Question

Do given above with the replacment of earilier transformer by 40000-220 V step down transformer. Neglect as before, leakage losses. Hence explain why high voltage transmission is preferred.

Answer 1

Here, `E_(v) = 40000` volt.
Since `P = E_(v) I_(v) :. I_(v) = (P)/(E_(v)) = (800 xx 10^(3))/(40000) = 20 amp`
Line power loss `= I_(v)^(2) = (20)^(2) xx 15 = 6000 W = 6 kW`.
plant supply `= 800 + 6 = 806 kW`
Voltage drop on the line `= I_(v) R = 20 xx 15 = 300` volt.
`:.` Voltage for transmission ` =40000 + 300 = 40300` volt.
`:.` Step up transformer needed at the plant is `= 440 V - 40300 V`
Power loss at higher voltage `= (6)/(800) xx 100 = 0.74 %`
Power loss at lower voltage `= (600)/(1400) xx 100 = 42.8%`
Hence high voltage transmission is preferred.