AIR UNIVERSITY
DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
EXPERIMENT NO 7
Lab Title:
Student Name: Reg. No:
Objective:
LAB ASSESSMENT:
Excellent Good Average Satisfactory Unsatisfactory
Attributes (5) (4) (3) (2) (1)
Ability to Conduct
Experiment
Ability to assimilate the
results
Effective use of lab
equipment and follows the
lab safety rules
Total Marks: Obtained Marks:
LAB REPORT ASSESSMENT:
Excellent Good Average Satisfactory Unsatisfactory
Attributes
(5) (4) (3) (2) (1)
Data presentation
Experimental results
Conclusion
Total Marks: Obtained Marks:
Date: Mark Signature:
EXPERIMENT 07
Three-Phase Transformer Connections
Delta-Wye & Wye-Delta Connections
Objectives
To be able to connect three-phase transformers in delta-wye and wye-delta configurations
To measure winding voltages to verify that the secondary windings are connected with the proper phase
relationships
To verify that the voltage within a delta equals zero before the delta is closed
Equipment required
EMS Workstation
Three Phase Transformer Module
Power Supply
Connection Leads and Accessories
Data Acquisition Module
Discussion
As seen in the previous exercise, primary and secondary voltages in delta-delta and wye-wye connections
are in phase and the voltage at the secondary is equal to the voltage at the primary times the inverse of
the turns ratio. In delta-wye and wye-delta connections however, there will be a 30︒ phase difference
between the primary and secondary voltages. Also, in the delta-wye configuration, the line voltage at the
secondary is equal to the line voltage at the primary times the inverse of the turn ratio times √3. On the
other hand, in the wye-delta configuration, the line voltage at the secondary is equal to the line voltage at the
primary times the inverse of the turn ratio times 1/√3.
The 30︒ phase shift between the primary and secondary does not create any problems for isolated groups
of loads connected to the outgoing lines from the secondary. However, if the outgoing lines from the
secondary of a three-phase transformer have to be connected in parallel with another source, the phase shift
might make such a parallel connection impossible, even if the line voltages are the same. Recall that in order
for three-phase circuits and sources to be connected in parallel, line voltages must be equal, have the same
phase sequence, and be in phase when the parallel connection is made.
Figure 7-1 shows a three-phase transformer, with a turns ratio equal to 1:1, connected in the delta-wye
configuration and feeding a three-phase load. The voltage across each primary winding EPri equals the
incoming line voltage, but the outgoing line voltage ESEC is √3 times that voltage because the voltage across
any two secondary windings is √3 times greater than the voltage across a single secondary winding.
Note that if the three-phase transformer had a turns ratio of 1:10, the line voltage at the secondary would be 10
x √3 times greater the line voltage at the primary, because the inverse of the turns ratio is multiplied by the √3
factor. The line current in the secondary is the same as the phase current, but the line current in the primary
is √3 times greater than the corresponding phase current.
Figure 7-1. Three-Phase Delta-Wye Configuration.
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!
1. Install the Power Supply, data acquisition module, Resistive Load, and Three-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 ccw. Set the voltmeter select switch to the 4-5 position, and then ensure the
Power Supply is connected to a three-phase wall receptacle.
3. Ensure that the POWER INPUT of the data acquisition module is connected to the main Power Supply,
and ensure the USB port cable from the computer is connected to the data acquisition module. Set the
24 V - AC power switch to the I (ON) position.
4. Display the Metering application.
5. Connect the Three-Phase Transformer module in the wye-delta configuration shown in Figure 7-2. Make
sure that the voltage within the delta is zero before closing the delta.
Figure 7-2. Three-Phase Transformer Connected in Wye-Delta.
6. Turn on the power and adjust the voltage control to obtain the line-to-line voltage ES given in Figure
7-2. Connect meter inputs E1, E2, and E3 to measure the line voltages at the primary (Each phase) and
record the results. Record also the average value of the primary line voltage given by the meter Avg. (E1,
E2, E3).
E1-6 = _________V E11-1 = ________V E6-11 =________V
Average line voltage (primary) =________V
7. Does the average primary line voltage indicate that the sum of the three primary line voltages is
approximately zero? 󠄁Yes 󠄁 No
8. Observe the voltage phasors on the Phasor Analyzer.
Paste the results of Phasor Analyzer here.
