A cost-reliability model with spares in electric power systems

The three-phase electric power system can be considered as a triple system since it includes within its different sections three similar components of certain items. These items may be transformers, rectifiers, thyristors. protection equipment...etc. In order to achieve a certain reliability level for this system, it is also necessary to include spares in the system for each item and this will bring about an increase in the cost. This paper presents the design issue for the optimal number of spare units in a triple section including faults due to common-cause failure. Two main problems are tackled in this paper: the first is how to minimize the average total system cost, subject to a certain reliability level, for different values of failure and repair rates; the second is how to maximize the system reliability with imperfect coverage and common cause failure included. Application and a numerical example illustrate the results which are compared with the results obtained from other triple systems