Investigation of Variable Speed Technology when Converting Hydropower Kaplan Turbines into Fixed Propeller Turbines

Abstract: With an evolving energy system, an increased flexibility is necessary, placing additional demand on hydropower plants. New technology, in particular full size frequency converters (FSFC) and doubly fed induction machines (DFIM), allows hydropower turbines to run at different speeds than originally designed, thus making the turbine more flexible. The Kaplan turbine is a common turbine with adjustable runner blades. Unfortunately, because of this design, mechanical failures are known to occur and if left untreated it could cause total turbine failure. In the industry, one solution used to avoid this is to lock the runner blades in one position. This master thesis investigates implementation of variable speed technology, in combination with locking the runner blades, thereby converting the turbines to variable speed fixed turbines. Two different Kaplan turbines were investigated, and operation parameters were simulated to determine how to operate the turbines for maximum electricity production. Additionally, for one of the turbines (K1), measurements were done on site to find out how the turbine is currently operated. In the results, combinations of parameters to use for maximum electricity production are presented. The results revealed that for K1, the runner blades should be locked at an angle of 9.5° and combined with variable speed technology to maximize electricity production. When compared to ordinary operation, the annual production increased slightly, from 34.72 GWh to 35.32 GWh.