Bangladesh University of Engineering and Technology
Department of Electrical and Electronic Engineering
EEE 272 – Electrical Machines and Electronics Sessional
Experiment 01
CHARACTERIZATION OF SINGLE-PHASE TRANSFORMER
Determination of Turns-ratio, Equivalent Circuit Parameters, and
Calculation of Efficiency and Regulation
Evaluation Form:
IMPORTANT! You must complete this experiment during your scheduled lab period. All
work for this experiment must be demonstrated to and verified by your lab instructor before
the end of your scheduled lab period.
STEP DESCRIPTION MAX SCORE
1 Pre-Lab 5
2 Data Collection Part A 3
3 Report Part A 2
4 Data Collection Part B 8
5 Report Part B 7
Total 25
Signatureof Evaluator: ___________________________________________________
AcademicHonestyStatement:
IMPORTANT!Please carefully read and sign the Academic Honesty Statement, below. You will not receive
credit for this lab experiment unless this statement is signed in the presence of your lab instructor.
“In signing this statement, I hereby certify that the work on this experiment is my own and that I have not copied
the work of any other student (past or present) while completing this experiment. I understand that if I fail to
honor this agreement, I will receive a score of ZERO for this experiment and be subject to possible disciplinary
action.”
Name: LabGroup:Date:
Student ID Signature:
Contents
Evaluation Form: ................................................................................................. 1
AcademicHonestyStatement:.............................................................................. 1
Pre-lab Study........................................................................................................ 1
1 Lab Overview ............................................................................................... 2
2 Theory ........................................................................................................... 2
3 Equipment .................................................................................................... 3
4 PART A: Determination of turns-ratio of 1φ power transformer ......... 4
4.1 Experimental Set-Up: ............................................................................. 4
4.2 Procedure ................................................................................................ 4
4.3 Data Collection ....................................................................................... 5
4.4 Report...................................................................................................... 5
5 PART B: Determination of the equivalent circuit parameters of a
transformer and Calculation of efficiency and voltage regulation. ........ 6
5.1 Experimental set-up ................................................................................ 6
5.2 Procedure: ............................................................................................... 6
5.3 Data Collection ....................................................................................... 7
5.4 Report...................................................................................................... 8
Pre-lab Study
Before attempting this lab, please do the following:
1. Reading Assignment:
• Reference: Chapter 2, Electric Machinery Fundamentals- Stephen J Chapman
• Read the lab-sheet BEFORE coming to class.
2. Draw the equivalent circuit of a real transformer. Name each of the components and
also, convert the equivalent circuit referred to its primary voltage level only.
3. A 2 KVA 230/115-V transformer has been tested to determine its equivalent circuit.
The measurement (on primary side) from the tests are as follows.
Open Circuit Test: VOC=230 V, IOC= 450 mA, POC=30 W
Short Circuit Test: VSC=13.2 V, ISC=6 A, PSC= 20.1 W
(a) Find the equivalent circuit parameters of the transformer.
(b) Find the transformer’s voltage regulation at rated conditions and 0.8 pf (lag).
(c) Find the transformer’s efficiency at rated conditions and 0.8 pf (lag).
Note down the equations clearly, you will need to use them in lab as well.
EEE 272 – Electrical Machines and Electronics Sessional – Experiment 1 Page-01
The lab sheet is prepared by Dr. Orchi Hassan, Shoilie Chakma, Suzit Hasan Nayem EEE, BUET, on 26-Nov-
23
Experiment 1: Characterization of Single-phase Transformer
Determination of Turns-ratio, Equivalent Circuit Parameters, and
Calculation of Efficiency and Voltage Regulation
1 Lab Overview
At the end of this lab, you will be able to characterize a single phase power transformer by:
• Determination of its turns ratio
• Determination of its steady-state equivalent circuit parameters by performing open-
circuit and short-circuit tests
• Determination of its efficiency and voltage regulation.
2 Theory
A single-phase power transformer is a device which steps up or down a given voltage.
Typically, a transformerhas two windings. One is called the primary (usually the source
side) and the other is called thesecondary (usually the load side). If there are more than
two windings, the additional windingsare called tertiary windings. The windings are
wound on a core made of ferromagnetic material.There is usually no direct electrical
connection between the pairs of windings.A power transformer is usually employed for
the purpose of converting power, at a fixed frequency, from one voltage to another. If it is
used for converting power from a high voltage to a low voltage, it is called a step-down
transformer. The conversion efficiency of a power transformer is extremely high
andalmost all of the input power is supplied as output power at the secondary winding.
