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Publications (10 of 27) Show all publications
Theocharis, A. & Popov, M. (2017). PV Generator Modelling in EMTP. In: 2017 IEEE SECOND INTERNATIONAL CONFERENCE ON DC MICROGRIDS (ICDCM): . Paper presented at 2nd IEEE International Conference on Direct Current Microgrids (ICDCM), Nurnberg, GERMANY, JUNE 27-29, 2017 (pp. 400-405). IEEE
Open this publication in new window or tab >>PV Generator Modelling in EMTP
2017 (English)In: 2017 IEEE SECOND INTERNATIONAL CONFERENCE ON DC MICROGRIDS (ICDCM), IEEE, 2017, p. 400-405Conference paper, Published paper (Refereed)
Abstract [en]

In this paper, the development of a photovoltaic generator model in EMTP is presented. The model is based on the linearization of the current-voltage nonlinear equations of a PV generator. The model is realized by using standard electrical components and MODELS language in ATP-EMTP. The operational environmental conditions are taken into account and the proposed model is suitable for transients and dynamic power systems studies.

Place, publisher, year, edition, pages
IEEE, 2017
Keywords
ATP-EMTP, photovoltaic systems, power systems dynamics, power systems transients component
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-69651 (URN)000426893200064 ()978-1-5090-4479-5 (ISBN)
Conference
2nd IEEE International Conference on Direct Current Microgrids (ICDCM), Nurnberg, GERMANY, JUNE 27-29, 2017
Available from: 2018-10-18 Created: 2018-10-18 Last updated: 2018-10-18Bibliographically approved
Theocharis, A., Popov, M. & Terzija, V. (2016). Computation of internal voltage distribution in transformer windings by utilizing a voltage distribution factor. Electric power systems research, 138, 11-17
Open this publication in new window or tab >>Computation of internal voltage distribution in transformer windings by utilizing a voltage distribution factor
2016 (English)In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 138, p. 11-17Article in journal (Refereed) Published
Abstract [en]

In this paper, a method for the application of the black-box transformer models to the lumped-parameter transformer winding models is presented. The methodology is based on applying terminal transformer voltages as input parameters that could be provided by using the powerful black box vector fitting. Then, internal voltage distribution is determined by applying a lumped-parameter model approximation. In particular, the paper is focused on the direct computation of the internal voltage distribution, by avoiding a complicated procedure of solving the lumped-parameter winding model. The method is based on the transformation matrix utilization of the voltage distribution factors. This transformation matrix reflects the voltage distribution at specific internal points along the winding with respect to the input terminal voltages. At this stage, the inputs for the lumped-parameters model are provided by measured voltages at transformer terminals and the transformation matrix is determined through geometrical data of the transformer. The implementation of the proposed method with the black-box modeling approach in existing simulation software tools like EMTP is under development. The method is verified by comparing measured with computed waveforms. © 2016 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Computer software; Linear transformations; Mathematical transformations; Matrix algebra; Metadata; Models; Transients; Voltage distribution measurement; Winding, Internal voltage; Lumped parameter modeling; Lumped-parameters models; Over-voltages; Simulation software tools; Transformation matrices; Transformer; Voltage distribution factor, Transformer windings
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kau:diva-63764 (URN)10.1016/j.epsr.2016.01.001 (DOI)000379374300003 ()2-s2.0-84955318226 (Scopus ID)
Available from: 2017-09-18 Created: 2017-09-18 Last updated: 2019-05-27Bibliographically approved
Theocharis, A., Popov, M., Seibold, R., Voss, S. & Eiselt, M. (2015). Analysis of switching effects of vacuum circuit breaker on dry-type foil-winding transformers validated by experiments. IEEE Transactions on Power Delivery, 30(1), 351-359
Open this publication in new window or tab >>Analysis of switching effects of vacuum circuit breaker on dry-type foil-winding transformers validated by experiments
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2015 (English)In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 30, no 1, p. 351-359Article in journal (Refereed) Published
Abstract [en]

