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

[geoffk]

Is it still planned for the 769s to work Stalybridge/Alderley Edge - Wigan NW services? At least until the complete routes are electrified.

 

[superkev]

Electric transmission was probably considerably more expensive than a torque converter system particularly in the past when commutator motors were the norm. Modern 3 phase drives systems are cheaper but have only become practical in the last 20 years. The pacers originally had a mechanical gearbox system but these proved unreliable and were replaced by a torque converter system. It was cheaper to use a bigger engine to cope with transmission losses and fuel consumption did not appear to matter as the railways can use duty free diesel.

Personally I think we should be looking at electric transmissions for all new build Diesel Multiple units. Not only are they more efficient than most mechanical systems (unless some mechanical whiz can come up with a efficient continuously variable transmission that can cope with railway conditions), but they can be easily integrated into hybrid, battery or Bi mode systems.

I don't think electric transmission is more efficient than mechanical as you have cumulative losses in the alternator followed by the power electronics followed by the motors. A purley mechanical (no hydraulics) box has an efficiency of over 90% and almost 100% in direct drive.
K

 

[507021]

Has there been anymore testing on the 769s, i've seen a post on youtube of 769434 but that was months ago.

Yes, 769456 is also being tested.

Units 3 and 4 are undergoing conversion at the moment.

 

[big all]

Yes, 769456 is also being tested.

Units 3 and 4 are undergoing conversion at the moment.

thanks for the update

 

[507021]

thanks for the update

No problem, Units 3 and 4 are 319431 and 319424 respectively.

 

[Billy A]

I don't think electric transmission is more efficient than mechanical as you have cumulative losses in the alternator followed by the power electronics followed by the motors. A purely mechanical (no hydraulics) box has an efficiency of over 90% and almost 100% in direct drive.
K

Just what I would have thought. The forthcoming Class 195 has ZF automatic gearboxes (mechanical transmission in rail parlance) and if electric drive was more efficient surely it would have been used. Also, you'd have it in your car/bus/truck.

 

[Mogster]

Is it still planned for the 769s to work Stalybridge/Alderley Edge - Wigan NW services? At least until the complete routes are electrified.

I hope so... Shortforming between Wigan and Manchester has almost become the norm since May. The overcrowding is horrendous.

 

[AM9]

I don't think electric transmission is more efficient than mechanical as you have cumulative losses in the alternator followed by the power electronics followed by the motors. A purley mechanical (no hydraulics) box has an efficiency of over 90% and almost 100% in direct drive.
K

A torque converter has a low efficiency when the input to output speed ratio is high. This caused by turbulence around the stator. Consequently, there is not much opportunity to run the diesel engine at its most efficient/highest output speed. Most TCs have a partial or full lock-up when the input output speed is nearly equal. That is when the efficiency reaches ~90%.
A diesel-electric traction system can run the engine at a speed where the generator produces full power even when the train is at a standstill. That power is then applied to the motors much in the same way as a normal electric-only system does, the only limitation then being wheel-rail adhesion.

 

[Meerkat]

Excuse my ignorance but if the generator is running at full power where is the power going if not to the motors?

 

[Billy A]

Excuse my ignorance but if the generator is running at full power where is the power going if not to the motors?

Heat. If the motors aren't turning they heat up. Same thing happens with a torque converter (or a clutch, come to that).

 

[The Lad]

Although even electric transmission cannot apply full power at the extremes of speed, at low speed current is the limit and at high speed the voltage limits the power. Big diesels can't usually put full power out below about 15 mph and have to use field weakening to extend the upper limit. Even a HST will be unloading the generator at full speed but using a alternator means field weakening is not required AIUI.

 

[AM9]

Excuse my ignorance but if the generator is running at full power where is the power going if not to the motors?

You've misunderstood what I menat. With a Diesel Electric traction system, the full power of th generator is available at the point of starting, i.e. as the brakes are released (when the train is about to move forward). With a torque converter, the inefficiency of the hydraulic coupling through turbulence within is low when the input speed is much higher than the output. Thus when the engine is revved-up in the station as the brakes are released, i.e. the wheels are not yet turning, most of the power is lost as heat in the TC churning up the fluid.
Below is a graph showing the efficiency (proportion of input power available at the output plotted over the range 1:0 and 1:1. As you can see, at standstill, very little power is availble at low wheelspeeds, irrespective of how fast the engine is spinning.
https://www.google.com/url?sa=i&rct...aw2m1GJu7nQn_gaWE2UoqFyx&ust=1543533529346238

 

[Jonny]

I don't think electric transmission is more efficient than mechanical as you have cumulative losses in the alternator followed by the power electronics followed by the motors. A purley mechanical (no hydraulics) box has an efficiency of over 90% and almost 100% in direct drive.
K

A torque converter has a low efficiency when the input to output speed ratio is high. This caused by turbulence around the stator. Consequently, there is not much opportunity to run the diesel engine at its most efficient/highest output speed. Most TCs have a partial or full lock-up when the input output speed is nearly equal. That is when the efficiency reaches ~90%.
A diesel-electric traction system can run the engine at a speed where the generator produces full power even when the train is at a standstill. That power is then applied to the motors much in the same way as a normal electric-only system does, the only limitation then being wheel-rail adhesion.

