State what is the significance of conducting phasing out test on a 3-phase transformer? Explain its procedure with a suitable connection diagram.

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Objective: - This test is carried out to identify primary & secondary windings belonging to same phase.

Figure:

Procedure:-  Short primary & secondary winding of other phases expect the one under test. Connect voltmeter to secondary winding. A small DC current is circulated through the primary winding through switch. Now with the help of switch interrupt the DC supply instantly & repeatedly. If voltmeter indicator deflects than it indicates the two windings concerned belong to the same phase. If not deflect then two windings are not belong to same phase. Repeat the procedure by connecting voltmeter to secondary side to next secondary winding till voltmeter gives deflection. In this way we can search the phasing out test.

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-Short primary & secondary winding of other phases expect the one under test. -Connect voltmeter to secondary winding. -A small DC current is circulated through the primary winding through switch. -Now with the help of switch interrupt the DC supply instantly & repeatedly. -If voltmeter indicator deflects than it indicates the two windings concerned belong to the same phase. -If not deflect then two windings are not belong to same phase. -Repeat the procedure by connecting voltmeter to secondary side to next secondary winding till voltmeter gives deflection. -In this way we can search the phasing out.

OR

-This test is carried to find out the corresponding HV and LV phase winding. -The circuit diagram is as shown in figure. Here normal ac voltage is applied to one of the HV or LV windings. In this case to HV winding and the voltages across all three LV windings are measured. -The winding across which is much more compared to other two windings represents the secondary of the winding to which supply is connected. -The test repeated for finding out remaining concerned secondary windings in the same manner.