Dear Sparks Fans ?
Most of the (sub)urban electric trains in UK are multiple units, where most if not all coaches have motors. The reason for this is the need to get high adhesion for rapid acceleration, by distributing the track forces to most if not all wheels. Rapid acceleration (and braking) are needed when stations are close together get a high service speed.
Inter City trains do not need urban rates of acceleration but high top speeds. Electric motor coaches are (much) more expensive than “trailer coaches”, so having one or two locomotives per train is a compromise over costs. THe TGV trains in France climb steeper gradients than most railways (3%) but 6 power bogies on an 18 coach (36 bogie) train is enough to get up the hills.
The Pendolinos on the WCML have alternative motor coaches ( and are expensive) to maximise the useable passenger space, including the “locomotive coach”. You will notice that all the seats in these face backwards when the coach is at the front of the train, to maximise the survival chances of passengers in the case of a head on collision.
Yes most of the long high speed trains have two or more pantographs, but always only one is used (the other is a spare). The reason for this is that high speed the pantographs induce complex (and harmonic) waves in the OHL. If a train had two pantographs up, the rear one would lose contact, arc or be physically damaged and threaten the OHL with damage. This is why all these trains have 25kV cables (along the roof) from one end to another, so that whichever pantograph is up, all coaches will be powered.
Yes if all UK railways were electrified the extra demand on the grid would be much less than demand variability, or practically undetectable. If more of the grid was “green power” this would reduce the carbon footprint of rail energy use. More importantly, if electrification led to attracting to rail more of the 3% of car trips over 30miles long, generating near 20% of the traffic km, then there would be a reduction in total transport carbon (and other emissions). As a comparison all rail trips carry just 7% of UK passengerkm, and 70% of these are London based, in, to or from. Getting just a third of these long distance car trips would nearly double train traffic.
Using the Royal Commission’s figures, long distance car trips average 1.0 MJ/km, compared to 0.5 by high speed train, and since average train occupancy is 40%, the marginal increase in rail energy consumption would be small. Getting occupancy to 80%, which many airlines manage, would reduce energy consumption to 0.3MJ/km by rail, so saving 0.7MJ/km compared to car, and a pro rata reduction of CO2, PM10s and NOx emissions.
Let’s hope that the public finances do not thwart the rail electrifications.
Happy weekend to all,
On 25 Jul 2009, at 12:29, starrfred wrote:
As Dave points out railway electrification (like trams) has a virtually insignificant affect on UK electricity demand.
The hammering of the tracks is a result of haviing the diesel engine, generators and driving motors all in the same vehicle.
It would be far more sensible to send the current along the train to driving bogies in each coach, as is done in the high speed trains on the Continent ( where the electricity comes from one or two pantographs).
And if the coaches were equipped with pantographs, they could be deployed on existing electrified lines, when needed.
If the diesels were to use biofuels, this would result in a near zero carbon emissions.
— On Fri, 24/7/09, dave andrews < wrote:
Subject: Re: [Claverton] Electrification nof (rail) transport
Chris – As I have said once before, we had a guy from the CEGB years ago, a
system planning engineer called Syratt – he stated that if ALL remaining
lines were electrified, then this would add 1% to the load (I assume
average) on the sustem – so no measurable additions needed.
2009/7/24 Chris Hodrien <
> BBC TV news: gov’t announcement of 8-year plan to electrify both the Great
> Western main line out to Swansea (NOT SW of Bristol) and the
> Liverpool-Manchester line (even more historic!)
> Something for us in Claverton to celebrate – a giant leap forward in
> affordable,sensible, low-technical-risk electrified transport for ‘UK plc’.
> (- would someone like to calculate how many million EV’s it’s equivalent
> The investment is 1 billion pounds and the timing has been driven
> (reluctantly, for Gov’t) by the urgent need to replace the existing
> ‘time-expired’ HST diesel trains which have been “hammered” far beyond their
> ‘natural’ service life, quite apart from the severe on-going track damage
> caused by these “overweight” vehicles (oh for a fleet of the lightweight,
> GT-powered tilting ‘APT’ 30 years ago!). The timing could hardly be worse
> in terms of the state of the UK economy to fund it, so thank heavens
> common-sense has still, (unusually!) prevailed.
> The Gov’t claim the new electric trains will be 35% cheaper to run and will
> generate 35% less CO2 at current (? or forecast future average?-don’t know)
> “grid mix”. But the straight financial payback (even for this very
> “low-tech”/proven option) is a disappointing 40 years (Dave- re. our
> discussions on investment cycles for the WT fleet) , which is why it has to
> be gov’t rather than private funding.
> The quoted cost and payback time above is just the ‘direct’ cost, the power
> industry infrastructure cost to supply the extra ‘juice’ is probably as
> large again. If I’m right this implies that the real payback time is
> disappointingly nearer 80 years! ( – “just typical” that the gov’t is not
> being honest about this). (Dave – you can’t “double-account” (off-set) this
> with replacements of existing powerplant, this is new extra system demand,
> and as it is required at grid peak periods, it also implies “100%” plant
> firm capacity additions as well as annual fuel use).
> I guess the front-end investment cost (inc’ energy supply infrastructure
> changes) to achieve a similar CO2 saving through road electrification is
> much higher than this – can anyone calc’ a figure for this?
> Chris Hodrien