Porterbrook Cl.769 'Flex' trains from 319s, initially for Northern

[507021]

Not at this stage

No problem, thanks anyway.

Aren't they extra units to provide cover while others are sent away for belated accessibility mods?

They are, I was just wondering if Philip knew what the unit numbers were.

 

[adc82140]

Will they be able to change modes on to go? For instance, leaving Guildford, first stop North Camp the 3rd rail runs out at Aldershot South junction, somewhat short of North Camp. It'd be a shame if they had to run on diesel all the way from Guildford.

 

[The Ham]

Will they be able to change modes on to go? For instance, leaving Guildford, first stop North Camp the 3rd rail runs out at Aldershot South junction, somewhat short of North Camp. It'd be a shame if they had to run on diesel all the way from Guildford.

That would only be the case for those services which didn't stop at Ash (which currently is half the services).

You'd have the same problem heading the other way out of Guildford, making the 769's no different than the current units (i.e. only able to use diesel engines) if they can't change power source on the move for many services.

 

[387star]

hang on how many 769s to GWR?
will they keep the DC/AC equipment then to use both systems plus have diesel engines?

that will require many mode changes on the north downs

 

[The Ham]

hang on how many 769s to GWR?
will they keep the DC/AC equipment then to use both systems plus have diesel engines?

that will require many mode changes on the north downs

Mode changes at:
Wokingham
Ash (or not at all if can't be done at speed)
Guildford (or not at all)
Dorking Reigate

That is 2 or 4 times each way, depending on if the change can happen (or is willing to be risked) whilst in motion.

(Edited to correct location)

 

[adc82140]

Not Dorking. No 3rd rail at Deepdene! Will be a change of mode at Reigate.

 

[The Ham]

Not Dorking. No 3rd rail at Deepdene! Will be a change of mode at Reigate.

Sorry, my mistake, anyway the general principle of number of changes is the same.

 

[D365]

Why is it assumed that the 769s will definitely be operating on third rail? The DC supply may not necessarily have the capacity to support additional services.

 

[jimm]

Perhaps because Clarence Yard, who knows his stuff about GWR rolling stock, posted the following on Wednesday in the thread about GWR taking over operating the Heathrow Express

No, they are going to be tri-mode, for exactly that reason.

Post #50 at https://www.railforums.co.uk/threads/heathrow-express-gwr-contract.162470/page-2

a comment that was made in response to this post

That said, do 769s retain the ability to run on third rail, or is that stripped out in favour of diesel? If they can be used on third rail, then the North Downs would be ideal for them...

 

[Non Multi]

It wouldn't be the first time new, or extra trains have demanded too much from the 3rd rail if that were the case...

 

[Clarence Yard]

Why is it assumed that the 769s will definitely be operating on third rail? The DC supply may not necessarily have the capacity to support additional services.

I fully anticipate that some at NR will say this. But we shall see what the actual electrical headroom is and in which hours they say they have issues. The advantage with the 769 is you can go all diesel in those hours and the performance of the unit is alleged to be the same.

 

[D365]

I fully anticipate that some at NR will say this. But we shall see what the actual electrical headroom is and in which hours they say they have issues.

I'll imagine they will have simulations produced to back up their assertions if needed

 

[LNW-GW Joint]

Will they be able to change modes on to go? For instance, leaving Guildford, first stop North Camp the 3rd rail runs out at Aldershot South junction, somewhat short of North Camp. It'd be a shame if they had to run on diesel all the way from Guildford.

Network Rail is very conservative about changing modes, as witness the 800s on GWR around Didcot, to avoid the risk of stranding.
On top of that, the 319s (and 313s) were not designed to switch to/from DC on the move, only while stationary.
Hence the changes at Farringdon and Drayton Park stations, and in the open on the West London line.
Some other designs have allowed changes on the move - class 373 for instance, and I think 350s.
We also have no idea how flexible the diesel switching side of 769s will be, compared to, say, the 800s, and how reliable it is.
The four changeovers possible on the North Downs line will certainly give it a tough test.
Presumably they will also have to reach Reading depot on diesel, unless the transfer underpass line is wired from 3rd rail territory.

