The document discusses the Sumpner's test, which is used to test large power transformers without actual loading. It has the following key points: 1. The Sumpner's test connects two identical transformers back to back, with their primaries in parallel and secondaries in series opposition, allowing them to be tested at full load conditions while only supplying power for losses. 2. This configuration causes the induced voltages in the secondaries to oppose each other, resulting in no net current flow between them. An auxiliary transformer is used to induce current and measure copper losses. 3. The test accurately determines total losses as they would occur in actual use, allowing efficiency and regulation to be found without full loading.

1. GANDHINAGAR INSTITUTE OF
TECHNOLOGY(012)
DC Machine And
Transformers(2130904)
Active Learning Assignment
Topic:-Sumpner Test on Transformers
Branch:-
Prepared By:-
Guided By:-

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. Sumpner’s Test
• Its a improved method of testing transformer efficien
cy & other parameters. This test gives the value of to
tal 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.

4. • The Sumpner's test requires two identical transformers.
• Both the transformers are connected to the supply such th
at one transformer is loaded on the other.
 Thus power taken from the supply is that much necessar
y for supplying the losses of both the transformers and the
are is very small loss in the control circuit.
.

5.  While conducting this test, the primaries of the two
identical transformers are connected in parallel across
that supply V1.
 While the secondary's are connected in series opposition s
o that induced e.m.f.s in the two secondary's oppose each
other.
 The secondary's are supplied from another low voltage sup
ply are connected in each circuit to get the readings.
 The connection diagram is shown in the Fig. 1

7. • The secondaries are so connected that their
potentials are in opposition to each other. Th
is would so if VAB=VCD and A is joined to C
while B is just joined to D.
• In that case there would be no secondary cur
rent flowing around the loop formed by the t
wo secondaries.

8. • T is an auxiliary low – voltage transformer whic
h can be adjusted to give a variable voltage and
hence current in the secondary loop circuit. By
proper adjustment of T. full-load secondary cu
rrent I2 can be made to flow as shown. It is see
n that I2 flows from D to C and then from A t
o B. Flow of I1 is confined to the loop FEJLGHM
F and it does not pass throughW1.

9. • Hence W1 continues to read the core loss and
W2 measures full-load Cu loss.
• Obviously, the power taken in is twice the lo
sses of a single Transformer.

10. Key Point:-
• Thus in the sumpner's test without supplyin
g the load, full iron loss occurs in the core w
hile full copper loss occurs in the windings
simultaneously.
Hence heat run test can be conducted on
the two transformer.

11. Advantages:-
• The power required to carry out the test is small.
• The transformers are tested at full-load conditi
ons.
• As the test results gives the value of core and co
pper losses occurring simultaneously so heat ru
n test can be conducted on two transformers.
• The secondary current(i.e I2) can be varied to a
ny value using regulating transformer. Hence w
e can determine the copper losses at full load co
ndition or at any load.

12. Conclusion:-
• In many electrical machines its seen that su
mpner's test or back to back test is done in o
ne or other way. As it is important to test ever
y electrical machines at its rated capacity an
d its inconvenient for machines of large ratin
g to actually fully load the equipment's and te
st. So for all electrical machines some form o
f back to back test becomes important.