On Sunday 31 August 2003 07:48, Pigeon wrote: > > I remember, at the GEC Hirst Research Centre in Wembley, London, being > struck by the fact that the maximum power draw of the whole site, > 3.5MW, was the same as a Class 87 on full bore belting down the West > Coast Main Line which ran past the site.
Umm, 3.5 MW - about 4000HP. The Class 91's on the East Coast Main Line are rated at 7000 HP, IIRC. This is just an indication of the sort of power you need to pull a high speed train. Where it's relevant to the question of diesels vs electrics is that nobody tries to build single-unit diesels of much over 3000 HP any more. They get too heavy. This is why the British diesel HST's had a power car at each end. In the US they just couple many diesels up in multiple to get the power required. If you can get the same power in one loco without the complication of multiple diesel engines to keep serviced, that's an obvious plus. > > Nope, and nope. Diesel electrics are popular because they give the > > most bang for the buck. > > ...and because (in Britain) the introduction of diesel-hydraulics was > cocked up badly, for silly reasons like the idea coming from those > nasty Germans we'd just fought a war against; also because of > commonality of transmission technology with straight electrics; > worldwide, a lot of country B seeing country A using diesel-electrics > and copying them, often buying similar designs from the same > manufacturer, making the whole process easier and cheaper. I don't normally disagree with you Pigeon ;), but here I do. If hydraulics had proved reliable, and cheaper, or significantly better in any way, d'you think they wouldn't have been more widely adopted by now? They were certainly tried in enough areas. > Diesel-hydraulics are in many ways a much better idea than the > diesel-electric - simpler, more reliable, lighter, no need for complex > high-power electrical control gear, inherently good resistance to > wheel slip and transmission overheating which makes them good choices > for heavy freight trains and/or heavily graded routes. The reasons > they're not more widely used are historical/political rather than > technical. You're not a Great Western enthusiast by any chance? <vbeg> Me - Southern. ;) > > Hydraulic transmission does seem to be making a comeback, though - > diesel multiple units in Britain since the 80s have all used hydraulic > transmission, with great success. It's far more reliable than the > mechanical transmissions on older DMUs, small and light enough for > underfloor mounting, and much cheaper than the experimental > diesel-electric version that was also built. Well, automatic cars all have hydraulic torque-convertor transmission. It works fine for low powers (by which I mean, up to a few hundred HP). It doesn't seem to work so well for high powers. Hence OK for railcars, not (apparently) for locomotives at higher powers. > > with fewer moving parts than the steam engines it replaced. > > Huh? Yes. Huh? ;) > > The > > railroads really couldn't give a damn about how much electric they're > > using since they're not having to string thousands apon thousands of > > miles of overhead lines (another costly expense railroads don't bother > > with unless they can get economic benefit from the typically heavier > > and faster trains that electrified lines run). > > and *maintain* all those flippin' wires... I think a bottom-contact > third rail system, using aluminium rails with steel wearing faces, on > around 3kV, would be a better bet; similar electrical losses, and a > whole lot more robust and easy on maintenance. (But maybe I'm biased > by knowledge of the UK East Coast Main Line electrification which was > a real cheapo job and blows down whenever too many cows fart at once.) > Electrification works better in densely-populated areas (Holland) or > mountainous areas with lots of hydro-power (Switzerland) than > somewhere as big as the US. And *also*, in places like Switzerland (or New Zealand), where there are long continuous grades, regenerative braking can put a lot of power back into the grid and save on train brake blocks. I believe some US diesel-electrics are equipped with regen braking but they just have to 'waste' the power produced. In NZ, the amount of traffic hasn't paid for the costs of electrification. In Switzerland it most certainly will have done, many times over. Incidentally, third-rail works fine for multiple-units, but has distinct limitations for single-loco trains in any place where there are, say, a lot of railway crossings. (Or, as in NZ, largely unfenced tracks in some areas). The Southern Railway's early electric locos had a motor-flywheel-generator set ingeniously wired in series with the traction motors to overcome the break in traction. But that's DC, I'm not sure it would work so well on AC. Also of course, 3kV third rail is a bit more dangerous than 600v DC. cr -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
