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For the no load test on a transformer, normally test voltage is applied on low voltage side. But for excitation current test voltage is applied on high voltage side. What is the reason for this?

For the diagnosis of internal fault normally test voltage is applied phase by phase and the phase currents are compared. If we are applying a three phase test voltage is the same relation between phase currents can be used for analysis of the internal winding or core fault?

Cdymk... following are the answers to your two questions:

o LV voltage is usually more readily available.

o Typically the 2-Watt meter method is used, but if the LV winding is wye-connected, then the 3-Watt meter method can be employed.

Regards, Phil Corso