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SHORT CIRCUIT OR IMPEDANCE TEST

The main purpose of this test is to compute the following:
  • Equivalent impedance of the transformer referred to primary and secondary.
  • Cu loss of the transformer at any desired load.
  • Total voltage drop of the transformer referred to primary and secondary.
Figure 1.37 shows the schematic diagram for the short circuit test of a transformer in which the low-voltage winding is short-circuited. During the short circuit test, we apply 5–10 per cent of the rated voltage to high-voltage side so that the full-load current flow both in primary and secondary. Voltage is slowly increased from zero to a value to get full-load current to flow. Since 5–10 per cent of rated voltage at the primary is easier to achieve smoothly and read by a voltmeter, instruments are always placed on the high-voltage side. A voltmeter, an ammeter and a wattmeter are placed on the high-voltage side. The low-voltage side is directly short-circuited by a thick conductor or by an ammeter.
Let PSC be the reading of the wattmeter, ISC be the reading of the ammeter and VSC be the reading of the voltmeter.
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Figure 1.37 Short Circuit Test
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