A complicating factor is that, at least in rail applications, diesel-hydraulic etc. systems are easily amenable to a multi-speed gearbox, which may be designed so as to provide high efficiency over a wide range of speeds. In contrast, electric motors (both diesel-electric and direct electric) when deployed as traction motors tend to have a single-ratio drive, for which the associated problems (back EMF, caused by the motor acting as a generator, builds up as rotation increases and impedes current flow. Hence 'weak field' systems on older electric trains, which enable higher speeds but with the loss of torque).

Perhaps someone could enlighten as to what the 'tricks' are to achieve similar effects with AC and/or permanent-magnet motors?

 

[AndrewE]

You've misunderstood what I meant. With a Diesel Electric traction system, the full power of the generator is available at the point of starting, i.e. as the brakes are released (when the train is about to move forward).

Except that it's not. Electric motors develop a back EMF and this doesn't apply at the point of startring, so there is a serious overheating risk. Hence diesel-electric (and pure electric) locos can only apply the maximum acceptable power, which might include a temporary over-load. As the train speeds up and the current drops back more power can be applied.
I don't know whether modern electronic transmissions and AC motors have the same problem, but I guess back-EMF must still exist!

 

[apk55]

Mechanically an electric transmission system is much simpler. A low maintenance alternator is normally bolted directly to the engine crankshaft and the traction motors are connected to the wheels via a simple spur gearbox immersed in an oil bath for long life. 3 phase traction motors as used on all new build stock are also low maintenance and the power electronics between the two is also low maintenance. The traction motor bogie will have motors selected to give high starting tractive effort, and these will be mass produced items for the vast EMU market. Electric motors are quite efficient even on part power and the only advantage of having a variable transmission to the axle would be that a smaller motor could be used against a complex mechanical system

A mechanical drive system involves the use of carden shafts to accommodate relative moment of the bogie to engine and transfer gear boxes to the axles. In addition to the transmission system a reversing gear box is required.
The transmission system has the job of either providing high torque (or tractive effort) at low speed or lower torque at high speed as well as controlling power from standstill.
Old (first generation) DMUs (and manual cars) use a gearbox which offers a range of gear ratios that are selected according to speed and power requirements with a clutch to control power from standstill to first gear lockup. It is quite efficient but is mechanically complex with many wearing parts and getting it to work reliably for the life of a unit was problematical. A torque converter does the same thing and is quite simple but rather inefficient.

One of the advantages of an electric transmission system is that it is effectual a continuously variable transmission system so the engine can deliver full power to the rails over a wide speed range or on part power settings under conditions of maximum efficiency. Under normal operating conditions this means a smaller engine can be used. Therefore compared to a mechanical drive system the overall system efficiency (fuel consumption) is probably as good as if not better than a mechanical drive system and much better than a torque converter.

 

[Bletchleyite]

Old (first generation) DMUs (and manual cars) use a gearbox which offers a range of gear ratios that are selected according to speed and power requirements with a clutch to control power from standstill to first gear lockup. It is quite efficient but is mechanically complex with many wearing parts and getting it to work reliably for the life of a unit was problematical. A torque converter does the same thing and is quite simple but rather inefficient.

Point of order, first generation DMUs don't use a clutch, they use a fluid coupling, the same as automatic car gearboxes do. This is similar to a torque converter, but due to the shape of the vanes (I think) it doesn't provide a "gearbox" (torque multiplication) type function, simply slips like a clutch (but without wear) to allow the engine to run at the required speed.

Class 15x use a torque converter, and Class 195 (and 172) are back to the mechanical gearbox with fluid coupling!

 

[DarloRich]

There was an interesting article in a recent Rail Engineer on this project. Worth a read.

 

[notlob.divad]

Any update on the testing, if there have been any further problems discovered, and if/when we are likely to see this out on the mainline. I note a month has now past since this question was last breached and there wasn't really any answer. I have seen the post that suggests they may be running in January, but that would seem an awful short time away when as far as I know they haven't returned to any mainline running yet to test all the electrical systems still run etc.

 

[samuelmorris]

I imagine they'd have to see at least some degree testing in the relevant areas of use before training. As far as I know I haven't seen any evidence they've moved away from the GCR and into areas controlled by the relevant depots so on that basis, presumably there's at least a few more months to go. March-April time maybe, if no further delays?

