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Which of the following is NOT correct with reference to full load testing of a single- phase transformer?
In SumpnerтАЩs test, two identical transformers are taken, in which primary windings are connected in parallel whereas secondary windings are connected in series.
In SumpnerтАЩs test, two identical transformers are taken, in which primary windings are connected in parallel whereas secondary windings are connected in series but in phase opposition.
This test is used to determine voltage regulation of the transformer.
This test is used to determine temperature rise and efficiency of the transformer.
In SumpnerтАЩs test, two identical transformers are taken, in which primary windings are connected in parallel whereas secondary windings are connected in series.
Sumpner's test, also known as the back-to-back test, is a method to perform a full-load heat run test on two identical transformers without wasting large amounts of power. The test requires the primary windings to be connected in parallel (across the rated supply voltage) and the secondary windings to be connected in series but in phase opposition so that the net voltage around the secondary loop is zero.
IS 2026 (Part 1): 2011 / IEC 60076-1
Sumpner's test, also known as the back-to-back test, is a method to perform a full-load heat run test on two identical transformers without wasting large amounts of power. The test requires the primary windings to be connected in parallel (across the rated supply voltage) and the secondary windings to be connected in series but in phase opposition so that the net voltage around the secondary loop is zero.
PTotalтАЛ=PIronтАЛ+PCopperтАЛ тАФ Total power drawn from the supply for the heat run test
ITotalтАЛ=ILoadтАЛ тАФ The circulating current set by the auxiliary low-voltage source
The primaries are excited at rated voltage to supply iron losses, while a low-voltage auxiliary source is used in the secondary circuit to circulate rated full-load current to supply copper losses. Since the induced EMFs in the secondary loop oppose each other, no power is circulated between the two secondaries from the primary source, allowing the transformers to operate at full load while only drawing the power equal to total losses (PironтАЛ+PcopperтАЛ) from the supply.
Used specifically for large transformers where direct loading is impractical.
Allows observation of the temperature rise under full load conditions.
Efficiency can be determined accurately as both losses are measured simultaneously.
Requires two identical transformers.
Very low power consumption compared to actual loading.
Enables observation of temperature rise under normal working conditions.
Requires two identical transformers.
Setup is complex compared to O.C. and S.C. tests.
Full-load heat run test for distribution and power transformers.
Determination of efficiency and regulation in industrial settings.
Option A is incorrect because it fails to mention the mandatory requirement of 'phase opposition' in the secondary series connection, without which a large short-circuit current would flow, damaging the windings.
Voltage regulation is generally calculated using the parameters obtained from O.C. and S.C. tests, although Sumpner's test provides sufficient data to characterize the transformer's performance.
A is correct тАФ Sumpner's test requires the secondary windings to be connected in series with phase opposition to prevent a short circuit while circulating full-load current.
Remember that in Sumpner's test, the power drawn from the primary source equals the total losses of both transformers; therefore, divide the measured power by two to find the losses of one transformer.
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