Question

Do the same exercise as above with the replacement of the earlier transformer by a 40,000-220V step-down transformer (Neglect, as before, leakage losses though this may not be a good assumption any longer because of the very high voltage transmission involved). Hence, explain why high volage transmission is preferred ?

Answer 1

Given primary voltage `V_(P)=40,000 V`
Let the current in primary is `I_(P)`
`therefore V_(P)I_(P)=P`
`800xx1000=40000 xx I_(P)`
`I_(P)=20A`
(a) Line power loss `= (I_(P))^(2)xxR`
`= (20)^(2)xx2xx0.5xx15`
`= 6000W = 6KW`
(b) Power supply by plant
`= 800+6=806KW`
Voltage drop of line `= I_(P).R`
`= 20xx2xx0.5xx15`
= 300 V
Voltage for transmission
`= 40000+300=40300V`
Power loss at higher voltage
`= (6)/(800)xx100=0.74%`
Power loss at lower voltage
`= (600)/(1400)xx100=42.8%`
Hence, the power loss is minimum at higher voltage. So, the high voltage transmission is preferred.