reddragon
Established Member
It was because the class 319 was originally planned to be a Networker. In 1990 319s & Networkers were under construction
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Porterbrook Cl.769 'Flex' trains from 319s, initially for Northern
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That was when North West and Thames Valley electrification was first announced and Lord Adonis suggested the ex-Thameslink trains would be 'extensively refurbished' before transferring. Although, with Thameslink delays and the Conservatives cutting rail budgets it never happened.
Bletchleyite
Veteran Member
The windows are in the 319 arrangement, it's just a bad artist's impression.
The doors...well, a trial was done of retrofitting plug doors to a 455, so not totally out of the question:
http://extra.southernelectric.org.uk/features/rolling-stock/455/index.html
absolutelymilk
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Not sure if it has already been posted, but the the first 769 will be delivered to Northern in January.
https://twitter.com/Modern_Railways/status/1059465962532102144
https://twitter.com/Modern_Railways/status/1059465962532102144
Bletchleyite
Veteran Member
So it's a race to which will be in service first...230 or 769...which will it be?
Grannyjoans
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That means an empty Pacer has a higher power to weight ratio than a loaded 319!
How come 319's still always accelerate faster ?
Yes they have comparable acceleration to a Pacer from 0 to 30mph. Then they are significantly quicker from 25mph to 75mph with the ability to go all the way to 100mph unlike a Pacer.
superkev
Established Member
Power rating can be misleading as the short term rating is much larger than the usually quoted continuous rating which is why electrics will always accelerate faster than diesels.
K
apk55
Member
A hydraulic system as used on a pacer can only deliver full engine power at one spot speed around 60MPH. At low speeds (below 40MPH) when the torque converter is operating at lest 30% of the engine power is lost in heating the torque converter (inefficiencies) and the engine is also not operating at full power (because the speed is limited). In contrast the electric transmission can deliver full engine power to the rails over a wide speed range probably from 15MPH to max speed.
After all why do practically all locomotives use electric transmision
A diesel engine is set for an absolute maximum power output essentially by injector rate and air mass. Once that level is reached there is no more power available, (which is just as well as the maintenance regime is set to allow for that level of stress and wear).
An electric traction system however is limited mainly by the operating temperature sustained when under power. The cooling systems will be rated to ensure continuous running at that power level. The motors/electrics of a train that has just stopped (even partially*) under mechanical braking, and then completed a station dwell, will be below the temperature it is designed for under continuous running so there is some additional power margin that can be used to improve acceleration. Once at linespeed, electric trains use relatively little power, and cooling systems keep the hardware well within normal operating temperatures.
*Heavy rheostatic or regenerative braking puts a load on the motors similar to that under acceleration, but braking using the motors is not effective to bring a train to a complete standstill.
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And most of that limitation is due to adhesion limits rather than motor torque shortfalls.
43096
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It has become usual for diesel power to be quoted as engine output, whereas electrics are usually quoted as power at the wheel rim. A diesel’s comparable power will be lower due to auxiliary loads and transmission losses, so it is not a straight comparison.
Surely electric rolling stock is stated as e.g. n x 224kW (300hp) motors, where the power is the continuous rating of the motor (at the nominal designed voltage on the trains). That power can be adjusted by onboard traction electronics to accommodate sub-standard supply infrastructure (3rd rail DC), low voltage conditions (ac or DC), high ambient temperatures, etc..
Class465fan
Member
Tbf it sort of looks like a combination of a networker and a class 700.
Not surprising considering the class 325 is basically a class 319 with the interior kitted out for parcels/letters and a Networker cab front fitted.
If electric drive is that good why have DMUs tended to move away from it to hydrodynamic and latterly "mechanical" (actually bus type automatic gearbox) drive? Also except in the context of hybridisation you never see it in a road vehicle.
superkev
Established Member
Getting bit off topic. The original pacers had uk made SCG mechanical gearboxes as previous dmu's. Unfortunatly for some reason reliability was very poor so German Voith hydraulic units as used subsequently on sprinter trains where substituted despite the 10% or so hit in fuel consumption.
Back on topic anyone know what the short term rating of a 319 is compared with its continuous rating.
In the days before electronics motors where often rated at up to double there continuous rating for short periods the limitation being temperature. I suspect these days it's the electronics which are the limiting factor
K
Back on topic anyone know what the short term rating of a 319 is compared with its continuous rating.
In the days before electronics motors where often rated at up to double there continuous rating for short periods the limitation being temperature. I suspect these days it's the electronics which are the limiting factor
K
If Wikipedia is to be believed, by inference, 1320hp per unit on a Class 319. Ironically it is better than 4x EE507 or like-for-like replacements on a Class 455 (the other likely candidate for future Flex-es).
The lower performance that the 3rd rail units have was less of a problem on ex-Southern routes where maximum speeds rarely go much above 90mph. The ac electrified routes have been capable of sustained 100mph speeds since the '60s so trains there have been equipped with higher powered versions of EE507 like motors, e.g. GEC WT401 (class 309) and G315BZ (class 319) to allow them to operate in amongst faster LHCS services.
Since privatisation, new EMUs have been delivered with higher powered traction packages which owing to the limitations of 3rd rail power supplies, have been limited by software to EE507 levels, i.e. Electrostars and Desiros run at just 50-70% of their full power.
apk55
Member
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.
Bletchleyite
Veteran Member
Though only put down through 2 (or is it 4?) axles, which can cause trouble - the 319 I took from Euston yesterday was wheelspinning like nobody's business all the way up and picked up a fair bit of delay as a result, not to mention some heavy juddering which reminded me of Mk3 LHCS "snatch" you used to get.
ac6000cw
Established Member
It's 4 axles per unit (all axles of the single power car). The other 'Mk3' derived BR-designed EMUs of the period have the same arrangement.
Yes unfortunately the 319s do require skill in driving during time of the worst railhead conditions. On the MML, most drivers learnt how to handle them and if there was bad slipping it was indicative of exceptionally bad conditions.
The benfit of three phase ac motors is that the frequency of the ac is varied to give spin speeds not much different to that which is needed for adhesion. A DC motor (especially one fed by a resistor chain) will draw less current once it speeds up so slipping is not mitigated by the drive current.
edwin_m
Veteran Member
It's mitigated to some extent in a series-wound DC motor but I can't recall the exact mechanism at present. But I agree an AC motor, which only turns at close to the exact speed dictated by the traction electronics, will be better for adhesion.
Bornin1980s
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Is that one reason for the widespread use of AC motors, despite the extra expense of the control equipment?
jonesy3001
Established Member
Has there been anymore testing on the 769s, i've seen a post on youtube of 769434 but that was months ago.
ac6000cw
Established Member
Yes.
You also get smaller, lighter, motors (for the same power output) that need minimal maintenance (as they have no commutator/brushgear), in exchange for box full of complex high-power electronics to drive them.
158820
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ROG said ina press release in October that they would be testing on WMCL from early November. I haven't seen any signs of this happening. So more delays again it appears
The ROG news page https://www.railopsgroup.co.uk/news/ also says that they are testing the Class 710s and Classes 745/755 so perhaps it is a ROG issue?