gui based per-unit representation of power system with

7/29/2019 GUI Based Per-Unit Representation of Power System With

http://slidepdf.com/reader/full/gui-based-per-unit-representation-of-power-system-with 1/5

Student Conference on Research and Development {SCOReD) 2003 Proceedings, Putrajaya, Malaysia

A GUI Based Per-Unit R epresentation of Power System withSymmetrical Components:* An E-L earningApproach

Marizan Sulaimanand Zainuddin Mat IsaFaculty of Electrical Engineering

Kolej Universiti Teknikal Kebangsaan MalaysiaEmail: mar~zar ~(i r~ku iktn.etlu.ni ~.z;~ii ~uddi ~~(i ir kutk~i i .~~t~.~i i ly

Abstract: Every textbook on power system analysis

discusses the per-unit system, varying in depth withproblems and solutions.. However, it is still not aninteractive method for teaching and learning the per-unit representation. Thus, it needs a new approach to

make teaching and leaming process more interactiveand interesting for students. The Graphical UserInterface (GUI) provides the user with interactive

- visual communication to analyze the power systems.This paper presents the GUI based per-unitrepresentation of power systems with symmetrical

components in the Visual Basic ( VB) environment,The software allows the user to draw the single linediagram representingthe power system with ratings ofeach component. l h s GU1 based per-unit system isdeveloped for the teaching and learning environmentof the power systemanalysis. The user can make useof this interactive software to calculate the per-unitimpedance with respect to the system common M VAbase, The reactance diagram of the three sequenceimpedances, namely,' the zero-, positive-, andnegative- sequence impedances, can be drawn eithermanually or automatically. It is hoped that this GUTsoftware will enhance the learningprocess andmake itmore interactive, interesting and user friendly.

. .K eywordsGraphical User Interface (GUI), Expert System,Power Engineering Education, Per-UnitRepresentation,Power System Analysis.

1. INTRODUCTION

Many students have difficulty on understandingthe concepts and mastering the analytical skillsrequired in their first course in power systems. Thisbecomes apparent in subsequent courses when thestudents falter in app1ying those concepts and skills to

the design, model and analysis power system. Theylose interest in power system and will result in adecrease in enrollment. The project featured in thispaper is aimed at the development of educationalsoftware tohelp students to understand more on powersystem analysis with symmetricaI components. Thesoftware package i s developed to help students tolearn and make the subject more interesting. Theinteractive and comprehensive software supplements

0-7803-8173-4/03/$17.0002003 EEE.

and enhances the Iearning process in the classroom. as

well as in the student's self-study.

11. POWER SYSTEM MODELING

Power system is a complicated electrical network.Therefore, it is necessary to create an equivalentrepresentation as a model of practical diagram that iseasier toread, understand and analysis.

A. Single-L ineDiagram

'

Single-linediagramisa simplified diagram whichdrawn by omitting the circuit line to neutra1,indicating the components by standard symbols ratherthan by their equivalent circuits [1,5-7]. It shows by asingle line representation and standard symbols howthe transmission lines and associated apparatus of anelectrical system are connected together. The purposeof this single-line diagram is to show importantinfomation of power system networks in a moresimplified and conipact form. It also will showlocation and connection between generator,transformer, transmission line, motor, static load,circuit breaker, reactor and different switch using their

ownstandard

symbol [1,5-71.'

E. ImpedanceDiagram

An impedance diagram is used to draw a single-

phase o f per-phase equivalent circuit o f the systemand it can be used to czlculate performance of thesystem under load conditionorupon the occurrenceofa fault. The impedance diagram is very usefuI in

power system analysis because all circuit parametersare always been given in per-unit scale. Standardnetwork analysis is used to analyze impedancediagram due to the changing of voltage Jevels incalculating the per-unit quantity. Resistance is oftenomitted when making fault calculations, even in

computer progmms, These small values of resistance(less than 0.1 percent) [1,5-6] compared to thereactanceof generator and transformerand sometimestransmission line, will not affect the result of

calculation. The omission of this resistance willchange the impedance diagram to the reactancediagram.

