A power plant produces 1000 MW to supply a city 40 km away. Current flows from the power plant on a single wire of resistance 0.050 Ω/km, through the city, and returns via the ground, assumed to have negligible resistance. At the power plant the voltage between the wire and ground is 115 kV.
(a) What is the current in the wire?
(b) What fraction of the power is lost in transmission?

Respuesta :

Our values are given as,

[tex]P_{plant} = 1000MW[/tex]

[tex]V = 115kV = 115*10^3V[/tex]

[tex]L = 40Km[/tex]

PART A)

Power is defined as the product between the current and the voltage, therefore the current would be

[tex]I = \frac{P}{V}[/tex]

[tex]I = \frac{1000}{115*10^3}[/tex]

[tex]I = 8704.34A[/tex]

PART B) The resistance unit length is,

[tex]\frac{R}{L} = 0.05\Omega /km[/tex]

[tex]R = 0.05*40[/tex]

[tex]R = 2\Omega[/tex]

Therefore for the calculation of the loss of Power we would have to apply the relation:

[tex]P_{l} = I^2 R[/tex]

[tex]P_l = (8704.34)^2*2[/tex]

[tex]P_l = 151.53MW[/tex]

Fraction loss power transmission is,

[tex]\frac{P_l}{P_{plant}} = \frac{151.53}{1000}[/tex]

[tex]\frac{P_l}{P_{plant}} = 0.151[/tex]

[tex]\frac{P_l}{P_{plant}} = 15.1\%[/tex]

(a) The current in the wire is [tex]8704\;A[/tex]

(b) The fraction of power lost in transmission is 15.1%

Electrical power:

Given that the electrical power produced is [tex]P=1000MW=1000\times10^6W[/tex],

the distance of the city is d = 40km,

resistance of wire per kilometer length is [tex]r=0.05\Omega /km[/tex] ,

and the potential difference [tex]V=115kV=115\times10^3V[/tex]

(a) The current is given by the following relation:

[tex]P=VI\\\\I=\frac{1000\times10^6}{115\times10^3}A=8704\;A[/tex]

(b) Power lost in the transmission:

the total resistance of the wire in 40 km is:

[tex]R=0.05\times40=2\Omega[/tex]

so the power lost in transmission is:

[tex]P_t=I^2R=(8704)^2\times2=151MW[/tex]

So the fraction of power lost is:

[tex]f=\frac{P_t}{P}\times100\%=\frac{151}{1000}\times100\% \\\\f=15.1\%[/tex]

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