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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? |
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Answer» Solution :(a) Hence 800 kW power is delivered at town sub station by two way TRANSMISSION line at 40,000 V. Hence, current through this line is, `I = ( P )/( V )` `= ( 800 xx 10^(3))/( 40,000)` = 20 A Power loss in the line wires is, `P. = I^(2) R` `= ( 20 )^(2) ( 15)` `:. P . = 6000 W = 6 kW` (b) Total power supplied by the PLAIN shouldbe, `P_(t ) = P + P.` `= 800 kW+ 6kW` = 806 kW (c ) Voltage drop across two way line, = IR ( 20) ( 15) = 300 V Voltage across secondary coil of a TRANSFORMER at power plant should be, = 300 + 40,000 = 40,300 V `rArr` Thus, at power station we should use a step-up transformer ( 440V - 40,300V ) Explanation about why power transmission is always preferred at very high voltage. (i) Power loss in the form of heat in exampleno. 7.25 is, `= ( 600)/( 1400) xx 100%` = 42.86 % (ii) Power loss in the form of heat in example no. 7.26 is, `= ( 6)/( 806) xx 100%` = 0.7444% Thus, when a GIVEN ELECTRICAL power is transmitted at very high voltage, power loss in the form of heat can be reduced considerbly. Hence, it is always preferred. |
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