 

[Billy A]

Point of order, first generation DMUs don't use a clutch, they use a fluid coupling, the same as automatic car gearboxes do. This is similar to a torque converter, but due to the shape of the vanes (I think) it doesn't provide a "gearbox" (torque multiplication) type function, simply slips like a clutch (but without wear) to allow the engine to run at the required speed.

Class 15x use a torque converter, and Class 195 (and 172) are back to the mechanical gearbox with fluid coupling!

At the risk of being pedantic....they use a conventional ZF automatic box (a mechanical box in rail talk) with a torque converter. The only genuinely mechanical transmission I can think of in recent times is the ZF automated manual with which some Danish DMUs were re equipped with in the 2000s. They use a clutch (unless somebody can tell me otherwise) and what I think is a 12 speed automated box.
The Voith transmission on the 150 and many others is more than just a torque converter. It works like this:
First speed: torque converter driving low gear
Second speed: fluid coupling driving low gear (less slip so effectively higher gearing)
Third speed: another fluid coupling driving high gear
To change gear, it just drains one element and fills another so no friction materials to wear and smooth changes at the cost of poor efficiency in first speed.

 

[edwin_m]

No train can deploy "full power" at low speed. Power equals force times speed so the power employed at the rail as the train starts is actually zero. At low speeds trying to use full power would result in the force being greater than adhesion can support and the wheels will just spin.

So it's more a question of the electric transmission at low speeds drawing relatively little power from the diesel and alternator or from the traction supply. At similar low speeds a hydraulic transmission draws much more power from the diesel engine, most of which goes to heat in the torque convertor.

Electric transmissions may be more efficient but for the rating of a truck or a typical DMU they are more expensive than mechanical. However the advent of hybrid and electric vehicles in the much larger automotive market ought to result in cheaper electric transmission for DMUs - and they are also easily adapted to bi-modes or on-board energy storage.

 

[Railperf]

No train can deploy "full power" at low speed. Power equals force times speed so the power employed at the rail as the train starts is actually zero. At low speeds trying to use full power would result in the force being greater than adhesion can support and the wheels will just spin.

So it's more a question of the electric transmission at low speeds drawing relatively little power from the diesel and alternator or from the traction supply. At similar low speeds a hydraulic transmission draws much more power from the diesel engine, most of which goes to heat in the torque convertor.

Electric transmissions may be more efficient but for the rating of a truck or a typical DMU they are more expensive than mechanical. However the advent of hybrid and electric vehicles in the much larger automotive market ought to result in cheaper electric transmission for DMUs - and they are also easily adapted to bi-modes or on-board energy storage.

As I understand it, your average truck doesn't have the space to fit a generator and electric motors - and of course this adds a whole load of extra weight in relation to the weight of the basic chassis. On a rail vehicle however, there is a lot more weight - and for traction purposes there needs to be. And of course there is a lot more space too. The weight of extra traction motors and alternators is a fraction of the vehicle's total weight. So this is why this set up seems unique to rail applications and does not extend to cars and trucks. A Tesla car uses electric motors and lightweight batteries. But if you had to add a 600hp diesel engine and a suitable alternator, it would probably weight twice as much, and it might only end up a two seater! Electric motors are more ideal for rail because they produce copious amounts of torque from zero rpm. This is a huge advantage over a mechanical system, which relies on a gearbox to keep the engine torque available across the whole speed range. Because at idle, there is very little engine torque - but at higher speeds on diesel engines, the torque tails off too. And of course you need a clutch or torque converter to get you moving in the first place - or your engine will stall.

 

[big all]

i worked out the average thumper at 11mhp would not overload so 10mph notch 6 so by the time the revs picked up to from memmory 850 rpm you wouldnt overload because you where beyond 11mph
now down hill you could be more agressive
uphill it may overload but mostly done on feel even from the dummy end
now that makes sense as 500hp traction motors with a 600hp engine with perhaps 10-20% losses would line up quite closely
indeed if train heating and compessor going and stationery and you reved up the engine under load you would overload the motors but thats because the train heat load drops out for a few seconds so after opening up but if your stationery and the train heating cuts back in before movement you can be on full power and not overload at a near to a standstill but wheels rolling
off course so many factors effect the equation like overload set too height [remember an oxted showing 1350amps as opposed to 1000-1100 amp=500hp]added to the equation perhaps aamp gauge or speedo over or under reading

 

[AM9]

As I understand it, your average truck doesn't have the space to fit a generator and electric motors - and of course this adds a whole load of extra weight in relation to the weight of the basic chassis. On a rail vehicle however, there is a lot more weight - and for traction purposes there needs to be. And of course there is a lot more space too. The weight of extra traction motors and alternators is a fraction of the vehicle's total weight. So this is why this set up seems unique to rail applications and does not extend to cars and trucks. A Tesla car uses electric motors and lightweight batteries. But if you had to add a 600hp diesel engine and a suitable alternator, it would probably weight twice as much, and it might only end up a two seater! Electric motors are more ideal for rail because they produce copious amounts of torque from zero rpm. This is a huge advantage over a mechanical system, which relies on a gearbox to keep the engine torque available across the whole speed range. Because at idle, there is very little engine torque - but at higher speeds on diesel engines, the torque tails off too. And of course you need a clutch or torque converter to get you moving in the first place - or your engine will stall.

