Computer aided-teaching-of-transformers-for-undergraduates


Abstract—In the era of technological advancement, use of
computer technology has become inevitable. Hence it has become the
need of the hour to integrate software methods in engineering
curriculum as a part to boost pedagogy techniques. Simulations
software is a great help to graduates of disciplines such as electrical
engineering. Since electrical engineering deals with high voltages and
heavy instruments, extra care must be taken while operating with
them. The viable solution would be to have appropriate control. The
appropriate control could be well designed if engineers have
knowledge of kind of waveforms associated with the system. Though
these waveforms can be plotted manually, but it consumes a lot of
time. Hence aid of simulation helps to understand steady state of
system and resulting in better performance. In this paper computer,
aided teaching of transformer is carried out using
MATLAB/Simulink. The test carried out on a transformer includes
open circuit test and short circuit respectively. The respective
parameters of transformer are then calculated using the values
obtained from open circuit and short circuit test respectively using
Simulink.
Keywords—Computer aided teaching, transformer, open circuit
test, short circuit test, Simulink.
I. INTRODUCTION
NDERGRADUATE courses consists of intensive
coursework of theoretical and laboratory exercises.
Theoretical course work of machine includes steady-state
operation of transformers used to compute various quantities
such as losses efficiency and voltage regulation. The trials
carried out during laboratory sessions include open circuit,
short circuit tests conducted to determine no-load losses and
equivalent circuit parameters, and load test to study
transformer performance under various loading conditions.
Since in the undergraduate course at Maharishi
Markandeshwar University in the Electrical Engineering
Department there is limited time allotted for laboratory
sessions. Students have to perform the experiments within the
stipulated time, which hinders students’ ability to understand
the experiment completely. Hence, to verify this survey was
conducted, and around 92% of the students felt that there
should be a virtual environment for electrical machinery
course work. The advantage of the virtual environment being
interactive learning and a boost to computer aided teaching.
The shift towards computer aided teaching among students is
Rajesh Kumar is with the Maharishi Markandeshwar University, Mullana,
133203, Haryana, India (corresponding author, phone: +918398069447, e-
mail: rjesh10391@gmail.com).
Roopali Dogra is with the Maharishi Markandeshwar University (phone:
+919622731576, e-mail:roopalidogra5@gmail.com).
Puneet Aggrawal is with the Maharishi Markandeshwar University (phone:
+918059931096, e-mail:puneet241@gmail.com).
due to availability of low cost personal computers with the
required computation software readily available [1]. Due the
familiarity of MATLAB/Simulink among the undergraduate
students of Maharishi Markandeshwar University, the virtual
environment used here is of MATLAB/Simulink. We can use
other simulation software such as Maple and Math Cad also
[2], [3]. Further advantage of the virtual environment include
that student can have a check on their circuit and then proceed
to perform the experiment. This in one way helps the students
to recheck their circuit, and on the other hand, also helps
students to apply their intuition logically and then check the
viability of circuit. After the viability is checked, the students
can now apply to hardware instruments, which would be great
help for students in their projects at the undergraduate level. It
should be also noted that software simulation cannot totally
replace hardware due to modeling assumptions [4]. Here, the
MATLAB/Simulink model is used for carrying out
transformers open circuit and short circuit test, respectively.
II.OPEN- CIRCUIT TEST
The open circuit test of a transformer is performed using the
circuit shown in Fig. 1.
Fig. 1 Experimental Set Up For Open-Circuit Test
As illustrated in Fig. 1, the high voltage (HV) side of the
transformer is open circuited and Voltmeter (V), Ammeter (A)
and Wattmeter (W) are shown connected to low voltage (LV)
side on transformer. The rated frequency voltage applied to
primary [5]. When voltmeter reading is equal to the rated
voltage of the LV winding, all the three instrument readings
are recorded [5]. The ammeter records the no load current or
the exciting current Ioc [5]. The input power is illustrated using
wattmeter. The wattmeter reading consists of core and ohmic
losses [5]. The exciting current being 2% to 6% of the full
load current, hence ohmic loss during open circuit test is
negligible [5]. Hence, wattmeter reading can be taken equal to
transformer core loss. A negligible amount of dielectric loss
may also exist.
Computer-Aided Teaching of Transformers for
Undergraduates
Rajesh Kumar, Roopali Dogra, Puneet Aggarwal
U
World Academy of Science, Engineering and Technology
International Journal of Electrical, Computer, Energetic, Electronic and Communication Engineering Vol:11, No:7, 2017
658International Scholarly and Scientific Research & Innovation 11(7) 2017 scholar.waset.org/1999.5/10007439
InternationalScienceIndex,EducationalandPedagogicalSciencesVol:11,No:7,2017waset.org/Publication/10007439

