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MISSISSIPPI STATE UNIVERISTY ELECTRICAL AND COMPUTER ENGINEERING DEPARTMENT ECE 3414 LAB MISSISSIPPI STATE UNIVERISTY
ELECTRICAL AND COMPUTER ENGINEERING
DEPARTMENT
ECE 3414 LAB
TITLE:
Open and Short Circuit Test of Transformers
OBJECTIVE:
To illustrate the methods of making open-circuit and short-circuit
tests of transformers, and to determine the characteristics of the
transformer using data taken in such tests.
PROCEDURE:
The 2400-240 volt transformer is to be used. The high-voltage
winding will be considered to be the primary winding.

With the primary winding open, apply the rated voltage on the
secondary side of the transformer (V
rated
= 240 VAC) and
measure the power input and exciting current.
With the secondary short-circuited, measure the voltage, power
input, and current. The voltage should be set so that one
reading is made at rated current. Do not exceed the rated
current (0.625 A) of the transformer.
The instructor will demonstrate the method to determine values
as provided on the transformer panel to compare with
measured values.
DANGER: The primary side of the transformer will
have HIGH VOLTAGE (2400 VAC) across it during the
test. Therefore, when performing the test, ensure
that all personnel are clear of all terminals,
connections, etc., when the circuit is energized. WIRING DIAGRAMS:


I
ac

V
ac

V
src

240 V
AC

A

B

1
2
3
4
G
+-
W
+-
+

-

Figure 1: Schematic for Open Circuit Test

V
ac
I
ac
= 625 mA
V
src

(see I
ac
)
G
+-
W
4
3
2
1
B
A
+

-

+-
Figure 2: Schematic for Short Circuit Test REPORT:
Theory:
1. Discuss flux linkage and how it relates to the turns ratio.
2. Discuss each component of the equivalent circuit.
3. Discuss the method of using an open circuit test to find
equivalent circuit values.
4. Discuss why rated low voltage is used in the open circuit test.
5. Discuss the method of using a short circuit test to find
equivalent circuit values.
6. Discuss why high voltage rated current is used in the short
circuit test.

CALCULATIONS:
Open Circuit Test Formulas (V
rated
= 240V)
Power Factor:



( )
cos
oc
oc
oc oc
P
pf
V I =
=

Core loss current:



( )
cos
h e
oc
oc
I
I +
=

Core Resistances:



2
oc
CLV
h e
CHV
CLV
p
s
V
R
I
R
a R
N
a
N
+
=
= =

Magnetizing current:



( )
sin
oc
oc
I
I
=

Magnetizing Reactances:



2
oc
mLV
mHV
mLV
V
X
I
X
a X =
=
Short Circuit Test Formulas (I
rated
= 625 mA)



1
2
2
2
1.5
625
2.4
rated
rated
sc
eqHV
sc
sc
eqHV
sc
eqHV
eqHV
eqHV
S
kVA
I
mA
V
kV
P
R
I
V
Z
I
X
Z
R
=
=
=
=
=
=
Other formulas:



2
_
%
100%
base
base
base
actual unit
pu
base
pu
V
Z
S
Z
Z
Z
Z
Z
=
=
=