A new optimization method for maintenance decision-making considering both power supply reliability of the substation and the life cycle cost(LCC)of equipment is proposed. According to the “Transmission Equipment Risk Assessment Guidelines” made by Southern Power Grid Company

transformers or circuit breakers to be maintained are chosen. Then the failure rate of equipment before and after maintenance is calculated based on the health index(HI)and the age reduction factor

respectively. Further

the variable quantity of the substation expected energy not served(EENS)and the LCC of equipment before and after maintenance can be quantified by applying the contingency analysis and the load reduction state enumeration

respectively. Finally

an optimized maintenance strategy is given according to three different assessment criteria

including the priority to reliability

economy and cost-effectiveness ratio. An application example in a 220 kV substation shows the method is able to improve maintenance efficiency and reduce cost with the risks to the substation effectively reduced.