 

[Clarence Yard]

The move from Reading station to Reading depot is currently planned to be made on 25kv, to try and further reduce the diesel noise for local residents, which is still an issue.

 

[LNW-GW Joint]

The move from Reading station to Reading depot is currently planned to be made on 25kv, to try and further reduce the diesel noise for local residents, which is still an issue.

Is the underpass line wired with a suitable AC/DC overlap and signalling for that move then?
It would make it the only tri-mode operation in the country!
If so they could run straight into the main line platforms if needed (but have to stop on the way to switch electric modes).

 

[MikePJ]

Helen Simpson, the designer of the 769 conversion, is quoted in this article from Rail as saying:

“The reason the engine is so efficient is not just because it’s modern. It runs at maximum efficiency all the time, whereas the engine in a diesel hydraulic DMU cycles through the rpm range when it’s running. This engine just runs at a near constant speed, in its maximum efficiency range, feeding the existing 750V line. We are effectively tricking the tracking system into thinking it is still a DC unit. It is effectively replacing the DC operation with diesel, but we could still retain the shoegear and have a tri-mode ‘319’ if it was needed."

Based on this, I'm hypothesising that the following changeover sequence could take place whilst the unit is under way:

- train is on 3rd rail power
- driver starts diesel engine
- driver (or train management electronics) confirms that the diesel is running and there's 750V available from the genset
- driver puts the train in "coast"
- driver opens a circuit breaker to disconnect the shoegear from the main bus
- driver closes another circuit breaker to connect the diesel genset to the bus
- driver engages power again, now on diesel

The circuit breaker changeovers could be very quick so as not to affect the traction electronics. After all, the electronics has to cope with a brief loss of power in neutral sections when operating on AC, so a brief interruption in the DC supply should be comparable.

 

[WatcherZero]

Simpler would just be to switchover in a platform raising and lowering the shoe, the diesel power isn't being relied on mechanically in bi-mode operation its purely feeding in to a battery buffer which is discharging to power the motors (how much buffer battery capacity would be a big question though), if the battery was getting full the engine would probably just be reduced to idle but could optionally be turned off completely. It could even still be charging the battery from diesel while operating on 3rd rail.

Of course with the issues of the 769 conversion it might have very little storage but a future purpose built bi-mode could become really efficent.

 

[D365]

Simpler would just be to switchover in a platform raising and lowering the shoe...

The third rail shoe on BR EMUs, where fitted, is fixed and cannot be retracted. This might be one of the secondary issues precluding the 769 from being a real "tri-mode".

 

[Domh245]

For what reason though? If the concern is the shoes becoming live away from the third rail then provided they are able to put proper isolation between the genset output and the third rail shoes, and a means of switching between the two properly then that is surely 'fixed'. If the concern is shoes hitting the ballast then it should be as simple as a gauge clearing it (presumably just lowering ballast shoulders?) and the question becomes who pays?

 

[northwichcat]

The third rail shoe on BR EMUs, where fitted, is fixed and cannot be retracted. This might be one of the secondary issues precluding the 769 from being a real "tri-mode".

'Tri-mode' is nothing but marketing rubbish from Porterbrook. Are the 319s retaining 3rd rail shoes bi-mode? No they are dual voltage EMUs - so a 769 which can operate off both overheads and third rail would be a dual-voltage bi-mode, not a tri-mode.

 

[edwin_m]

The third rail shoe on BR EMUs, where fitted, is fixed and cannot be retracted. This might be one of the secondary issues precluding the 769 from being a real "tri-mode".

For what reason though? If the concern is the shoes becoming live away from the third rail then provided they are able to put proper isolation between the genset output and the third rail shoes, and a means of switching between the two properly then that is surely 'fixed'. If the concern is shoes hitting the ballast then it should be as simple as a gauge clearing it (presumably just lowering ballast shoulders?) and the question becomes who pays?

