Tshwane University of Technology
Department Electrical
Engineering
Experimental 1 Report
Surname & Initials: L.V Sebaetse
Student Number : 221275950
Project Number:
Date: 18 March 2022
Qualification: Beng Tech Electrical engineering
Subject Name: Conversion Systems
Project Heading: The Polarity Testing of Single-phase
Transformers
Lecturer: Mr. A.J. Visser
1. Abstract
Normally, when a flow of current is present in a conductor then there is always a
query whether it is a neutral or a phase. An electric tester is used to check the wire.
When we check the two terminals of batteries, one acts like a positive and the other
one works like a negative terminal. It is known as a DC supply. In this scenario, the
flow of current includes only a single way which does not rotate. In AC supply, the
direction of current is reversed for each cycle because the current direction is not
constant here. Hence, for the operation of any device polarities of its terminals must
be known for proper connections.
We do polarity tests on electrical equipment such as transformers to ensure that we
connect the same polarity windings and not the opposite ones. If we accidentally
connect the opposite polarities of the windings, it will result in a short-circuit and
eventually damage the machine. An experiment was conducted to test the polarity of
a single phase transformer, whether its additive or subtractive. It was found that the
single phase transformer used for this experiment was subtractive. If the voltage
difference of the primary and secondary of the transformer being subtractive.
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2. Index/content
Table of Contents
1. Abstract
1
2. Index/content
2
Table of Figures
2
3. Purpose
3
4. Project design
3
4.1 Equipment
3
4.2 Parts list
3
4.3 Circuit Diagram
3
4.4 Wiring list
4
4.5 Procedure
4
4.6 Safety Procedures
5
5. Results and/or Findings:
6
6. Comments and Conclusion:
6
7. References:
6
8. Appendix A
7
Assignment
7
Table of Figures
Figure 1. . Single phase transformer polarity testing circuit diagram.
Figure 2. Single phase transformer with numbered wire connections.
Figure 3. Single phase transformer polarity testing using the battery method.
3
4
7
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3. Purpose
The purpose of this experiment was to determine whether a single phase transformer had either an
additive polarity or subtractive polarity.
4. Project design
4.1 Equipment
●
A single phase transformer of 100VA, 230/15.6V.
●
An AC variable power supply.
●
A voltmeter.
●
Leads.
4.2 Parts list
The list of all the components used for this experiment are mentioned below:
● A calculator.
● Nine jumper cables
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4.3 Circuit Diagram
Figure 1. . Single phase transformer polarity testing circuit diagram.
4.4 Wiring list
Figure 2. Single phase transformer with numbered wire connections.
The list of connections done for this experiment can be seen in figure 2 above, with
numbered connections a given below:
● Wire connection label 1 was connected between the voltmeter V1 and primary
transformer windings H1.
● Wire connection label 2 was connected between the voltmeter V1 and
secondary transformer windings H1.
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● Wire connection label 3 was connecting low voltage primary windings H2 and
secondary windings L1of the transformer together.
● Wire connection 5 was connecting the ground terminal of the voltmeter to low
voltage primary winding of transformer H2.
● Wire connection 4 was connecting the positive terminal of the voltmeter to the
high voltage primary winding of transformer H1.
● Wire connection 7 was connecting the single phase transformer, low voltage
primary winding H1 to an AC variable power supply.
● Wire connection 6 was connecting the single phase transformer, highvoltage
primary winding H1 to an AC variable power supply.
● Two wire connections were made to the voltmeter ground terminal and AC
variable power supply, and another to both equipment to label 3 wire
connections.
4.5 Procedure
The procedure that was followed to carry out the polarity test of a single phase
transformer is listed below:
● Connect the primary windings of the transformer to an alternating current
source of 230 volts.
● Connect a voltmeter V1 between primary windings and secondary windings of
the transformer's high and low voltage terminals.
● Connect a voltmeter V2 across the primary windings of the transformer’s high
and low voltage terminals.
● Connect the jumper between primary windings and secondary windings of the
transformer’s high voltage and low voltage terminals.
● The last part is to switch on and carefully turn the variable supply till the rated
high voltage is indicated on the voltmeter, V2.
Interpretation of the voltmeter readings:
● If the reading of V1 > V2, the polarity is additive. This then indicates that H1
and L1 are diagonally opposite.
● If V1 < V2, the polarity is subtractive and H1 and L1 are adjacent.
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4.6 Safety Procedures
The safety procedures that need to be followed when performing this experiment are
as follows:
● No eating and drinking allowed in the laboratory as this can cause distraction
and lead to damaging of equipment.
● Never change wiring of the circuit while the power source is turned on.
● Maintain a work space clear of extraneous material such as books, papers,
and clothes.
● Use only tools and equipment with non conducting or exposed wire handles
when working with electrical devices.
● Turn off the power of the equipment before inspecting it.
● Turn off circuit breakers or unplug the equipment.
● To turn off a safety switch, use your left hand (wear insulating gloves made of
leather or heavy cotton or rubber). Circuits may discharge violently when
being turned on or off and the cover to the junction box may be blown open.
● Avoid contacting circuits with wet hands or wet materials.
● Stay focused, observe and be aware of your surroundings.
● Always check circuits for proper grounding with respect to the power source.
● Keep access to electrical panels and disconnect switches clear and
unobstructed.
● Never plug leads into a power source unless they are connected to an
established circuit.
● Once done with the laboratory equipment and tools switch them off and return
everything to its storage.
● Make sure the work bench is neat when done with the experiment.
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5. Results and/or Findings:
The measured voltage across V2 was 220 volts and the measured voltage across V1
was 105 volts. The measured current was 0.164 amperes.
6. Comments and Conclusion:
The results show that V2 is greater than V1, which means that If V1 < V2, the
polarity is subtractive and H1 and L1 of the single phase transformer are adjacent to
each other.
7. References:
[1] Circuit globe, ‘Polarity Test of Transformer’, Available at
https://circuitglobe.com/polarity-test-of-transformer.html, (Accessed: 18 March 2022).
[2] https://www.electrical4u.com/transformer-polarity-test/
[3] https://www.ee.iitb.ac.in/course/~emlab/assets/polarityxmr.pdf
[4]
https://www.labmanager.com/lab-health-and-safety/electrical-safety-in-the-lab-20059
[5] https://ehs.ucsc.edu/programs/research-safety/safe-lab-practices.html
[7]
https://pressbooks.bccampus.ca/singlephasetransformers/chapter/additive-and-subtr
active-polarity/
[8] https://energycentral.com/c/iu/transformer-polarity
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8. Appendix A
Assignment
The alternative method of testing transformer polarity is the battery method or direct
current (DC) method. When the switch is closed, as in figure 3 below, if the
secondary voltage shows a positive reading, with a moving coil meter, the assumed
polarity is correct. If the meter kicks back then the assumed polarity is wrong.
Figure 3. Single phase transformer polarity testing using the battery method.
The battery method of determining polarity of a transformer would be limited by the
size of the battery being used, as the size of the battery might be small to induce
enough electromotive force across the windings. The importance of knowing how to
determine transformer polarities is fundamental to grasping how transformers
function and how they’re utilized. Understanding polarity is essential to properly
paralleling single-phase transformers and connecting instrument transformers
(current and potential) to metering devices and protective relays.
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