So to summarise, a diesel-electric traction system is a good match for rail use giving maximum torque for starting limited only by adhesion and the cooling of the motors when fully loaded. It also allows the diesel engine to run at the speed at which it provides maximum power - almost throughout the rail speed range, making cruising quite economical.
Capital cost may be higher than Diesel Mechanicatrains but the cost of ownership is far lower on running and maintenance costs, and operational life can be much longer than diesel hydraulic/mechanical types.

 

[notlob.divad]

I imagine they'd have to see at least some degree testing in the relevant areas of use before training. As far as I know I haven't seen any evidence they've moved away from the GCR and into areas controlled by the relevant depots so on that basis, presumably there's at least a few more months to go. March-April time maybe, if no further delays?

Thank you, at least someone can keep vaguely on topic on this thread.

Yes, that is my current position. I have seen no evidence anywhere that they have left the Great Central Railway. I have seen no evidence of testing them working in multiple (apart from reading that there are 2 on site at GCR). At the same time, I have read no reports of any further issues with the initial units. So am rather perplexed as to what stage in the testing cycle we are at.

Will these units be expected to gain the same amount of accumulation miles as a brand new unit?
Is the driver training going to be a simple add-on course to 319 training, or is the additional weight and change in distribution going to mean that the acceleration and breaking are so far removed from a 319 that it is a completely new training as if it is a brand new unit?

All of this is unknown as far as I can tell, and thus I am inclined to take any predictions of entry into service with the same large dose of salt that I take TPEs MK5s, and Northerns 195s/331s.

 

[AndrewE]

Thank you, at least someone can keep vaguely on topic on this thread.

Yes, that is my current position. I have seen no evidence anywhere that they have left the Grand Central Railway.

Agreed, it's nice to read relevant comments, but please note that in the UK we have a Great Central Railway, there are also a couple of other things aping a certain New York railway station, as though a name copied from the USA gives them some sort of cachet or credibility.

 

[notlob.divad]

Agreed, it's nice to read relevant comments, but please note that in the UK we have a Great Central Railway, there are also a couple of other things aping a New York Railway station, as though a name copied from the USA gives them some sort of cachet or credibility.

My bad.

 

[samuelmorris]

Thank you, at least someone can keep vaguely on topic on this thread.

Yes, that is my current position. I have seen no evidence anywhere that they have left the Great Central Railway. I have seen no evidence of testing them working in multiple (apart from reading that there are 2 on site at GCR). At the same time, I have read no reports of any further issues with the initial units. So am rather perplexed as to what stage in the testing cycle we are at.

Will these units be expected to gain the same amount of accumulation miles as a brand new unit?
Is the driver training going to be a simple add-on course to 319 training, or is the additional weight and change in distribution going to mean that the acceleration and breaking are so far removed from a 319 that it is a completely new training as if it is a brand new unit?

All of this is unknown as far as I can tell, and thus I am inclined to take any predictions of entry into service with the same large dose of salt that I take TPEs MK5s, and Northerns 195s/331s.

For the same routes as 319 I imagine a conversion course would be fairly meaty in terms of driving a DMU vs EMU, but not unworkable since the cab would be fairly similar otherwise. The difficulty is that the main point of the 769s is to operate on routes EMUs can't, thus you'd be adapting Pacer and Sprinter drivers. That's probably a fairly lengthy training course. I don't know how similar 150s and 319s are in that regard.

 

[AM9]

For the same routes as 319 I imagine a conversion course would be fairly meaty in terms of driving a DMU vs EMU, but not unworkable since the cab would be fairly similar otherwise. The difficulty is that the main point of the 769s is to operate on routes EMUs can't, thus you'd be adapting Pacer and Sprinter drivers. That's probably a fairly lengthy training course. I don't know how similar 150s and 319s are in that regard.

Well they must have recently trained ex-sprinter/pacer drivers on the 319s when they started taking ex-Thameslink trains at Allerton for the Chat Moss electrified lines. So they could maybe do a mix and match with a short conversion course for them on the 369s whilst taking on fresh drivers for some of the all-electric diagrams.

 

[43096]

My bad.

Your bad what?

Horrible, horrible, horrible imported US phrase that should never be used!