EEL1010 Introduction to Electrical Engineering
Lab Report
Roll Number
B23CS1044
Name
Neeraj kumar
Experiment Number
10
Experiment Title
Transformer Assembly and Equivalent Circuit
Lab Partner’s Name
Prajna Agrawal
Sake Akshay
Objective
The aim of this experiment is to investigate the assembly of a transformer and ascertain its
equivalent circuit parameters through the execution of Open-Circuit and Short-Circuit tests.
Brief Theory and Circuit DiagramThis experiment involves disassembling and assembling a transformer, winding secondary
coils, and measuring voltages in various configurations and determining equivalent circuit
parameters.
Transformer Assembly
Experiment A To conduct the test, first, connect the transformer's primary winding to a variac and supply
230 V as input.
Use a multimeter to measure the voltage on each of the two secondary windings individually.
Next, connect two terminals from each of the secondary windings in series and measure the
total output voltage across the remaining terminals.
Ensure four distinct combinations are tested (S1-S2, F1-F2, S1-F2, S2-F1), avoiding
connection between endpoints of the same winding.
This comprehensive testing approach provides a detailed analysis of the transformer's
performance under different configurations.
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Observation table-
Connection between
Measurement between
Multimeter Reading (V)
S1 – S2
F1 – F2
12.16
S1 – F2
F1 – S2
0.4
F1 – S2
S1 – F2
2
F1 – F2
S1 – S2
1
Transformer Equivalent CircuitThe determination of equivalent circuit parameters in a transformer involves two essential
tests:
Open-Circuit test (OC Test) and the Short-Circuit test (SC Test). These parameters, derived
from the tests, are used in evaluating the transformer's regulation and efficiency under
diverse load and power factor conditions.
Experiment a. Open Circuit (OC) Test-
In the open-circuit test, the transformer's low-voltage (LV) side receives the rated voltage at
the rated frequency, while the high-voltage (HV) side remains open, as shown in the figure.
The recorded readings include V1 for voltage, Io for the no-load current measured by the
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ammeter, and W for the wattmeter, representing both core and winding losses. The ammeter
registers a small no-load current (2 to 10% of rated load current), and V1 measures the
applied voltage on the LV side, set at 115 V, the rated voltage.
Procedure for Open Circuit Test
1. Make the connections as per the circuit diagram for transformer of rating 1 kVA,
connect wattmeter to setting (2.5 A, 150 V).
2. After checking the minimum position of autotransformer, switch ON the Power
supply.
3. Adjust the autotransformer variac to get the rated low voltage (LV rating).
4. Note the voltmeter, ammeter and wattmeter readings on LV side.
5. Bring the autotransformer to minimum position again and switch OFF the power
supply.
Observation Table for Open Circuit Test
S. No.
1.
V1
Io
Wi
114
1.8
20
cos ϕ = W /V Io
i
1
0.097
Shunt parameters
R = 649.8 ohm
X = 260.63 ohm
cL
mL
Experiment b. Short Circuit (SC) Test-
In the short-circuit test, we energize the high-voltage (HV) side with the low-voltage (LV) side
shorted.
Apply a voltage such that the rated current flows through the windings.
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Record readings from the voltmeter, ammeter, and wattmeter corresponding to the rated
current. In the short-circuit test, the wattmeter reading is equivalent to the copper losses
(Wcu) in the windings.
This test provides crucial information about the transformer's behaviour under short-circuit
conditions.
To conduct the Short Circuit Test:
1. Carefully adjust the variac until the rated current flows through the circuit. For a 1 kVA
transformer, it's 4.35 A. The variac voltage should typically be set between 10 – 20 V.
2. Make the necessary connections according to the circuit diagram, ensuring the low-voltage
(LV) side of the transformer is shorted. For a 500 VA transformer, set the wattmeter to (2 A,
150 V), and for a 1 kVA transformer, use (5 A, 150 V).
Observation Table for Short Circuit Test
S. No.
Vsc
Isc
Wsc
1.
15
4.3
40
Series parameters
X = 2.71 ohm
H
R = 2.16 ohm
H
Experiment c. EfficiencyThe efficiency (η) of the transformer under any load xS (where S is the capacity of the
transformer in VA, x is the loading factor in per unit, and cos ϕ is the power factor of the load)
can be computed using the formula:
η = xS cos ϕ / (xS cos ϕ + x W +W ).
2
sc
oc
This formula allows for the determination of transformer efficiency by considering both
copper and iron losses under the specified load conditions.
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Observation Table for Efficiency
S. No.
Power Factor
Load Factor (x)
1
cos ϕ = 0.6
x = 0.2
x = 0.4
x = 0.6
x = 0.8
x = 1.0
2
cos ϕ = 0.8
x = 0.2
x = 0.4
x = 0.6
x = 0.8
x = 1.0
3
cos ϕ = 1.0
x = 0.2
x = 0.4
x = 0.6
x = 0.8
x = 1.0
Efficiency (η)
0.84
0.90
0.91
0.91
0.90
0.88
0.92
0.93
0.93
0.93
0.90
0.93
0.94
0.94
0.94
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Experiment d. RegulationThe regulation vs. power factor (PF) curve illustrates how the voltage regulation of a
transformer varies with the power factor of the load.
Regulation: It measures a transformer's ability to maintain a nearly constant output voltage
under different load conditions. The regulation is expressed as a percentage and is calculated
as
(∣V1∣−∣V2∣)/∣V1∣
Power Factor (PF): It represents the phase relationship between voltage and current in an AC
circuit. It can be leading (inductive) or lagging (capacitive).
Observation Table for Regulation Curve
S. No.
1
Power Factor
Lag
Power Factor (x)
cos ϕ = 0.2
cos ϕ = 0.4
cos ϕ = 0.6
cos ϕ = 0.8
cos ϕ = 1.0
2
Lead
cos ϕ = 0.2
cos ϕ = 0.4
cos ϕ = 0.6
cos ϕ = 0.8
cos ϕ = 1.0
Regulation (ε)
0.89
0.96
0.99
0.96
0.62
-0.63
-0.46
-0.25
0.035
0.62
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Regulation vs. Power Factor Curve:
Lagging-
Leading-
ConclusionIn conclusion, the Transformer Assembly and Equivalent Circuit experiment provided valuable
insights into the behaviour of transformers. Through practical assembly and circuit analysis,
we gained a better understanding of the interplay between primary and secondary voltages,
current components, and the transformer's regulation. This hands-on experience reinforced
theoretical concepts and demonstrated the impact of factors such as resistance, reactance,
and power factor on the transformer's performance.
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