Reliability-centred maintenance of 11KV switchgear



  • 11KV switchgear in a regional power distribution network
  • 75,000+ items of plant
  • 8 year “maintenance” cycle, costing approx. £1m per annum
  • No method in place for predicting possible failures
  • Difficult to incorporate into business planning


  • Optimisation of switchgear inspection and maintenance, to reduce costs and minimise engineering disruption


  • Analysis of failure incident reports by switch type, age, duty and failure mode – as data exist
11kV switchgear


  • Quantification of failure rates and reliability measures, for switch types with sufficient populations, as a function of age
  • Calculation of the effect on reliability of varying the maintenance interval
  • Calculation of the effect on reliability of different sampling levels for inspection, recognising that intrusive inspection can initiate problems
  • Insufficient data to identify any effects of duty or environment


  • Specification of initial inspection and maintenance plans, with rules for their continued optimisation as results are accrued
  • Considerable savings on inspection and maintenance costs
  • Understanding and control of system reliability


Brear, J.M., Dean, R.J., Johnson, T.D. and Jones, G.T.
“Increasing condition monitoring to reduce unplanned outages and equipment replacement”
ERA Conf ‘Engineering Asset Management for Utilities, Industry and Commerce’
London, October 1999

Plant Integrity