Modeling Of Power System Components During

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IJISET - International Journal of Innovative Science, Engineering & Technology, Vol. 1 Issue 10, December 2014.www.ijiset.comISSN 2348 – 7968Modeling of Power System Components DuringElectromagnetic TransientsPaweł Sowa, 2Rafał Kumala and 3Katarzyna Łuszcz11, 2 ,3Faculty of Electrical Engineering, Silesian University of Technology/Institute of Power Systems and ControlsGliwice, 44-100/ Silesia, PolandAbstractThis paper presents a practical approach to electromagnetictransient study. After describing many cases of simulations themodeling requirements for selected power system elements areshown. In this paper, there are also compared the results ofinvestigations on correct and incorrect power system modelsduring electromagnetic transients.Keywords: electromagnetic transients, power system modeling,model requirements.1. IntroductionThe modeling of modern power systems is the first andmost important step during the analysis of disturbancetransients. The main idea of modeling is to highlight thesignificant features of the investigated element from thespecified phenomena point of view. Due to it, the workconnected with the analysis of the research results isaccelerated and facilitated.Selected elements designed for modeling should beassigned to appropriate replacement schemes [1, 4]. At thesame time it is important to remember that, during theprocess of creating those schemes there should be takeninto account only those parameters that are important fromthe analyzed phenomena point of view.Proper selection of system elements is the essence of goodmodeling of those components whose models will becreated. This is a very important aspect that should betaken into account because of the huge number anddiversity of elements that appears in the contemporarypower systems.Another important aspect is the mapping of real functionalconnections occurring while creating models. It is alsovery important to remember that describing the analyzedelements with use of complex mathematical functions and,at the same time, using very simple models for theneighboring elements is incorrect. The most difficult taskwhen constructing models of the power system is to find abalance between the simplicity of the model and the bestrepresentation of real parameters of a given element.The next stage after the modeling during the process ofanalyzing the effects of disturbances is to carry outappropriate analyzes of simulation, which should allow forresearch of the dynamics and properties of the receivedwaveform changes.In practice, due to a very long duration time of particulartransient phenomena, the analysis of disturbance has to bedone in a narrow time interval. Assuming an appropriatecalculation step and time duration of the simulation, it ispossible to find hot spots in the test system in a preciseway. Fig. 1 shows the way of analyzing theelectromagnetic transients and creating the models ofelements in the power system.Identification of the problemChoice of the system componentsCreation of the models(replacement scheme mathematicaldescription)Preparation of the simulation(step calculation, calculation time, thechoice of parameters)Analysis and/or verification of the resultsFig. 1. Idea of the electromagnetic transient analysisToday there are many types of EMTP software. Asa matter of fact, almost all of them have been repeatedlyverified in a two ways - by the comparison of the resultsobtained from different programs, and also with the datafrom real objects [3, 5]. For the purpose of this paper therewas used the most popular simulation program which isEMTP-ATP (Electromagnetic Transients Program Alternative Transients Program).715

