This document discusses transformer tests, including open circuit and short circuit tests. It explains that these tests are done to determine the equivalent circuit parameters, impedance, currents, efficiency, and losses of a transformer. The open circuit test is used to determine the core or iron losses, while the short circuit test determines the copper losses. Examples of calculations for each test are provided.

1. Transformer Tests
Open Circuit Test and
Short Circuit test
EECE – 203: ELECTRICAL MACHINES

2. The performance of a transformer can be calculated on
the basis of its four main parameters of equivalent circuit:
(i) Equivalent resistance 𝑅01 as referred to primary (or
secondary 𝑅02)
(ii) The equivalent leakage reactance 𝑋01 as referred to
primary (or secondary 𝑋02)
(iii) The core-loss conductance 𝐺0 (or resistance 𝑅0)
(iv) The magnetising susceptance 𝐵0 (or reactance 𝑋0).
These constants or parameters can be easily determined
by two tests
(i) open-circuit test and (ii) short circuit test.

3. Why Open Circuit Test(OCT) & Short Circuit Test (SCT) are done?
 To find out the impedance, no load current, short
circuit current and the efficiency of the transformer
 OCT is done to determine the core losses or the iron
losses of the transformer
 SCT is done to determine the Cu losses of the
transformer
 These tests are very economical and convenient,
because they furnish the required information without
actually loading the transformer

4. Open Circuit Test

5. Open Circuit Test
μ

6. Open Circuit Test
Admittance 𝑌0 of the transformer is given by -
conductance 𝐺0 is given by -
susceptance 𝐵0 is given by -

7. Example. In no-load test of single-phase transformer, the following test data were
obtained, Resistance of the primary winding = 0.6 ohm:
Primary voltage : 220 V ; Secondary voltage : 110 V ; Primary current : 0.5 A ; Power input
: 30 W.
Find the following :
(i) The turns ratio (ii) the magnetising component of no-load current (iii) its working (or
loss) component (iv) the iron loss.

8. Short Circuit Test
This is an economical method for determining the following :
 Equivalent impedance (𝒁 𝟎𝟏or 𝒁 𝟎𝟐), leakage reactance (𝑿 𝟎𝟏or 𝑿 𝟎𝟐) and total
resistance (𝑹 𝟎𝟏 or 𝑹 𝟎𝟐) of the transformer as referred to the winding in
which the measuring instruments are placed.
 Cu loss at full load (and at any desired load). This loss is used in calculating
the efficiency of the transformer.
 Knowing 𝒁 𝟎𝟏 or 𝒁 𝟎𝟐, the total voltage drop in the transformer as referred to
primary or secondary can be calculated and hence regulation of the
transformer determined.

9. Short Circuit Test

10. Short Circuit Test

11. Short Circuit Test
If Vsc is the voltage required to circulate rated load currents, then 𝑍01 =
𝑉 𝑆𝐶
𝐼1

12. Separation of Core losses
• The core loss of a transformer depends upon the frequency and the
maximum flux density when the volume and the thickness of the core
laminations are given.
• The core loss is made up of two parts
• hysteresis loss =
• eddy current loss =
Steinmetz’s empirical relation
• The total core-loss is given by