i) This test is carried out on 3-ph transformer to identify primary & secondary winding belonging to the same phase.
ii) As shown in fig above all primary & secondary phases are short circuited except the phases to be checked
iii) Low voltage DC supply is given to primary winding. The galvanometer is connected to terminals of secondary winding which is not short circuited.
iv) The switch ‘S’ is connected as shown in fig. When switch is closed deflection of galvanometer is observed.
v) Similarly galvanometer is connected to other secondary terminals and procedure is repeated. The winding across which maximum deflection occurs is the secondary phase winding that corresponds to primary winding to which source is connected.
vi) The procedure is repeated for remaining primary windings.
vii) Phasing out test can be carried out by using AC voltage source also. Voltmeter is connected at secondary terminals to observe deflections.
The purpose of this test is to check the respective phases of primary & secondary windings in 3-ph transformer