Question

DC and AC power distribution schemes are illustrated in the circuits below. Both are intended to supply customers with power at voltage V.

zPowerGrid Consider an AC power grid with components like the circuit on the right. A transmission line that has a line resistor RT with a resistance per unit length of 4.80 ⨯ 10−4 Ω/m is to be used to transmit 5.00 MW over 400 miles (6.44 ✕ 105 m). The output voltage of the generator VS is 480 V (rms).

(a) What is the line loss if a transformer is used to step up the voltage Vs to 494 kV (rms)?

kW HINT: Find current IAC from power and voltage, then RT, then power in RT

(b) What fraction of the input power is lost to the line under these circumstances?

%

(c) What is the line loss if the DC Power Grid could be used (circuit on the left)

kW

(d) What difficulties would be encountered on attempting to transmit the 5.00 MW at the generator voltage of 480 V (rms) as in the DC circuit at the left? Include what might happen to the transmission line wire and a possible voltage difference between multiple customers. Could you 'fix' such problems?

Answer 1