Answer / jaswinder

% impedence is use to determine the max fault current the
transformer is capable of delivering to a downstream short
circuit.
Fault current=FLC*100/%imp.
this fault current is use to cal fault MVA
Fault MVA = 1.732 x fault current x V.

eg: If transformer of 2000kVA,5%imp having flc of around
1200A is use to supply to a motor of same flc carrying
capacity and if the voltage drop at transformer terminal is
more than the permissible voltage drop (+- 10%)during
stating of motor then the above transformer will be of
lower rating hence we have to select the transformer rating
higher than 2000kVA eg:-3000kVA (In other words transformer
having higher SC current capability ).If voltage remain
within the rated voltage of the motor then no oversizing of
tranformer is required.

Answer / akr

hieght of winding effect on impedane

if there is nutral in phase why we use earthing wire and grounding? even at fault condition the fault current flows to neutral (it is a lower path)

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