A.Open-Circuit Test Using Simulink
The open-circuit test for calculation of parameter can be
done using Fig. 2 [4]. The linear transformer block in the
Simulink diagram, as shown in the figure, can be modeled
according to the values as shown in the table given below:
TABLE I
PARAMETER SPECIFICATIONS
PARAMETER VALUES
Nominal Power and Frequency [Pn(VA) fn(Hz)] [50e3, 50]
Winding 1 Parameters[V1(Vrms) R1(ohm) L1(H)] [120 36.3 0.03]
Winding 2 Parameters [V2(Vrms) R2(ohm) L2(H)] [2400 0.0047 3.18]
Magnetizing Resistance and Inductance [Rm(ohm) Lm(H)] [57600 183.35]
Fig. 2 Open-circuit test Using Simulink
The measurements either from experimental or simulation
enables us to compute resistance (Rc) and reactance (Xm)
approximately of the excitation branch referred to the primary
side [4]. The magnitude of the excitation impedance from the
open circuit voltage and current is computed as:
|Z | R jX (1)
where Rc is the core resistance and Xm is the magnetizing
reactance. The phase angle of admittance can be computed
from the knowledge of power factor. The power factor PFOC is
given by,
PF ∗ I (2)
Once the power factor is computed, angle ϕ is known, Rc
and Xm can be computed as follows [4]:
R |Z | ∗ cos ϕ,
X |Z | ∗ sin ϕ (3)
III. SHORT CIRCUIT TEST
The short circuit is performed using the circuit as shown in
Fig. 3 [5].
Fig. 3 Experimental Setup for Short-Circuit Test
In the following test, the LV side of transformer is short
circuited and the instruments are placed on high voltage side,
as illustrated in Fig. 3 [5]. The applied voltage is adjusted such
that rated current flows in the circuit. A primary voltage of
about 2% to 12% of rated voltage is sufficient for the flow of
rated current in both primary and secondary windings [5]. The
wattmeter in short circuit test of transformer reads ohmic loss
in both the windings [5].

A.Short- Circuit Test Using Simulink
The short-circuit test of transformer can be performed using
Simulink model shown in Fig. 4 [4]. The linear transformer
block in the Simulink diagram can be modeled according to
parameters as shown in Table I.
Fig. 4 Short-circuit test using Simulink
The input voltage, short circuit current and real power are
measured. A negligible current flow through the excitation
branch since a reduced voltage is applied to the primary of the
transformer [4].The magnitude of series impedance referred to
primary side of transformer can easily be computed by
neglecting this current as:
Z |Z | (4)
Neglecting the core loss at the low value of Vsc, the
equivalent leakage reactance and resistance can be found by,
X X Z R
R R (5)
The equivalent resistance and reactance are the sum of
resistance and reactance of the primary and secondary referred
to primary side. The primary and secondary windings have
equal contribution to total resistance and reactance is general
assumption [4].
IV. HYSTERESIS IN SATURABLE TRANSFORMER
The simulation of saturable transformer is carried using Fig.
3 [6].
The transformer in Fig. 3 consists of three coupled windings
wounded on a same core [6]. Winding resistance and the
leakage inductance as well as the magnetizing characteristics
of the core are taken into account in this model. The
magnetizing characteristic of the core is modeled by a
resistance Rm simulating core active losses and saturable
inductance Lsat. With the help of the hysteresis design tool of
powergui, block hysteresis is carried out. Eddy current losses
are modeled by a linear resistance Rm. The transformer block
is modeled according to the parameters as given in Table II
[6].
TABLE II
SATURABLE TRANSFORMER PARAMETERS
PARAMETER VALUES
Nominal Power and Frequency[Pn(VA) fn(Hz)] [150e6 50]
Winding 1 parameters[V1(rms) R1(pu) L1(pu)] [500e3/sqrt(3) 0.002 0.08]
Winding 2 parameters[ V2(rms) R2(pu) L2(pu)] [230e3/sqrt(3) 0.002 0.08]
Winding 3 parameters[ V3(rms) R3(pu) L3(pu)] [181.87e3 0.002 0.08]
Saturation Characteristic[i1 phi1; i2 phi2;….](pu) [0 0; 0.0 0.85; 0.015 1.2; 0.03 1.35; 0.06 1.5; 0.09 1.56 ; 0.12 1.572]
Core loss resistance and initial flux[Rm phio] or [Rm] (pu) [200 0]

