Reliability Comparison of Two Deterministic Criteria for Planning High Voltage Autotransformer Stations

This paper describes a reliability study that has been performed at Hydro One to compare the reliability of two deterministic criteria used in the planning of high voltage auto-transformer stations. One criterion calls for designing the station to withstand the loss of one unit transformer (single contingency criterion) while the other calls for designing it to withstand the loss of two units (double contingency criterion). Two system reliability measures are used in the comparison namely the system availability index and the loss of energy index. The study proposed a number of Markov models to evaluate the probability of system failures under each criterion. Examples are provided to illustrate these models and see how the two deterministic planning criteria are compared from the reliability point of view.