UNIVERSITI MALAYSIA PERLIS
FUNDAMENTAL OF ELECTRICAL ENGINEERING
EMT 113/4
EXPERIMENT 2
SINGLE PHASE TRANSFORMER
– Voltage and Current Ratios
MARKS
Result &
Calculation
31
NAME :
MATRIC NO. :
PROGRAMME :
DATE :
Discussion
Conclusion
Total
%
10
5
46
100
EMT113/4
Single Phase Transformer-Voltage and Current Ratios
EXPERIMENT 2
SINGLE PHASE TRANSFORMER – VOLTAGE AND CURRENT RATIOS
2.1
OBJECTIVES
1.
2.
To familiar with voltage and current characteristics of a single phase transformer.
To be able to use the transformer turns ratio to predict the voltage and current
that will flow in the secondary winding.
2.2
EQUIPMENTS
EMC Workstation Model 8110
Single Phase Transformer Model 8341
Power Supply Model 8821
Data Acquisition Interface Model 9062.
2.3
INTRODUCTION
The windings of a standard single-phase transformer are called the primary
winding and the secondary winding. The primary winding is the power input
winding and this is the side that is connected to the ac power source. The
secondary winding is connected to the load and is physically and electrically
isolated from the primary. The voltage and current that flow in the secondary are
related to the primary voltage and current by the transformer turns ratio N1/N2 (or
Np/Ns) through a very simple relationship. The ratio of primary voltage to
secondary voltage equals N1/N2, while the ratio of the primary to secondary is
equal to the inverse of the turns ratio, N2/N1. This result in the following,
EPRI = N1
ESEC
N2
which gives:
ESEC
= EPRI
X
N2
N1
and
IPRI = N2
ISEC
N1
which gives:
ISEC
= IPRI
N1
N2
X
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EMT113/4
2.4
Single Phase Transformer-Voltage and Current Ratios
PROCEDURE
CAUTION
High voltages are present in this laboratory exercise! Do not make or modify any
banana jack connections with the power on unless otherwise specified!
Figure 2-1: Single –Phase Transformer Measurements
1. Install the Power Supply, Data Acquisition Interface (DAI) and Single-Phase
Transformer modules in the EMS Workstation.
2. Make sure that the main switch of the Power Supply is set to the O (OFF)
position, and the voltage control knob is turned fully counter clock-wise (ccw). Set
the voltmeter select switch to the 4-N position.
3. Ensure that the DAI LOW POWER INPUT is connected to the main Power
Supply, set the 24V-AC power switch to the 1 (ON) position.
4.
Display the Metering application.
5. Set up the transformer circuit shown in Figure 2-1. Connect E1 and I1 as shown
and use E2 to measure the different secondary voltages.
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EMT113/4
Single Phase Transformer-Voltage and Current Ratios
6. Turn on the power and adjust the voltage control for the value of Es given in
Figure 2-1. Measure the transformer primary current (IPRI) and the different
terminal voltages (E1-2, E3-4, E5-6, E3-7, E7-8, E8-4, E5-9, E9-6). [Modify each
connection for different terminal voltages and record each reading]. After
recording the measurements, rotate the voltage control fully ccw and then turn off
the power.
Note: When measuring the various voltages, turn off the Power Supply before
modifying the connections of the DAI to the circuit.
Figure 2-2: Determining the ratio of Primary Current to Secondary Current
7. Connect I2 as shown in Figure 2-2 and note that it short-circuits secondary
winding 5-6. Turn on the power and slowly adjust the voltage control to obtain the
value of current Is given in Figure 2-2.
8. Record the values of primary voltage (EPRI) and current (IPRI) and the value
of the short-circuit secondary current (ISEC) in winding 5-6.
9. Return the voltage control to zero and turn off the power. Calculate the ratio of
primary current to secondary current. Show your calculations.
10. Replace the connection I2 to terminals 3-4. Turn on the Power Supply and slowly
adjust the voltage control knob for the same value of current used in step 7.
Once again, record the values of primary voltage (EPRI) and current (IPRI) and
the secondary winding current (ISEC).
11. Return the voltage control to zero and turn off the power. Again, calculate the
ratio of primary current to secondary current. Show your calculations.
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EMT113/4
Single Phase Transformer-Voltage and Current Ratios
Figure 2-3: Effect of Core Saturating on Exciting Current
Table 2.1: Impedance Table for the Load Modules
Impedance Ω
Switch positions for load elements
240V
50 Hz
1
2
3
4
5
6
7
8
9
400
|
-
|
|
|
|
-
-
-
12. Set up the transformer circuit shown in Figure 2-3. It will be used to show how
exciting current is affected when the transformer core becomes saturated. Since
the exciting current is so small, the corresponding voltage across a sense
resistor R will be used to illustrate its variation. Connect the transformer primary
terminals to Power Supply terminals 4 and 5 through sense resistor R (refer to
Table 2.1 for impedance configurations). Connect E1, E2 and E3 to measure
the transformer voltages.
13. Turn on the power and use the output voltage control to obtain values for E2
equally spaced at about 10% intervals over the complete control knob range. At
each voltage adjustment, click the Record Data button to enter the
measurements in the Data Table. Then, record your data.
14. When all data values have been recorded, rotate the voltage control fully ccw,
and turn off the Power Supply.
15. Display the Graph screen, select E1 as the X-axis parameter and E2 as the Yaxis parameter. Click the Line Graph button to observe the curve of primary
voltage versus exciting current, represented by E1. Then copy this graph into
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EMT113/4
Single Phase Transformer-Voltage and Current Ratios
the graph paper provided with appropriate scale, correct axis parameters
and graph title.
16. Ensure that the Power Supply is turned off, the voltage control is fully ccw and
remove all leads and cables.
2.5 RESULTS
Note: Your results should include:
1) Transformer primary current and the different terminal voltages.
(4.5 M)
2) Values of primary voltage (EPRI) and current (IPRI) and the value of the shortcircuit secondary current (ISEC) in both short circuit secondary terminal 5-6 and 34.
(3 M)
3) The ratio of primary current to secondary current for the two cases above, and
compare results with turn ratios.
(4 M)
4) Table for Transformer voltages.
5) Graph
2.6
(16M)
(3M)
DISCUSSION (10M)
Analyze your result. Discuss the voltage and current ratios for a single transformer.
2.7
CONCLUSION (5M)
Make your overall conclusion by referring to the objective of this experiment (your
answer should be in simple notes)
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