Q7.25 (c)  A small town with a demand of 800 kW of electric power at 220V is situated 15km away from an electric plant generating power at 440VThe resistance of the two wire line carrying power is 0.5\Omega  per km. The town gets power from the line through a 4000-220V step-down transformer at a sub-station in the town.  Characterise the step up transformer at the plant.

Answers (1)
P Pankaj Sanodiya

Power required 

P=800kW=800*10^3kW

The total resistance of the two-wire line

R=2*15*0.5=15\Omega

Input Voltage 

V_{input}=4000V

Output Voltage:

V_{output}=220V

RMS Current in the wireline

I=\frac{P}{V_{input}}=\frac{800*10^3}{4000}=200A

Now,

Voltage drop in the power line = IR=200*15=3000V

Total voltage transmitted from the plant = 3000+4000=7000

as power is generated at 440V, The rating of the power plant is 440V-7000V.

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