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Question 4. Three 3 substations A, B and C are spaced 75 km apart as shown in figure below. B and C are connected together by a cable (velocity of propagation 2 x 108 m/s), and the remaining connections are all overhead lines (velocity of propagation 2.4 x 108 m/s). The attenuation factors and the surge impedances of the lines are shown alongside the lines. The overhead lines beyond A and C on either side are extremely long and reflections need not be considered from their far ends. Determine using the Bewley lattice diagram the overvoltages at the 3 substations, at an instant 1.3ms after a lightning surge of magnitude unity (1pu) and duration 3 ms reaches the substation A from the outside. Draw the voltage profile at the 3 substations for the first 1.5 ms. Attenuation factor Characteristic impedance 0.9 600 0.8 0.5 66.6 400 600 A B с