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29 September 2018

Why starting current 1/3 for star delta

September 29, 2018 Posted by AK No comments
as we know in DELTA connection the phase voltage equal the line voltage and the phase current equal to the line current times 1/root(3)
then V(phase)=V(line) = V
and I(phase)=I(line)/root(3) = I/root(3)

In STAR connection if again the line voltage equal to V(line)= V , the phase voltage will equal to line voltage time 1/root(3)  V(phase)=V(line)/root(3) = V/root(3) and as per Ohm's Law (V=I*Z) and in both connection (star & Delta) we have the same winding impedance, any change in Voltage will change the current in the same amount.
so the phase current for star connection will be equal to

I(phase-star)= I(phase-delta)/root(3)
=(I/root(3))/root(3)
= I/3
and as we know in star connection the line current equal to the phase current
I(line)=I(phase)= I/3

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