Investigations of Transient Pressure Loading on a High Head Francis Turbine
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
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 emergency shutdown with a transition into total load rejection. Total load rejection is one of the most damaging transient conditions. The amplitudes of unsteady pressure pulsations were significant when the runner accelerated to the runaway speed. Separate measurements at runaway conditions were carried out to investigate the consequences in detail. Investigations of the pressure loading during the steady-state runaway speed are discussed in the sixth publication. The measurements indicated that the blades experience high amplitude pressure pulsations that are more than two times the amplitudes observed for the BEP load. Thus, a high head hydraulic turbine is subjected to high amplitude pressure pulsations during the transients. The unsteady pressure loading can cause fatigue to the blades and affect the runner operating life. The current investigations may contribute to improved runner design to a certain extent. Ideally, the runner should be able to withstand extreme loading without much effect on the operating life and produce increases in the power grid reliability. The current work has been used to initiate a series of workshops, i.e., Francis-99 (www.francis-99.org), beginning in December 2014. The workshops will be jointly organized by LTU and NTNU. During the coming years, the Francis-99 workshops aim to determine the state-of-the-art of high head Francis turbine simulations (flow and structure) under steady and transient operating conditions and promote their development and open knowledge dissemination. The investigations presented in this thesis will be further explored in these workshops. The steady-state measurement data will be discussed in the first workshop scheduled for December 2014.
Place, publisher, year, edition, pages
Luleå tekniska universitet, 2015. , 165 p.
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Fluid Mechanics and Acoustics
Research subject Fluid Mechanics
IdentifiersURN: urn:nbn:se:ltu:diva-17783Local ID: 52ab0392-ba6e-46ae-845e-1d206f8954c3ISBN: 978-91-7583-005-6 (print)ISBN: 978-91-7583-006-3 (electronic)OAI: oai:DiVA.org:ltu-17783DiVA: diva2:990789
Godkänd; 2014; 20140901 (chitri); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Chiragkumar Hasmukhlal Trivedi Ämne: Strömningslära/Fluid Mechanics Avhandling: Investigations of Transient Pressure Loading on a High Head Francis Turbine Opponent: Associate Professor Gabriel Ciocan, Université Laval, Québeck, Canada/project manager ALSTOM Power Hydro, Grenoble Cedex, France Ordförande: Professor Michel Cervantes, Avd för strömningslära och experimentell mekanik, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Tid: Fredag 27 mars kl 09.30 Plats: E246, Luleå tekniska universitet2016-09-292016-09-29Bibliographically approved