Power substations as infrastructures with highest outage rate closest to the consumers and power generation facilities, should be well analysed. This paper presents an upgrade of a method for evaluation of the reliability of power substations, considering uncertainty and imprecision of the input data, based on fuzzy logic. The probability of failure is modelled as a triangular fuzzy number and the Energy Not Supplied (ENS) is calculated. The method is presented on a 400/110 kV/kV substation. The case study shows that the usage of triangular fuzzy numbers gives satisfactory results from an engineering point of view and provides a high level of precision and model simplicity.