Class 387 coming to Thames Valley - ongoing discussion

[whole diary]

[paul7575]

I'm obviously locked in a timewarp from when I used to travel to school on the Class 302 EMUs^▸ (Electric Multiple Unit) on the Southend line. Like all first generation BR^▸ (British Rail(ways)) EMUs they had a single motor coach and you certainly knew if you were travelling in it. Apart from all the electro-mechanical noises it rode like a sack of potatoes!

Yes, it seems the BR standard for quite a while was a single motor coach, this can be seen in most EMUs of the era including the 442, where the motor coach was the middle of the five in the set.

Siemens and Bombardier have subsequently taken slightly different approaches though, with Siemens Desiro UK^▸ (United Kingdom) having both bogies motor fitted in each end car, with Bombardier normally having them spread fairly evenly throughout the train except in the PTSO.

Paul

[DidcotPunter]

Yes, it seems the BR^▸ (British Rail(ways)) standard for quite a while was a single motor coach, this can be seen in most EMUs^▸ (Electric Multiple Unit) of the era including the 442, where the motor coach was the middle of the five in the set.

Siemens and Bombardier have subsequently taken slightly different approaches though, with Siemens Desiro UK^▸ (United Kingdom) having both bogies motor fitted in each end car, with Bombardier normally having them spread fairly evenly throughout the train except in the PTSO.

Paul

I was standing opposite a 442 motor coach while waiting at Gatwick - must have put it into my mind. Interesting that the trend now is for EMU manufacturers to use distributed traction, though with different configurations. I guess that it improves adhesion. I can't recall exactly without looking it up but I thought that Hitachi have gone for the same with the 800s/IEPs^▸ (Intercity Express Program / Project.), though with these the driving cars with pantograph and transformers are unpowered.

[Electric train]

I'm obviously locked in a timewarp from when I used to travel to school on the Class 302 EMUs^▸ (Electric Multiple Unit) on the Southend line. Like all first generation BR^▸ (British Rail(ways)) EMUs they had a single motor coach and you certainly knew if you were travelling in it. Apart from all the electro-mechanical noises it rode like a sack of potatoes!

Yes, it seems the BR standard for quite a while was a single motor coach, this can be seen in most EMUs of the era including the 442, where the motor coach was the middle of the five in the set.

Siemens and Bombardier have subsequently taken slightly different approaches though, with Siemens Desiro UK^▸ (United Kingdom) having both bogies motor fitted in each end car, with Bombardier normally having them spread fairly evenly throughout the train except in the PTSO.

Paul

Yes, it seems the BR standard for quite a while was a single motor coach, this can be seen in most EMUs of the era including the 442, where the motor coach was the middle of the five in the set.

Siemens and Bombardier have subsequently taken slightly different approaches though, with Siemens Desiro UK having both bogies motor fitted in each end car, with Bombardier normally having them spread fairly evenly throughout the train except in the PTSO.

Paul

I was standing opposite a 442 motor coach while waiting at Gatwick - must have put it into my mind. Interesting that the trend now is for EMU manufacturers to use distributed traction, though with different configurations. I guess that it improves adhesion. I can't recall exactly without looking it up but I thought that Hitachi have gone for the same with the 800s/IEPs^▸ (Intercity Express Program / Project.), though with these the driving cars with pantograph and transformers are unpowered.

There has been a big change in technology since the last BR design of an EMU, high power static inverters that can produce poly phase alternating current has enabled the introduction of the much lighter AC ploy phase squirrel cage induction traction motors instead of the heavier DC^▸ (Direct Current) series traction motors; this means it is easier to place traction motors on most boogies.  Distribution the traction motors also means less chance of wheel spin.

     

[ellendune]

There has been a big change in technology since the last BR^▸ (British Rail(ways)) design of an EMU^▸ (Electric Multiple Unit), high power static inverters that can produce poly phase alternating current has enabled the introduction of the much lighter AC ploy phase squirrel cage induction traction motors instead of the heavier DC^▸ (Direct Current) series traction motors; this means it is easier to place traction motors on most boogies.  Distribution the traction motors also means less chance of wheel spin.

Phew - I am glad I paid attention in first year electrical engineering lectures!

[Chris from Nailsea]

... the introduction of the much lighter AC ploy phase squirrel cage induction traction motors ...

I can think of at least one of our Coffee Shop forum members who will be less than happy with that aspect ... 

[Worcester_Passenger]

Isn't there also something about cables between vehicles? The old overhead wire units had everything within one power car in the middle of the unit, while the third rail ones had a power car at each end of the set (to reduce the problems of gaps in the third rail). That way there were no power cables between vehicles - has there been a technical change about what can be done (or indeed, what's allowed to be done)?

[paul7575]

Isn't there also something about cables between vehicles? The old overhead wire units had everything within one power car in the middle of the unit, while the third rail ones had a power car at each end of the set (to reduce the problems of gaps in the third rail). That way there were no power cables between vehicles - has there been a technical change about what can be done (or indeed, what's allowed to be done)?

There must have been certain changes, not least because the Pendolino passes 25 kV from the one raised pantograph to 2 or 3 transformers fitted throughout the train (in 9 or 11 car versions). 

