Trimode cl 769 to operate Reading to Oxford and Gatwick.

[whole diary]

[RichT54]

319s coped with a quite significant gradient between City T/L and Blackfriars for years…

But they were using electric traction not diesel.

I thought the 769 still used the electric traction motors when running on diesel. The diesel engines just drive alternators which generate the electricity.

But when using diesel power the traction motors can only provide enough power if the alternators can supply that power.  If the diesel engines or the alternators are not powerful enough it doesn't matter how powerful the traction motors are. 

Agreed and, if there was not enough power to get up an incline, would it come to a halt due to wheelspin (loss of adhesion), or because the motors just couldn't turn the wheels?

[stuving]

Here's a comment about the 769s that may be relevant:

“Rebuilding can often be more difficult than building from new. Making the existing and new components work together can be a real challenge.”

Helen Simpson, innovation and development manager, Porterbrook

She's probably now saying to herself "well, that's one thing I got right at least".

That's from an article in May 2019, so when the programme was already running late. Another quote suggests one of the areas of awkward co-operation:

Wabtec’s biggest engineering challenge was the new electronic control cubicle, which controls local power on the driving cars.

The "bus" isn't an infinite busbar, or anything like. The two alternators and the four motor/converter loads are looking at only each other, and that close coupling offers a lot of scope for instability, surges, etc. And if that damages the motors, they may even fail when not on diesel power. Also, if the alternators can't meet the motors' current demands, that limits the power and torque available.

I know the GTO converters do what the big series resistors do in a tram: allow the starting volts across the motor to be low and then to rise as the train speeds up. That should mean that the starting current from the alternators is quite low, while in the motors it's high. I can't find out whether the controllers still use field switching or weakening for higher speeds.

Neither have I found out anything about the ABB alternators, though this is a key component. Vivarail had a lot of problems with their light-weight modern TSA^▸ (Ticketing and Settlement Agreement. The TSA sets out the various arrangements between the train operators relating to the carriage of passengers and the retailing of tickets.) ones (similar to the ones in 800s, I think) in the 230s, and ended up replacing them all with much heavier but more robust old-style ones.

Making the train accelerate depends on the adhesion (at low speed) and power (in the middle and higher speed ranges). Adhesion depends on the fraction of the weight on driven wheels, which for a 319 is 0.36 (4/16 axles motored, but a lot of weight in the MSO^▸ (Motor Standard Opens)). Adding the two diesel generators adds 15 t (over 10%) to two trailers, bringing that fraction down to 0.33. That's similar to an HST^▸ (High Speed Train (Inter City class 43 125 units)), and much lower than most modern units (typically 0.5-0.6).

Here is a more explicit statement from Porterbrook about the available power (specially for OTC):

Simon explains: “The MAN engines have a rail pedigree and are compliant with Stage IIIb emissions rules. Their maximum rating is 390kW, but we decided to have them working at less than that to give ourselves some ‘headroom’. In service, the two engines will deliver around 720kW at the DC^▸ (Direct Current) Link (just under 1,000hp), which is somewhat less than the 1.2MW available in electric mode, but in general speeds are expected to be lower when working on diesel, and this arrangement gives good power in the mid-range. Performance should be comparable to a Class 150.”

An unusual usage of "somewhat"?

[nickswift99]

That’s a useful post.

So if I have read that right the Diesel engines have added 10% to the weight while the available power has dropped 20%?

I appreciate there are other factors at play but that does suggest that performance is never going to be anywhere near that of a 319.

Does anyone know if a 150 has ever done the North Downs route?

[ellendune]

That’s a useful post.

So if I have read that right the Diesel engines have added 10% to the weight while the available power has dropped 20%?

No you fell into the trap as I did initially comparing 1000hp to 1.2MW

"In service, the two engines will deliver around 720kW at the DC^▸ (Direct Current) Link (just under 1,000hp), which is somewhat less than the 1.2MW available in electric mode"

1.2MW to 720kW is a 40% drop in power!

Hence stuving's comment about an unusual usage of "somewhat".

[Fourbee]

Does anyone know if a 150 has ever done the North Downs route?

Not sure, but when pairs of ex-Southern 456s were used on the Guildford-Ascot runs they really struggled to get out of Guildford and that was on lightly loaded trains, without extra engines and equipment added. Wikipedia quotes the power output as 373kW (so about 750kW as a pair of 2-cars).

[onthecushions]

Again, by analogy, the  unlamented "Tadpole"units that once inhabited this route weighed in at 113t with a 500hp diesel and only one motor bogie.

Slipping was a minor feature of the Southern's EE507, big traction motor, single motor car policy - part of the reason the 508's were banished to Merseyside.

