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Hydropower generator and power system interaction
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Hydropower)
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 [en]
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: urn:nbn:se:uu:diva-182188ISBN: 978-91-554-8486-6 (print)OAI: oai:DiVA.org:uu-182188DiVA: diva2:558758
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
List of papers
1. Standstill Frequency Response Test on a Synchronous Machine Extended With Damper Bar Measurements
Open this publication in new window or tab >>Standstill Frequency Response Test on a Synchronous Machine Extended With Damper Bar Measurements
2016 (English)In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 31, no 1, 46-56 p.Article in journal (Refereed) Published
Abstract [en]

Standstill Frequency Response (SSFR) test data from a salient-pole synchronous machine with reconfigurable damper winding is presented. In addition to the regular measurements, the damper bar currents are measured and used to obtain the stator-to-damper transfer functions. The test is performed three times with physically different damper winding configurations. An extension to the standard SSFR test analysis scheme is suggested where the stator-to-damper transfer functions are included. The validity of the identified models is substantiated by comparison of the simulated and measured machine response to a drive torque step disturbance. It is found that the damper winding measurements can be incorporated in the analysis scheme to isolate the effect of the damper circuits. However, for a machine of the type studied, also the standard SSFR test produce yields models that are accurate enough for power system studies.

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-182155 (URN)10.1109/TEC.2015.2450994 (DOI)000372024100005 ()
External cooperation:
Available from: 2012-10-04 Created: 2012-10-04 Last updated: 2017-12-07Bibliographically approved
2. Torsional stability of hydropower units under influence of subsynchronous oscillations
Open this publication in new window or tab >>Torsional stability of hydropower units under influence of subsynchronous oscillations
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.

National Category
Energy Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-182150 (URN)10.1109/TPWRS.2013.2263811 (DOI)000326184100032 ()
Available from: 2013-10-17 Created: 2012-10-04 Last updated: 2017-12-07Bibliographically approved
3. Synchronised measurements on hydropower units during power system startup
Open this publication in new window or tab >>Synchronised measurements on hydropower units during power system startup
(English)In: Hydro Review Worldwide, ISSN 1072-9542Article in journal (Refereed) Submitted
Abstract [en]

During a recent full-scale blackstart test of the Nordic power system, measurements of electrical and mechanical quantities using both phasor measurement units (PMUs) and synchronised local acquisition devices was performed. This paper describes the measurement system and discusses a few important considerations for synchronised measurements in multiple hydropower stations. One generator's response to a \unit[100]{MW} load step is shown and an observed subsynchronous oscillation is discussed. It is shown that comprehensive measurements using multiple synchronised data acquisition devices can be performed using off-the-shelf hardware and existing infrastructure. The findings show the danger of assuming that all the interesting information is found at the fundamental frequency.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-182157 (URN)
Available from: 2012-10-04 Created: 2012-10-04 Last updated: 2017-12-07Bibliographically approved
4. Estimation of Hydropower Generator Parameters Through Field Simulations of Standard Tests
Open this publication in new window or tab >>Estimation of Hydropower Generator Parameters Through Field Simulations of Standard Tests
2010 (English)In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 25, no 4, 931-939 p.Article in journal (Refereed) Published
Abstract [en]

Four standard test procedures-the three phase short-circuit test, the field decrement test, the slip test, and the applied voltage test-for estimation of synchronous generator parameters have been implemented in a time-stepping finite-element software. In this paper, the main features of the implementation and the post-processing of data are described. The validity of the application is demonstrated by comparison with test results from the commissioning of a large hydropower generator. The method is shown to be effective in estimating most parameters. Better representation of the exciter and the interpole connections of the damper circuit is believed to enhance the compliance even further.

