Download Lab 2

ECE 385
Lab 2 Measurements on Single-Phase Transformers
Due: Oct 4, 2007
Group 27Bravo
Authors:
David Gitz
Scot Shelton
Salman
B. Measurement of the Transformer Ratio
Objective:
To measure the transformer ratios in a multi-terminal transformer.
Theory:
V
N
o  2 a
V
N
i
1
Procedure:
2. Connect the transformer primary and secondary windings in series, as shown in fig. 5. Make sure the
terminal switches are in the up position. The transformer connected in this manner is used as a step-up
transformer: the X side (low voltage) will be connected to the source, and become the primary side; the
H side (high voltage) will be connected to the load, and become the secondary side.
3. Apply 60 V across the X1-7, and measure, using a hand-held voltmeter, the voltages between H1-5,
H2-5, and H4-5.
Results:
Series Connection: (Actual)
Supply:
60.0 Vac
H1-5:
120.0 Vac
a=2
H2-5:
104.0 Vac
a = 104.0/60.0=1.733
H4-5
60.0 Vac
a = 1.0
Parallel Connection: (Theoretical)
Supply:
60.0 Vac
H1-3:
60.0 Vac
H4-5:
60.0 Vac
Conclusion:
Transformers can be used to provide operator-selectable input and output voltages as are required by
their application.
Questions/Problems:
Since the Series connection has an HV output of 120.0, in parallel the 2 outputs should be half as much,
i.e. 60.0 Vac each.
C. Open-Circuit Test
Object:
To perform measurements on the transformer under open-circuit (no-load) conditions; to measure the
core losses and the excitation current; to use the measurements to characterize the magnetizing branch
of the transformer circuit.
Theory:
It is possible to measure certain parameters of a transformer circuit using the Open-Circuit test.
Procedure:
1. Connect the transformer as in fig. 6, with the X side connected to the variable source and the
instruments shown in the figure, and the H side terminals connected to a voltmeter.
2. Turn on the power source while the voltage knob is turned to zero. Increase the source voltage to 60
V. Record the voltage Vh across the secondary.
3. Record the power into the primary Px, and the current into the primary Ix.
Results:
I x  3.0 mA
Voc  60.0 V
Poc  .15W
Conclusion:
Using the open-circuit test, it is possible to measure the Resistance of the Core and the Reactance of the
Core.
Questions/Problems:
Rc 
Voc 2
Poc
 24.0k
 I  V 2 
X m  1  oc    oc 
 Voc   Poc 
2
2
 36k
D. Short-Circuit Test
Object:
To perform measurements on the transformer under secondary side short-circuit, to measure the series
losses, to use the measurement sot characterize the series impedance of the transformer equivalent
circuit.
Theory:
Using the Short-Circuit test, it is possible to measure other certain parameters of a transformer.
Procedure:
1. Connect the transformer in fig. 7, with the H side terminals shorted, and the X side connected to the
variable source through the same instruments in the previous procedure.
2. Turn the power source on, while the voltage knob is turned to zero. Slowly turn the voltage knob up
to raise the voltage. The current will rise rapidly. Slowly increase the voltage until the primary current
Ix is .85 A. This is the rated primary current. Record the current, the power Px, and the primary voltage
Vx across X1-7.
Results:
Vsc  9.00 V
I sc  .85 A
Psc  3W
Req 
Psc
 4.15 
I sc 2
2
V 
2
X eq   sc   Req  3.12j
 I sc 
Rated Current: .428 A
Ploss  I sc Req  2.86W
2
PFLloss  Vsc I sc  7.65W

Pout
PFLloss
7.65W
 100% 

 .7038
Pin
PFLloss  Poc  Ploss 7.65W  .36 W  2.86 W
Conclusion:
By using the Short-Circuit test, it is possible to measure the resistance of the transmission wires and
their inductance.
Graphs:
Req
4.15 Ohms
1
Xeq 3.12 Ohms
2
1
2
2
Z-Load
Xm
40.0 kOhms
Rc
333.0 Ohms
2
Vsource
1
1
E. Operation Under Load
Object:
To measure the transformer performance under load; to observe the effects of the load power factor on
the transformer voltage regulation.
Theory:
Operationally parameterizing a transformer system is done while the system is under load.
Procedure:
1. Make the connections in fig. 8. Connect the current and watt-meter to the secondary (H side).
Connect the resistive and reactive part of one phase of the RLC-100 load across the secondary as showin
in the figure. Leave the terminals of the other phases open.
2. Add resistive load. Set switches 1 through 4 of the resistive load to the up position and the remaining
switches in the down position.
3. Turn the reactance knob to the full lagging position.
4. Adjust the primary voltage until the secondary voltage is 120 V. Record the primary voltage Vx, the
load current Ih, and the load power Ph.
5. Turn the reactance knob to the zero position. Fine-tune the position by observing where the
secondary current indication is its minimum. Repeat step 4.
Results:
Lagging:
V X  72.1V
I H  .38 A
PH  32 W
VH  aVX  142.2V
S L  VH I H  142.2V  .38 A  54.8VAR
QL 
S L  P  54.82  32 2  44.49 VA
2
 L  tan 1
2
QL
 54.27
PH
pf L  cos   .584
VR 

VNL  VFL
V  VH
120.0  142.2
100%  oc
100% 
100%  15.6%
VFL
VH
142.2
PL
32W

 .9709
2
2
PL  Req  I H  Poc 32W  4.15  .38 A  .36W
Unity:
V X  72.3V
I H  .25 A
PH  34 W
VH  aVX  144.6V
S L  VH I H  36.15VAR
QL 
S L  PH
 L  tan 1
2
2
12.28VA
QL
19.86
PH
pf L  cos   .94
VR 

VNL  VFL
V  VH
120.0  144.6
100%  oc
100% 
100%  17.%
VFL
VH
144.6
PL
34W

 .9821
2
2
PL  Req  I H  Poc 34W  4.15  .25 A  .36W
Conclusion:
This lab has fulfilled its purpose of defining different characteristics of a transformer system and
realizing the realistic factors of a non-ideal transformer.