Answer Posted / yousef madhi

Suppose That the line voltage on DELTA connection
V(line)= V
and the line current I(line)= I

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





Conclusion:

the line current in star connection is reduced by 1/3 time the line current in delta connection

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