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(ENGAA) Sample Paper section 2: 2nd problem watch

1. Hi,
Could someone solve this problem? Thank you beforehand.

2. A power station generates 1GW of electricity and supplies it to a city 100 km away over a pair of aluminium cables, each of diameter 30 mm. The voltage between the cables at the power station is 400 kV. The resistivity of aluminium is 2.6 x10–8 Ωm.

b. Which of the following is approximately the total power lost in the cables?
A.) 18.4 kW B.)135 kW C.)11.5 MW D.)23 MW E.)46 MW

(In question a., I have calculated the resistance of one cable and it is 3.7 ohm's).

The answer is E., but I dont know the reason.
2. (Original post by Pabloha)
Hi,
Could someone solve this problem? Thank you beforehand.

2. A power station generates 1GW of electricity and supplies it to a city 100 km away over a pair of aluminium cables, each of diameter 30 mm. The voltage between the cables at the power station is 400 kV. The resistivity of aluminium is 2.6 x10–8 Ωm.

b. Which of the following is approximately the total power lost in the cables?
A.) 18.4 kW B.)135 kW C.)11.5 MW D.)23 MW E.)46 MW

(In question a., I have calculated the resistance of one cable and it is 3.7 ohm's).

The answer is E., but I dont know the reason.
P=IV
P=I^2 X R

1GW=1X10^9
400kV=400X10^3
R=3.7ohm

(1x10^9)/(400x10^3)=2500amp

now to find power lost

P=(2500^2)(3.7)=23x10^6W=23MW

notice how it says total power lost, 2 cables -> 46MW.

I am truly scared for this exam as I do not know what to expect. The specification is very vague.

I scored 32 on paper one and 23 on paper two, how did you do?

Updated: October 31, 2016
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