IJISET - International Journal of Innovative Science, Engineering & Technology, Vol. 1 Issue 10, December 2014.www.ijiset.comISSN 2348 – 7968In the further part of this paper there are given therecommendations for the proper modeling of selectedsystem components. In addition, the results of the analysisof how the model affects the quality of transientdisturbances in the real network system during thesimulation are presented.Open/closeoperationsLightning1)2. Representation of models of selected powersystem elementsIn real systems, the analysis of various types of transientphenomena is complex. That is why simulation models areused. To illustrate the methodology of the process shownin Fig. 1 an attempt was made to focus on the analysis anddescription of the most common models of elements whichappear in power system. These elements are: power transformers, power overhead lines and cables, synchronous generators, induction machines.It is obvious that the studies for other elements of thepower system are performed. However, it should be notedthat they less affect the accuracy of mapping the actualstate of the tested network system. In order to create acorrect representation of the models that are used in theprocess of simulation, in the first step there should beselected the right parameters and in the next step thereshould be determined the appropriate operating conditions.For the elements mentioned above there was performedthe analysis of different types of disturbances, such as: symmetrical and asymmetrical short circuit in thetransmission lines and busbars,switching of unloaded transmission lines,lightning strike to the lightning conductors andworking and supporting structures,start up of high power asynchronous motors andinfluence of ground short circuit on the mainbusbars on operation of these machines (severalMW),start-up and loss of excitation generatorsModel requirements/featuresSimple model - Sr , Xr , Rr(uRr , uXr ) parameters 2)Open/closeoperationsAs above magnetic corecharacteristicsTable 3:Requirements for the induction machines during theelectromagnetic transientsType of the studyModel requirements/featuresThe most important parameter: ILR / IrShort-circuitDynamic motor startinganalysis during startand load impact/rampLoad characteristic model, kind of thestart mode , operation mode of motorVoltage dropAs above include reactors modellocated to machine 3) and cableconnection with significant length 4)3)the value of reactor impedance is important (particularly for reactorswith uKR 4 %) located to the two next nodes (bus)4)for cables with length above 100 m (it is particularly important for lowvoltage networks)Table 4: Requirements for the synchronous generators during theelectromagnetic transientsType of the studyShort-circuitDynamic motorstarting analysisduring start andload impact/rampModel requirements/featuresSingle block model, frequency depends (Marti/Noda)Type of the studyOpen/closeoperations2)if uRr is unknown, it is possible to determine this parameter based onratio X/R and parameter Sr (e.g. IEEE St. C57.12.10-2010 [8])Table 1: Requirements for the models of lines and cables during theelectromagnetic transientsShort-circuitif the surge arrester model is representativeTable 2: Requirements for the models of transformers during theelectromagnetic transientsBased on those analysis, the requirements for the systemelement models listed in the following tables were defined.Marking of electrical characteristics is consistent with thestandard IEC 60909-0 and IEC 60909-1 [6, 7].Type of thestudySingle block model, frequency depends (Marti/Noda), capacity and inductance of “neighbors”- very important7 segments on both sides, frequency depends(Marti/ Noda), pole model: complex(for H 30 m), surge arrester model - yes,insulator model - not necessary 1)Model requirements/featuresThe most important parameter: ILR / Ir1st type of faults 5): the most importantparameters - X”d and Sr (simple model)2nd type of faults 6): as above includearmature resistance Ra, stator and rotorwinding and dumping circuits (complexmodel) - represent by suitable timeconstants in d and q axisLoad dump andramp, voltagechanges, lossexcitation, startmodeLoad characteristic, type of generatorregulator (which parameters arecontrolled), type of excitationIsland modeAs above include power protection timesettings and sequence of close/openoperation5)for remote faults6)for close faults716

IJISET - International Journal of Innovative Science, Engineering & Technology, Vol. 1 Issue 10, December 2014.www.ijiset.comISSN 2348 – 79683. Analysis of impact of models on selectedelectromagnetic transient phenomenaFor the purposes of this paper, the most commonly types ofdisturbances occurring in a modern power system wereexamined. The system components which influence thesystem operation in the deciding way were analyzed. Theresults of the analysis are summarized in Tables 1 to 4 (seeSection 2). The investigations were performed for the realpart of the power system. The most important elements ofthe modeled system during electromagnetic transientinclude:- model of the asynchronous machine with theconstant Ig / Ir values regardless of the powerrating,- model of the transformer without the activecomponent of voltage during the short circuit. monorail lines 220 kV with lengths from severalseveral tens of kilometers, block transformers and synchronous generatorswith power ratings of at least 190 MVA, asynchronous machines of high power(above 2.9 MW).As an example which shows the effect of the propermodels selection of the system, there was chosen a skewthree-phase short circuit at the end of the 220 kV lines witha length about 92 km (Line1). The final transientswaveforms were observed on the BUS 14 220 kV.The total duration time of the simulation in this case wastdot 0.3 s. The analyzed fragment of the network system isshown in Fig. 2.For the assumed short-circuit interference two cases werecompared: structure with the properly chosen models ofselected elements of system components (labeledas JM), i.e.:- power lines represented by the model dependenton frequency (Marti with a suitably selectedfrequency range [2]),- model of the synchronous machine in whichthere is taken into account the resistance of thearmature and the time constants in the d and qaxis,- model of the asynchronous machine with thereal Ig / Ir values depending on the power rating,- model of the transformer with the activecomponent of voltage during the short circuit, structure with the wrongly chosen models ofselected elements of system components (labeledas BE), i.e.:- power lines represented by the model withlumped parameters (Bergeron),- model of the synchronous machine without theresistance of the armature and the time constantsin the d and q axis,Fig. 2. Part of the analysis network - fault at the BUS 14.During the analyzed type of short circuit the instantaneouswaveforms of currents and voltages were verified. Figures3 and 4 show the mentioned waveforms for the JM model.The corresponding waveforms for the BE model are shownin Figs. 5 and 6. To show precisely the differences in thedynamics of the waveforms of currents and voltages inFigs. 3 to 6, they are presented for t 0.1 s.Fig. 3. Current transient for the JM modelFig.4. Voltage transient for the JM model717

