Computer Aided

A Computer-Aided EducationalTool for Induction MotorsCETIN GENCER,1 MEHMET GEDIKPINAR2

1Department of Electrical&Electronic Engineering, Tunceli University, Tunceli 62000, Turkey

2Faculty of Technical Education, Department of Electronic&Computer Education, Firat University, Elazig 23119, Turkey

Received 24 November 2009; accepted 18 January 2010

ABSTRACT: The computer-aided educational tools have gained popularity in the last years with successfulimplementation in many areas, including in engineering education. These tools are aimed to help the studentsfor visualization of the concepts and to provide the graphical feedback during the learning process. This paperpresents a computer-aided educational tool for induction motors, which is a part of laboratories in the electricalmachinery courses. This tool helps to students and educators in subject to teaching/of the equivalent circuit, andthe vector/phasor diagrams in induction motors. The tool software was prepared in DELPHI environment. It hasexible structure which is enable to users to change motor label values, and to solve equivalent circuit parametersand winding account. The proposed educational tool was utilized in laboratories of electric machinery coursesand well received by students. 2010 Wiley Periodicals, Inc. Comput Appl Eng Educ; Published online in WileyInterScience (www.interscience.wiley.com); DOI 10.1002/cae.20418

Keywords: computer-aided educational tool; induction motor; equivalent circuit; DELPHI

INTRODUCTION

The quality of education which has been given in universities, espe-cially in faculties of engineering can be increased by using modernteaching techniques. Computer-aided educational tools are one ofthe modern teaching techniques and have been increasingly usedby the students of engineering subjects, such as the electrical, com-puter, mechanical and civil engineering. Most of the subjects taughtin these faculties, consist of the theoretical and practical studies.The quality of education in these theoretical and practical subjectsis increased by using computer-aided educational tools [14] andthe topics which are difficult to compute by students, became morevisual with the aid of some computer programs [57]. Computer-aided teaching process has been increased the interaction betweenthe student and educator and enhanced the learning processes ofmany students [8].

Several well-known commercial software packages such asMatlab-Simulink, Auto-CAD, Mathcad, OrCAD PcPice, RT-LABoffers many other useful toolboxes for many electrical machinesin engineering subjects [914]. The direct use of these softwarepackages is a major advancement in simplifying simulation proce-dures for many practicing engineers as well as for undergraduateengineering students [4]. However, some of these software pack-ages can be expensive and time consumer for both educators and

Correspondence to C. Gencer ([email protected]). 2010 Wiley Periodicals, Inc.

students. In addition, some of these packages require code and alsoassistance for simulation tools [13].

In this paper, a computer-aided educational tool for induc-tion motor is presented for cost effective education and training.The results of introducing educational software are now used asa teaching tool in the laboratories of the electrical machinerycourses at Firat University, in Turkey. The program is pre-pared in DELPHI environment and setup files are available fromweb.firat.edu.tr/cgencer.

Using this software, the equivalent circuit parameters of athree-phase induction motor can be calculated and vector/phasordiagrams can be drawn easily. This educational tool can be suc-cessfully applied to the laboratory of electric machinery coursesand used by educators for curriculum development and teaching.

EQUIVALENT CIRCUIT AND VECTOR/PHASORDIAGRAM OF THE INDUCTION MOTORS

Induction motors are important topics of the electric machinerycourses. These motors are robust, easily maintained, and cheap.Most of the books on the electrical machines, presents the equiv-alent circuit of induction motors in a similar way to that of atransformer [15]. Generally, the stator and the rotor circuits are firstpresented separately and few are said about the electromagneticcoupling when the motor is operating [16].

Thus, the usual explanation relates the equivalent circuit of aninduction motor at standstill with that of the transformer, replacing

1

2 GENCER AND GEDIKPINAR

Figure 1 Equivalent circuit of a conventional induction motor.

in both cases the actual rotor (actual secondary winding of thetransformer), by an equivalent rotor (an equivalent secondarymotor), having the same number of turns per phase, disposed inthe same way, as those of the stator (the primary winding) [1622].

The standard equivalent circuit for induction motors is shownin Figure 1.

All quantities are referred to the stator and represent onphase [16]. Vs is input voltage per phase, I is stator current perphase, Rs is stator winding resistance per phase, (ms/2)Xs isstator leakage reactance per phase, (ms/2)Xr is rotor leakagereactance per phase referred to stator, Rr is rotor resistance perphase referred to stator, RFe is the resistance representing the corelosses, (ms/2)Xsm

(is ir

)is magnetizing reactance, ir is the rotor

current referred to stator per phase ms is number of stator windingphase, mr is number of rotor phase and s is slip factor. The rotorcurrent ir refers to the portion of the stator current that flows tobalance the rotor magneto-motive force (MMF).

Vector/phasor diagrams are important to observe the relationsbetween current and voltage phasors in different working condi-tions and to find out their values [21]. These diagrams are mostlyused to find the currents, the voltage or the parameters. The vec-tor/phasor diagrams can be drawn by using Equations (1) and (2).In these equivalences, iFe=0 and is ir = ism

Vs = (Rsis) +(jms

2Xsis

)+(jms

2Xsmism

)(1)

0 =(

Rriss

)+(jmr

2Xri

r

)(jms

2Xsmism

)(2)

Rs, Xs,ms, Xsm, Rr, Xr,mr, s, is0 = ismParameters are usually known and Vs, ir, is,Qs, Er = Es can

be drawn in the vector/phasor diagrams as follow steps. The vec-tor/phasor diagram in Figure 3, 20 V = 1 cm and 10 A = 1 cm.

