Investigations of Transient Pressure Loading on a High Head Francis Turbine

This doctoral thesis includes six peer-reviewed publications. Beginning with an extensive literature review, this work discusses the study of turbine performance, investigations of the unsteady pressure loading during transient operations, and consequences at runaway speed. The liberalization of the electricity market and the introduction of intermittent power have changed the operating trends for hydraulic turbines. The first publication discusses how the operating trends have changed since 1981. The turbines are subjected to an increased number of transient operations, i.e., load variations, start-stop, and total load rejection. As a consequence, a turbine experiences high amplitude unsteady pressure pulsations during the transients, which significantly affect the runner life. Surprisingly, no investigations specifically on the unsteady pressure loading during the transients have been reported in the literature. The main objective of the current work was to investigate the unsteady pressure loading in a high head hydraulic turbine of the Francis type during transient operations. The test facility and a model Francis turbine available at NTNU were used for these investigations. The turbine was a scale (1:5.1) model of the prototype (head = 377 m, diameter = 1.78 m, power = 110 MW) operating at the Tokke power plant in Norway. The observed head for the model turbine was 12 m at the best efficiency operating point (BEP). The measurements were divided into two categories: (1) steady state and (2) transient. The turbine steady-state performance characteristics and a numerical study are discussed in the second publication. A constant efficiency hill diagram was prepared over the operating range, and the maximum hydraulic efficiency of 93.4% was observed at the BEP. Investigations on transient operation during load variation are discussed in the third publication. Analysis of the acquired pressure data revealed that the blades are subjected to high amplitude unsteady pressure loading. The amplitudes of the pressure pulsations are higher during load rejection than at load acceptance. The fourth publication discusses investigations of the turbine startup and shutdown processes. Two schemes, i.e., rapid and slow, were selected for the guide vane movements. It was observed that the rate of guide vane movement significantly affects the instantaneous amplitude of the pressure fluctuations. The fifth publication discusses the investigations carried out during emergenc