what is the role of impedance in transformer?based on secondary f.l.current(13

what is the role of impedance in transformer?based on
secondary f.l.current(139 amps) and impedance(4.07) of
415/415v of 100 kva transformer. what is the primary
current?

Question Posted / ravishankar

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what is the role of impedance in transformer?based on secondary f.l.current(139 amps) and impedanc..

Answer / ma.amulraaj,b.e. mba.,

It is %impedance Voltage.In Transformer,%impedance Voltage plays significant role .Here 100KVA,11KV /415 V.

Full load current Sec .current= VA / 1.732x V (Sec.Voltage)

=(100x 1000 )/(1.732x415 ) =139 Amps, ok

Full load current Primary .current= VA / 1.732x V (Primary
Voltage)

=(100 x 1000)/(1.732 x 11000)
=5.25 Amps

Here ,the full load secondary current is 139 Amps,the rated secondary voltage is 415 V,we can do Short circuit test by applying secondary voltage 415 V,we cannot get the full load secondary current,due to impedance of Transformer.Then we have to raise the secondary voltage gradually, at particular voltage it delivered the full load secondary current,note down the voltage say 440V.From that voltage we have to find out % impedance.440 /11000 = 4% %Z=4.0 %.As this case %Z=4.07,ie. it is (4.07 x11000)/100 =447.7 V.It means This transformer may delivered a full load current at 447V.

This % Impedance may vary from Transformer to Transformer.