Question

ELEG 330 Power System Analysis Problem 2: A generator is feeding 30 MW to an infinite bus through two parallel transfer lines. In one of the lines occurs a three-phase short-circuit which decreases the transfer capacity of the lines by 75 %. At which value of the power-angle should the faulty line's breakers be opened to maintain stablity? There is no re-closing action. The maxmom loading capacity of one line is 40 MW and 60 MW for both lines

Answer 1

Given Max power transferred when two lines are present is 60MW P_max1 = 60 mW Max power transferred with one line P_max3 = 40 mW Max power transferred with a 3-straightphi fault is P_max2 = 25% of P_max1 [75% decreased] P_max2 = = 0.25 times 60 = 15 MW [given transfer capacity decreased by 75%] Before fault power transferred to the 'infinity' bus bar is p_e = p_max1 sin delta given p_e = 30 MW: 30 mW = 60 mW sin delta Therefore delta_0 = sin^-1 (0.5) = 30 degree \r\n = > when a 3-straightphi fault occurs in any of the line the electrical power transferred to infinite bus bar is p_e2 = p_max2 sin delta (During fault). P_e2 = 15 sin delta = > let the circuit breaker be opened at 'delta_c' and the power transferred to 'infinity' bus bar with one line is p_e3 = p_max3 sin delta p_e3 = 40 sin delta (After fault cleared and one