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ANADOLU UNIVERSITY
DEPARTMENT OF
ELECTRICAL AND ELECTRONICS ENGINEERING
EEM 311
Principles of Energy Conversion Laboratory
Summer, 2013-2014
Experiment Week#2
Experiment 4 :
Determination of Transformer Parameters
and Its Performance
Experiment 5 :
Three-phase Transformer Connections and
Determination of Voltage Regulation
ANADOLU UNIVERSITY
EEM311 – Experiment Week#2
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Experiment 4:
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
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EEM311 – Experiment Week#2
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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.
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;
ANADOLU UNIVERSITY
EEM311 – Experiment Week#2
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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    n2  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
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EEM311 – Experiment Week#2
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Procedure :

Connect the transformer as given in Fig.3.
Rated current and voltage values are written on the figure.
Part-4A: Open Circuit Test

Connect all necessary instrumentations to perform the open-circuit test. Perform the test and
record the data.
Voc
Ioc
Poc
220 V
Part-4B: Short Circuit Test

Connect all necessary instrumentations to perform the short-circuit test. Perform the test and
record the data.
Vsc
Isc
Psc
4.5 A
Using the results you have found on Part-1 and part-2, try to find the approximate equivalent
circuit parameters of the test transformer referred to HV winding.
Part-4C: 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. ( t.b.a. : to be
arranged by your assistant )
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EEM311 – Experiment Week#2
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Position
1
2
3
4
5
6
7
cos φ
Load
position
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
I1
V2
P
(Watt)
I1-rated
n
Ph+e
Pcu
η
1
2
1
(resistive)
3
4
5
6
1
2
t.b.a.
(inductive)
3
4
5
6
In Report :
1. Calculate all elements and draw the approximate equivalent circuit of the test transformer referred
to 220 V winding. Show values of all elements on your drawing. (in Conclusion section,
individually)
2. Calculate and plot efficiency versus loading (x axis) curves for unity and a lagging power factor.
(in Results section)
3. In general what is the load condition at which transformers have maximum efficiency?
4. Observe efficiency plots and comment on why efficiency tends to decrease, after making a peak,
towards the full-load.
5. Explain why the efficiency is lower under lagging power factor loading compared to unity power
factor loading.
ANADOLU UNIVERSITY
EEM311 – Experiment Week#2
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Experiment 5:
Purpose :
Using the three-phase transformer provided, to realize possible three-phase transformer
connections and verify rated line voltages and currents with measurements. For all possible three-phase
transformer connections, the voltage regulation will be determined.
Background and Theoretical Discussion :
Three-phase transformer banks are design either using a single three-phase transformer, which has
internal connection depending upon the application or using three single-phase transformers, which are
connected in any possible way that the application requires. As long as the redundancy is concerned,
using three singlephase transformers has some advantages. One of which is that; if one of the transformer
fails, threephase power can still be obtained by using two singlephase transformers at the cost of loosing
some fraction of the rated power.
The possible three-phase transformer connections are;




Delta Delta Δ−Δ
Wye Delta Y −Δ
Delta Wye Δ− Y
Wye-Wye Y − Y
The voltage regulation of a transformer under load condition is defined as the difference between
the noload voltage and the load voltage when the primary voltage and the frequency remain unchanged.
The voltage regulation actually gives the percent of value of required change in primary in order to keep
the secondary voltage constant. Percent regulation is given as
%V 
V2 noload  V2load
100
V2 no load
Equipment List :
1
DL 1013M2
Power Supply
1
DL 1031
Digital Power Measuring Unit
1
DL 1080
Three Phase Transformer
1
DL 1017R
Resistive load bank
1
DL 1017L
Inductive load bank
1
Wavetek
Hand Multimeter
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EEM311 – Experiment Week#2
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Procedure :
1- In the laboratory, you will be provided with a transformer bank of 6 single-phase transformers each
rated 190V / 70V as depicted in Figure 1. The bank with 6 transformers has a rated total power of
1000VA.







First, connect upper transformers with lower ones in series to obtain three 380V / 140V
single-phase transformers.
Next, connect 3 single-phase transformers as a three-phase Delta Wye transformer bank,
Figure 2, and connect low voltage side to R & L load bank.
In this configuration, without applying the power to the experimental setup, calculate rated
line voltages and currents. Verify your results with your T.A.
Once your calculations are correct adjust load banks so that very low secondary current will
flow, and apply rated primary voltage to the setup.
Then adjust load banks to draw rated primary current.
Record primary current and voltage and measure secondary voltage using handheld
multimeter.
Compare measurements with your calculations.
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EEM311 – Experiment Week#2
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2- Adjust primary to rated voltage and keep it at that value. Using only R load (unity power factor) and
RL load (lagging power factor) fill out the following table by loading the transformer at fractions of
rated primary current.
DELTA WYE CONNECTION
cos φ
Load
position
I
Irated
I / Irated
V2no-load
V2load
%V
1
2
3
1
(resistive)
4
1.52 A
5
6
7
1
2
3
t.b.a.
(inductive)
4
1.52 A
5
6
7
t.b.a.: to be arranged by your assistant
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EEM311 – Experiment Week#2
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3- Repeat steps 1 and 2 for Delta Delta connection.
DELTA DELTA CONNECTION
cos φ
Load
position
I
Irated
I / Irated
V2no-load
V2load
%V
1
2
3
1
(resistive)
4
1.52 A
5
6
7
1
2
3
t.b.a.
(inductive)
4
1.52 A
5
6
7
t.b.a.: to be arranged by your assistant
Important !
All groups must perform rated line voltage and current calculations and verify the correctness of
the results with T.A.s . If a group fails to calculate them correctly, that group will not be allowed to
perform the measurements. This basically means that you will fail this laboratory assignment. One way of
avoiding this trouble is that, since you have all necessary data, you make your calculations before coming
to laboratory. Then you will make your measurements and go.
Report :
1. Present your line current and voltage calculations for three-phase transformer connections and
compare them with measured results.
2. Present your percent regulation results and plot percent regulation versus loading (x axis) for both
resistive and inductive loading on the same graph. Explain the fact that under the lagging power
factor loading percent regulation is higher
3. Comment if there is any significant variations in percent regulation under same loading but
different three-phase connections.
ANADOLU UNIVERSITY
EEM311 – Experiment Week#2