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Torsional stability of hydropower units under influence of subsynchronous oscillations
(Hydropower)
(Hydropower)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Hydropower)
2013 (English)In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 28, no 4, 3826-3833 p.Article in journal (Refereed) Published
Abstract [en]

Hydropower units are known to be comparatively insensitive to subsynchronous power oscillations. During a startup test of an electrical island in the Nordic power system, a series capacitor tripped due to a subsynchronous oscillation within the normal frequency range of hydropower unit torsional modes. Since no thermal units were connected, it is motivated to question the traditional view. In this paper, the small-signal and transient torsional mode stability of hydropower units is assessed through time-domain simulations. The model is based on the first IEEE benchmark model for subsynchronous resonance which has been tuned to fit one of the blackstart test system units for which detailed measurements are available. The stability conditions are investigated for several load conditions and machine configurations. It is found that the damping in the startup test system is sufficient to prevent growing oscillations. A fault however could expose the machines to high transient torques.

Place, publisher, year, edition, pages
2013. Vol. 28, no 4, 3826-3833 p.
National Category
Energy Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-182150DOI: 10.1109/TPWRS.2013.2263811ISI: 000326184100032OAI: oai:DiVA.org:uu-182150DiVA: diva2:558589
Available from: 2013-10-17 Created: 2012-10-04 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Hydropower generator and power system interaction
Open this publication in new window or tab >>Hydropower generator and power system interaction
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

After decades of routine operation, the hydropower industry faces new challenges. Large-scale integration of other renewable sources of generation in the power system accentuates the role of hydropower as a regulating resource. At the same time, an extensive reinvestment programme has commenced where many old components and apparatus are being refurbished or replaced. Introduction of new technical solutions in existing power plants requires good systems knowledge and careful consideration. Important tools for research, development and analysis are suitable mathematical models, numerical simulation methods and laboratory equipment. This doctoral thesis is devoted to studies of the electromechanical interaction between hydropower units and the power system. The work encompasses development of mathematical models, empirical methods for system identification, as well as numerical and experimental studies of hydropower generator and power system interaction. Two generator modelling approaches are explored: one based on electromagnetic field theory and the finite element method, and one based on equivalent electric circuits. The finite element model is adapted for single-machine infinite-bus simulations by the addition of a network equivalent, a mechanical equation and a voltage regulator. Transient simulations using both finite element and equivalent circuit models indicate that the finite element model typically overestimates the synchronising and damping properties of the machine. Identification of model parameters is performed both numerically and experimentally. A complete set of equivalent circuit parameters is identified through finite element simulation of standard empirical test methods. Another machine model is identified experimentally through frequency response analysis. An extension to the well-known standstill frequency response (SSFR) test is explored, which involves measurement and analysis of damper winding quantities. The test is found to produce models that are suitable for transient power system analysis. Both experimental and numerical studies show that low resistance of the damper winding interpole connections are vital to achieve high attenuation of rotor angle oscillations. Hydropower generator and power system interaction is also studied experimentally during a full-scale startup test of the Nordic power system, where multiple synchronised data acquisition devices are used for measurement of both electrical and mechanical quantities. Observation of a subsynchronous power oscillation leads to an investigation of the torsional stability of hydropower units. In accordance with previous studies, hydropower units are found to be mechanically resilient to subsynchronous power oscillations. However, like any other generating unit, they are dependent on sufficient electrical and mechanical damping. Two experimentally obtained hydraulic damping coefficients for a large Francis turbine runner are presented in the thesis.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 119 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 978
Keyword
Amortisseur windings, applied voltage test, automatic voltage regulators, damper windings, damping torque, empirical modelling, equivalent circuits, excitation control, finite element method, hydropower generators, power system restoration, power system stability, synchronous machines, self excitation, shaft torque amplification, short circuit test, single machine infinite bus, slip test, standstill frequency response test, subsynchronous oscillations, synchronising torque, synchronous generators, torsional interaction.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-182188 (URN)978-91-554-8486-6 (ISBN)
Public defence
2012-11-16, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2012-10-26 Created: 2012-10-04 Last updated: 2013-01-23

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Bladh, JohanSundqvist, PerLundin, Urban

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