This document discusses Sumpner's test, which is used to determine the regulation and efficiency of large power transformers. Sumpner's test involves connecting two identical transformers back-to-back, with their primaries in parallel and secondaries in series opposition. This allows them to be tested at full load conditions without actual loading. The test provides accurate measurements of total losses, including both iron and copper losses occurring simultaneously as in actual use. Its advantages are that it requires little power and tests transformers under full load conditions. The limitation is that it requires two identical transformers.

1. SUMPNER’S TEST OF
TRANSFORMERS
Presented by-
Girin Chutia
Assam Engineering College

2. Introduction -
• The Sumpner's test (back to back test) is the very practical,
convenient, efficient and minimum power consumption test
which is done without actual loading to find regulation and
efficiency of large power transformer.

3. Two
Basic
Tests
Open
Circuit
Test
Short
Circuit
Test
Test to determine the iron loss/core
losses. In this test the secondary of the
transformer is kept open circuited.
Test to determine the copper losses.
In this test the secondary of the
transformer is kept short-circuited.

4. Already Two Tests..!
Why do we need Sumpner’s Test
to determine the same things …..??

5. • In O.C. test, there is no load on the transformer while in S.C. circuit
test only fractional load gets applied. In all O.C. and S.C. tests, the
loading conditions are absent. Hence the results are inaccurate.
• In open and short circuit test iron losses and copper losses are
determined separately but in actual use both losses occurs
simultaneously.
• The temperature rise in the transformer is due to total loss that
occurs simultaneously during actual use, it cant be determined by
O.C and S.C tests.

6. SUMPNER’S TEST
Its a improved method of testing transformer efficiency & other parameters.
This test gives the value of total loss accurately as it occurs when it is in actual
use. Sumpner's test or back to back test requires two transformers. Both
transformers are connected to supply in such a way that one transformer is
loaded on another.

7. Circuit diagram of Sampner’s test :

8. Operations of Sumpner’sTest :
• 1st the primaries of the two identical
transformers are connected in parallel
across the supply V1 and secondary's are
connected in series opposition.
• The switch S2 is opened and switch S1 is
closed. Now the no load current I0 flows
in primaries and I2 is zero.
• Then switch S2 also closed and the
voltage at the output of the regulating
transformer is varied until the full load
current I2 flows in the secondary circuit
loop.
• W1 = Core losses of both the
transformers, W2= Copper losses of both
transformers.

9. Advantages of the test:
• The power required to carry out the test is small.
• The transformers are tested at full-load conditions.
• As the test results gives the value of core and copper losses
occurring simultaneously so heat run test can be conducted on two
transformers.
• The secondary current(i.e I2) can be varied to any value using
regulating transformer. Hence we can determine the copper losses
at full load condition or at any load.
Drawbacks of the test:
Only limitation is that two identical transformers are required. In
practice exact identical transformers cannot be obtained and as two
transformers are required, the test is not economical.

10. CONCLUSION:
In many electrical machines its seen that sumpner's test or back to back test is
done in one or other way. As it is important to test every electrical machines at
its rated capacity and its inconvenient for machines of large rating to actually
fully load the equipment's and test. So for all electrical machines some form of
back to back test becomes important.

11. THANK YOU