The dual voltage Electrostars have retractable shoes. However the shoes on the 319 (and the 700) are non-retractable, and the AC routes they operate on need to have clearances maintained so the shoes don't hit anything, and this would have to be true on the GWR 769 routes unless they plan to fit retractable shoes. I imagine the 769s elsewhere would have their shoes removed, and that the GWR ones will have to have circuit breakers to isolate them when on AC or diesel (if whatever is done on the 319 can't be re-used)

 

[swt_passenger]

Is the underpass line wired with a suitable AC/DC overlap and signalling for that move then?
It would make it the only tri-mode operation in the country!
If so they could run straight into the main line platforms if needed (but have to stop on the way to switch electric modes).

The underpass is not currently electrified at all, as built.

 

[The Lad]

Post 1487 I don't think that there is any traction battery planned (ie not hybrid)

 

[HSTEd]

Wait, wasn't the North Downs engineered for 92s and 373s?

Surely the service over it has not increased so much as to make a 1000kW EMU excessive?

 

[JN114]

Wait, wasn't the North Downs engineered for 92s and 373s?

Surely the service over it has not increased so much as to make a 1000kW EMU excessive?

Depends on your definition of the North Downs. Tonbridge - Redhill was electrified in the early 90s as a Chunnel freight diversion with adequate power supply for 92s.

Reigate - Guildford and Aldershot Jcns to Wokingham are not electrified.

 

[LNW-GW Joint]

Depends on your definition of the North Downs. Tonbridge - Redhill was electrified in the early 90s as a Chunnel freight diversion with adequate power supply for 92s.

Was it ever used by 92s though?
I thought BR had so much trouble with track circuits to suit the 92s that all the (limited) traffic on that route was handled by class 47s.
But I may be mis-remembering...

But no wires in the underpass rather stymies the DC/AC transfers in Reading.

 

[Sean Emmett]

Surely easier to electrify the underpass with 750V DC and changeover to AC in P13-15.

The sleepers are 3rd rail ready i.e. with predrilled holes for the pots. For once a bit of forward thinking.

 

[jimm]

'Tri-mode' is nothing but marketing rubbish from Porterbrook. Are the 319s retaining 3rd rail shoes bi-mode? No they are dual voltage EMUs - so a 769 which can operate off both overheads and third rail would be a dual-voltage bi-mode, not a tri-mode.

Or we could perhaps adopt the French terminology for regional units that can run-on diesel, 1,500v DC or 25kv AC - a bi+bi - for bi-mode, bi-courant.

 

[Elecman]

Helen Simpson, the designer of the 769 conversion, is quoted in this article from Rail as saying:

Based on this, I'm hypothesising that the following changeover sequence could take place whilst the unit is under way:

- train is on 3rd rail power
- driver starts diesel engine
- driver (or train management electronics) confirms that the diesel is running and there's 750V available from the genset
- driver puts the train in "coast"
- driver opens a circuit breaker to disconnect the shoegear from the main bus
- driver closes another circuit breaker to connect the diesel genset to the bus
- driver engages power again, now on diesel

The circuit breaker changeovers could be very quick so as not to affect the traction electronics. After all, the electronics has to cope with a brief loss of power in neutral sections when operating on AC, so a brief interruption in the DC supply should be comparable.

As its a dc bus there is no need to isolate the shoegear before closing the genset breaker, it can be opened afterwards so no interruption to the Traction electronics

 

[apk55]

I would expect these units to be considered for use anywhere on the network. If there is clearance problems with the shoegear then they would need removing or replaced with retractable versions. I would also expect the shoegear to have an isolator so the shoes are not live when when running on AC or diesel. However there could still be a use for for 3rd rail and diesel operation.

I would also be interested to see how the units compare with a diesel hydraulic unit such as a class 150. The continuously variable nature of a electrical transmission means full engine power can be used over a wide speed range (after all why do most diesel locomotive use electric transmission) whereas a hydraulic transmission system means that full engine power is only available at a single speed. At other speeds the engine would not be running at full power and at low speed the inefficient torque converter would sap power.