257



C. Per-Unit System

The solution of interconnected power systemhaving several different voltage levels requires t he

cumbersome transformation of all impedances to asingleMVA system. In this way, all reactance in this

system can be expressed as a percent or per unit Amnimum of four base quantities. i s required to

completely define a per-unit system: volt-ampere,voltage, current and impedance. Selected MVAe ischosen from the biggest available in the system andusually at generation part. Base current and baseimpedance are then calculated from SBand VB andmust obey t he circuit laws 11-81.

Thenew irripedance can be calculated fromthe change of impedance referred to the old system isgivenby

Component

D SymmetricalComponents

The method o f symmehical components wasintroduced by Fortescue [I-81 in 1918and had been

, improved by Wanger and Evans in 1993 [1,5].

According to Fortescue's theorem, three unbalancedphasors of a three-phase system can be resolved intothree balanced systems of phasors. The balanced setsof components are positive-, negative- and zeru-

sequence asshowninTable 1 .

Table1. Symmetrical Component~ ~- I Phase

Diagramriteria

Positive-sequence

- a-b-c sequence

- Samemagnitude- Phase different.

120" , V,

I I1 - a-c-bsequence I "*- Same magnitude,- Phase different

egative-sequence

120"Vd

- Samemagnitude- Phasedifferent0" ""

Zero-sequence

-c Vd,

i. The Symmetrical ComponentsofUnsymmetricalPhasor

With reference to Figure 1 and by substitutingrelated formulas (reference [ ]), the phase voltage andcurrent capbeexpressed inmatrix formas below:

. .

The sequence voltage and current can be obtain byinversing the phase voltage and current and can bederive in matrix formasbelow:

(4)

where, a = 1L120"= -0.5+j0.866 is operator of

symmetrical components. These equations show howto resolve three unsymmetrical phasors into theirsymmetrical components. The neutral currentequation for generator and motor can be expressed asbelow

ii . SequenceNetworks for Generator andMotor

In general, the equation for phase voltages of

generator ormotor can be derived as below [1,4-6]

where E, =E,{ and - sign for generator; on the otherhand, E, =E,, and-I- ignformotor.

iii. Zero-Sequence Networks for Three PhaseTransformers

The positive- and negative- sequence networks

arc the same for three-phase transformer but differ forzero- sequence where connections between primary

258



and secondary depend on wye, grounded wye anddeltu configurations[1 . .

111. SOFTWARE DEVELOPMENT TOOL

A Windows based Graphical User Interface(GUI)software tool was developed to facilitate the teachingand learningof power system This software is written

in M icrosoft Visual Basic 6.0(VB) which i s knownasone of the best Windows programming tools becauseof its' coding environment. Hence, VB can be used todevelop many Windows based applications from thesimplest to thecomplicated ones.

The main advantage of VI3 is the combinationbetween graphical visual programming and codeprogramming. That is to- say, the visual descriptionofthe application can be seen on the development anddesign process. Therefore, the application criteria suchas size, color, interface and position of eachcomponent can be decided before the coding iscreated. The programmer can also use standard built-in functions or can make a little modification of these

functions dependingupon the applications; thismakesVB a choice to create high quality and professionalapplications. Besides, Vl3 is easy to leam and moref un rather than Usi ng other programming languageeither FOTRAN orC++

IV. IM PLEM ENTATION SOFTWARE

In generally, this softwarecanbe divided into fewmain parts or steps that user must followed tocomplete the analysis of power system. The first partis to draw a singleline diagram. With interactive GUI,user can draw corresponding singleline diagram byselecting t he graphical menu that represent thecommon power system symbols. User can choosewhich. User can choose graphical menus using mouse

and then place it at the white canvas to create acomplete single-line diagram. The value of componentsuch as vol tage and impedance can be entered afteruser placed the selected componenton canvas and thisvalue can be change from time to time. Fig. 3 showsthe example of s ingl e- l i ne diagram created by thissoftware.

