jim" but a much more efficient use of current with less transmission loss.

[Joseph_Pestell]

French 1500 locos use both pans on starting and drop the 2nd one at a relatively low speed, about 10mph.   AC regeneration ahs only started in recent years as the control electronics have become available.  However ISTR reading somewhere that two descending MGR's on Woodhead brought the next one up for free.  There were large resistance grids however at the feeder stations at Penistone to dissipate excess current if nt trains were drawing the regenrated power.  The OLE on the DC is I think about 2 square inches in area in total against less than 1 sq inch for AC due to the lowere currents and voltage losses.

 

Jamie

 

I recall being told by one of my customers who was a driver at Narbonne depot that if one did not have both pantos raised at the moment of starting a heavy rain, current draw was such that the panto head could weld itself to the catenary. As soon as the train is on the move, one can drop one panto as movement wil mean that the loco is not in contact with the wire at any given point for the heat raised to have that effect. 

[Edwin_m]

I have always struggled a bit with 3-phase. But, as I understand it, you would not regenerate as such. Each train would be drawing current from one of the positive phases and then returning current into another phase which would be the one used by the following train. So long as 33% of your train fleet is drawing from each of the three phases, everything should work nicely. It's not regeneration "as we know it, Jim" but a much more efficient use of current with less transmission loss.

I think you may be confusing a couple of things here.  A few railways do or did use a true three-phase supply with (I think) either three overhead lines or two with the rail providing the third, and three-phase motors.  These motors would draw current equally from all three phases but would only run steadily at one of a limited number of speeds, because their rotational speed is related to the frequency of the supply. 

 

AC OLE with one wire is single-phase but is normally fed from a three-phase grid supply.  This does indeed feed different sections of railway from different phases, hence the need for neutral sections to avoid connecting different phases together.  It also means that a train can only regenerate if there is another train drawing current on the area connected to the same phase (but it's quite a large area) or if the feeder station is able to return power to the grid.  This system can result in a fairly big phase imbalance in the current drawn from the grid, which the supply people don't like. 

 

Modern power electronics used in trains can power three-phase electric motors continuously at any speed off a DC or single-phase AC supply.  They can also be used in feeder stations to balance the load across the three grid phases.  In principle an entire single-phase AC network could probably then be fed in phase and neutral sections eliminated, but I don't think this actually happens. 

[Dave Scott]

I think you may be confusing a couple of things here.  A few railways do or did use a true three-phase supply with (I think) either three overhead lines or two with the rail providing the third, and three-phase motors.  These motors would draw current equally from all three phases but would only run steadily at one of a limited number of speeds, because their rotational speed is related to the frequency of the supply. 

 

AC OLE with one wire is single-phase but is normally fed from a three-phase grid supply.  This does indeed feed different sections of railway from different phases, hence the need for neutral sections to avoid connecting different phases together.  It also means that a train can only regenerate if there is another train drawing current on the area connected to the same phase (but it's quite a large area) or if the feeder station is able to return power to the grid.  This system can result in a fairly big phase imbalance in the current drawn from the grid, which the supply people don't like. 

 

Modern power electronics used in trains can power three-phase electric motors continuously at any speed off a DC or single-phase AC supply.  They can also be used in feeder stations to balance the load across the three grid phases.  In principle an entire single-phase AC network could probably then be fed in phase and neutral sections eliminated, but I don't think this actually happens. 

At the risk of being a willy waver I would like to corect one small point. AC traction is phase - phase not phase - neutral. At a two transformer sub one will be say red - blue the other blue - yellow. The next feeder station might be red -yellow and blue yellow. To perhaps understand it better the cable in your street is 3 phase 415v phase - phase 230/240 phase - neutral. By swapping phases you ballance flows across the National Grid  EDIT I should have made it clear that I was reffering to NG side. As has been pointed out the HV suply, 132kV 275KV and 400Kv , depending of date of installation, may be phase - phase but the LV side at 25kV is phase earth. Note National Grid does not have a neutral in its transmission lines only phase conductors and earth.

 

Early ac locos could not regenerate becausre they used dc motors and control gear. AC is collected and goes to a tapable transformer to give rough control. the supply then  goes through a rectifier, dc control gear to dc motors. Whilst the dc motors could be made to regenerate it would create dc. You need to convert DC back to AC. Today this could be done using a power inverter, not readily available in the 60s.The NG - EDF 2000MW link uses multiple power inverters  in series and paralel strings to convert DC back to AC

[Titan]

At the risk of being a willy waver I would like to corect one small point. AC traction is phase - phase not phase - neutral. At a two transformer sub one will be say red - blue the other blue - yellow. The next feeder station might be red -yellow and blue yellow. To perhaps understand it better the cable in your street is 3 phase 415v phase - phase 230/240 phase - neutral. By swapping phases you ballance flows across the National Grid

 

 

AC traction is phase-phase on the National grid side of the substation transformer, but on the railway side it is 25kV - neutral/earth. If it was not there would be some serious current leakage issues from the traction return rail, not to mention all your rolling stock becoming live...

[Edwin_m]

At the risk of being a willy waver I would like to corect one small point. AC traction is phase - phase not phase - neutral. At a two transformer sub one will be say red - blue the other blue - yellow. The next feeder station might be red -yellow and blue yellow. To perhaps understand it better the cable in your street is 3 phase 415v phase - phase 230/240 phase - neutral. By swapping phases you ballance flows across the National Grid

Good point - hadn't really thought about that one but it makes sense to do it that way especially as the neutral conductor on the Grid is only designed for very low currents. 

[Xerces Fobe2]

I have always struggled a bit with 3-phase. But, as I understand it, you would not regenerate as such. Each train would be drawing current from one of the positive phases and then returning current into another phase which would be the one used by the following train. So long as 33% of your train fleet is drawing from each of the three phases, everything should work nicely. It's not regeneration "as we know it, Jim" but a much more efficient use of current with less transmission loss.

I think that you may be understandably confused here. AC power is delivered to the train as a single phase supply and the on board train electronics such as quadrative converters convert it to 3 phase to drive the motors. Regeneration occurs when the train brakes by turning the motors into generators feeding power back through the electronics into single phase that is synchronised with line electrical supply.