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4.21 A 138-kV, three-phase short transmission line has a per-phase impedance of (2 + j4) 2. If the line supplies a 25-MW load at 0.8 power factor lagging, calculate (a) the efficiency of transmission and (h) the sending-end voltage and power factor. Ans. (a) 98.78 percent; (b) 139.5 kV, 0.99

4.21 A 138-kV, three-phase short transmission line has a per-phase impedance of (2 + j4) 2. If the line supplies a 25-MW load at 0.8 power factor lagging, calculate (a) the efficiency of transmission and (h) the sending-end voltage and power factor. Ans. (a) 98.78 percent; (b) 139.5 kV, 0.99

Introductory Circuit Analysis (13th Edition)
Introductory Circuit Analysis (13th Edition)
13th Edition
ISBN:9780133923605
Author:Robert L. Boylestad
Publisher:Robert L. Boylestad
Chapter1: Introduction
Section: Chapter Questions
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4.21 A 138-kV, three-phase short transmission line has a per-phase impedance of (2 + j4) 2. If the line supplies a 25-MW load at 0.8 power factor lagging, caleulate (a) the efficiency of transmission and (h) the sending-end voltage and power factor. Ans. (a) 98.78 percent; (b) 139.5 kV, 0.99 4.22 A three-phase short transmission line having a per-phase impedance of (2 + j4) 2 has equal line-to-line receiving-end and sending-end voltages of 115 kV while supplying a load at 0.8 power factor leading. Calculate the power supplied by the line. Ans. 839.2 MW 4.23 A three-phase, wye-connected, 20-MW toad of power factor 0.866 lagging is to be supplied by a transmission line at 138 kV. It is desired that the line losses not exceed 5 percent of the load. If the per-phase resistance of the line is 0.7 2, what is the maximum length of the line? Ans. S1 km The per-phase constants of a 345-kV, three-phase, 150-km-long transmission line are resistance = 0.1 2/km, inductance = 1.1 mH/km, and capacitance = 0.02 µF/km. The line supplies a 180-MW load at 0,9 power faetor Iagging. Using the nominal-Il circuit, determine the sending-end voltage. 4.24 Ans. 350.8 kV 4.25 Repeat Problem 4.24 using the nominal-T eircuit. Ans. 359.3 kV 4.26 The per-phase parameters of a 345-kV, 500-km, 60-Hz, three-phase transmission line are y = j4 x 10 S/km and z = (0.08 + j0.6) 2/km. If the line supplies a 200-MW lond at 0.866 power factor lagging, calculate the sending-end voltage and power. Ans. 372 kV; 240.8 MW 4.27 Determine the ABCD constants of the line of Problem 4.24. Ans. A = D = 0.965/0.5"; B = 64/76.4" 2; c 0.982/0.25° S 4.28 List the ABCD constants and determine the sending-end voltage for the transmission line of Problem 4.26, considering the line as a two-port network. Ans. A = 0.7147/0", B = 270.88/90, C = 1.8 x 10 190", D = 0.7147/0; V, = 372 kV 4.29 The sending- and receiving-end voltages of a three-phase short transmission line are V, = 33 kV and V = 31.2 kV, respectively. The per-phase line parameters ure R = 102 und X, = 20 2. Calculate the maximum power that can be transmitted by the line. Ans. 26,57 MW For a three-phase long transmission line, Z, = 406.4/-5.48" 2, V = 215/0" kV und I = 335.7/0 A, all per phase. Calculate the sending-end line voltage. 4.30 Ans. 238.8 kV 4.31 How much power is transmitted over the line of Problem 4.30? Ans. 137.5 MW
Transcribed Image Text:4.21 A 138-kV, three-phase short transmission line has a per-phase impedance of (2 + j4) 2. If the line supplies a 25-MW load at 0.8 power factor lagging, caleulate (a) the efficiency of transmission and (h) the sending-end voltage and power factor. Ans. (a) 98.78 percent; (b) 139.5 kV, 0.99 4.22 A three-phase short transmission line having a per-phase impedance of (2 + j4) 2 has equal line-to-line receiving-end and sending-end voltages of 115 kV while supplying a load at 0.8 power factor leading. Calculate the power supplied by the line. Ans. 839.2 MW 4.23 A three-phase, wye-connected, 20-MW toad of power factor 0.866 lagging is to be supplied by a transmission line at 138 kV. It is desired that the line losses not exceed 5 percent of the load. If the per-phase resistance of the line is 0.7 2, what is the maximum length of the line? Ans. S1 km The per-phase constants of a 345-kV, three-phase, 150-km-long transmission line are resistance = 0.1 2/km, inductance = 1.1 mH/km, and capacitance = 0.02 µF/km. The line supplies a 180-MW load at 0,9 power faetor Iagging. Using the nominal-Il circuit, determine the sending-end voltage. 4.24 Ans. 350.8 kV 4.25 Repeat Problem 4.24 using the nominal-T eircuit. Ans. 359.3 kV 4.26 The per-phase parameters of a 345-kV, 500-km, 60-Hz, three-phase transmission line are y = j4 x 10 S/km and z = (0.08 + j0.6) 2/km. If the line supplies a 200-MW lond at 0.866 power factor lagging, calculate the sending-end voltage and power. Ans. 372 kV; 240.8 MW 4.27 Determine the ABCD constants of the line of Problem 4.24. Ans. A = D = 0.965/0.5"; B = 64/76.4" 2; c 0.982/0.25° S 4.28 List the ABCD constants and determine the sending-end voltage for the transmission line of Problem 4.26, considering the line as a two-port network. Ans. A = 0.7147/0", B = 270.88/90, C = 1.8 x 10 190", D = 0.7147/0; V, = 372 kV 4.29 The sending- and receiving-end voltages of a three-phase short transmission line are V, = 33 kV and V = 31.2 kV, respectively. The per-phase line parameters ure R = 102 und X, = 20 2. Calculate the maximum power that can be transmitted by the line. Ans. 26,57 MW For a three-phase long transmission line, Z, = 406.4/-5.48" 2, V = 215/0" kV und I = 335.7/0 A, all per phase. Calculate the sending-end line voltage. 4.30 Ans. 238.8 kV 4.31 How much power is transmitted over the line of Problem 4.30? Ans. 137.5 MW
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