Electrical Machines Lab
for
B.Tech / B.E /Diploma
&
Electrical And Electronics Engineering
SUMPNER’S TEST ON
To perform sumpner’s test n
pair of identical 1- phase transformers to find the full load copper
losses & iron losses of transformers.
From test results calculate
1)
Equivalent parameters.
2) Percentage Efficiency
3) Percentage r egulation at
given power factor & loads.
THEORY
While OC
and SC tests on a transformer gives its equivalent circuit parameters. These
can not be used for the heat run test where the purpose is to determine the
steady temperature rise if the transformer was fully loaded continuously this
is so because under each of these tests the power loss to which the transformer
is subjected is either the core loss or copper loss but not both. The way out
of this impasse with out conducting an actual loading t est is sumpner’s test which
can only be conducted simultaneously on
two identical transformers. In conducting the sumpner’s test the primaries of the two transformers are
connected in parallel across the rated voltage supply (V1), while the two
secondaries are connect ed in phase opposition as in fig. Current at low
voltage (V2) is injected in to secondaries to rated value.
As per
superposition theorem, if V2 source is assumed shorted the two transformers
appear in open circuit to source V1 as their secondaries are in phase opposition
and therefore no current can flow in them. The current drawn from sorce V1 is
thus 2Io (twice the no load current of each transformer) and power is 2Po
( 2P1, twice the core loss of each
transformer). When V1 is regarded as shorted, the transformers are series
connected across v2 and are short circuited no the side of primaries. Therefore
the impedance seen at V2 is 2Z and when
V2 is adjustes to circulate full load current (If1), the power fed in is
2Pc ( twice the full load copper loss of each transformer). Thus in sumpner’s
test while transformers are not
supplying any load, full load iron loss occurs in their cores and ull copper
loss occurs in their windings net power input to the transformer being (2Po*
2Pc).
The heat run test could, therefore, be conducted on the
two transformers, while only losses are supplied.
RESULT:
Sumpner’s
test is done on identical pair of 1 phase transformer from which the following
are obtained.
The equivalent parameters are
1) Ro
2) Xo
3) Ro1
4) Xo1
5) Percentage
efficiency
6) Percentage
regulation (lag); Percentage regulation (lead)
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