A large power plant generates electricity at 12.0kV. Its old transformer once co
ID: 1351673 • Letter: A
Question
A large power plant generates electricity at 12.0kV. Its old transformer once converted the voltage to 335kV. The secondary of this transformer is being replaced so that its output can be 750 kV for more efficent cross country transmission on upgraded transmission lines.
(a) what is the ratio of turns in the new secondary compared with the old secondary?
(b) what is the ration of new current output to old output (at 335 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?
Explanation / Answer
a) Apply, N_new/N_old = V_new/Vold
= 750/335
= 2.2388
b) power suppled in both cases is same.
P_new = P_old
V_new*I_new = V_old*I_old
I_new/I_old = V_old/V_new
= 335/750
= 0.4467
c) ratio of power loss = P_new/P_old
= I_new^2*R/(I_lod^2*R)
= (I_new/I_old)^2
= 0.4467^2
= 0.1995
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