That is true. But what I will say is that there should be interlocking to ensure the pan drops when required irrespective of traction type and regardless of the actual command method, for obvious reasons - pulling the OLE down is very unsafe. If a pan had stayed up when it shouldn't then I'm pretty sure it would be prudent for an operator to pull the relevant fleet and investigate with a matter of urgency.
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Porterbrook Cl.769 'Flex' trains from 319s, initially for Northern
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There are a lot of things that the 769s should have but don't and I am sure that a modern purpose built bi-mode would include them. Do the 802s or 755s? I don't believe any 769s were out today (with services only going as far as Bolton they weren't necessary, I note there was a 3 car 158 in the Southport - Bolton circuit and a single 150 doing a Stalybridge - Victoria shuttle) and there won't be any out tomorrow with it being a Sunday, so we will have to see if they return next week. I don't know why they're still necessary with 156s arriving from EMR.
But of course on AC traction you aren't dropping the pan in service (now dual voltage is a different story)
But this is nothing new. All EMUs have upper limit detection that is set when the pantograph rises above the limit set at just over the maximum required for the lines it is running on. The 319s also dropped their pantographs when switched to DC (that happened over 100 times everyday at Farringdon every day). We've been told that the 769s from an electrical pov are effectively running in DC mode when self-powered, the main difference being the DC bus is fed from the output of the gensets rather than the collector shoes.
Pantographs colliding with infrastructure because they weren't lowered (or faulty) were always possible owing to human error, and indeed happened from time to time.
The ability to drop a pan immediately and reliably in case of a driver encountering an OLE defect has always been an important consideration.
nightflyian
Member
Morning all 434 is back out with a new shiny pan attached to it. Currently running as the 2K82 01716 SOP-ALD Service.
www.realtimetrains.co.uk
Realtime Trains | 2K82 0716 Southport to Alderley Edge | 07/02/2022
Real-time train running information for 2K82 0716 departure from Southport to Alderley Edge on 07/02/2022. From Realtime Trains, an independent source of train running info for Great Britain.
Jamesrob637
Established Member
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Morning all 434 is back out with a new shiny pan attached to it. Currently running as the 2K82 01716 SOP-ALD Service.
Realtime Trains | 2K82 0716 Southport to Alderley Edge | 07/02/2022
Real-time train running information for 2K82 0716 departure from Southport to Alderley Edge on 07/02/2022. From Realtime Trains, an independent source of train running info for Great Britain.
I saw it leave Heaton Chapel and wondered why it was so shiny.
Perfectly normal for industrial diesels, tbh.
No driver of a BR-era EMU actually knows the pan has dropped though, tbf.
Line light doesn't mean 'pan is up', it just means there's electrical power being fed to the unit from the normal traction supply. So; Line light could be out for various reasons, but the pan could still be up (VCB open, OLE lost 25kV supply etc).
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hat's what the standards now say (and because there are so few old EMU's still around then yes, basically all EMU's do indeed have it) but it's not right to say that all do...
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Well the 319s do because the settings were adjusted before two two of them went through the Channel Tunnel. That's the kit this thread is about and the only ac EMU older than them still in service is class 317.
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DustyBin
Established Member
And some on the Glasgow suburban network!
childwallblues
Established Member
And Merseyrail and the 313s at Brighton.
Do the remaining 508s and 313s still operate from OLE?
Well that didn’t take long. Hopefully it will be out again on Wednesday when I plan to go to Manchester and see where the bridge has been removed on the way through Westhoughton.
What about 313121, the departmental unit?
No. The 507s and 508s have never had pantograph wells, let alone run on AC. Note they are numbered in the 5xx series for DC only EMUs which have never had AC capability. 313s were the only ones to be dual voltage but Southern ones had their pantographs and AC equipment, needing to be hauled dead by 313121 under the wires when visiting AC lines.
Speed43125
Member
No, 313s have also had pantographs removed ISTR.
Greybeard33
Established Member
This cab ride video, from Wigan Wallgate to Southport (click the link to watch on YouTube) was shot from a 769 in diesel mode (identifiable from the background noises). A couple of other Northern 769s are passed.
Mmm, interesting, - it seems that the noise levels are pretty good considering as they were from the front car when I did that stretch. At some points the motor whine can be heard and they areat least. twice as far away as the engines. Compare that with the Victoria to Wallgate trip from the same video company which follows the 769 one (presumablyrecorded in a 150), where the din in the cab makes the 769s seem almost silent.
