The document outlines the objectives and procedures for conducting open circuit and short circuit tests on transformers to determine performance parameters, such as core loss and copper loss, without loading the transformer. The open circuit test measures core loss with the low voltage side connected, while the short circuit test measures copper loss with the high voltage side connected. Key readings during tests include voltage, current, and wattage, with an emphasis on the safety and efficacy of instrument placement.

1. Prof.Prasant Tiwari
ELECTRICAL
TRANSFORMER
LAB DIAGRAM OF TRANSFORMER TEST

2. OPEN CIRCUIT & SHORT CIRCUIT TEST
 Aim of conduction transformer Open Circuit & Short Circuit test
 To predict its performance without actual loading.
 Determination of equivalent circuit parameters
 To determine parameters of transformer like voltage regulation and
efficiency.
After going through this session you will be able to answer the following questions.
 • Which parameters are obtained from O.C test?
 • Which parameters are obtained from S.C test?
 • What percentage of rated voltage is needed to be applied to carry out O.C
test?
 • What percentage of rated voltage is needed to be applied to carry out S.C test?
 • From which side of a large transformer, would you like to carry out O.C test?
 • From which side of a large transformer, would you like to carry out S.C test?

3. OPEN CIRCUIT TEST
 To carry out open circuit test rated voltage at rated
frequency is applied to LV side of the
transformer and HV side is left opened as shown
in the circuit diagram.
 HV side is left opened because it is easier to
arrange rated voltage supply on LV side because
no load current which is quite small about 2 to 5%
of the rated current.
 Metering instrument connected at LV side are
economical & always safer to work.
 The voltmeter, ammeter and the wattmeter readings
are taken and suppose they are Voc , Io and Poc
respectively.
 Strictly speaking the wattmeter will record the
core loss as well as the LV winding copper loss.
But the winding copper loss is very small
compared to the core loss as the flux in the core is
 Open circuit test is carried out to determine core loss and shunt parameters.
 Open circuit test is carried out at rated voltage and rated frequency . During this test, rated flux is
produced in the core .

4. OPEN CIRCUIT TEST
Poc = Core loss in watts
Voc = Rated supply voltage
Io = No load current
Ro = Fictitious resistance
Xm = Magnetizing/fictitious reactance
W =Wattmeter
Im = Magnetizing current
Iw = Active component of no Current

5. SHORT CIRCUIT TEST
 Short circuit test is carried out to determine copper loss & transformer Equivalent parameters.
 Short circuit test is carried out at rated current.
 It should be noted that voltage required to be applied for rated short circuit current is quite small
(about 5%).
 All measuring instruments connected in HV side
(Low current) of the transformer where rated
current is applied and LV side is short circuited as
shown in the circuit diagram.
 Metering instrument connected at low current(HV)
side are economical & always safer to work.
 LV side is short circuited because it is easier to
arrange low rated current on HV side because
Supply voltage required is quite small about 2 to 5%
of the rated voltage.
 The voltmeter, ammeter and the wattmeter readings are
taken and suppose they are,Vsc Isc , Psc respectively.
 Strictly speaking the wattmeter will record the
copper loss as well as the core loss. But the core loss is
very small compared to the copper loss so it is
neglected as the flux in the core is small.

6. SHORT CIRCUIT TEST
Psc = Copper loss in watts
Vsc = supply voltage
Isc = Rated SC current
Req = Equivalent resistance
Xeq = Equivalent reactance
V,A &W =Voltmeter, Ammeter & Wattmeter

7. CAPSULES OF TRANSFORMER TEST
To carry out open circuit test rated voltage at rated frequency is
applied to LV side of the transformer and HV side is left
opened as shown in the circuit diagram.
HV side is left opened because it is easier to arrange rated
voltage supply on LV side because no load current which is
quite small about 2 to 5% of the rated current.
Metering instrument connected at LV side are economical &
always safer to work.
The voltmeter, ammeter and the wattmeter readings are taken and
suppose they are Voc , Io and Poc respectively.
Strictly speaking the wattmeter will record the core loss as well
as the LV winding copper loss. But the winding copper loss is
very small compared to the core loss as the flux in the core is
rated.