EPS 2018 2019 02

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Electric Power Systems Exam #2: 23/07/2019 1° Part Exercise 1 Consider a generation plant made of two identical synchronous machines connected in parallel to the plant terminals as shown in the figure bellow. Each synchronous machine is characterized by: Nominal apparent power 7 MVA Nominal operating voltage (line-to-line) 3 kV Phase synchronous reactance 1.3 Ω Phase resistance 0.2 Ω Maximum turbine mechanical power 6.5 MW emf 𝐸0 (phase-to-ground) at maximum excitation current 3.3 kV Stator windings connection Y In normal operating conditions the voltage at the plant terminals is equal to the nominal voltage of the synchronous machines, the two synchronous generators are equally loaded, the emf of both generators is 𝐸0 = 2.6 𝑘𝑉 while the load angle is 𝛿 = 13.5°. 1. compute the current phasor supplied by the generators to the plant’s load and the corresponding power factor; 2. compute the real and reactive powers supplied by the generators to the plant’s load; 3. considering that SG1 is producing the entire real po wer required by the plant’s load while SG2 the entire reactive power required by the plant’s load, compute the emf phasor 𝐸0̅̅̅ for each of the two synchronous generators of the plant; 4. for the operating conditions identified at point 3 check the capabilit y limits for both synchronous generators of the plant. 5. considering the operating conditions identified at point 3 and assuming the plant’s load is constant, by how much must SG2 reduce its reactive power production such that SG1 operates at power factor 𝐜𝐨𝐬 𝝋𝟏 = 𝟎. 𝟗 – lagging maintaining constant its real power output. Exercise 2 Consider the following electrical network Line L [km] xl [/km] Vn [kV] L1.1 55 0.4 220 L1.2 55 0.4 220 L2 40 0.4 220 Generator G An Vn Real power output: PG Operating…