Saved Bookmarks
| 1. |
Do the same exercise as above with the replacement of the earlier transformer by a 40,000 - 220 V 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 voltage transmission is preferred ? |
|
Answer» Solution : If power is transmitted at 40,000 V, then current in the line `I = P/V = (8 xx 10^(5))/(40,000) = 20 A` (a) `therefore`Line power loss as heat =`I^(2)R = (20)^(2) xx 15 = 6000 W = 6 KW` (b)TOTAL power supplied by the plant = 800 kW + 6 kW = 806 kW (c) Voltage drop along the line = IR = 20 x 15 = 300 V`therefore`Voltage at generating station side of line = 40,000 + 300 = 40,300 V Thus, a step up transformer of 440 V - 40,300 V be used at the generator plant. A comparison of Exercises 7.25 and 7.26 shows that at 4000 V, power loss as heat is 600 kW but at 40,000 V, power loss as heat for same line is reduced to 6 kW only. It is due to this reason (i.e., to reduce the transmission loss) that power transmission is preferred at a highest possible voltage. |
|