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An open-circuit test measures a transformer's iron losses. With no current flowing in the secondary windings, and only a tiny 'magnetising' current flowing in the primary windings, there is no significant energy lost due to the resistance of the winding conductors. So a wattmeter attached to the primary of the transformer will not read any 'copper losses', only the 'iron losses' that occur in the core.
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How will be conduct test on transformer?
Short circuit test and open circuit test are widely used to test the efficiency of the transformer.
Why low power factor wattmeter is used for open circuit test of transformer?
For open circuit test of transformer, the secondary is open circuit and the circuit impedance is largely inductive due to the core impedance having high L as compared to R. hence the power factor is reduced, thus , we use low power factor wattmeters.
What is the purpose of open circuit test and short circuit test of a transformer?
An open-circuit test is done with the transformer running at its rated voltage but with no load. This measures the power lost in the magnetic core. (IR Losses) A short-circuit test is done with the transformer running at its full rated current in all windings but at a low voltage. The secondary is shorted and the primary voltage is adjusted to give the rated current. This measures the power lost in the copper windings. (Copper losses)
What does reading of wattmeter indicate in case of open circuit test of transformer?
In case of open circuit test of transformers we measure iron losses and hence the power lost here is being measured by the wattmeter.
Why is it assumed that during open circuit all the losses are core losses?
Since this is an open circuit test, there is no load attached, thus all losses must be internal to the transformer.