Greybeard33
Established Member
The grinding of the 150's tread brakes is a giveaway - the 769's disc brakes are inaudible in the cab.
A video of the return journey from Southport to Wigan has now been uploaded, also in a 769:
The overrun on during braking may be because of compressors recharging and possibly to provide a higher cooling rate, however, the speed of the gensets is not directly realted to their output as the excitation will ensure that the bus line is kept within limits. Clearly you can't get full power at low revs, but free running at about half speed doesn't necessarily use much fuel or engine life.
That's another good video. I timed the run on the straight from Bescar Lane crossing to New Lane crossing and it took 1:52 to cover 2.11 miles. I make that just under 68mph.
The engine revs on 769s are very odd, you take power in say notch 2 and revs rise but then they increase markedly again at a few mph despite not touching the power controller again. When you then open up to notch 3 there is another slight increase in engine revs but increasing from notch 3-4 seems to have no noticeable effect on engine revs.
On braking to a stand the engine revs only die down to idle when the unit reduces below around 5mph. This is consistent every time and isn't related to the compressor starting up - when the compressor runs the engine note doesn't noticeably change, whether at idle or taking traction power.
On braking to a stand the engine revs only die down to idle when the unit reduces below around 5mph. This is consistent every time and isn't related to the compressor starting up - when the compressor runs the engine note doesn't noticeably change, whether at idle or taking traction power.
Greybeard33
Established Member
I suspect (though without knowledge of the engineering detail) that the odd behaviour of the 769 engines is because the units still have the original 319 GTO thyristor traction control electronics. This system has no way to directly control the engine speed. Therefore the new, separate, genset control system has to ensure that the engines can immediately deliver enough power to maintain the 750V DC bus voltage if the driver suddenly advances the power controller. This means that high revs must be maintained even when coasting or braking.
At low train speeds, the traction electronics reduce the motor voltage to limit the traction motor current, even in a high notch, and so avoid overheating or commutator flashover. Therefore less electrical power is needed than at higher speed in the same notch. The genset control system can allow engine revs to drop to idle at a stand, yet still react quickly enough to spool up the engines as the driver takes power.
On a "normal" diesel-electric, e.g. Class 66 loco or Class 22x DEMU, the driver's power controller interfaces directly with the engine control system and so engine revs vary with the power demand, dropping to idle during coasting or braking.
To be honest it was only speculation, hence my saying 'may be'.
On the subject of the acceleration patterns, it makes more sense, There are two nominally independant control systems here:
1) the traction electronics whose purpose is to take DC power from the bus line and according to the driver's setting of the control lever, apply the appropriate power to the DC motors - exactly as it has always done on a 319.
2) the genset control's role is to maintain the bus line voltage, - in effect replicating the 750VDC supply from the 3rd rail collector shoes or the rectified output from the transformer when fed by 25Kv 50Hz OLE.
So, when the driver selects a notch on the controller, (notch 2 in your case for starting), the traction electronics will set a current for the motors to meet that demand that must also be correct for the speed. At brakes release, the motors are stalled, so their current must be limited until their speed is such that it can be increased. This places a load on the bus line which causes the genset to increase it's output to maintain the voltage which initially only requires a moderate speed of the engines. Once the traction electronics senses the drop in the motor current due to its rotationa speed, it can increase the drive up to the normal current for notch 2. This loads the bus more and the genset responds by spinning up and increasing the excitation to produce more power. Selecting notch 3 then applies more power to the motors, causing a further demand on the bus, to which the genset responds. Now further traction demand (e.g. nootch 4 or an adverse gradient) requires more power but if the engine and generator have been optimally matched the engine will already be near the speed at which it can produce maximum power, so the excitation on the genset can then extract more power from the generator without much (if any) increase in its speed. When I was on a 769, once the speed was in the '60s the engine was effortlessly humming away at a relatively moderate speed and was almost drowned out by the whine of the traction motors 3 cars back.Apologies for the convoluted explanation but hopefully it explains the fact that the driver controller does not directly affect the diesel engine spin speed and that the spin speed is not necessarily proportionate to the load on the engine, - the two independent control system manage that.
That is why a diesel-electric traction system is generally quieter, smoother, more efficient, and dare I say it here, more reliable*. The MAN D2876 is a proven rail traction engine, and in this application is running well within its design limits. The ABB generator is a proven commmercial 3 phase alternator and the traction electronics and motors, although 30+ years old under diesel power are running at less than 80% their class 319 maximum power levels. Indeed, the track limitations on the 769 speed even under OLE should further mitigate the reliability impact of their age.