Keyword
Applied voltage tests, finite-element (FE) methods, parameter estimation, short-circuit tests, slip tests, synchronous generators
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-139402 (URN)10.1109/TEC.2010.2064776 (DOI)000284415900002 ()
Available from: 2010-12-27 Created: 2010-12-23 Last updated: 2017-12-11Bibliographically approved
5. Use of a finite element model for the determination of damping and synchronizing torques of hydroelectric generators
Open this publication in new window or tab >>Use of a finite element model for the determination of damping and synchronizing torques of hydroelectric generators
2013 (English)In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 44, no 1, 844-851 p.Article in journal (Refereed) Published
Abstract [en]

Damping and synchronizing torque coefficients are calculated from time-stepped finite element simulations of a hydroelectric generator connected to an infinite busbar. The calculated torque coefficients are compared to those obtained from two-axis equivalent circuit simulations as well as classical analytical expressions. The influence of the damper winding type, and the size and nature of the system disturbance on the damping and synchronizing torques is explored. It is found that a finite element model of a hydroelectric generator typically exhibits both higher damping and synchronizing properties compared to a two-axis circuit equivalent of the same unit. In particular, the damping and synchronizing contributions from a continuous damper winding are substantially higher in the finite element model than in the equivalent circuit model. Moreover, explicit consideration of dynamic iron losses is found to not affect the damping and synchronizing torques predicted by the finite element model.

Keyword
Damping torque, finite element method, single-machine infinite bus system, synchronizing torque, synchronous machines
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-182158 (URN)10.1016/j.ijepes.2012.08.027 (DOI)000311864800094 ()
Available from: 2012-10-04 Created: 2012-10-04 Last updated: 2017-12-07Bibliographically approved
6. Comparison of field and circuit generator models in single machine infinite bus system simulations
Open this publication in new window or tab >>Comparison of field and circuit generator models in single machine infinite bus system simulations
2010 (English)In: Electrical Machines (ICEM), 2010 XIX International Conference on, 2010Conference paper, Published paper (Refereed)
Abstract [en]

This paper compares the transient response of a finite element salient pole synchronous generator model connected to an infinite network bus to that of a system model based on an equivalent circuit representation of the machine. The characteristics and operating conditions of the two models are made equal as far as possible by thoroughgoing initiation and by using the finite element model for estimation of the circuit model parameters. It is found that the circuit model underestimates the stiffness and damping properties of the machine in comparison with the electromagnetic model, which largely is believed to be attributable to inadequate representation of the rotor circuits. The results raise questions regarding some common applications of equivalent circuit models.

Keyword
damping, equivalent circuits, finite element analysis, rotors, synchronous generators, transient response, circuit generator model, circuit model parameter estimation, electromagnetic model, equivalent circuit representation, field generator model, finite element salient pole synchronous generator model, infinite network bus, machine damping property, machine stiffness property, rotor circuit, single machine infinite bus system simulations
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-140377 (URN)10.1109/ICELMACH.2010.5608259 (DOI)
Conference
XIX International Conference on Electrical Machines (ICEM)
Available from: 2011-01-05 Created: 2011-01-05 Last updated: 2016-04-18
7. Effects of including automatic excitation control in transient field simulations of hydrogenerators
Open this publication in new window or tab >>Effects of including automatic excitation control in transient field simulations of hydrogenerators
2009 (English)In: Proceedings of the 44th International Universities Power Engineering Conference, University of Strathclyde Glasgow, 2009Conference paper, Published paper (Refereed)
Abstract [en]

This paper addresses effects of automatic excitation control in time-stepped finite element analysis of hydroelectric generators. A simple method to incorporate exciter and automatic voltage regulator models in a finite element software is presented and tested on a small hydropower generator connected to a three-phase power system equivalent. Three simulations are performed to demonstrate the impact of the controller and to compare the field voltage and the field current as two possible excitation source variables. It is shown that inclusion of the excitation system greatly enhances the damping of rotor-angle oscillations and that the field voltage should be chosen as source variable to include the transient field winding inductance in the field problem.

Place, publisher, year, edition, pages
University of Strathclyde Glasgow: , 2009
Keyword
Electrical Machines and Drives, Generator dynamics and control 2
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-121652 (URN)
Conference
UPEC 2009
Available from: 2010-03-26 Created: 2010-03-26 Last updated: 2016-04-14Bibliographically approved

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