The other problem is the perennial Diesel electric problem, that the generator/alternator produces more power at "right away" than the TM^▸ (Train Manager, or possibly Ticket Machine, depending on context)'s can use, leading to excessive windings' temperature rise. I think the 47's had a minimum continuous speed of 27mph to avoid TM damage, which limited their freight use.

What it does mean is that the makers need time to get even an adaptation right before launching anything new into service and making the public or at least the TOC^▸ (Train Operating Company)'s driver managers put up with an unfinished job.

OTC

[eightonedee]

As a non-engineer who struggles to follow some of this (but very grateful to Stuving and others for trying to explain) can I add a few (largely anecdotal) points from a user of the North Downs Line?

Wikipedia informs us that each coach of a Turbo has a 350 hp/261 kW engine, so currently if all engines are working that's 1050 bhp/783 kW for a three coach train. Even then, in poor railhead conditions in autumn wheelspin has been a regular feature of the journey on the gradients around Sandhurst.

There have been journeys I have been on when an engine has been "out" on a coach when the Turbo (hint for those who will be using then when they eventually get to the West Country - it's the quietest and most restful part of Turbo travel if you travel in the coach without a working engine), and they have coped, but that still puts 700 hp down for a three coach train with the traction helped by the weight being over the active traction equipment. And I assume that a "conventional" hydraulic transmission does not suffer the power generation issues canvassed above.

[Electric train]

As a non-engineer who struggles to follow some of this (but very grateful to Stuving and others for trying to explain) can I add a few (largely anecdotal) points from a user of the North Downs Line?

Wikipedia informs us that each coach of a Turbo has a 350 hp/261 kW engine, so currently if all engines are working that's 1050 bhp/783 kW for a three coach train. Even then, in poor railhead conditions in autumn wheelspin has been a regular feature of the journey on the gradients around Sandhurst.

There have been journeys I have been on when an engine has been "out" on a coach when the Turbo (hint for those who will be using then when they eventually get to the West Country - it's the quietest and most restful part of Turbo travel if you travel in the coach without a working engine), and they have coped, but that still puts 700 hp down for a three coach train with the traction helped by the weight being over the active traction equipment. And I assume that a "conventional" hydraulic transmission does not suffer the power generation issues canvassed above.

The service operated with class 117 type DMU^▸ (Diesel Multiple Unit) which were 300 hp per power car for a 3 car a total of 600 hp.  Those DMU had a less efficient transmission.

Part of the reason I suspect for the higher power rating originally for the 165/6 would have been for increased acceleration to improve journey times on the Thames Valley NSE^▸ (Network South East) timetable in the early 1990's

[eightonedee]

This morning there are 3 769s at the west end of the Reading depot, one of which has been vandalised by an aerosol paint attack.

How often has this happened to rolling stock before it enters service?

[grahame]

This morning there are 3 769s at the west end of the Reading depot, one of which has been vandalised by an aerosol paint attack.

How often has this happened to rolling stock before it enters service?

There is a good argument that suggests that this rolling stock entered service between 1987 and 1990, and what's happening now is a mid-life upgrade. Not uncommon for stock to be put out to grass, face the ravages of weather and vandalism, and then be brought back - what is different here is that it has been brought back and refurbished and THEN been vandalised!

[RichT54]

If they can't prevent trains from being vandalised at Reading Depot, where can they?

[IndustryInsider]

Reading depot is quite an easy target for the determined individual - very long and with little used roads and tracks nearby and not overlooked by anything other than the main railway lines at the western end.

North Pole is probably the best protected as it has all of the fencing put in that used to protect the Eurostar trains.

[RichT54]

It's interesting to note there have been a number of additional posts in the thread on RailUK Forums that I quoted previously. Several have dismissed the original comments about the 769 class not being able to handle the climbs on the North Downs Line as being nothing more than 'mess room gossip'. Some members there have said that the Northern and TfW^▸ (Transport for Wales)'s 769s are regularly managing climbs on diesel power that are steeper than anything on the NDL.

[IndustryInsider]

They will be able handle the climbs.  They won’t be able to handle them quite as well as Turbos when on diesel.  The big issue is if one engine isn’t working - that leaves only one left and then they will struggle - especially during Autumn.  The engines are proving unreliable.

[Fourbee]

The service operated with class 117 type DMU^▸ (Diesel Multiple Unit) which were 300 hp per power car for a 3 car a total of 600 hp.  Those DMU had a less efficient transmission.

Part of the reason I suspect for the higher power rating originally for the 165/6 would have been for increased acceleration to improve journey times on the Thames Valley NSE^▸ (Network South East) timetable in the early 1990's

I remember drivers occasionally having to change down on the 117s out of Guildford (3rd to 2nd I think at about the "half way" point), maybe more frequently during leaf fall as not as much speed had been picked up at the bottom of the slope.

The turbos tend to be going a fair old lick at the bottom and power their way through.