* yes I know, this is a 769 thread, but it seems that the subsystem on the trains are in themselves reasonably reliable, - I believe that most of the issues are problems with their integration.
edwin_m
Veteran Member
Bear in mind also that the power needed at the rail to start the train is very low. Power equals force times speed so at zero speed it theoretically needs zero power at the rail to start the train moving. Obviously there are various losses in the system, but in diesel-electrics these are relatively small so the engine doesn't need to be doing much to get the train moving. Power demand will increase as movement starts, but tractive effort (force) is still limited by available adhesion so the power employed at rail will increase linearly with speed until maximum power is reached.
In units with fluid transmissions such as Sprinters, the same happens in theory but at low speeds the transmission is dissipating a lot of power as heat, so the engine has to do much more to start the train moving.
In units with fluid transmissions such as Sprinters, the same happens in theory but at low speeds the transmission is dissipating a lot of power as heat, so the engine has to do much more to start the train moving.
It seems that we concur on most of this. I started my tome two hours ago then got interrupted. I didn't know that the class 22xs controlled the engines directly, but in fact that they are functionally composed of 4 or more complete diesel-electric vehicles, operating more as a train of diesel-electric locos controlled by the leading loco. Some diesel locos do seem to have the initial spin-up (37s and 47s in my experience), and then a pause whilst the generator whince cane be heard and wheels start turning before a step up at about 15-20mph.
Acccording to Wikipedia, the flex programme specifically set out to keep the 769s the same as 319s to drive as much as possible to make driver training easier. That would be important when running digrams over electrified and non-electrified track, (and even running 319+769 consists).
Interesting replies, thanks. It's worth noting that there was another company instruction posted warning us not to open up power controllers on 769/319 units too quickly (but failing to furnish us with what are deemed to be acceptable speeds for each power setting) due to traction motor damage. If this notice was taken to the letter on face value then no driver would ever put a 769 in power notch 4 in diesel mode because we are advised to wait until traction power begins to fall away in each notch before applying the next higher power setting - and there is no discernible difference at any speed (at least up to 75mph which is the fastest most 769s will ever reach on their current diagrams) between power notches 3 and 4 in a 769 on diesel mode.
The Class 313/2s are dc only units. As built they were not allowed to have a dc bus active in the underground tunnels so each motor coach had its separate dc pick up. On ac the pantograph and transformer fed both motor coaches. On the West Coastway lines there are loads of wide level crossings at the end of platform ramps so there was a real risk of the units becoming gapped and they wouldn't have been able to keep to the timetable pulling away on half power so the 313/2 conversion disconnected the ac equipment and used the previous cables from the dc side of the transformer to the motor coaches, linked together to provide a dc bus so either set of shoes can power all the traction motors.
If you are soley judging the lack of difference in power between notches 3 & 4 by engine spinspeed, that doesn't necessarily mean that there isn't more power from notch 4. As I mentioned above, engines are matched to generators such that at that speed, more power can be drawn from the generator by increasing the field excitation, but that makes the input shaft 'stiffer' to turn. By running the engine at a speed where there is plenty of torque, the engine can accept more fuel and maintain that speed so there is no need to run the engine at the highest speed where efficiency drops off because there are breathing issues. Also wear and tear increases with higher speeds. Think of the generator field controls as an electric gearbox, more (electrical) power out for the same speed but more resistance to turn the shaft.
No I was judging it by actual acceleration 'feel' as the notice says we should. In fact when you put a 769 in diesel mode from notch 3 into 4 there seems to be a tiny pause/power drop off as you go into 4. This doesn't happen in AC mode, and if I'm not mistaken there was no field weakening on 319s in power notch 4 in DC mode, so I assume 769s are the same in that respect.
I'm sure that you are right that notch 4 will provide more power above notch 3, but the intent of the notice is that we should only increase traction power to the next power notch once we notice by feel that the rate of acceleration is reducing in the existing notch - and there is no perceptible increase in rate of acceleration between 3 and 4, certainly at the usual speeds the 769s are running at.
I'm sure that you are right that notch 4 will provide more power above notch 3, but the intent of the notice is that we should only increase traction power to the next power notch once we notice by feel that the rate of acceleration is reducing in the existing notch - and there is no perceptible increase in rate of acceleration between 3 and 4, certainly at the usual speeds the 769s are running at.
edwin_m
Veteran Member
Perhaps the amount of power used in Notch 4 is just more than the gensets can supply?