Peaking Unit Considerations in Generating Capacity Adequacy Assessment

Generating capacity adequacy assessment is an important task in power system planning and development. The basic model used to incorporate a generating unit in an adequacy assessment is a two state representation in which the unit is available or unavailable for service. This model is a valid representation for base load units but does not adequately represent intermittent operating units used to meet peak load conditions. Peaking units are started when they are needed and normally operate for relatively short periods. The two-state model for a base load unit has been extended to a four-state representation, which is widely used in practice. The indices used to represent the unavailability of a peaking unit are the utilization forced outage probability (UFOP) and the derated adjusted utilization forced outage probability (DAUFOP). The UFOP and DAUFOP values are used to incorporate peaking units in analytical generating system reliability assessments. The UFOP used in an analytical method is normally a fixed value calculated under a certain system condition and is applied to a wide range of situations. The actual UFOP, however, is not a fixed value and varies with changes in the system operating conditions. This paper illustrates the utilization of a sequential Monte Carlo simulation technique for generating system adequacy assessment and examines the variability of peaking unit UFOP as a function of the unit loading order, system load levels and required operating reserve. The concepts presented in this paper are illustrated by application to a practical test system