This document discusses short circuits, open circuits, and transformer tests. It explains that a short circuit allows current along an unintended path with little resistance, while an open circuit lacks a complete path for current flow. Transformer tests include open circuit and short circuit tests. The open circuit test determines core losses and shunt branch parameters, while the short circuit test determines copper losses and approximate circuit parameters. Instruments are connected and measurements recorded to evaluate losses and parameters from the tests.

1. By:
Name: Pooja Dubey
Course: EEE
Roll No:120104026

2. Short Circuit
Open Circuit
Transformer
Short Circuit Test
Open Circuit Test
Conclusion
Source

3. A short circuit is an electrical circuit that allows a current to
travel along an unintended path, often where essentially no
(or a very low) electrical impedance is encountered.
In circuit analysis a short circuit is a connection between two
nodes that forces them to be at the same voltage.
In an ideal short circuit, this means there is no resistance and
no voltage drop across the short.
In real circuits, the result is a connection with almost no
resistance. In such a case, the current that flows is limited by
the rest of the circuit.

4. An electrical circuit is an "open circuit" if it lacks a complete
path between the terminals of its power source; in other words,
if no true "circuit" currently exists, because for instance a
power switch is turned off.
The electrical opposite of a short circuit is an "open circuit",
which is an infinite resistance between two nodes.
The open circuit test, or "no-load test", is one of the methods
used in electrical engineering to determine the no load
impedance in the excitation branch of a transformer.
.

7. A transformer is a static electrical device that transfers energy by
inductive coupling between its winding circuits.
A varying current in the primary winding creates a varying magnetic flux
in the transformer's core and thus a varying magnetic flux through the
secondary winding. This varying magnetic flux induces a varying
electromotive force (emf) or voltage in the secondary winding.
In electrical engineering, two conductors are referred to as mutual-inductively
coupled or magnetically coupled when they are configured
such that change in current flow through one wire induces a voltage
across the ends of the other wire through electromagnetic induction. The
amount of inductive coupling between two conductors is measured by
their mutual inductance.

10. These two tests are performed on a transformer to determine:-
(i) equivalent circuit of transformer
(ii) voltage regulation of transformer
(iii) efficiency of transformer.
The power required for these Open Circuit test and Short
Circuit test on transformer is equal to the power loss occurring
in the transformer.

12. A voltmeter, wattmeter, and an ammeter are connected in LV side of
the transformer as shown in the figure below.
The voltage at rated frequency is applied to that LV side with the help
of a variac of variable ratio auto transformer.
The HV side of the transformer is kept open. Now with help of variac
applied voltage is slowly increase until the voltmeter gives reading
equal to the rated voltage of the LV side.
After reaching at rated LV side voltage, all three instruments reading
(Voltmeter, Ammeter and Wattmeter readings) are recorded.

13. The ammeter reading gives the no load current Ie.
As no load current Ie is quite small compared to rated current of the
transformer, the voltage drops due to this electric current then can
be taken as negligible.
Since, voltmeter reading V can be considered equal to secondary
induced voltage of the transformer. The input power during test is
indicated by watt-meter reading.
As the transformer is open circuited, there is no output hence the
input power here consists of core losses in transformer and copper
loss in transformer during no load condition.
The no load current in the transformer is quite small compared to
full load current so copper loss due to the small no load current can
be neglected.
Hence the wattmeter reading can be taken as equal to core losses in
transformer.

14. Let us consider wattmeter reading is Po.

15. These values are referred to the LV side of transformer as
because the test is conduced on LV side of transformer.
These values could easily be referred to HV side by
multiplying these values with square of transformation ratio.
Therefore it is seen that the open circuit test on transformer
is used to determine core losses in transformer and
parameters of shunt branch of the equivalent circuit of
transformer.

16. Open circuit Power Factor
PF = cos q = P
oc
V I
oc oc
Open circuit Power Factor Angle
q = cos-1 P
oc
V I
oc oc

18. A voltmeter, wattmeter, and an ammeter are connected in HV
side of the transformer as shown in figure.
The voltage at rated frequency is applied to that HV side with
the help of a variac of variable ratio auto transformer.

19. The LV side of the transformer is short circuited . Now with
help of variac applied voltage is slowly increase until the
ammeter gives reading equal to the rated current of the HV
side
After reaching at rated current of HV side, all three
instruments reading (Voltmeter, Ammeter and Watt-meter
readings) are recorded
The ammeter reading gives the primary equivalent of full load
current IL.
As the voltage, applied for full load current in short circuit
test on transformer, is quite small compared to rated primary
voltage of the transformer, the core losses in transformer can
be taken as negligible here.

20. Let’s, voltmeter reading is VSC . The input power during test is
indicated by watt-meter reading.
As the transformer is short circuited, there is no output hence
the input power here consists of copper losses in transformer
Since, the applied voltage Vsc is short circuit voltage in the
transformer and hence it is quite small compared to rated
voltage so core loss due to the small applied voltage can be
neglected.
Hence the wattmeter reading can be taken as equal to copper
losses in transformer.

21. Let us consider wattmeter reading is Psc .

22. These values are referred to the HV side of transformer as
because the test is conduced on HV side of transformer.
These values could easily be referred to LV side by dividing
these values with square of transformation ratio.
Therefore it is seen that the Short Circuit test on transformer is
used to determine copper loss in transformer at full load and
parameters of approximate equivalent circuit of transformer.

23. Power Factor of the current
PF = cosq = P
sc
V I
sc sc
Angle Power Factor
q = cos-1 P
sc
V I
sc sc

25. the open circuit test on transformer is used to determine
core losses in transformer and parameters of shunt branch of
the equivalent circuit of transformer.
the Short Circuit test on transformer is used to determine
copper loss in transformer at full load and parameters of
approximate equivalent circuit of transformer.

26. www.ee.iitb.ac.in/~drivelab/EE003/EE003_EXPT2.pdf
www.ece.vt.edu/ece3354/labs/xformermodel.pdf
theego.com/HND/UEE.PDF