A set of open circuit test and short circuit test have been performed on a transformer. A supply voltage of 480 V is applied to the primary side of the transformer and the following data is obtained for the open circuit test.
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Poc
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720 W
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Voc
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240 V
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Io
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9.7 A
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Then, the following set of data is taken for a short circuit test.
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Psc
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750 W
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Vsc
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37.2 V
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Isc
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51.9 A
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Later, the high side of the transformer is connected to a multi-meter with the low side left open. The meter registers a reading of 0.11 ?. Afterwards, the multi-meter is connected to the low side with the high side left open. The meter registers a reading of 0.029 ?.
It is generally assumed that for this 2:1 transformer that the reactance at both sides contributes equally to the equivalent reactance of the transformer.
Find the following parameters for open circuit test:
1. The core loss resistance
2. The magnetizing reactance
3. The power factor
Find the following parameters for short circuit test:
4. The equivalent impedance
5. The leakage resistance
6. The leakage reactance
The resistance readings collected after the open and short circuit tests are the resistance reading when the transformer is operating with DC. Supposedly, the resistance collected should be the same as the leakage resistance, distributed with the same ratio on the primary and secondary side of the transformer. However, this is not always true. Due to certain unknown factors, the leakage resistance deduced from short circuit test is higher than the value obtained with DC source.
Find out the following:
7. The leakage resistance on the primary and secondary sides
8. The leakage reactance on the primary and secondary sides
Please give a conclusive summary to the following questions.
9. What are the purposes of an open circuit test?
10. What are the purposes of a short circuit test?
11. Is the leakage resistance higher than the value obtained with DC source? Please give a reasonable account for such finding.