Failure Modes and Effect Analysis of Turbine Units of Pumped Hydro Energy Storage Systems

In the present paper subject of the investigations is the reliability assessment of the single-stage reversible Hydropower Unit No. 3 (HU3) in the Bulgarian Pumped Hy-dro-Electric Storage (PHES) plant “Chaira”, which processes the waters of the “Belmeken” dam and “Chaira” dam. Preceding destruction of HU4 and its virtual simulation, analysis and the conclusions for the rehabilitation and safety provided the information for the possible processes in HU3. Detailed analysis of the consequences of prolonged use of HU3 was carried out. The Supervisory Control and Data Acquisition (SCADA) system records were studied. Fault Tree Analysis (FTA) is applied to determine the component relationships and subsystem failures that can lead to an undesired primary event. The functional structure of the system was depicted as a causal chain of failure effects. The probability of system failure was estimated based on the failure probabilities of the primary events. The effects of static loads, dynamic loads and low-cycle loads were investigated. Based on the experience and the investigations of the HU4 and its damages, as well as of the failures in the stay vanes of HU3 it is recommended to organize monitoring for water ingress into the drainage holes, which will allow detecting failures in a timely manner.