An Assessment of the Embedding of Francis Turbines for Pumped Hydraulic Energy Storage

Abstract

In this paper, analyses of Francis turbine failures for powerful Pumped Hydraulic Energy Storage (PHES) are conducted. The structure is part of PHES Chaira, Bulgaria (HA4—Hydro-Aggregate 4). The aim of the study is to assess the structure-to-concrete embedding to determine the possible causes of damage and destruction of the HA4 Francis spiral casing units. The embedding methods that have been applied in practice for decades are discussed and compared to those used for HA4. A virtual prototype is built based on the finite-element method to clarify the influence of workloads under the generator mode. The stages of the simulation include structural analysis of the spiral casing and concrete under load in generator mode, as well as structural analysis of the spiral casing under loads in generator mode without concrete. Both simulations are of major importance. Since the failure of the surface between the turbine, the spiral casing, and the concrete is observed, the effect of the growing contact gap (no contact) is analyzed. The stresses, strains, and displacements of the turbine units are simulated, followed by an analysis for reliability. The conclusions reveal the possible reasons for cracks and destruction in the main elements of the structure.