In the case of DC^▸ (Direct Current) pickup, the cars with the pick up shoes were not necessarily those with the traction motors, (the 442 being a good example, with shoes on all cars except the motor car).  As we have mentioned, most BR^▸ (British Rail(ways)) era DC units had a single motored car, wherever the pick up shoes happened to be, so must have had a DC connection between vehicles within the unit.

I think there might have been a rule whereby power wasn't connected between DC units working predominantly in tunnels, but could be on normal EMUs^▸ (Electric Multiple Unit).

Paul

[Rhydgaled]

Isn't there also something about cables between vehicles?

Not sure, but I think there was at some point because the APT^▸ (Advanced Passenger Train)-P (Advanced Passenger Train Prototype) had two power cars in the middle of the train (I think) rather than one at each end which would seem to be more sensible from a passenger's perspective.

[Worcester_Passenger]

The Wikipedia entry about the APT^▸ (Advanced Passenger Train) says that:

Two power cars were necessary to maintain the design speeds over the northern banks with 12 coaches. Normally these would be situated at the front and rear of the train (as with the HST^▸ (High Speed Train) and TGV^▸ (Train a Grande Vitesse) etc.) but, due to the design of the overhead line, a "wave" was set up in it by the front pantograph, thus causing problems for current collection from the rear unit. The obvious answer was an on-board 25 kV "roof-line" link to the rear power car but this was considered infeasible at the time.

So why was a roof-line link infeasible at the time, but quite OK nowadays?

The problem of two pantographs causing resonance is still with us - it was an issue when London Midland had some of their class 350s uprated for 110 mile/h operation. As a result, LM^▸ (London Midland - recent franchise) had to operate these as single 4-car trains instead of the 8-car ones that they'd wanted.

[Electric train]

The 25kV train bus will not link 2 pans together, there would be a big bang and flash as the train went over a neutral section 

Modern trains (like the class 700) have a 400V 3 phase train wire with a bus section circuit breaker that allows the train to operate with only one pan up

[paul7575]

The 25kV train bus will not link 2 pans together, there would be a big bang and flash as the train went over a neutral section 

Modern trains (like the class 700) have a 400V 3 phase train wire with a bus section circuit breaker that allows the train to operate with only one pan up

Won't there still have to be a roof level 25kV bus line between the two transformer cars on the 700s though?

Agree the pans themselves can never be electrically linked, but with transformers in cars 2 and 11 of a 12 car train, either the inputs must be linked at 25 kV, or they must be separate and run with both pans up.   The train must be too long to run off one transformer.

Paul

[Electric train]

The 25kV train bus will not link 2 pans together, there would be a big bang and flash as the train went over a neutral section 

Modern trains (like the class 700) have a 400V 3 phase train wire with a bus section circuit breaker that allows the train to operate with only one pan up

Won't there still have to be a roof level 25kV bus line between the two transformer cars on the 700s though?

Agree the pans themselves can never be electrically linked, but with transformers in cars 2 and 11 of a 12 car train, either the inputs must be linked at 25 kV, or they must be separate and run with both pans up.   The train must be too long to run off one transformer.

Paul

There is no 25kV bus on the 700's

The 395's have a 25kV bus but not between units

[paul7575]

So will the 700s run with both pans up?

Paul

[Electric train]

So will the 700s run with both pans up?

Paul

Yes, their performance especially the 12 car versions is reduced with only one pan up

[stuving]

There's am RSSB^▸ (Rail Safety and Standards Board) "Research Brief" on "Simulation and verification of results from 125mph current collection modelling for two pantographs" T841 - January 2011

To summarise rather broadly, it concludes that 160 km/hr is OK with any spacing, but 200 km/hr isn't possible without major changes. 180 km/hr can be done with spacings of 50 m and 200 m, but in between (125 m) only with the right choice of pantograph design and/or slightly more cable tension

That should be true for any train, but the work was done to help with the IEP^▸ (Intercity Express Program / Project.) requirement. That includes:

3.8 Performance
It is accepted that 125mph may not be achieved under the following circumstances:
...

• where, in the event of failure of the IEP Train, it is not possible to raise two pantographs at the maximum pantograph spacing permitted by the train formation. In this event, subject to the other provisos of this provision, at least 100mph must be achieved if the pantograph spacing is 75m or greater and no less than 80mph shall be achieved for lesser spacings; and
• in the event that it is not possible to show compatibility between the pantograph and the infrastructure, when an IEP Train is operating with two pantographs raised, on any portion of the Great Western Main Line between Paddington and Airport Junction where the line speed is greater than 100mph. In this event, the IEP Train shall be capable of 100mph or the speed at which operation is shown to be compatible with the overhead line, whichever is greater.

That seems to suggest that two pantographs far enough apart (within the 207 m length of a 9-car train? Or the 312 m limit of train length, single or multiple-unit?) would permit 125 mph. Which is not what the RSSB found. There is more stuff about multi-unit trains, which hints that two units can be powered off one pantograph. But it doesn't say clearly either it is or isn't required to.