Author(s): Carlos Miguel-Espinar; Rafel Roig; Oriol Gomis-Bellmunt; Xavier Escaler

Linked Author(s):

Keywords: Co-simulation; Eccentricity; Finite Element Analysis; Kaplan Turbine; Synchronous Generator

Abstract: Over the last years, the increasing demand for clean generation sources has increased interest in renewable energies such as wind, solar, and hydropower. One of the main reasons is to reduce CO2 offset payments due to the last EU policies. Nonetheless, electricity generation in the current energy context makes renewable energies to be running intermittently and unpredictably. Hydropower plants can use stored hydraulic energy to provide baseload and be switched off and powered up quickly to accommodate the fluctuating electricity demand. However, this framework does hydro work out of their best efficiency points which lower their performance and adds structural problems like undesirable vibrations. Hence, according to the current grid system's needs, such as peak load and flexibility, hydropower generators are expected to play a vital role in the future integrated EU energy market. One common negative consequence of such operation in the electromagnetic and mechanical behaviour is the Unbalanced Magnetic Pulls (UMPs) caused by an asymmetric air gap flux distribution around the rotor due to an off-centred rotor movement. Some authors have studied the possibility to neutralise these effects with active methods. For example, Lundin et al. proposed an active compensation system to monitor uneven air gaps and mitigate UMPs between the rotor and stator through unbalanced rotor forces. This paper proposes a numerical investigation of the consequences of a rotor eccentricity movement on the electromagnetic and structural domains through a co-simulation framework of a full scale 10 MW Kaplan turbine. In particular, the air gap flux density, electrical voltage and current in the stator windings, and surface forces in the rotor will be simulated. Subsequently, these results will be used to investigate their effects on the turbine rotor's structural response and estimate the induced deformations and stresses. A finite element model (FEM) has been set up for the synchronous electromagnetic generator using ANSYS-Maxwell, and the turbine rotor using ANSYS-Structural to accomplish the article's objective. Different simulation conditions in the time and frequency domains will be employed to analyse the results derived from the coupled interactions between the electromagnetic field and the structural deformation. The analysis will evaluate from no-load to full-load operating conditions, pointing out the off-design ones.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022974

Year: 2022