Power Transformer Stability Test

Hello sundararajan27

Is this a Class or Homework Question?

Kind Regards....

Dear Sir,

At Present i am handling one project in Qatar,i have completed all the test related to Transformer except above test.So, i need your help to carry out above test.

Best Regards

G.Sundararajan

The System details are:
Transformer - 34.5kV/.480kV,Delta-Star,3Ph,60Hz
The Transformer Secondary Neutral point is connected to Earth through a High Resistance Ground Unit.
A typical Transformer Differential protection scheme is applied.

For testing the diffrential scheme-we apply a reduced voltage of 480V on the Transformer Primary.
The Secondary bus is shorted. A current equivalent to the rated primary current is forced to flow through the transformer primary winding.

At this condition we measure the Secondary current.
However we noted that the measured Secondary current is much less than the rated Secondary current.
Does this mean that the % Transformer Impedance is not correct
Z=6.75% in this case.
Or is it that the % Transformer impedance is applicable to its rated primary Voltage and will vary based on the applied Primary voltage.

good answer...but the sentence is ewact copy from some other site :P