IJISET - International Journal of Innovative Science, Engineering & Technology, Vol. 1 Issue 10, December 2014.www.ijiset.comISSN 2348 – 7968Fig. 5. Current transient for the BE modelcharacteristics for the selected group of the power systemelements. In many cases, the power rating of the elementand the voltage level have a huge impact on the structureof the model. Therefore before the creation of models forthe analysis of electromagnetic transients, the deep analysisof the problem has to be carried out. Also the properselection of the time interval for which the givenphenomena will be analyzed is extremely important. Asshown in the example of non-simultaneous three-phaseshort-circuit for a 220 kV line in a real system, an incorrectchoice of models of system components causes:Fig. 6. Voltage transient for the BE model- obtaining wrong values of the analyzed electricalquantities (for the analyzed case, the biggest error of theinstantaneous value of current exceeded 177% and in thevoltage was about 5%),In order to determine the difference between the results in aaccurate way, specified the maximum of the instantaneouscurrent and voltage values, and the total duration time ofthe electromagnetic transients for both models. The resultsare summarized in Table 5.Tabel 5: Comparision of selected electromagnetic transient parametersfor JM and BE modelsParameter umax , kVimax , kAtmax , sType of model ---JM351.5317.210.1BE369.7930.580.3Difference 5.19%177.69%300%umax - maxium value of the voltage transientimax - maxium value of the current transienttmax - maximum duration time of the transient- distortion of instantaneous waveforms - "falsification"dynamics of the trajectory,- "artificial" increasing the duration time of the transient.The biggest problem is always to determine the negativeimpact of incorrect choice of models. It is impossible toestimate at the beginning of whole process whether thewrong model is the result of an increase or decrease in theinstantaneous amplitude value waveforms, and how itinfluences the decay time of the oscillations.Optimally created models of the power system should be acompromise between the simplicity of the structure of theequivalent circuit (a mathematical description of themodel) and the precision of mapping the most significantfeatures of the selected element.References4. ConclusionsDevelopment of the appropriate power system modelsduring the electromagnetic transient analysis is the mostimportant activity in the modeling process. Besides theproper determination of the real element parameters whichshould reflect the model, one should remember that someof the parameters are dependent on frequency. This is veryimportant in the case of phenomena for which thefrequency is expected to change in a wide range (generatorisland mode, frequency start-up motors especially forpower more than 1 MW, etc.).Determining universal models of the elements, dependingon the investigated phenomena, creates a difficulty in themodeling process. The authors tried to unify selectedmodels of the power system during testing various types ofelectromagnetic transients. Recommendations featured inTables 1 to 4, have to be considered as a starting point, notas the only right approach. It is impossible to define auniversal model which will take into account all the[1] Sowa P., “Dynamic equivalents for the electromagnetictransients”, Wydawnictwo Politechniki Śląskiej, Gliwice 2011.[2] Marti J. R., “Accurate modelling of frequency-dependenttransmission lines in electromagnetic transient simulations”,IEEE Transactions on Power Apparatus and Systems, Vol. PAS101(1), 1982.[3] Kumala R., Sowa P., “Intersystem faults in the coupledhigh-voltage line working on the same tower construction”, XIIMiędzynarodowa Konferencja Naukowo - TechnicznaPrognozowanie w elektroenergetyce - PE 2013, Przeglądelektrotechniczny 4/2014,141-144.[4] Sowa P., Łuszcz K., “Equivalent for ElectromagneticTransient Calculation in Power System with MultipleTransmission Line”, Energy and Power Engineering, 2013,1449-1455.[5] Hevia Orlando P., “Alternative Transients ProgramComparison of transmission line models”, Can/Am EMTP News- Voice of the Canadian/American EMTP User Group, Vol. 98-1,January 1998.[6] IEC 60909-0, “Short-circuit currents in three-phase a c.systems - Calculation of currents”, First edition, 2001.718

IJISET - International Journal of Innovative Science, Engineering & Technology, Vol. 1 Issue 10, December 2014.www.ijiset.comISSN 2348 – 7968[7] IEC 60909-1, “Short-circuit currents in three-phase a c.systems - Factors for the calculation of short-circuit currentsaccording to IEC 60909-0”, Second edition, 2002.[8] IEEE St. C57.12., “IEEE Standard for General Requirementsfor Liquid-Immersed Distribution”, Power, and RegulatingTransformers. First edition, 2000.First Author Graduated from Silesian University of Technology inGliwice Dean of the Faculty of Electrical Engineering, Director of theInstitute of Power Systems and Control, Silesian University ofTechnology.Specialist in power engineering, power system modelling, and transientelectromagnetic phenomena. Author of nearly 200 scientificpublications.Second Author Fourth year PhD student in Silesian University ofTechnology at Faculty of Electrical Engineering, current research andinterests: multi-voltage lines, electromagnetic transients, intersystemfaults, power plant design.Third Author Fifth year PhD student in Silesian University ofTechnology at Faculty of Electrical Engineering, current research andinterests: thermovision diagnostic, modeling and analysis of operatingconditions in selected power systems, ferroresonance in transformers.719

standard IEC 60909-0 and IEC 60909-1 [6, 7]. Table 1: Requirements for the models of lines and cables during the electromagnetic transients . Type of the study Model requirements/features Short-circuit . Single block model

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