Consider a magnetic core as shown in Fig. 2.1,
carrying primary and secondary windings having N1
and N2 turns, respectively. When a sinusoidal
voltage is applied to the primary winding, a flux
will exist in the core which links both the primary
and secondary windings, inducing the RMS
voltages:
𝑉1 = 4.44 𝑓 𝑁1 𝜙 (in primary winding)
𝑉2 = 4.44 𝑓 𝑁2 𝜙 (in secondary winding) Fig. 2.1: Ideal Transformer
The transformer is said to have a turns ratio of:
𝑉1 𝑁1 𝐼2
𝑎= = =
𝑉2 𝑁2 𝐼1
In Part A of this experiment we determine the turns ratio of the supplied transformer
using this formula.
Equivalent Circuit of Transformer
The transformer may be represented by the equivalent circuit shown in Fig. 2.2. The
parameters may be referred to either the primary or the secondary side.The series
resistances R1 and R2 represent the copper loss in the resistance ofthe two windings. The
series reactances X1 and X2 are leakage inductances andaccount for the fact that some of
the flux established by one of the windingsdoes not fully couple the other winding. These
reactances would be zero if therewere perfect coupling between the two transformer
windings.The shunt resistance Rp accounts for the core losses (due to hysteresis andeddy
currents) of the transformer. The shunt inductance Xp is representative ofthe inductances
of the two windings and would be infinite in an ideal transformer if the number of turns
EEE 272 – Electrical Machines and Electronics Sessional – Experiment 1 Page-02
The lab sheet is prepared by Dr. Orchi Hassan, Shoilie Chakma, Suzit Hasan Nayem EEE, BUET, on 26-Nov-
23
of the two windings were to be infinite.
Fig 2.2: Equivalent circuit of single-phase transformer
A knowledge of the equivalent circuit parameters permits the calculation of transformer
efficiency and of voltage regulation without the need to conduct actual load tests. But
experimental data must first be obtained in order to determine those parameters.
Fig 2.3: Equivalent circuit of single-phase transformer referred to the primary side
It will be confirmed at the end of Part B of the experiment that the impedances of the
series branch of the transformer equivalent circuit are substantially smaller than the
impedances of the parallel branch. Because of this large discrepancy in the magnitudes of
the elements we can redraw the equivalent circuit shown in Fig. 2.3. The large difference
in the magnitudes of the transformer parameters allows for the determination of the
elements in the series branch using one set of measurements and the elements in the
parallel branch using another set of measurements.
In Part B of the experiment, we will also be determining the efficiency and voltage
regulation of the transformer from practical measurements. The practical measurements
can then be compared to the calculated transformer efficiency and regulation from the
equivalent circuit.
3 Equipment
1) Two ac voltmeters/multimeters (0-300V, 0-150V)
2) Two ac ammeters (0-10A, 0-30V)
3) Two single phase wattmeters
4) One single phase transformer
5) One rheostat (current rating greater than or equal to 5A)
6) One inductance bank
7) One Variac (Variable Voltage Source)
8) Connecting Wires
EEE 272 – Electrical Machines and Electronics Sessional – Experiment 1 Page-03
The lab sheet is prepared by Dr. Orchi Hassan, Shoilie Chakma, Suzit Hasan Nayem EEE, BUET, on 26-Nov-
23
4 PART A: Determination of turns-ratio of 1φ power transformer
4.1 Experimental set-up:
Figure 4.1.1: Connection diagram for voltage ratio measurement
Figure 4.1.2: Connection diagram for current ratio measurement
4.2 Procedure
We will be measuring turns ratio of the transformer by measuring the voltage and current
ratio of the primary and secondary side.
• Note down the transformer ratings (Nameplate Data)
If it is not written on the transformer body, ask the lab instructor/attendant for details.
Voltage Ratio
1) Connect the primary (H1- H5) terminals of the primary side of the transformer to
the variable ac supply and set to 220V ac as shown in the Fig.4.1.1.
2) Measure the voltage at the supply, V1 (H1-H5) and across secondary V2(X1-X7).
3) Determine the turns ratio: 𝑎 = 𝑉1 /𝑉2
4) Repeat step1 to step3 for supply voltage of 180 V, 140V and 120 V.
5) Record the measured data in the data table.
Current Ratio
1) Make the connections to the transformer as shown in Fig. 4.1.2
2) Adjust the rheostat such that the reading of any ammeter does not exceed the
current rating of the ammeters and the rheostat.
3) Take four readings of both meters by adjusting the rheostat.
4) Find the turn ratio using the formula: 𝑎 = 𝐼2 (𝑋1 − 𝑋7 )⁄𝐼1 (𝐻1 − 𝐻5 )
5) Record the measured data in the data table.
