Back-to-Back Test (Sumpner’s Test) on Transformer:
Definition:
The full load test on a small transformer is very convenient, but on large transformer, it is very difficult.The maximum temperature rise in a large transformer is determined by the full load test.This test is called, back-to-back test, regenerative test or sumpner’s test.
Back to Back Test Circuit
The back to back transformer requires two identical transformers. The figure shown below, the circuit diagram of the back to back test on two identical single phase transformer Tr1 and Tr2.The primary winding of the two transformers are connected in parallel and supplied at rated voltage and rated frequency.A voltmeter, an ammeter and a wattmeter are connected to the side as shown in the figure below.
The secondaries of conductor are connected in series with their polarities in phase opposition, which can be checked by the voltmeter V2.The range of this voltmeter should be double the rated voltage of either transformer secondary. The secondary of the transformer is connected in series opposition between any two terminals and the voltage is measured between the remaining terminals A and D.
If the voltmeter V2 reads zero, the secondaries are in series opposition and terminals A and D are used for the test. If the voltmeter reads a value approximately equal to twice the rated secondary voltage of either transformer, then the secondaries are acting in the same direction. Then the terminal A and C are joined and terminal B and D used for the test.
If the primary circuit is closed, then the total voltage of the secondaries which is connected in series will be zero.There will be no current in the secondaries winding and it behaves as an open circuited.The reading of wattmeter W1 gives the iron losses of both the transformer.
A small voltage is injected into the secondary circuit by a regulating transformer TR excited by the main supply.The magnitude of the injected adjusted till the ammeter A2 reads full secondary current.The secondary produces the full load current to flow through the primary windings.
The current will follow a circulatory path through the main bus bar shown in the dotted lines.The reading of wattmeter W2 will not be affected by this current.Thus, wattmeter W2 gives the full load copper loss of the two transformers.The ammeter A1 gives total no load current of the two transformers.
The temperature rise of the transformer can be determined by operating these transformer back-to-back for a long time, say 48 hours, and measuring the temperature of the oil at periodic interval say one hour.
the full load efficiency of each transformer is:
Definition:
The full load test on a small transformer is very convenient, but on large transformer, it is very difficult.The maximum temperature rise in a large transformer is determined by the full load test.This test is called, back-to-back test, regenerative test or sumpner’s test.
Back to Back Test Circuit
The back to back transformer requires two identical transformers. The figure shown below, the circuit diagram of the back to back test on two identical single phase transformer Tr1 and Tr2.The primary winding of the two transformers are connected in parallel and supplied at rated voltage and rated frequency.A voltmeter, an ammeter and a wattmeter are connected to the side as shown in the figure below.
The secondaries of conductor are connected in series with their polarities in phase opposition, which can be checked by the voltmeter V2.The range of this voltmeter should be double the rated voltage of either transformer secondary. The secondary of the transformer is connected in series opposition between any two terminals and the voltage is measured between the remaining terminals A and D.
If the voltmeter V2 reads zero, the secondaries are in series opposition and terminals A and D are used for the test. If the voltmeter reads a value approximately equal to twice the rated secondary voltage of either transformer, then the secondaries are acting in the same direction. Then the terminal A and C are joined and terminal B and D used for the test.
If the primary circuit is closed, then the total voltage of the secondaries which is connected in series will be zero.There will be no current in the secondaries winding and it behaves as an open circuited.The reading of wattmeter W1 gives the iron losses of both the transformer.
A small voltage is injected into the secondary circuit by a regulating transformer TR excited by the main supply.The magnitude of the injected adjusted till the ammeter A2 reads full secondary current.The secondary produces the full load current to flow through the primary windings.
The current will follow a circulatory path through the main bus bar shown in the dotted lines.The reading of wattmeter W2 will not be affected by this current.Thus, wattmeter W2 gives the full load copper loss of the two transformers.The ammeter A1 gives total no load current of the two transformers.
The temperature rise of the transformer can be determined by operating these transformer back-to-back for a long time, say 48 hours, and measuring the temperature of the oil at periodic interval say one hour.
the full load efficiency of each transformer is:
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