T G Robson BSc CEng MIET MInstMC

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 Reliability Analysis -
 Power Supplies to London Underground

London Underground train

As part of a private finance initiative, EDF Energy Powerlink owns and operates the power distribution network of interconnected substations that deliver power to London Underground stations and depots.

As part of the PFI contract, EDF are required to determine the reliability of each delivery point by means of a theoretical relaibility analysis using specified data and methods of analysis agreed with London Underground.


To provide theoretical reliability analysis of each delivery point in the network: approximately four types of delivery point at each of the 200 substations in the network.


McLellan was engaged by EDF to set up and carry out the analyses for all sites.

Each delivery point required calculation of failure rate, mean time between failures (MTBF), outage time and mean time to repair (MTTR), using the 'cut set' method of IEEE Std 493.

The work included:

  • Sketches of the network showing all components to be considered in the analysis
  • Concise calculations considering each component and computing its contribution to overall delivery point reliability
  • Detailed calculation sheets showing the details of every step in the calculation, presented in the format agreed with London Underground
  • Tools for project management

There were several repeat orders for McLellan:

  • a complete set of calculations for the state of the distribution system as it stood in the first year of the PFI contract
  • a set of calculations, with major revisions to data and methods, to represent the state of the network in year 5 of the contract
  • special studies for particular groups of sites, to assist EDF and LU in choosing between alternative equipment configurations
  • studies to assess the impact of changes in the basic reliability data.

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 TGR 07-06-11