An equivalent substation model can be generated by making a detailed model that excludes all feeder breakers. A reliability analysis will produce an annual outage rate and an annual outage duration for each low voltage bus of the substation. The following formulae can then be used to compute equivalent failure rates and repair times for equivalent buses in the distribution reliability model: ? equiv = OR MTTR equiv = OD / OR ?equiv=Equivalent bus failure rate (failures per year) MTTRequiv: Equivalent bus mean time to repair (hours) OR: Computed bus outage rate (outages per year) OD: Computed bus outage duration (hours per year) For more information you can refer to: R. Billinton and G. Lian,