A procedure for estimating the overall system worth associated with generating unit refurbishment

Quantitative reliability evaluation is an important element in power system planning and operation and the indices generated can be used to make a wide variety of planning decisions. Quantitative reliability evaluation methodologies are now firmly established in the area of generating capacity adequacy assessment and are routinely used in planning new capacity additions. Generating system adequacy is primarily governed by the unavailabilities of the units in the system and therefore one alternative to adding additional capacity is to consider improving the availabilities of existing units in the system. Generating unit availability can be improved by unit and plant refurbishment, i.e. by investing capital to reduce the unit forced outage rate (FOR). Many electric power utilities are doing this rather than investing in new generation equipment. Generating unit unavailability has a major impact in a number of overall system areas, most of which are not normally considered by power station designers, plant operators and managers responsible for actual power plant modifications. This paper presents a comprehensive and basic approach to recognizing the impacts of generating unit unavailability on expected energy production costs, expected failure costs and capacity costs. The procedure is energy-based and utilizes an interrupted energy assessment rate applicable to the consumers served by the system to incorporate the expected load curtailment costs. The worth of generating unit refurbishment is assessed in terms of overall system costs. The cost of any specific unit refurbishment can be compared with the resulting net benefits and used to make decisions.