9. Are they approximately equal with a 120︒ phase shift between each of them? 󠄁Yes 󠄁 No
10. Turn off the power without modifying the setting of the voltage control. Connect meter inputs E1, E2,
and E3 to now measure the line voltages at the secondary. Turn on the power and record the line voltages
as well as the average value of the secondary line voltage [meter Avg (E1, E2, E3)].
E3-5 =________V E8-10 =________V E13-15 =________V
Average line voltage (secondary) =________V
11. Does the average secondary line voltage indicate that the sum of the three secondary line voltages is
approximately zero? 󠄁Yes 󠄁 No
12. Observe the voltage phasors on the Phasor Analyzer.
Paste the results of Phasor Analyzer here.
13. Does the display confirm they are equal with a 120︒ phase shift between each of them?
󠄁Yes 󠄁 No
14. Turn off the power without modifying the setting of the voltage control. Connect meter input E2 to
measure line voltage E1-6 on the primary side. Turn on the power and compare the voltage phasor of
E1-6 on the primary side with that of E3-5 on the secondary side.
Paste the results of Phasor Analyzer here.
15. Does the Phasor Analyzer display confirm a phase shift of around 30︒ between the two?
󠄁Yes 󠄁 No
16. Calculate the ratio Average secondary line voltage / Average primary line voltage using the values
recorded in steps 6 and 10.
Average secondary line voltage
= =
Average primary line voltage
17. Is it approximately equal to 1/√3? 󠄁Yes 󠄁 No
18. Turn off the power and connect the Three-Phase Transformer module in the delta-wye configuration
shown in Figure 7-3. Set the Resistive Load module for the given values of R, and connect inputs I1,
I2, and I3 to measure the three line currents to the load.
19. Connect inputs E1, E2, and E3 to measure the line voltages at the primary, turn on the power, and adjust
the voltage control to obtain the line-to-line voltage of ES given in Figure 7-3. Record the value of the
line voltages, as well as the average value of the primary line voltage [meter Avg (E1, E2, E3)].
E1-2 =________V E6-7 =________V E11-12 =________V
Average line voltage (primary) =________V
Figure 7-3. Three-Phase Transformer Connected in Delta-Wye.
20. Observe the voltage and current phasors on the Phasor Analyzer.
Paste the results of Phasor Analyzer here.
21. Does the display confirm that the voltage and current phasors are in phase? 󠄁Yes 󠄁 No
22. Turn off the power without modifying the setting of the voltage control. Connect meter inputs E1, E2,
and E3 to now measure the line voltages E3-8, E8-13, and E13-3 on the secondary side.
E3-8 =________V E8-13 =________V E13-3 =________V
23. Observe the voltage and current phasors on the Phasor Analyzer.
Paste the results of Phasor Analyzer here.
24. Does the Phasor Analyzer display show that the voltage phasors lead the current phasors by 30︒?
󠄁Yes 󠄁 No
Note: Since the currents in the secondary are in phase with the voltages in the primary, the Phasor
Analyzer display is equivalent to observing all voltage phasors at the same time, except for the
difference in scale between the parameters.
25. Return to the Metering application and record the measured values for the line voltages at the secondary,
and also the average value of the secondary line voltage [meter Avg (E1, E2, E3)].
E3-8 =________V E8-13 =________V E13-3 =________V
Average line voltage (secondary) =_________V
26. Calculate the ratio Average secondary line voltage / Average primary line voltage using the values
recorded in steps 19 and 25.
Average secondary line voltage
= =
Average primary line voltage
27. Is it approximately equal to √3? 󠄁Yes 󠄁 No
28. Turn off the power and connect meter inputs I1 and I2 to measure the line and phase currents on the
primary side of the delta-wye configuration by opening the circuit at points X and Y shown in Figure
7-3. Remember to reconnect the load resistors at the secondary when meter inputs I1 and I2 are
disconnected.
I1(LINE) =________A I2(PHASE) =________A
29. Turn on the power and calculate the ratio ILINE / IPHASE for the primary circuit using the measured
currents.
𝐼𝐿𝐼𝑁𝐸
= =
I𝑃𝐻𝐴𝑆𝐸
30. Is the ratio approximately equal to √3? 󠄁Yes 󠄁 No
31. Is the line current on the primary side approximately equal to the line current on the secondary side?
󠄁Yes 󠄁 No
32. Ensure that the Power Supply is turned off, the voltage control is fully ccw, and remove all leads and
cables.
Conclusion
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