Transport for Wales 769's

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pompeyfan

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Looks quite spirited in that video, I know they’re not quick, but there’s certainly slower stock out there.
 

37057

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Anyone know why they've taken the pantograph off and kept the transformer?
I'd guess there could be multiple factors. Weight retention (affects suspension then tractive effort), option to reinstate 25kV in future, perhaps having the pan in place caused gauging issues?
 

D365

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I'd guess there could be multiple factors. Weight retention (affects suspension then tractive effort), option to reinstate 25kV in future, perhaps having the pan in place caused gauging issues?
That would be my first answer.
 

coppercapped

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That would be my first answer.
I don't like to be a know-it-all, but are you sure?

I would reckon that a pantograph, including its frame and mounting feet, probably has a total mass of around 200kg. This is about 0.6% of the empty mass of a 35 tonne coach. Even if its mass is twice as much this is still only just over 1% of the mass of the coach. Five 80kg passengers weigh as much! Weight saving wouldn't appear to be significant.

If one doesn't need the pantograph then removing it saves maintenance and something else to go wrong. It's easy enough to put it back when its needed.
 

D365

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I don't like to be a know-it-all, but are you sure?

I would reckon that a pantograph, including its frame and mounting feet, probably has a total mass of around 200kg. This is about 0.6% of the empty mass of a 35 tonne coach. Even if its mass is twice as much this is still only just over 1% of the mass of the coach. Five 80kg passengers weigh as much! Weight saving wouldn't appear to be significant.

If one doesn't need the pantograph then removing it saves maintenance and something else to go wrong. It's easy enough to put it back when its needed.
Apologies, my post was rather ambiguous. My posting was intended as a response to the fact that the Class 319 transformers are retained in all 769s, rather than being removed from the TfW units.
 

AM9

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In which case that is entirely understandable!
I think that is standard practice on all trains that are designed or delivered with transformers. Electrostars that were delivered as ac/DC but used on DC only for long periods (e.g. some 375s, 377/2s) have their pantographs removed to avoid branches gathering in the well equipment, but the transformers are left in situ. The ac/DC design trains that were delivered as DC only, carry a concrete 'transformer weight'. In both of those cases, there is no need to adjust the suspension dynamics as would be required if a tare weight variation of a ton* or more was involved. The class 707 were also designed to be dual voltage (and the first two were delivered with pantographs fitted). I presume that the whole class carried transformers.
* I have no idea how much a 2MW transformer would weigh.
 

norbitonflyer

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I would imagine the transformer may well be an integral part of the complete electrical system, and would need a redesign if it wasn't there. A ballast weight would also be needed to avoid changing suspension settings etc. Contrariwise, a pantograph is exposed and vulnerable to damage, and is light enough that removing it has little affect on the suspension balance
 

Nym

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I would imagine the transformer may well be an integral part of the complete electrical system, and would need a redesign if it wasn't there. A ballast weight would also be needed to avoid changing suspension settings etc. Contrariwise, a pantograph is exposed and vulnerable to damage, and is light enough that removing it has little affect on the suspension balance
On a 319. It's not.

For reference. Most pantographs are between 150 and 200kg
 

AM9

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You presume wrong. Analysis of pictures of the underframes of a 707 shows a distinct lack of, well, anything on the pantograph well vehicles.
OK, well if the first two (707001 & 707002) have had all of the ac kit removed including the transformer, there must have been some adjustment of the bogie dynamics to compensate unless they still have concrete underneath. It says that they were delivered to Wildenrath for ac testing, maybe they went back to the factory for removal of kit so not typical of current new EMU practice.
 

37057

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OK, well if the first two (707001 & 707002) have had all of the ac kit removed including the transformer, there must have been some adjustment of the bogie dynamics to compensate unless they still have concrete underneath. It says that they were delivered to Wildenrath for ac testing, maybe they went back to the factory for removal of kit so not typical of current new EMU practice.
The 444s and 450s have no transformer or ballast weight in place either. I think because they're trailer vehicles there's no effect on tractive effort. However the brakes will be and so they're fitted with an EP brake panel with different pressure settings to that of an equivalent Cl350 PTS car.

So, my thoughts...

