A large power plant generates electricity at 12.0 kV. Its old transformer once c
ID: 1264772 • Letter: A
Question
A large power plant generates electricity at 12.0 kV. Its old transformer once converted the voltage to 403 kV. The secondary of this transformer is being replaced so that its output can be 478 kV for more efficient cross-country transmission on upgraded transmission lines.
(a) What is the ratio of turns in the new secondary to turns in the old secondary?
=
(b) What is the ratio of new current output to old output (at 403 kV) for the same power?
=
(c) If the upgraded transmission lines have the same resistance, what is the ratio of new line power loss to old?
=
Ns, new Ns, oldExplanation / Answer
a) What is the ratio of turns in the new secondary to turns in the old secondary?
N new/Nold=478/403=1.1861
(b) What is the ratio of new current output to old output (at 403 kV) for the same power?
Inew/Iold=403/478=0.8430
(c) If the upgraded transmission lines have the same resistance, what is the ratio of new line power loss to old?
P=I^2*R
Pnew/Pold=(0.8430)^2=0.7108
Loss is less in new transformer
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