Fig. 3 Hysteresis in Saturable Transformer
V.RESULTS
Using the Simulink diagram as shown in Figs. 1 and 4,
respectively, the open circuit and short circuit parameters of
transformer is noted in Table III:
TABLE III
SIMULATION RESULTS
Test V(V) I(A) P(W) Q(VAR)
Open-Circuit 1697 0.041 42.05 43.3
Short- Circuit 36.68 0.047 0.0481 0.093
Using the results obtained from Table II, transformer
parameters are calculated using (1), (2), (3), (4) and (5),
respectively. After the calculations, the values are tabulated in
Table IV. After obtaining the parameters from the
calculations, the simulations results are compared with the
experimental value, and hence, the error is tabulated in Table
V.
TABLE IV
PARAMETER CALCULATIONS
Rc(Ω) Xm(Ω) Req(Ω) Xeq(Ω)
32975.87 433.42 18.10 780.21
TABLE V
ERROR IN SIMULATION
Rc(Ω) Xm(Ω) Req(Ω) Xeq(Ω)
Error (%) 1.188 0.835 0.1002 0.0399
After simulating Fig. 3, the hysteresis curve is obtained, as
shown in Fig. 4. The other related waveforms obtained after
the simulation of Fig. 3 are shown in Fig. 5.
Fig. 4 Hysteresis Characteristics for Saturated Transformer

Fig. 5 Waveforms for Saturated Transformer
VI. CONCLUSIONS
Since the error lies within the range of 1%, the simulation
model for the transformer so made using Simulink is
appropriate. This helps the students to check and perform the
virtual tests using simulation at their personal computer any
time and then proceed to laboratory experiment. The virtual
environment, hence, makes the learning more interactive and
helps student to get a clearer view of working of transformer.
After successful implementation of these tests the students are
asked to perform further experiments as an assignment to
boost up their simulation skills. The virtual environment
implemented at undergraduate courses at Maharishi
Markandeshwar University helped students to understand the
gap between simulations and hardware, and they drew
conclusions. That is, we cannot replace an exact model of
hardware in simulations due to hardware limitations, which
gives an explanation to the error so obtained in comparison of
the modeling and laboratory results.
REFERENCES
[1] W. M. Daniels and A. R. Shaffer, “Reinventing the electrical machines
curricullum”, IEEE Transaction on Education 41(1998), 92-100.
[2] C. A. Canizares and Z. T. Faur, “Advantages and disadvantages of using
computer tools in electrical engineering courses”, IEEE Trans Educ
40(1997), 166-171.
[3] C. Domnisoru, “Using MATHCAD in teaching power engineering”,
IEEE Trans Educ 48(2005), 157-161.
[4] S. Ayasun and C. O. Nwankpa, “Transformer Test Using
MATLAB/Simulink and their integratiion into undergraduate electric
machinery courses.” Inc.Comput Appl Eng Educ 14: 142-150, 2006.
[5] Dr. P. S. Bhimbra, “Electric Machinery”, 7th
edition, Khanna Publisher.
[6] “MATLAB Documentation”. Mathsworks. Retrieved 14th
Aug 2013.
Rajesh Kumar born in Kural, Bhiwani, Haryana, India on 10th
March 1992. He is currently pursuing Masters in Technology on
Electrical Engineering, Maharishi Markandeshwar University,
Mullana, Haryana, India He completed his B.Tech on 2014 from
National Institute of Technology Goa, Ponda, Goa, India.
He did training on “Embedded Systems” from International Institute of
Information Technology, Pune. Mr. Kumar was a student Member of
IEEE.Mr. Kumar was Editor-In-Chief of The Electrical Student Luminous
Association (TESLA), National Institute of Technology Goa. He was Campus
Ambassador of Innovians Technology Greater Noida and organized National
Level Workshop on “Industrial Automation”. His areas of interest include
Control System, Power systems, Renewable energy, Power Electronics and
Drives.
Roopali Dogra born in Jammu, India on 6th
May 1988. She
completed her Bachelor of Technology and Masters (M.Tech) in
the years 2013 and 2015 respectively. Her area of interests
includes Machines, Control System and Power Systems.
Puneet Aggrawal born in Ambala Cantt., Haryana, India on 24th
November 1981. He is currently working as an A.P. in Electrical
Department, Maharishi Markandeshwar Engineering College,
Mullana, India. He completed his Bachelor of Technology and
Masters (M.Tech) in the years 2003 and 2010 respectively. His
area of interest includes Power Electronics and Drives, Networks, Operation
Research, and Application to Power Electronics and Power Systems.

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