A vehicle that is motored must maintain it's weight for tractive and brake effort. If you remove equipment from a motor vehicle, you may have to introduce a power-limit-on-start-up feature to prevent wheel slip and reduce the brake pressure settings to prevent sliding (overbraking).

Trailer vehicles aren't so affected by tractive effort, so if you alter the weight all you do is alter the brake pressure settings (in the Desiro case, you swap EP Brake Panels).
 

Nym

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They all have loadweigh for brake effort anyway, so probably won't even need adjustment.

Last time I worked on something to convert from passenger to non-passenger duties, having consulted with our brakes specialist, loadweigh was enough to take up the changes, even with significant underframe equipment change. Tractive effort on the other hand did need some tweaking.
 

37057

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The reason I said that is (in terms of Desiros - it's what I know best), each vehicle with in a unit has a different set-up in each EP brake panel. That goes for specific vehicles of 185s, 350s, 360s etc. The only weight difference I can think of between the two end vehicles of the Class 350 for example is the addition of a compressor module to one of them and the EP brake panels are fitted accordingly. However all train designs vary and I guess at the end of the day it all depends on the stock (and it's applications, route etc).
 

Nym

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Understandable, I've not worked with Desiros much or at all over the years. Generally with the much older stuff, newest braking systems I've worked on is 1992TS, but the 319s use "Westcode" 7 step valves IIRC.
 

AM9

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I would imagine the transformer may well be an integral part of the complete electrical system, and would need a redesign if it wasn't there. A ballast weight would also be needed to avoid changing suspension settings etc. Contrariwise, a pantograph is exposed and vulnerable to damage, and is light enough that removing it has little affect on the suspension balance
Back to the situation on the 769s, - I've done some calculations to arrive at a rough figures for percentage of the total unit weight available for traction on both 319s and 769s. It's normally expressed as adhesive weight on locos, but as the non-adhesive weight on an MU is defined, it is better defined as a percentage of the total train weight.
Assuming the following:
weights of 319 cars are based on their stated axle loading​
passenger loads are based on an average of 80kg per passenger​
the additional weight of a flex conversion is 7.5 tonnes for each of the DTOs​
the three load situations are, tare i.e. no passengers, full load - all seats occupied and crush load - 160% of seating capacity.​
interestingly the figures are not that much different from the original 319s.
Now of course percentage adhesive weight isn't everything, but it does impact on performance on poor railhead conditionns, and provided that the maximum available torque is sufficient to drag the train up the steepest gradient, the train will travel on its routes although due allowance would need to be made for slower running. Note, the 319s were required to make standing starts up the 1:27 bank from City Thameslink to Blackfriars with full loads.
If anybody has better verified additional weights of the conversion, it is easy to update the figures.

class/subclasstarefull loadcrush load
class 319/0 or 336.1%34.5%33.5%
class 319/436.1%34.7%33.8%
class 769/032.6%31.6%31.0%
class 769/432.6%31.8%31.2%
 
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Adlee Turner

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Colas 37421 is on its way from Rhymney to Cardiff Canton Sidings as 5Z70 this morning. I presume it’s heading back to swap places with 37418 on class 769 thunderbird duties when they restart
 

Bob Price

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Colas 37421 is on its way from Rhymney to Cardiff Canton Sidings as 5Z70 this morning. I presume it’s heading back to swap places with 37418 on class 769 thunderbird duties when they restart
Can't see a return working in RTT. The 769 paths are still in though. Find it interesting that the 230 runs are happening daily (and boy are they hammering it) but the 769's are not.
 

PHILIPE

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Can't see a return working in RTT. The 769 paths are still in though. Find it interesting that the 230 runs are happening daily (and boy are they hammering it) but the 769's are not.
Wonder why 5Z70 and not as an 0 as I thought there was nothing to haul from Rhymney. The 769 paths have been booked in the event of being able to operate as and when
 

PHILIPE

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Colas 37421 is on its way from Rhymney to Cardiff Canton Sidings as 5Z70 this morning. I presume it’s heading back to swap places with 37418 on class 769 thunderbird duties when they restart
37421 came down and is booked to haul 2 x 56s to Nottingham (Colas) and 37418 has gone up to Rhymney. The mystery is why a Class 5 and noted timed as a DMU but this probably counts for nothing.
 

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