Step 1: is0 current is taken, j(ms/2)Xsm ism = Er = 0BStep 2: Rr, s, Xr,mr are known from tan r= ((mr/2)Xr)/

(Rr/2) and r is found and the direction of ir is drawn.Step 3: Er = |j(ms/2)Xsmism| diametric circle is drawn and

the A point is shown.The A point shows that where the ir line cuts the circle (Fig. 2).The reduced rotor current is found using ir phasor equation

as in Equation (3).

A0 = Rr

sir (3)

The real rotor current ir is calculated as in Equation (4)

ir = msmr

ir (4)

Step 4: is = 0Q can obtain from is = ir + ism relation.Step 5: OK = j(ms/2)Xsmism is drawn by taken Es = ErStep 6: OM = Vs can obtain from Rsis = KL and

j(ms/2)Xsis = LM

Figure 2 Vector/phasor diagram of a three-phase induction motor.

COMPUTER-AIDED EDUCATIONAL TOOL 3

Figure 3 Label values window.

Figure 4 Experimental results window.


Figure 5 Winding calculations window.

Figure 6 Equivalent circuit parameters calculation window.


Figure 7 The equivalent circuit of per phase of the induction motor.

Figure 8 Vector/phasor diagram of the induction motor.


THE OPERATIONAL PROCEDURE OF THEEDUCATIONAL TOOL

The software is developed using Delphi 7.0 visual package pro-gram and it works in a Windows environment [23]. It is preparedto help students to improve their knowledge about the inductionmotors. The program operation can be observed on a PC monitorand can be modified by choosing appropriate windows. A mainwindow and other selected window can be seen simultaneously byclicking desired button on the top of the screen.

MAIN WINDOW

A view of the main program window is shown in Figure 3. Thevalue input window can be seen by operating the program. Thevalue input window has three sub-windows. These windows areshown in Figures 35. The contents of the value input windowchange according to the chosen sub-windows. Although the usermay start the tool directly by using default values of the programgiven for a specific parameters of squirrel-cage induction motor,to start a new calculation should be entered by the user.

The label values of three-phase induction motor can be seenin label values window (Fig. 4). The values of locked-rotor and no-load test experimental results can be seen in experimental resultswindow (Fig. 5). The users have opportunity to change these resultsvalues in both windows (Figs. 4 and 5). The winding calculationwindow can be seen in Figure 6. This window can give opportunityto user a change whether or not to calculate winding parameters.

According to the default values, the phase resistance, phaseimpedance, phase reactance, slip, power input, core losses, cop-per losses, efficiency, and winding parameters of the three-phaseinduction motor are estimated by clicking calculations button inmain window (Fig. 6).

The Equivalent circuit of three-phase induction motor can bedrawn by clicking circuit button in main window (Fig. 7).

The vector/phasor diagrams of three-phase induction motorcan be drawn by clicking phasor diagram button in main window(Fig. 8).

THE EVALUATION OF THE EDUCATIONAL TOOL

The proposed educational tool utilized laboratory of electricmachinery courses at Firat University, Turkey, and has been wellreceived by our students. The tool is expected to achieve followingeducational goals. One who uses this tool should be able to:

Improve his/her knowledge on the induction motor fundamen-tals.

Save in time while developing his/her knowledge. Interpret and draw conclusions related to induction motor

parameters and vector/phasor diagrams. To draw of vector/phasor diagrams as a result more easy.

The results obtained by using the tool and the results obtainedwithout using the tool were compared. Students response to the useof the tool was obtained through evaluation sheets. The feedbackfrom the introduction of the educational tool was very positive. Theaccuracy is well supported by the fact that the computed resultsagree closely with the experimental results [10,11,14,19]. The edu-cators also may develop new ideas and teaching methods by using

the tool. With this philosophy, it is aimed that the tool is availablefor everyone who wants to use or try it so that students may use itin a laboratory of electric machinery or at home.

CONCLUSIONS

In this paper, computer-aided educational tool for the three-phaseinduction motor is presented for cost-effective education and train-ing. The tool helps students to improve their trough understandingon equivalent circuit and vector/phasor diagram of inductionmotor. It is intended as an aid to teaching and may be used byeducators for curciculum development. The tool can be installedon a PC operating in a Windows environment (Windows XP, Vista,or NT) and freeware. The tool has flexible structure enables usersto change motor label parameters and to solve winding account.It can be used as a classroom teaching aid or as a self-study tooloutside the classroom.

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M. Gedikpinar received the BS degree fromthe Department of Electrical Education, Facultyof Technical Education, Gazi University, Ankara,Turkey, in 1981, the MSc degree from Instituteof Science and Technology, Firat University, in1998, and the PhD degree from Institute of Sci-ence and Technology, Gazi University, in 2002,respectively. He is currently teaching in Depart-ment of Electronic and Computer Education, Fac-ulty of Technical Education, Firat University. His

research interests include intelligent control, electrical machines anddesigning, electronics instruments and measurements, analyzing of circuit.

BIOGRAPHIES

C. Gencer received the BS degree from theDepartment of Electrical Education, Faculty ofTechnical Education, Gazi University, Ankara,Turkey, in 1995, the MSc degree from Instituteof Science and Technology, Firat University, in1999, and the PhD degree from Institute of Scienceand Technology, Gazi University, in 2005, respec-tively. He is currently teaching in Department ofElectrical&Electronic Engineering, Tunceli Uni-versity. His research interests include intelligent

control, electrical machines and drives, educational tools, engineering tech-nology education, web-based distance learning.

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Computer Aided