Modeling the Impact of Spare Transformer on a Set of Subtransmission Substations Reliability

Due to developing sensitive industries and increasing investments in these industries, the economic value of electricity has increased and therefore loss incurred to consumers has significantly increased by temporary and permanent outages. Failure of power transformer cause interruption of electricity services. Use of spare transformers is one of the most important approach to improve reliability of energy supplied to consumers. In this paper, a new Markov model is proposed to study impacts of a spare transformer on reliability of a network comprising of a number of two-transformer substations. In proposed model, it is demonstrated that the optimal capacity of spare transformer in an area is affected by both maximum loading percentage of substations in that area and the difference between the maximum and the minimum capacity of transformers in the area. Here, the expected energy not supplied (EENS) is used as the reliability index. A practical network in Mazandaran province consisting of 84 substations is selected and impacts of spare transformers with various capacities on system reliability and the related costs are studied. Moreover, the effects of value of lost load (VOLL) variations on utilities’ cost, caused by transformer outage, are investigated via sensitivity analysis.