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EEE210 Energy conversion and power system fundamentals 2nd SEMESTER 2022/23 FINAL EXAMINATION
发布时间：2024-06-07
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EEE210
Energy conversion and power system fundamentals
2nd SEMESTER 2022/23 FINAL EXAMINATION
Question 1 (25 marks)
Write down the answers to the questions below in your answer booklet
(1) A single-phase low-voltage network has a voltage of 10∠30° V and a current of 30∠18° A at
the supply side. Find the active and reactive power at the supply side. [8]
(2) A hydropower plant with a net output of 50 MW has the following efficiencies: ηh = 0.97; ηt =
0.84; ηe = 0.93. Determine the turbine and theoretical power. [8]
(3) If an average of 121 000TW that reaches the earth is distributed uniformly over the earth’s
surface, the area of the earth's surface is 510 ∗ 106 km2 , determine the available solar energy per
m2 throughout a year under two circumstances (average daytime hours = 8 hours/day, only 1/1000 of earth's surface could be used to collect solar energy) [9]
Question 2 (25 marks)
A balanced delta-connected load of 21 + j12 Ω per phase is connected at the end of a three-phase line. The line impedance is 0.5+j4 Ω per phase. The line is supplied from a three-phase source with a line-to-line voltage of 390 V (rms). Taking the voltage on phase a as the reference, determine the following:
(1) Determine the voltage in phase a (taking phase a as the reference) [4]
(2) Determine the current in phase a [6]
(3) Determine the total complex power supplied from the source. [8]
(4) If the line impedance is neglected, determine the impedance (in 。) of the shunt capacitor per phase to improve the power factor to 0.9. [7]
Question 3 (25 marks)
A two-winding transformer rated at P = 90 kVA, VL / VH = 240 / 1200 V, f = 60 Hz. When this
two-winding transformer operates at rated load and power factor pf = 0.8, its efficiency is 90%.
(1) Calculate the primary currents on the low-voltage side ILV and high-voltage side IHV . [4]
(2) The above transformer is to be connected as an autotransformer, i) calculate the secondary current Isecondary of the autotransformer; ii) draw the relevant diagram and label all relevant currents and voltages if this transformer is to be used as a 1440/1200 V step-down autotransformer in a power distribution system. [6]
(3) Calculate the transformer kVA rating when used as an autotransformer. (For this part assume an ideal transformer.) [5]
(4) Calculate the total transformer loss Ploss when it operates at rated load and power factor pf = 0.8. [5]
(5) Calculate the efficiency η with the kVA loading of the part (1) and power factor pf = 0.8. [5]
Question 4 (25 marks)
The one-line diagram of a three-phase power system is shown in the bellowing figure. Impedances are marked in per unit on a Sbase = 100 MVA, vbase = 200 kV base. the line impedances are Z12 = j320Ω, Z23 = j100Ω . The load on bus 2 is S2 = 18 MW − j30 Mvar, and at bus 3 is S3 = 80 MW + j15 Mvar. It is required to hold the voltage at bus 3 at 200∠00 kV. This system works in per unit. (Reminder: State your complex powers and currents in rectangular form, and
voltages in polar form.)
(1) Calculate the per-unit values for loads S2 and S3 .. [2]
(2) Calculate the per-unit voltage and current at bus 3 [4]
(3) Calculate the per-unit line impedance from bus 2 to bus 3, per-unit voltage and the magnitude of the line-to-line voltage at bus 2. [7]
(4) Calculate the per-unit current at bus 2, per-unit current from bus 1 to bus 2 and per-unit line impedance from bus 1 to bus 2. [8]
(5) Calculate the per-unit voltage at bus 1 and the magnitude of the line-to-line voltage at bus 1 [4]
