Dr. Ömer Cihan KΔ±vanç EEE458 ELECTRICAL DISTRIBUTION SYSTEMS MID-TERM EXAM 13.04.2020 1. A power plant single-line diagram is shown in Fig. 1. A breaker is connected to 10 kV bus. Calculate the trip short-circuit current and power (πΌπ , ππ ). [π = 0.8] (20 PTS) ππ" = 3000 πππ΄ 110 ππ 30 πππ΄ π’π = 12% 25 πππ΄ 30 πππ΄ π₯π" = 12.5% π’π = 12% 10 ππ Fig. 1 Power plant single-line diagram. 2. A 10 kV medium voltage distribution line is shown in Fig. 2. Calculate rated cable cross sections. [π£ ≤ 10%, π₯ " = 0.4 β¦/ππ, k = 56 m/β¦ππ2 ] (15 PTS) 10 ππ 6 ππ 4 ππ 500 πππ΄ 20 π΄ cos π = 0.8 cos π = 0.6 Fig. 2 Medium voltage distribution line. 3. A low voltage distribution line is shown in Fig. 3. Calculate the end-line voltage value, rated cable cross sections and total power losses. [π£ ≤ 3%, π₯ " = 0.4 β¦/ππ, k = 56 m/β¦ππ2 ] [Rated Cable Cross Sections: 2.5; 4; 6; 10; 16; 25; 35; 50; 70; 95 (ππ2 )] (15 PTS) 220 380 π 50 π π΄ 30 π π΅ 20 π πΆ M 25 π΄ 15 π΄ Fig. 3 Low voltage distribution line. 13 πππ΄ cos π = 0.8 4. Calculate the starting 3Ø short-circuit current value at 34.5 kV bus (B). Simulate the power system shown in Fig. 4, using Matlab/Simulink and show the current and power flow in scopes (assuming that there is no short-circuit anywhere). (35 PTS) ππ" = 2500 πππ΄ 154 ππ ππΊ = 25 πππ΄ 2π₯ ππ" = 12.5% πππ = 30 πππ΄ π’π = 12% π΄ 10 ππ 3 π₯ 31.14 ππ 2 3 π₯ 62.44 ππ 2 π₯0 = 0.4 Ω/ππ ππΊ = 10 πππ΄ ππ" = 12.5% π₯0 = 0.4 Ω/ππ 8 ππ ππ΄πΏ = 27.77 π/Ωππ 2 34.5 ππ π΅ M πΌπ = 176 π΄ πΌπΌπΆ = 5π₯πΌπ Fig. 4 Distribution system single-line diagram. 5. Calculate maximum voltage drop point & value at Fig. 5. [k = 56 m/β¦ππ2 , ππ = 25 ππ2 , π₯ππππ = 0.1 Ω/ππ] Simulate the power system shown in Fig. 5, using Matlab/Simulink and show the current and power flow in scopes. (35 PTS) 500 ππ cos π = 0.8 630 πππ΄ 400 π cos π = 0.6 500 π 800 π 10 ππ 600 π 500 π 380 ππ 500 πππ΄ 36 π΄ cos π = 0.8 Fig. 5 A distribution system.