-
Our booking engine at tickets.railforums.co.uk (powered by TrainSplit) helps support the running of the forum with every ticket purchase! Find out more and ask any questions/give us feedback in this thread!
Pendelino Pantograph questions
- Thread starter CosherB
- Start date
- Status
Sponsor Post - registered members do not see these adverts; click here to register, or click here to log in
R
RailUK Forums
The pendolinos defintely are the first train to have a high voltage bus between transformers since the early waterloo and city EMUs (though their voltage wasn't anywhere near 25kv).
Twice as much current going through the "would-be" low voltage bus would lead to four times as much heat produced which would need to go somewhere.
Also the further down a wire, the less "voltage" one can get due to electrical resistance.
Twice as much current going through the "would-be" low voltage bus would lead to four times as much heat produced which would need to go somewhere.
Also the further down a wire, the less "voltage" one can get due to electrical resistance.
O L Leigh
Established Member
Nick,
You misunderstand.
I'm not talking about transporting enough juice to run an extra transformer, but just enough to run the train systems after it has been stepped-down. For example, a Cl315 uses up to 900V DC for it's traction requirements. This is stepped-down from 25kV by the transformer and rectified from AC to DC before being sent between the cars to the traction equipment under each motor coach, just as a Cl390 does within each 4 car sub-unit. Unless there's some specific reason why the Pendo needs to have two transformers running the whole time and can't just manage with one as every other AC EMU does, there should be no problems providing power to both ends of the unit from a single supply at the actual voltages each train system requires. At these sorts of voltages, the cables could be lighter and would require less rigorous insulation.
As for voltage drop as one progresses down the length of a cable, this wouldn't be a problem when we're just talking about the length of a 9 car EMU.
one TN
You misunderstand.
I'm not talking about transporting enough juice to run an extra transformer, but just enough to run the train systems after it has been stepped-down. For example, a Cl315 uses up to 900V DC for it's traction requirements. This is stepped-down from 25kV by the transformer and rectified from AC to DC before being sent between the cars to the traction equipment under each motor coach, just as a Cl390 does within each 4 car sub-unit. Unless there's some specific reason why the Pendo needs to have two transformers running the whole time and can't just manage with one as every other AC EMU does, there should be no problems providing power to both ends of the unit from a single supply at the actual voltages each train system requires. At these sorts of voltages, the cables could be lighter and would require less rigorous insulation.
As for voltage drop as one progresses down the length of a cable, this wouldn't be a problem when we're just talking about the length of a 9 car EMU.
one TN
ChrisCooper
Established Member
For something like a Pendolino there are 2 ways of getting power along the whole train. You can either have one pantograph which via a 25kV powerline along the train supplies both transformers, which then step down the voltage to supply the traction equipment for each "half set". That option is used on the likes of TGVs, where the transformer on the front power car is fed from the back powercar's pantograph. In the UK, this was not allowed by regulations, with the exception being the APT-P where the two adjacent powercars were linked. The other option is to have the pantograph supplying the transformer on it's own coach, which then steps down the voltage and supplies the traction equipment on the whole train. That is inefficient, since the transformers each have to be twice as powerful, so likely twice as big and heavy, but one will always be dead weight. With this in mind, plus the fact that I'm sure I have seen referance in quite a few places to changes in regulations to allow a 25kV line on the pendolinos, I'm pretty sure the former is used. As far as rectification to DC is concerned, this can be done either done on the same coach as the transformer, or on each coach (the rules about power lines along trains only apply to high voltage, not AC). On the 314s and 315s the power is not rectified on the pantograph coach, the supply to the motor coach is AC, which is needed since standard thyristors can only work with AC (they can only be switched on, they require the voltage to drop to 0 during the AC cycle to switch off). This is why trains running of DC supplies like 313s and 455s had mechanical resistor control some time after electronic thyristor control replaced tap changers on AC only trains. The thyristors are actually built into the rectifier, replacing 2 of the diodes (rectifiers have 4 diodes, which allows them to reverse the negative current, rarther than just cut it off). Gate Turn Off (GTO) thyristors, also known as choppers, were a slightly later development which allowed the thysistor to be turned on and off, and these can work on DC aswell as AC, and were first fitted to the 319s.
Pendos def do have the transformer cars linked at 25KV, so each transformer powers its own half set. As someone else stated, if only the transformer in the car with its panto raised was used for both half sets, it would need to be much bigger and heavier, and the unused one in the other panto car would be dead weight.
The 25KV doesn't run the length of all 9 coaches - just over the 3 interveining coaches between the transformer/panto cars.
The powered vehicles (the first, second , and fourth in each half set counting from the driver's cab end) each have two underfloor traction motors driving the inner wheels of the bogies through drive shafts. Each of those pairs of motors is powered through a control system under the coach (so 3 such control systems per half set) - which no doubt uses stepped-down AC from the relevant transformer car in a form of 'thyristor control' for the two AC traction motors (so no rectification as such), and must also play a part in the regenerative braking system to ensure that regenerated AC is correctly phased to be fed back into the overhead line.
CS
The 25KV doesn't run the length of all 9 coaches - just over the 3 interveining coaches between the transformer/panto cars.
The powered vehicles (the first, second , and fourth in each half set counting from the driver's cab end) each have two underfloor traction motors driving the inner wheels of the bogies through drive shafts. Each of those pairs of motors is powered through a control system under the coach (so 3 such control systems per half set) - which no doubt uses stepped-down AC from the relevant transformer car in a form of 'thyristor control' for the two AC traction motors (so no rectification as such), and must also play a part in the regenerative braking system to ensure that regenerated AC is correctly phased to be fed back into the overhead line.
CS
thefab444
Established Member
New coach would probably be a TCWL though...
According to therailwaycentre.com it's a TSO.
O L Leigh
Established Member
Not necessarily so.
If the transformer was man enough to provide power for the entire set, there would only need to be one and a single pan. Why cart around a duplicate set of kit if it really is just going to be dead weight?
Incidentally, I'm not arguing that Cl390's don't have a 25kV bus as they obviously do. My point very simply is that the whole hassle of getting a safety case to allow them to have this feature could have been avoided with a bit of forethought on the part of Alsthom.
one TN
- Status