A thermal power plant produed electric power of 600kW at 4000V, which is to be transported to a place 20 km away form the power plant for consumer's usage. It can be transported either directly with a cable of large current carrying capacity or by sing a combination of step-up and step-down transfprmers at the two ends. THe drawback of the direct transmission is the large energy dissipation. In the method wsing transformers, the dissipatiion is much smaller. In this method a step-up transformers is used at the plant side so that the current is reduced to a smaller value. At the consumers'end, a step-down transformer is used to supply power to the consumers at the specified lower voltage. It is reasonable to assume that the power cable is purely resostive and the transformers are ideal with power factor unity. All the currents and voltagementioned are values.
In the method using the transformers assume that the ratio of the number of turns in the primary to that in the secondary in the step-up transformer is 1:10 if the power to the consumers has to be supplied at 200V, the ratio of the number of turns in the primary to that in the secondary in the step-down transformer is

Options

A. `200:1`
B. `150:1`
C. `100:1`
D. `50:1`

Answer

B

Explanation

(b) we know that `P=V xx I`
:. I=P/v=(600xx1000)/(4000)`
`:. I=150A`
Total resistance `=0.4xx20= 8 omega`
`:. Power dossipated as heat`=I^(2)R=(150)^(2)xx8`
`=180,000W=180kW`
`:. % loss=180/600xx100=30%`
(b) is the correct answer.