# EXPERIMENT 4 Single and Three-Phase Transformer Equivalents

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EXPERIMENT 4
Single and Three-Phase Transformer Equivalents

1.        Objectives: Demonstrate understanding of the single phase and three-phase transformer
models, how to use them and how to find their equivalent circuit parameters.

LAB INSTRUCTOR WILL HELP YOU PREPARE THE MATLAB CODE.

2.        Statement of the Problem
Single-Phase Equivalent Circuits
A 100-kVA, 4000/400 V single-phase transformer has the parameters as shown in Fig. 1.
(a) Determine the equivalent circuit referred to the high voltage side
(b) Find the primary voltage and the voltage regulation when the transformer is
operating at full load, 0.8 power factor lagging and 240 V.
(c) Find the primary voltage and the voltage regulation when the transformer is
operating at full load, 0.8 power factor leading and 240 V.
(d) Verify your answer by using MATLAB. A sample code will be provided. Obtain
transformer efficiency for Parts (b) and (c).

+                                                                                       +
0.4     j1.0                                          0.04      j0.1
j2000Ω

1500Ω

V1                                                                                      V2

-                                                                                       -
10:1
Fig. 1 Transformer equivalent circuit
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3.     Statement of the Problem
Three-Phase Equivalent Circuits

Three identical 5-kVA single-phase transformers, rated at 120V/240V are to be connected in a
three-phase bank. Each transformer has a series impedance of 0.004 + j 0.18 Ω referred to its
120V side winding.
(a) The transformers are connected Y on its high voltage side and Y on the low
voltage side. Calculate
(i) the voltage and power rating of the 3-phase connection
(ii) the equivalent impedance as referred to its low voltage side and high
voltage side.
a                                                                           a′

?                                                                                     ?
b                                                                          b′

c                                                                           c′

(b) The transformers are connected Y on its high voltage side and ∆ on the low
voltage side. Calculate
(i) the voltage and power rating of the 3-phase connection
(ii) the equivalent impedance as referred to its high voltage side and low
voltage side.
a                                                                          a′

?                                                                                     ?
b                                                                          b′

c                                                                            c′
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(c) The transformers are connected ∆ on its high voltage side and Y on the low
voltage side. Calculate
the voltage and power rating of the 3-phase connection
(ii) the equivalent impedance as referred to its high voltage side and low
voltage side.

a                                                                           a′

?                                                                                        ?
b                                                                               b′

c                                                                           c′

(d) The transformers are connected ∆ on its high voltage side and ∆ on the low
voltage side. Calculate
the voltage and power rating of the 3-phase connection
(ii) the equivalent impedance as referred to its high voltage side and low
voltage side.
a                                                                      a′

?                                                                                    ?

b                                                                          b′

c′
c

(e) If a rated load at 0.8 power factor lagging is connected to the HV side of the
∆-Y transformer of Part (b) at rated voltage, find the line voltage at the low
voltage side of the transformer. Draw the phasor diagram. Also find the
voltage regulation and the efficiency.

4. Describe your Solution to the Problem and any problems encountered.

5. Results Obtained:
-Show your results. Include plots if requested.
-Show a listing of any programs or changes to programs that you made.

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