Lab Experiment No 05
Title:Performance parameter of Three Phase Transformers
Objective:
The objectives of this experiment are to find the approximate per phase equivalent circuit parameters of a
3-φ transformer bank using short circuit and open circuit tests and to determine the regulation and
efficiency of the transformer bank through load test. The regulation and efficiency of the transformer
bank determined through load test will be compared with those calculated using the transformer
parameters.
Apparatus:
1. 1 3-φ Verica
2. 2 Test tables
3. 4 mustimeter’s
4. 2 wattmeter’s
5. 1 15 kVA 3- φ transformer Bank
6. 1 3-φ Resistive load bank with fan
7. 1 3-φ Capacitive Load Bank
Procedure:
1. Short Circuit Test:
a) Refer to Fig.1 for Short circuit test. Connect the high voltage windings of each 1-φ transformer in
parallel and then connect them in STAR configuration. Connect the low voltage windings of each 1-φ
transformer in parallel and then connect them in DELTA configuration. Make sure that the transformer is
connected according to nameplate specifications.
b) Connect the three phases of the low voltage windings to test table 2. Connect the three phases of the
high voltage windings through the test table to the output terminals of the variac. Make sure that all test
table line switches are open. Connect the input terminals of the variac to the 120V AC power panel. Do
not turn on power. Have the lab instructor check your set up.
c) With the test table's line switches still open, turn on power and adjust the variac until its output voltage
is zero.
d) Calculate the rated current for the input windings. Check your value with the lab instructor. Make sure
that your current transformer is set up to handle this current.
e) Protecting the measuring instruments, close the test table line switches. Immediately after closing the
line switches check the current in lines 1,2 and 3. The current should be close to zero. If the current is not
close to zero de-energize your circuit and recheck it
f) Increase the output voltage of the variac until the ammeter in line 1 indicates rated current. Measure
and record VH12, VH23, VH31, IH1, IH2, IH3, IX1, IX2, IX3, PHWM1 and PHWM2. Protect your measuring
instruments and de-energize the circuit. Readings should be taken with great precaution as you may see
currents as high as 100A!
2. Open Circuit Test:
a): Refer to Fig for Open circuit test. Connect the high voltage windings of each 1-φ transformer in
parallel and then connect them in STAR configuration. Connect the low voltage windings of each 1-φ
transformer in parallel and then connect them in DELTA configuration. Make sure that the transformer is
connected according to nameplate specifications.
b): Connect the three phases of the high voltage windings to test table 1. Make sure that the output
connections are open circuited! Connect the three phases of the low voltage windings through test table 2
to the output terminals of the 120V AC power panel. Make sure that all test table line switches are open.
Do not turn on power. Have the lab instructor check your set up.
g): Measure and record VX12, VX23, VX31, IX1, IX2, IX3, PXWM1, PXWM2, VH12, VH23 and
VH31. Readings should be taken with great precaution as you may see voltages as high as 420V!
Circuit Diagram:
Table1:
Short Circuit Test:
Quantity
HV Side
Readings
PHWM1
PHWM2
VH12
VH23
VH13
IH1
IH2
IH3
LV Side
Readings
IX1
IX2
IX3
Measured reading
Table 2:
Open Circuit Test:
Quantity Measured reading
LV Side
Readings
PXWM1
PXWM2
VX12
VX23
VX13
IX1
IX2
IX3
HV Side
Readings
VH1
VH2
VH3
Circuit Diagram of Short circuit Test :
Circuit Diagram of Open Circuit Test: