Memorandum submitted by DJ Hartland
LONDON UNDERGROUND POWER SUPPLIES. ELECTRIC
CURRENT FLOW IN CONDUCTOR RAILS. SAVINGS IN ENERGY WITH LOW LOSS
RAILS
INTRODUCTION
London Underground trains are powered by electricity
drawn from the National Grid. The power passes to substations
along the line and then is fed to two conductor rails laid along
the track. The trains run on two additional rails and pick up
current by means of shoegear making sliding contact with the conductor
rails.
The current passing along the rails generates
losses which appear as heat. The losses depend on the style of
rail and the condition—worn steel rails create more losses
than new steel, and composite aluminium rails create lower losses
still.
EXTENT OF
LOSSES
For the whole London Underground system, the
losses in the conductor rails amount to approximately 13% of the
total electricity bill, 130 million kWhr, or 130,000 tons of CO2.
EFFECT OF
CHANGE TO
ALUMINIUM
For every kilometre of steel rail which is changed
to aluminium, the annual saving is 46,000 kWhrs and 46 tons of
carbon dioxide emissions.
MONETARY SAVINGS
At 5p/kWhr the energy saving is £2,300
per year.
On the carbon credit scheme, a saving of 46
tons of CO2 is worth £887 (using the price at
22 February for carbon, of €22 per ton).
The rail should last 50 years—over the
50 year life this is a total energy saving of £115,000 and
a carbon saving of £34,900.
Detailed calculations are attached.
ENERGY AND
CARBON SAVINGS
CALCULATIONS
Carbon usage equivalent in energy
1. The British Wind Energy Association quotes
0.86 kg of CO2 emissions for one kWhr of energy production
at coal fired power stations.
2. The Parliamentary Office of Science and
Technology quotes 0.93-1.08 kg of CO2 per kWhr.
For the purposes of these notes we will take
a figure of 1 kg per kWhr.
LUL energy usage
3. LUL Environmental report 2004 quotes
1,087 gigawatt hours as the total LUL usage, of which 90% is used
for traction purposes. This is 978 gigawatt hours or 978 million
kWhr.
LUL energy bill
The general rate payable is 5p per kWhr, so
that the annual bill is £48.9 million for traction current.
LUL carbon usage
4. LUL Environmental report 2004 shows 160
watt hours per passenger km on the Underground. Using the rate
of 1kg=1kWhr this is 160 g of CO2 per passenger km.
5. LUL Environmental report 2005 shows 54.5g
of CO2 per passenger km, down 1.38g from 2004.
6. The All Party Climate Change Group quotes
85.9 g CO2 per passenger km on the Underground.
7. The Tyndall Centre quotes 107g per passenger
mile on the Tube, which is 66.9g CO2 per passenger
km.
It is not clear what is the actual figure for
LUL carbon usage.
Conductor rail losses
8. There are 826 single track km on the
running lines of London Underground, with 1652 km of conductor
rails (two per track). Of this, 150km is aluminium, 1502 km steel.
9. The calculated average current in a conductor
rail on London Underground is 900 amps. For steel rails the average
conductor rail resistance is 16 microohms per metre, so that the
average heat lost from steel conductor rails is 12.8 watts per
metre, or 83 kWhr per year.
10. For aluminium rails the average conductor
rail resistance is 7 microohms per metre so that the average heat
lost from aluminium conductor rails is 5.6 watts per metre or
37 kWhr per year.
11. The total heat loss from all rails on
the London Underground per year is 1,502,000 x 83 + 150,000 x
37 = 130 million kWhr. This is 13% of the total electricity bill.
EFFECT OF CHANGING STEEL TO ALUMINIUM
Savings
|
| | Annual saving per metre
| Annual saving per kilometre
| Saving per kilometre over 50 years
|
|
| Energy | 46 kWhr
| 46,000 kWhr | 2,300,000 kWhr
|
| Carbon | 46 kg
| 46 tons | 2,300 tons
|
| Monetary | £2.36
| £2,360 | £118,000
|
|
| 2,300 tons of CO2 is valued at £34,900 at February 2006 prices.
|
February 2006
| 
