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ANADOLU UNIVERSITY
DEPARTMENT OF
ELECTRICAL AND ELECTRONICS ENGINEERING
EEM 311
Principles of Energy Conversion Laboratory
Fall 2016-2017
Experiment 4 :
Determination of Transformer Parameters
Determination of Transformer Performance
(Load Test)
ANADOLU UNIVERSITY
EEM311 – Experiment 4
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Purpose :
To determine the equivalent circuit parameters of a single-phase transformer using open and shortcircuit test data and calculating the efficiency curves of a single-phase transformer under various loading
schemes
Background and Theoretical Discussion :
The parameters of the transformer approximate equivalent circuit are readily obtained from opencircuit and short-circuit test.
In the open circuit test, rated voltage is applied to high voltage (HV) side winding while low voltage
(lv) side is open circuited. Instruments are connected to measure the input voltage, the no-load
input current (excitation current), and the input power. If the secondary is open circuited, the secondary
current will be zero and only the excitation current will be drawn from the supply. Also, the primary voltage
drop due to the small excitation current is neglected, and therefore following equivalent circuit given in
Fig. 1. is considered.
Measurements performed on an unloaded transformer are open circuit voltage VOC , which is the
rated high side voltage (HV), excitation current I ex , and open circuit power POC . The excitation current is
inductive in nature and lags VOC by;

POC 

 VOC  I ex 
OC  cos 1 
Knowing  OC ,
I  I ex  cos OC
I h e  I ex  sin OC
ANADOLU UNIVERSITY
EEM311 – Experiment 4
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Next, shunt components are calculated as follows;
RC 
VOC
I he
and X m 
VOC
I
The shunt elements can also be determined as;
RC 
VOC 2
V
, I he  OC ,
POC
RC
I
 I h2e  and X m 
since I ex is available we can calculate
I 
2
ex
VOC
I
As mentioned before, no-load test is performed from the high voltage (HV) side of the transformer
since HV side has a lower rated current than low voltage (LV) side. This prevents too high currents from
flowing through instrumentations. Similarly short circuit test is performed from the LV side to avoid high
voltages across instrumentations
In the short-circuit test, a reduced voltage VSC is applied at terminals of LV winding while HV
terminals are short circuited. Instruments are connected to measure the input voltage VSC , the input current
I SC , and the input power PSC . The applied voltage is adjusted until rated LV side current is flowing. The
voltage required to produce rated current in this case is just a few percent of rated LV side voltage. At such
correspondingly low voltage and therefore flux, the exciting current and core loss are negligible and the
shunt branch can be omitted. Thus, the power input can be taken to represent the winding copper loss.
ANADOLU UNIVERSITY
EEM311 – Experiment 4
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Assume that LV side is the secondary while HV is primary, shorted and the approximate circuit referred
to secondary is given in Fig.2. In this case, winding equivalent circuit elements referred to secondary are
calculated as;
Z eq 2 
VSC
I SC
, and knowing the input power;
Req2 
PSC
and X eq 2 
2
I SC
Z
2
eq
 Req2 2 
An important aspect of transformer performance is the efficiency. Power transformer efficiencies are high
and around 95 to 97 percent. The actual efficiency of a transformer is given by

Output Power
Input Power
And the conventional efficiency of a transformer at n fraction of the full-load power is given by

n  S  pf
 n  S  pf    n 2  PCU   Ph e
Where
S = Full-load rated volt-ampere
PCU =Full-load copper loss
n
I
I rated
per-unit loading
Equipment List :
1
DL 1013M2
Power Supply
1
DL 1031
Digital Power Measuring Unit
1
DL 1093
Single Phase Transformer
1
DL 1017R
Resistive load bank
1
DL 1017L
Inductive load bank
1
Wavetek
Hand Multimeter
ANADOLU UNIVERSITY
EEM311 – Experiment 4
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Procedure :
Part 4A: Determination of Transformer Parameters

Connect all necessary instrumentations to perform the open-circuit test. Perform the test and
record the data.
Practical Diagram for Open Circuit Test:
Voc
Ioc
Poc
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220 V
EEM311 – Experiment 4
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
Make all necessary instrumentations to perform the short-circuit test. Perform the test and record
the data.
Practical Diagram for Short Circuit Test:
Vsc
Isc
Psc
2.27 A
Using the data recorded from open and short circuit tests, try to find out the elements of approximate
equivalent circuit of the test transformer referred to primary winding. Draw your circuit.
ANADOLU UNIVERSITY
EEM311 – Experiment 4
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Part 4B: Determination of Transformers Performance (Load Test)






Using the R and L load banks provided, run the load test for the transformer to fill the following
table. The load configuration will be given to you by your teaching assistant.
Calculate and record I1rated.
Calculate n.
Using the results recorded from open and short circuit tests, calculate Ph+e and Pcu for each step.
Calculate the efficiency for each step.
Plot efficiency versus loading (x axis) curves for unity and lagging power factor cases.
cos φ
Load
position
I1
V2
P
(Watt)
I1-rated
n
(I/Irated)
Ph+e
Pcu
η
1
2
3
1
(resistive)
4
5
6
7
1
2
3
_____
(inductive)
4
5
6
7
Position
1
2
3
4
5
6
7
DL 1017R
DL 1017L
Resistive load bank Inductive load bank
1050 Ω
4.46 H
750 Ω
3.19 H
435 Ω
1.84 H
300 Ω
1.27 H
213 Ω
0.90 H
150 Ω
0.64 H
123 Ω
0.52 H
ANADOLU UNIVERSITY
EEM311 – Experiment 4