Select Committee on Environmental Audit Written Evidence


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





 
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