Numerical fatigue damage analysis of a variable speed Francis pump-turbine during start-up in generating mode

Abstract

Variable speed hydropower units offer a large spectrum of grid regulation services and may therefore contribute to the stability of future power supply systems. Full Size Frequency Converters (FSFC) already found real world application in Pumped Storage Hydropower Plants up to a rated power of 100 MW and are even considered scalable up to a few hundred MW. Apart from the extension of the power range and grid regulation capacities, the FSFC technology also provides new control possibilities during transient operations such as start-up in generating mode. Thus, harsh conditions with damaging impact on the hydromechanical components may be avoided by tuning the operating point trajectory in the start-up phase. In this paper, runner fatigue damage during start-up in generating mode of a 5 MW variable speed Francis pump-turbine prototype equipped with a FSFC is numerically analyzed. The fixed speed solution is compared to a variable speed solution following a BEP tracking control strategy. 1D hydraulic transient simulations provide boundary conditions for detailed 3-D CFD/FEA simulations. Full and reduced numerical domains are used and compared. The overall outcome of the present numerical study indicates an important reduction of partial damages using variable speed drives for turbine start-up manoeuvres.

Online Loss Calculation and Optimization of an M3C-Driven Externally Excited SM

“…Thanks to the speed control possibilities enabled by the FC, soft starts can be realized by avoiding damaging operating ranges. Based on Computational Fluid Dynamics (CFD) simulations and structural Finite Element Analysis (FEA) performed by [15], a fixed speed turbine start-up sequence is compared to the variable speed start-up sequence with hydraulic BEP tracking strategy considered in this paper.…”

“…The main contributions of this paper include the system level efficiency optimization of a PHSP as well as a RT compatible converter loss evaluation. Given the torque and speed references from a hydraulic Best Efficiency Point (BEP) tracking strategy during start-up in turbine mode [15], this work evaluates the overall system efficiency exploiting the machine flux as controllable degree of freedom. To achieve the efficiency optimization, a RT HIL compatible system loss calculation for the M3C using the sub-cycled average model is developed in this work.…”

Optimization of turbine start-up sequence of a full size frequency converter variable speed pump-turbine

“…The runner damage function's aims to minimize the runner's partial damage induced by the start-up sequence. The damage hill-chart has been deduced from one-way coupled FSI simulations using full CFD and FEM models of the pump-turbine, see [9]. The fatigue damage induced on the runner structure by the unsteady pressure fields is expresses in form of a standardized damage rate based on the stress-life approach as detailed in [9].…”

“…The damage hill-chart has been deduced from one-way coupled FSI simulations using full CFD and FEM models of the pump-turbine, see [9]. The fatigue damage induced on the runner structure by the unsteady pressure fields is expresses in form of a standardized damage rate based on the stress-life approach as detailed in [9]. The penstock fatigue function's minimize the penstock pipe wall stress variation induced by the pressure fluctuations in the hydraulic scheme during the transient events, as mentioned in [10].…”