•Cavitation phenomena causes oscillations in bulb turbines with low tailwater level.•Oscillations can be tied to a disturbance on a single runner blade.•Turbine model based on draft tube pressure for ...simulation of oscillations.•Proposed model is validated using real hydro power plant data and measurements.
Generic dynamic models of hydraulic turbines are unable to capture power oscillations phenomena originating from a torque disturbance on a single runner blade. In this paper, an improved dynamic model of a double-regulated hydraulic turbine which takes into account torque oscillations identified from draft tube pressure measurements was presented. It was experimentally identified that specific power oscillations of a bulb turbine operating with low tailwater level can be connected to cavitation-related phenomena on a single runner blade. Furthermore, it was shown that these oscillations do not originate from grid fault-induced resonance between the turbine rotor and generator, nor from the excitation system. The proposed simulation model was validated against measurement data of hydro power plant Dubrava and the validation shows good agreement between measured and simulated results.
The paper introduces, describes and analyses the specific power oscillations in hydroelectric power plant Dubrava that can appear in large bulb turbines operating with low tailwater levels. The ...procedure for the identification of the cause of oscillations is described and it is experimentally shown that the cause of power oscillations is a disturbance on a specific runner blade. The physical background of the cavitation-related phenomena that causes these oscillations is presented. Furthermore, it is shown that neither the automatic voltage regulator nor the transmission network disturbance is the source of oscillations, while the power system stabiliser can only partially damp them. Power oscillations reduce the average power output due to the operation in the unsteady output zone. These oscillations can cause damage to the equipment and reduce its lifespan. The effectiveness of various measures for treatment of these oscillations is discussed. A simple model for simulation of these oscillations is shown and verified against measurements.
Mathematical and simulation models enable hydroelectric power unit dynamic behavior analysis using computers. To approximate the power unit dynamics as accurate as possible, nonlinear high-order ...model is required. This paper describes a hydroelectric power unit with double regulated Kaplan turbine. The runners of such turbines permit the blades angle to be varied on the run depending on operating conditions. This ensures maximum turbine efficiency under all operating conditions. Detailed mathematical and digital simulation model of the hydroelectric power unit with double regulated turbine was presented for turbine control system analysis. Simulation model developed for Varazdin HPP (power unit 1) is verified by several comparisons with real measurement results.
Synchronous generator theory has been known since the beginning of its use, but the modelling and analysis of synchronous generators is still very existent in the present-day. Modern digital ...computers enable development of detailed simulation models, thus individual power system elements, including synchronous generators, are represented by the highest degree order models in power system simulation software packages. In this paper, first, a detailed mathematical model of a synchronous generator is described. Then, a simulation model of a synchronous generator developed based on the presented mathematical model. Finally, a transient stability after a short-circuit is simulated using real generator parameters.
Maintenance of the power generating facilities in due time is essential for reliable and secure operation of the electric power system. In liberalized electricity market the economical aspects, ...pointed to the greatest possible revenue, have to be satisfied. On the other hand, technical aspects, which keep the power system above the desired level of safety and reliability, i.e. which are opposed to economical aspects, have to be satisfied as well. Therefore, these two opponent standpoints have to be confronted in order to provide optimal solution which will comply with the strict technical limitations, and which will meet investor's economical requirements. This paper addresses the problem of obtaining the optimal maintenance schedule of hydro generating units. For this purpose, the paper discusses the mathematical programming method - Benders decomposition. After a brief description of the mathematical method, the application of the Benders decomposition on three Croatian hydroelectric power plants in a cascade on the Drava River is carried out.Original Abstract: Pravovremeno odrzavanje proizvodnih postrojenja od iznimne je vaznosti za pouzdan i siguran pogon elektroenergetskog sustava. U uvjetima liberaliziranog trzista elektricne energije ekonomski aspekti, orijentirani na najvecu mogucu dobit, moraju biti zadovoljeni. S druge strane, i tehnicki aspekti, kojima je cilj odrzati elektroenergetski sustav iznad zeljenih granica sigumosti i pouzdanosti, odnosno koji su protivni ekonomskim ciljevima, takoder moraju biti zadovoljeni. Stoga se dva suprotna gledista sukobljavaju u svrhu pronalaska optimalnog rjesenja koje ce zadovoljiti sve tehnicke kriterije i investitora u ekonomskom pogledu. U radu se obraduje problem pronalazenja optimalnog rasporeda odrzavanja hidrogeneratora. U tu svrhu se koristi metoda matematickog programiranja - Bendersova dekompozicija. Nakon kratkog opisa matematicke metode, iznesena je primjena Bendersove dekompozicije na tri hrvatske hidroelektrane u nizu na rijeci Dravi.
Because of many different instability reasons, power unit stability problems should be analyzed in details for each specific case. This paper describes a specific case of power oscillations problem ...of hydroelectric power unit with double regulated bulb turbine. In some working conditions, natural frequency of electromechanical oscillations could be close to the rotor speed frequency and small disturbance on turbine would be amplified few times because of electromechanical resonance. Influence of operating conditions on natural frequency is analyzed using mathematical model of synchronous machine with excitation system. Simulation model results show that natural frequency decreases significantly with active power increase and near maximum active power becomes close enough to the rotor speed frequency to enter resonance mode.
This paper analyses solutions for optimal bidding for hydro units operating in simultaneous markets for energy and ancillary services and decision making process for plant refurbishment and ...generating capacity upgrade. Methodology based on the Decision Theory will be applied to identify the optimal solutions which minimize the expected costs and the related risks. The proposed methodology will be demonstrated for a real hydropower plant in Croatia (Varazdin HPP) which will be refurbished.
Pravovremeno održavanje proizvodnih postrojenja od iznimne je važnosti za pouzdan i siguran pogon elektroenergetskog sustava. U uvjetima liberaliziranog tržišta električne energije ekonomski aspekti, ...orijentirani na najveću moguću dobit, moraju biti zadovoljeni. S druge strane, i tehnički aspekti, kojima je cilj održati elektroenergetski sustav iznad željenih granica sigurnosti i pouzdanosti, odnosno koji su protivni ekonomskim ciljevima, također moraju biti zadovoljeni. Stoga se dva suprotna gledišta sukobljavaju u svrhu pronalaska optimalnog rješenja koje će zadovoljiti sve tehničke kriterije i investitora u ekonomskom pogledu. U radu se obrađuje problem pronalaženja optimalnog rasporeda održavanja hidrogeneratora. U tu svrhu se koristi metoda matematičkog programiranja – Bendersova dekompozicija. Nakon kratkog opisa matematičke metode, iznesena je primjena Bendersove dekompozicije na tri hrvatske hidroelektrane u nizu na rijeci Dravi.
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