The user can also rotate the selected componenton canvas to 90', 180' or 270' by pressed CTL+ Rkeys. Selected component can also be moved or drag

from one place to another to place it at a suitableposition just by pressed the left mouse button andwithout released it, move the mouse cursor around lhecanvas. When user release mouse button, the selected

component will be moved to new position dependingon position of mouse cursor. The second part is tocalculate or convert the impedance value of every

component to per unit value. Themain window forper-unit calculation is shown' in Fig. 4. User canaccess this window by choosing "V iew" menu fromsingle-line diagram window.

Fig. 3.Single Line Diagram

This window allow user to convert impedance

value to per-unit value manually and this will helpuser to compare the result with automatic calculationmake by this software which will be shown atsequences diagram. However, the selected base M V Aand base voltage must be entered fi rst before any

conversion can be made. T hi s base afso will be usedby software in automatic calculation or in otherwords, user must enter this window to fill the selectedbase MVA and base voltage. The full result ofmanually conversion to per-unit value can be view bypressing the "Data" button. A n example result ofmanually conversion is shown in Fig. 5 .

fig. 6 shown the sequences impedance diagramwith respective per-unit value that had be obtained

from the single-line diagram drawn in Fig. 3. Thisdiagram can be view when user pressed "PositiveSequence" tab to view positivesequence diagram or"Negative Sequence" t ab to view negative- sequencediagram or "Zero Sequence" tab to view zero-sequence diagram and oiily one sequence impedancesdiagram can be view at certain time. The "M ainView" tab used to shown the original single-linediagram.

Fig. 2. Main Window for Software

259



(a) Positive Sequence Diagram

Fig. 4. MainWindow forPer-Unit Calculation

(b) Negative Sequence Diagram

Fig.5.Table ShownResultfor M anuallyPer-Unit Value Conversion

V CONCLUSION .

A Windows based graphical form to facilitatethelearning of power system analysis was presented inthispaper. Thispackage is written inMicrosoft VisualBasic 6.0. Thi s software provides a user-friendlyenvironment and easy to use tool to aid students forbetter visualizing on power system analysis. Ths toolhas threemai n modules: 1.A user designed single-linediagram, 2. Automatic or manual per-unit conversion,and 3. Displaying the corresponding positive-,negative and zero- sequence diagrams. This sof tware

( c) ZeroSequenceDiagram

Fig. 6.SequenceImpedance ofElectricalPowerNetwork

will be upgraded to make it even more user friendly.Thissoftware will be upgrade until fault analysis andcan simplified the sequence diagrams depending onfault location.

V. REFERENCES

[I] Marizan, Zainuddin, et al, “An Expert SystemBased Power System Modeling With SymmetricalComponents”, Seminar Kebangsaan

Pascasiswazah, Universiti Malaysia Sabah,March.2003.

[ 2 ] Y u, Chen, et al, “A Windows Based GraphicalPackage for Symmetrical Components Analysis”,

260



IEEE Transaction on Power System, Vol. 10,No. 4. Nov. 1994.

[3] Yu, Liu, Wu, et al, “A GUI Based Visualizationfor Sequences Network”, IEEE TruiisacfiorionPowerSystems,VoI. 13, No. 1. Feb. 1998.

141 Negnevitsky, M., et al, “A K nowledge BasedTutoring System for T eaching Fault Analysis”,

IEEE Transaction on Power Systems, Vol. 13,

No. 1. Feb. 1998.[SI Glover, S a m , “Power System Analysis and

Design”,BrooksK ole, 2002[6] Grainger, Stevenson, J r., “Power System

Analysis”,McGraw-Hill Book Company, 1994[7] Saadat, H., “Power System Analysis”, McGraw-

Hill Book Company, 1999[8] Chan Wei Lun, “Anatisis Sistem K uasa

Menggunakan Sistem Pintar”, Pusat Pengajian

Kejuruteraan Elektrik dan E lektronik, UniversitiSains M alaysia,2002

[9] Brown, S., “Visual Basic Developer Guide”,SYBEX Inc., 1994

c, --

VII . ACKNOWLEDGEMENT

This project is supported by the short-termgrant fromK olej Universiti Teknikal K ebangsaan Malaysia(KUTKM).

261

gui based per-unit representation of power system with

Documents