Correct Answer : Option (C) : Primary is supplied rated voltage.
Explanation : Open circuit test is performed to find the core loss in the transformer. In this test, the transformer's secondary winding is kept open-circuited, and a wattmeter is connected to the primary side. An ammeter (Used to measure the current) is connected in series with the transformer's primary winding, and rated voltage is applied at the primary side.
If normal voltage is applied at the primary side, flux is induced, and iron loss will occur. Hence the iron loss is maximum at rated voltage, and it is measured by using the wattmeter.
