MCQs on Power Systems

01․ Transmission line parameters of the short transmission line are

ABCD or transmission line parameters: V_s = AV_r - BI_r I_s = CV_r - DI_r Where, V_s = Sending end voltage V_r = Receiving end voltage I_s = Sending end current I_r = Receiving end current For short transmission line, line capacitance is neglected. Therefore, I_r = -I_s, i.e., C = 0 and D = 1 V_s = V_r + Z Is i.e., A = 1 and B = Z

02․ Which of the following statements is/are true

Voltage regulation = (V_rnl - V_rfl)/V_rfl V_rnl = No load receiving end voltage V_rfl = full load receiving end voltage V_s = AV_r + BI_r At no load I_r = 0 V_s = A Vrnl V_rnl = V_s/A, V_rfl = V_r For short transmission line A = 1, therefore, V_rnl = V_s Voltage regulation for short transmission line = (V_s - V_r) / V_r

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° ℧. The sending end voltage is 400 kV. The receiving end voltage under no load condition is

ABCD parameters V_s = AV_r + BI_r I_s = CV_r + DI_r Where, V_s = Sending end voltage V_r = Receiving end voltage I_s = Sending end current I_r = Receiving end current Under no load condition, I_r = 0 400 = 0.8∠1° * V_r V_r = 500∠-1° kV

04․ Surge impedance loading of a 3-phase, 400 kV transmission line is 400 Ω. The surge impedance loading is

Where, V_ph = Phase voltage I_ph = Phase current V_l = Line voltage Z_s = surge impedance

05․ Surge impedance loading of a transmission line can be increased by

Where, V_ph = Phase voltage I_ph = Phase current V_l = Line voltage Z_s = surge impedance Therefore, SIL can be increased by increasing its voltage level. Z_s 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 (V_s - V_r)/V_r *100%. Hence,

Voltage regulation = (V_rnl - V_rfl)/V_rfl V_rnl = No load receiving end voltage V_rfl = full load receiving end voltage V_s = AV_r + BI_r At no load I_r = 0, V_s = A V_rnl V_rnl = V_s/A, V_rfl = V_r For short transmission line A = 1, therefore, V_rnl = V_s Voltage regulation for short transmission line = (V_s - V_r)/V_r

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 X_c = 1/ωC ∝ 1/ length as C ∝ length Charging reactance is inversely proportional to length of the trasnmission line. Therefore, new charging reactance