Experimental Investigation of Repurposed Kaplan Turbines as Variable-Speed Propellers for Maximizing Frequency Containment Reserve

TL;DR

This work compares two retrofit approaches to enhance Frequency Containment Reserve (FCR) in Run-of-River Kaplan turbines: (i) retrofitting the unit with a full-size frequency converter for Variable-Speed (VARspeed) operation with fixed blade angles, and (ii) hybridizing the same turbine with a Battery Energy Storage System (BESS). Using a 1:20 reduced-scale Kaplan model on an advanced grid-emulated testing platform, the authors perform 12-hour experiments under identical grid scenarios to evaluate FCR quality, wear, and hydraulic/global efficiency, aided by a data-driven efficiency meta-model and CAM curves. The results show that both approaches improve FCR quality and substantially reduce blade servomotor wear, with VARspeed achieving complete blade-stationarity and BESS hybridization delivering the strongest FCR tracking gains; however, VARspeed can reduce global efficiency due to converter losses and its benefits are operating-point dependent. The study highlights that the choice between VARspeed retrofit and BESS hybridization should be asset-condition dependent and points to future work on detailed economic feasibility to guide CAPEX investments for aging RoR HPP assets.

Abstract

This study explores the practical viability of repurposing aging Kaplan turbines into variable-speed propellers by employing full-size frequency converters. The motivation behind this approach is to improve the provision of \emph{Frequency Containment Reserve} (FCR) while reducing fatigue in the Kaplan blades servomechanism. We evaluate the performance of these modified Kaplan turbines against the one of another hydro asset composed of the same Kaplan turbine hybridized with a \emph{Battery Energy Storage System} (BESS). Experiments are conducted on a one-of-its-kind reduced-scale model testing platform. Our findings reveal that Kaplan turbines repurposed as variable-speed propellers exhibit similar dynamic response characteristics compared to the standalone Kaplan operation, with the added benefit of effectively eliminating blade movements. Furthermore, the ability to control the speed increases the hydraulic efficiency for certain operating points. In summary, investment in variable speed technology emerges as a viable alternative to BESS-based hydropower hybridization.

Figures (8)

• Figure 1: Schematics of the PTMH PF3 power grid in different operating modes
• Figure 2: HBM strain gauge on the connecting rod of one blade of the Kaplan Turbine
• Figure 3: Frequency Time Series for the test. Measurement from SwissGrid during the system split of the 8th of January 2021 ics_investigation_expert_panel_continental_2021
• Figure 4: CAM Curves and expected efficiency for the Kaplan runner for a constant head $H= 10m$ and a fixed speed of $n=1500\min^{-1}$
• Figure 5: Efficiency hill-chart and speed CAM of the VARspeed propeller with RBA = 18°