01․ Transmission line parameters of the short transmission line are
ABCD or transmission line parameters: Vs = AVr - BIr Is = CVr - DIr Where, Vs = Sending end voltage Vr = Receiving end voltage Is = Sending end current Ir = Receiving end current For short transmission line, line capacitance is neglected. Therefore, Ir = -Is, i.e., C = 0 and D = 1 Vs = Vr + Z Is i.e., A = 1 and B = Z
02․ Which of the following statements is/are true
Voltage regulation = (Vrnl - Vrfl)/Vrfl Vrnl = No load receiving end voltage Vrfl = full load receiving end voltage Vs = AVr + BIr At no load Ir = 0 Vs = A Vrnl Vrnl = Vs/A, Vrfl = Vr For short transmission line A = 1, therefore, Vrnl = Vs Voltage regulation for short transmission line = (Vs - Vr) / Vr
03․ The ABCD constants of a 3-phase transmission line are A = D = 0.8∠1°, B = 170∠85° Ω , C = 0.002∠90.4° â„§. The sending end voltage is 400 kV. The receiving end voltage under no load condition is
ABCD parameters Vs = AVr + BIr Is = CVr + DIr Where, Vs = Sending end voltage Vr = Receiving end voltage Is = Sending end current Ir = Receiving end current Under no load condition, Ir = 0 400 = 0.8∠1° * Vr Vr = 500∠-1° kV
04․ Surge impedance loading of a 3-phase, 400 kV transmission line is 400 Ω. The surge impedance loading is
Where, Vph = Phase voltage Iph = Phase current Vl = Line voltage Zs = surge impedance
05․ Surge impedance loading of a transmission line can be increased by
Where, Vph = Phase voltage Iph = Phase current Vl = Line voltage Zs = surge impedance Therefore, SIL can be increased by increasing its voltage level. Zs can be decreased by the addition of lumped capacitance in series which reduces the effective reactance of the line resulting into higher SIL.
06․ For transmission line which one of the following relation is true?
For transmission line, Symmetry network A = D Reciprocity network AD - BC = 1
07․ A 3-phase transmission line has its conductors at the corners of an equilateral triangle with side 3m. The diameter of each conductor is 1.63 cm. The inductance of the line per phase per km is
Inductance of a transmission line Where, d = distance between the conductors = 3m r' = 0.7788 r
08․ For some given transmission line the expression for voltage regulation is given by (Vs - Vr)/Vr *100%. Hence,
Voltage regulation = (Vrnl - Vrfl)/Vrfl Vrnl = No load receiving end voltage Vrfl = full load receiving end voltage Vs = AVr + BIr At no load Ir = 0, Vs = A Vrnl Vrnl = Vs/A, Vrfl = Vr For short transmission line A = 1, therefore, Vrnl = Vs Voltage regulation for short transmission line = (Vs - Vr)/Vr
09․ The capacitance of an overhead transmission line increases with
Capacitance of a transmission line Where, h = height of conductors above ground r = radius of the conductors ε = permittivity Therefore, as the height of the conductor increases from the ground, the capacitance will also decrease. Where A = area d = geometrical mean distance Therefore, as an increase in mutual geometrical mean distance, the capacitance will decrease. Therefore, both statements are wrong statements.
10․ The charging reactance of 50 km transmission line is 1500 Ω. What is the charging reactance for 100 km length of line?
Charging reactance Xc = 1/ωC ∝ 1/ length as C ∝ length Charging reactance is inversely proportional to length of the trasnmission line. Therefore, new charging reactance