In this paper, the prestrike and the restrike effects during switching a vacuum circuit breaker (VCB) connected to a dry-type foil-winding transformer are theoretically and experimentally analyzed. The analysis is conducted by performing a wide range of experimental three-phase switching ON/OFF tests for a 3.75-MVA prototype test transformer connected to a VCB by a cable with different lengths and for different loading conditions. A refined transformer model is successfully applied for the computation of the voltage distribution along the transformer windings. In particular, the winding properties are separately investigated, for which the core influence for frequencies above some tens of kilohertz is studied, and the terminal impedance variation for a broad frequency range is accurately calculated. The simulated results are excellent. Based on these results, an analysis was performed to evaluate the severity of the switching operations by applying spectral analysis of the recorded signals. The statistical analysis of the overvoltages with respect to the cable length and the load value shows that long cables do not guarantee lower overvoltages because of the load and its interaction with the system that makes each case unique. © 2014 IEEE.

Place, publisher, year, edition, pages
IEEE, 2015
Keywords
Cables; Electric transformer testing; Models; Resonance; Spectrum analysis; Switching; Transformer windings; Transients; Winding, Broad frequency range; Over-voltages; Severity factor; Switching operations; Transformer; Transformer modeling; Vacuum circuit breaker; Voltage distribution, Electric circuit breakers
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kau:diva-63766 (URN)10.1109/TPWRD.2014.2327073 (DOI)000348375100040 ()2-s2.0-85027955909 (Scopus ID)
Available from: 2017-09-18 Created: 2017-09-18 Last updated: 2019-05-27Bibliographically approved
Theocharis, A., Popov, M. & Terzija, V. (2015). Computation of internal voltage distribution in transformers windings by utilizing the voltage distribution factor. In: : . Paper presented at International Conference on Power Systems Transient IPST 2015, 5th - 18th of June 2015, Cavtat, Croatia..
Open this publication in new window or tab >>Computation of internal voltage distribution in transformers windings by utilizing the voltage distribution factor
2015 (English)Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kau:diva-64303 (URN)
Conference
International Conference on Power Systems Transient IPST 2015, 5th - 18th of June 2015, Cavtat, Croatia.
Available from: 2017-09-28 Created: 2017-09-28 Last updated: 2019-05-27Bibliographically approved
Theocharis, A. & Pyrgioti, E. C. (2015). Development of a linearized photovoltaic generator model for simulation studies with electromagnetic transient programs. International Transactions on Electrical Energy Systems, 25(3), 454-470
Open this publication in new window or tab >>Development of a linearized photovoltaic generator model for simulation studies with electromagnetic transient programs
2015 (English)In: International Transactions on Electrical Energy Systems, E-ISSN 2050-7038, Vol. 25, no 3, p. 454-470Article in journal (Refereed) Published
Abstract [en]

In this paper, a linearized equivalent electrical circuit of a photovoltaic generator is developed. The proposed model is based on nonlinear and well-tested current-voltage equations which are however used in an alternative mathematical manner. The application of a linearization process, which differs from the well-known piecewise linear scheme and is based on Taylor’s series approximation, leads to uncoupling of the current and voltage quantities in each time step of a digital simulation. Using the proposed equivalent photovoltaic generator circuit, the application of nodal analysis on equivalent resistive circuits derives a photovoltaic system model of linear algebraic equations. This remarkably simplifies photovoltaic systems modeling because one can develop a photovoltaic generator element in electromagnetic transient programs for power systems analysis, of great value to power engineers who are involved in photovoltaic systems modeling. Copyright © 2014 John Wiley & Sons, Ltd.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2015
Keywords
Equivalent circuits; Linear algebra; Linear equations; Linearization; Nonlinear equations; Photovoltaic cells; Piecewise linear techniques; Solar cells; Systems analysis; Transients, Current-voltage equations; Electromagnetic transient program; Electromagnetic transients program (EMTP); Equivalent electrical circuits; Linear algebraic equation; Nonlinear circuit; Photovoltaic power systems; Taylor’s series approximation, Electric network analysis
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kau:diva-63767 (URN)10.1002/etep.1853 (DOI)000351455400005 ()2-s2.0-84925011987 (Scopus ID)
Available from: 2017-09-18 Created: 2017-09-18 Last updated: 2019-05-27Bibliographically approved
Theocharis, A. & Popov, M. (2015). Modelling of foil-type transformer windings for computation of terminal impedance and internal voltage propagation. IET Electric Power Applications, 9(2), 128-137
Open this publication in new window or tab >>Modelling of foil-type transformer windings for computation of terminal impedance and internal voltage propagation
2015 (English)In: IET Electric Power Applications, ISSN 1751-8660, E-ISSN 1751-8679, Vol. 9, no 2, p. 128-137Article in journal (Refereed) Published
Abstract [en]

