A survey on the reliability of protective systems for large hydro generating units

This paper presents the results of a survey on the reliability of the protective systems of five 240 MW hydro generating units, using operating records that cover 17 years. It includes the computation of reliability indices and the modeling of failures and repairs for the protective systems associated to generators, substations, auxiliary services, turbines and spherical valves. Results show that: i. The most reliable protective systems are those associated to the substations; the second more reliable are the ones associated to the generators. ii. The less reliable protective systems are those associated to the auxiliary services; the second less reliable are those associated to the turbines. iii. Dependency of the protective systems associated to the generators and substations is lower than its security, while the contrary happens for the protective systems of the auxiliary services, turbines and spherical valves. iv. The processes of arrival of false openings, false closings, failures to close and their corresponding repairs are stationary, what means, there is no a pattern of increase or decrease in the occurrence of failures and the duration of repairs.