EEE 272 – Electrical Machines and Electronics Sessional – Experiment 1 Page-04
The lab sheet is prepared by Dr. Orchi Hassan, Shoilie Chakma, Suzit Hasan Nayem EEE, BUET, on 26-Nov-
23
4.3 Data Collection
Transformer Ratings:
KVA rating:
Voltage ratings:
Current ratings:
Table 1: Data table for turns-ratio determination
Voltage Ratio Current Ratio
Supply Secondary Ratio Primary Secondary Ratio
Voltage Voltage 𝑉1 Load Current Current 𝐼2
𝑎= 𝑎=
V1(H1-H5) V2 (X1-X7) 𝑉2 𝑰𝟏 𝑰𝟐 𝐼1
1 220 V 1
2 180 V 2
3 150 V 3
4 120 V 4
4.4 Report
1. Determine the turn ratio (a) of the transformer from the voltage and current readings
using the appropriate formula. Discuss the discrepancies, if any.
Which method of determining turn ratio is more accurate and why?
2. Why transformers are rated in kVA instead of kW?
EEE 272 – Electrical Machines and Electronics Sessional – Experiment 1 Page-05
The lab sheet is prepared by Dr. Orchi Hassan, Shoilie Chakma, Suzit Hasan Nayem EEE, BUET, on 26-Nov-
23
5 PART B:Determination of the equivalent circuit parameters of a
transformer and Calculation of efficiency and voltage regulation.
5.1 Experimental set-up
Fig. 5.1.1: Connection diagram for open-circuit test
Fig. 5.1.2: Connection diagram for short-circuit test
Fig. 5.1.3: Connection diagram for loading test
5.2 Procedure:
Open Circuit Test:
1. Complete connections for the open circuit test at shown in Fig. 5.1.1
2. Apply rated voltage (VOC) to secondary side (Low Tension side, X1-X7).
3. Note the readings of the ammeter, voltmeter & wattmeter.
Short Circuit Test:
1. Complete connections for the short circuit test at shown in Fig. 5.1.2
EEE 272 – Electrical Machines and Electronics Sessional – Experiment 1 Page-06
The lab sheet is prepared by Dr. Orchi Hassan, Shoilie Chakma, Suzit Hasan Nayem EEE, BUET, on 26-Nov-
23
2. Gradually apply voltage across the primary side (High Tension side, H1-H5)of the
transformer until rated primary current (ISC) flows through the ammeter.
3. Note the readings of the ammeter, voltmeter & wattmeter.
Loading Test:
1. Complete connections for the loading test at shown in Fig. 5.1.3.
2. Apply rated voltage across the HT side.
3. First connect resistive load at LT side
4. Measure the current, voltage, and readings of the wattmeters on both sides for three
sets of load.
5. Now connect lagging load at LT side and repeat procedure 4.
6. Now connect leading load at LT side and repeat procedure 4.
7. Now repeat the loading test with the resistive/lagging/leading loads connected at HT
side.
5.3 Data Collection
Open circuit test (referred to LT side):
Input power (WOC), watts =
Input current (IOC), amps =
Input power (VOC), volts =
Short circuit test (referred to HT side):
Input power ( WSC), watts =
Input current ( ISC), amps =
Input power (VSC), volts =
Loading test (referred to LT side)
resistive load
Load V1 V2 I1 I2 WIN WOUT
lagging load
Load V1 V2 I1 I2 WIN WOUT
EEE 272 – Electrical Machines and Electronics Sessional – Experiment 1 Page-07
The lab sheet is prepared by Dr. Orchi Hassan, Shoilie Chakma, Suzit Hasan Nayem EEE, BUET, on 26-Nov-
23
leading load
Load V1 V2 I1 I2 WIN WOUT
5.4 Report
1. Determine the equivalent circuit of the transformer from your measurements.
i. Calculate the core loss resistance and magnetizing reactance of the transformer
from the open circuit test measurements.
ii. Calculate the copper loss components of the transformer from the short circuit
test measurements.
2. Efficiency and Voltage Regulation:
i. Determine the efficiency and voltage regulation from your measurements.
ii. Calculate the efficiency and voltage regulation of the transformer for the three
types of load used in the experiment theoretically using values found in (1).
iii. Compare the two results and comment.
EEE 272 – Electrical Machines and Electronics Sessional – Experiment 1 Page-08
The lab sheet is prepared by Dr. Orchi Hassan, Shoilie Chakma, Suzit Hasan Nayem EEE, BUET, on 26-Nov-
23
EEE 272 – Electrical Machines and Electronics Sessional – Experiment 1 Page-09
The lab sheet is prepared by Dr. Orchi Hassan, Shoilie Chakma, Suzit Hasan Nayem EEE, BUET, on 26-Nov-
23