The goal of this work is to develop an efficient numerical model of foil-type windings. An equivalent lumped-parameter circuit model is presented, which is suitable for the computation of the terminal impedance within a broad frequency range and for internal voltage propagation studies. Owing to the special geometrical winding shape, particular attention has been paid to the calculation of the involved lumped parameters where efficient and accurate formulas for parameter determination are presented. The core influence is investigated for the broad frequency range by taking into account the frequency dependency of core material properties. Simulated results compared to measurements show that the proposed equivalent circuit in combination with the applied formulas for parameter determination can be used with full success for the computation of the terminal impedance and internal voltage distribution studies. © The Institution of Engineering and Technology 2015.

Place, publisher, year, edition, pages
Institution of Engineering and Technology, 2015
Keywords
Coremaking; Transformer windings; Winding, Accurate formulas; Broad frequency range; Equivalent lumped parameters; Frequency dependencies; Lumped parameter; Parameter determination; Simulated results; Terminal impedance, Parameter estimation
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kau:diva-63765 (URN)10.1049/iet-epa.2014.0135 (DOI)000350570400004 ()2-s2.0-84923861615 (Scopus ID)
Available from: 2017-09-18 Created: 2017-09-18 Last updated: 2019-05-27Bibliographically approved
Theocharis, A., Popov, M. & Gustavsen, B. (2013). An EMTP-based Analysis of Transformer Switching Overvoltages. In: : . Paper presented at EEUG Meeting 2013 and European EMTP-ATP Conference. Dublin, Ireland.
Open this publication in new window or tab >>An EMTP-based Analysis of Transformer Switching Overvoltages
2013 (English)Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kau:diva-64304 (URN)
Conference
EEUG Meeting 2013 and European EMTP-ATP Conference. Dublin, Ireland
Available from: 2017-09-28 Created: 2017-09-28 Last updated: 2019-05-27Bibliographically approved
Theocharis, A. & Pyrgioti, E. C. (2013). Electromagnetic transient programs and the photovoltaic input. In: : . Paper presented at 12th International Conference on Environment and Electrical Engineering, ΕΕΕΙC, Poland, 5-8 May 2013. (pp. 346-351). IEEE
Open this publication in new window or tab >>Electromagnetic transient programs and the photovoltaic input
2013 (English)Conference paper, Published paper (Refereed)
Abstract [en]

In this paper, a linearized equivalent electrical circuit of a photovoltaic generator is developed. The application of a linearization process, which differs from the well-known piecewise linear approximation and is based on Taylor’s series scheme, leads to uncoupling of the current and voltage quantities. This uncoupling is represented by a equivalent electrical circuit. Using the proposed equivalent photovoltaic generator circuit, the photovoltaic systems modeling is remarkably simplified. This is because one can develop a photovoltaic generator element in electromagnetic transient programs for photovoltaic power systems transient analysis. © 2013 IEEE.

Place, publisher, year, edition, pages
IEEE, 2013
Keywords
Electromagnetic transient program; Electromagnetic transients program (EMTP); Equivalent electrical circuits; Linearization process; Nonlinear circuit; Photovoltaic power systems; Photovoltaic systems; Piecewise linear approximations, Linearization; Networks (circuits); Photovoltaic cells; Piecewise linear techniques; Solar cells, Transients
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kau:diva-63768 (URN)10.1109/EEEIC.2013.6549540 (DOI)000395539900063 ()2-s2.0-84881426639 (Scopus ID)
Conference
12th International Conference on Environment and Electrical Engineering, ΕΕΕΙC, Poland, 5-8 May 2013.
Available from: 2017-09-18 Created: 2017-09-18 Last updated: 2018-06-04Bibliographically approved
Theocharis, A., Tzinevrakis, A. E., Charalampakos, V. P., Milias-Argitis, J. & Zacharias, T. (2012). Development of a nonlinear geometric transformer model based on an incremental circuit of its magnetic core. Electrical engineering (Berlin. Print), 94(4), 217-232
Open this publication in new window or tab >>Development of a nonlinear geometric transformer model based on an incremental circuit of its magnetic core
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2012 (English)In: Electrical engineering (Berlin. Print), ISSN 0948-7921, E-ISSN 1432-0487, Vol. 94, no 4, p. 217-232Article in journal (Refereed) Published
Abstract [en]

In this paper, the investigation is focused on the topology-based geometric models of power transformers. These models take into account any type of core design, the geometrical characteristics of the magnetic core, and the nonlinear characteristics of the core material. These models differ from each other in the way in which the magnetic part is described. Themethods, which have been proposed for the description of the magnetic part of a power transformer, are based on the conventional magnetic circuit of the core and present disadvantages. In this paper, a new method for the derivation of the differential equations of the magnetic core of the transformer is proposed by introducing a newauxiliary incremental circuit, more easily handled mathematically in antithesis to the conventional magnetic circuit that is used in the literature until now. Specifically, using the proposed circuit one can directly write the differential equations of the magnetic part of the transformer, the coupling between the windings of the transformer is easily calculated, the equations of the electric and the magnetic part are decoupled as well as the state equations of the electrical part can be written in standard form. The proposed method can be combined with anymethodology presented in the literature on the core losses modeling without any restriction. The simulation results show forth that the proposed method of transformer modeling is suitable for transients and power quality studies. Moreover, the proposed method can be a useful tool on sensitivity analysis during the design stage of small and large power transformers as well. © Springer-Verlag 2012.

Keywords
Core design; Core loss; Core material; Design stage; Electrical parts; Geometric models; Geometrical characteristics; Incremental parameters; Large power transformers; Nonlinear characteristics; State equations; Transformer modeling; Transformer models, Coremaking; Differential equations; Electric transformers; Equivalent circuits; Magnetic circuits; Magnetic cores; Power transformers; Time domain analysis, Transformer windings
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kau:diva-63769 (URN)10.1007/s00202-011-0231-5 (DOI)2-s2.0-84870255076 (Scopus ID)
Available from: 2017-09-18 Created: 2017-09-18 Last updated: 2019-05-27Bibliographically approved
Theocharis, A., Olivares-Galvan, J. C. & Zacharias, T. (2012). Eddy-currents modelling in transformers magnetic cores using ohmic resistances. In: 2012 11th International Conference on Environment and Electrical Engineering: . Paper presented at 11th International Conference on Environment and Electrical Engineering, ΕΕΕΙC, Italy, 18-25 May 2012. (pp. 549-554). IEEE
Open this publication in new window or tab >>Eddy-currents modelling in transformers magnetic cores using ohmic resistances
2012 (English)In: 2012 11th International Conference on Environment and Electrical Engineering, IEEE, 2012, p. 549-554Conference paper, Published paper (Refereed)
Abstract [en]

The inclusion of eddy-currents effects in transformers cores is a very hot subject on transformers modeling. The dominated modeling approach is based on the usage of equivalent ohmic resistances placed in the equivalent electrical circuit which represents the electrical part of the transformer. In this paper, a comparison study, between the main different models using ohmic resistances for the eddy-currents in transformers magnetic cores, is conducted. Specifically, the selection of the suitable ohmic resistance, according to the study that is going to be conducted using an appropriate transformer model, is clarified; a topic that has not sufficiently been investigated and presented in the literature. The methods for determination of the ohmic resistances, in the simple case of a single-phase core-type transformer, are presented. Corresponding numerical results are given, which are compared to measured values if possible. © 2012 IEEE.

Place, publisher, year, edition, pages
IEEE, 2012
Keywords
Comparison study; Electrical parts; Equivalent electrical circuits; Modeling approach; Numerical results; Ohmic resistance; Transformer models, Eddy currents; Electric transformers; Electrical engineering; Magnetic cores; Magnetic materials, Ohmic contacts
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kau:diva-63772 (URN)10.1109/EEEIC.2012.6221437 (DOI)2-s2.0-84864225056 (Scopus ID)
Conference
11th International Conference on Environment and Electrical Engineering, ΕΕΕΙC, Italy, 18-25 May 2012.
Available from: 2017-09-18 Created: 2017-09-18 Last updated: 2019-05-27Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-9750-9863

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