EPS 2021 02

Pagina 1

Electric Power Systems Exam #2: 20/07/2021 1° Part Exercise 2 Consider a generation plant made of two different synchronous machines connected in parallel to the plant terminals as shown in the figure bellow, where 𝑃𝑝𝑙 and 𝑄𝑝𝑙 are the total real and reactive power prodiced by the plant, respectively. The synchronous machines are characterized by: SG1 SG2 Nominal apparent power MVA 50 15 Nominal operating voltage (line-to-line) kV 15 15 Phase synchronous reactance Ω 6 3 Maximum turbine mechanical power MW 45 12 Emf 𝑬𝑬 (phase-to-ground) at maximum excitation current kV 17.5 10.5 Stator windings connection - Delta Y(Star) In initial operating conditions breaker B is opened and SG2 is turned off while SG1 is operated with an emf of 𝐸01 = 17 𝑘𝑉 and a load angle of 𝛿1 = 10 + 𝑵°. Considering the voltage at the plant terminals equal to the nominal voltage of the synchronous machines: 1. compute the total real (𝑃𝑝𝑙) and the total reactive (𝑄𝑝𝑙) plant load, respectively, supplied by the plant to the external network and the phasor of the phase current of SG1; 2. Draw the phasor diagram that represents the operating conditions of SG1; 3. Considering breaker B closed, therefore both synchronous machines in operation, compute the emf phasors for both machines knowing that SG1 produces the entire total real load of the plant (𝑃𝑝𝑙) while SG2 produces the entire total reactive load of the plant (𝑄𝑝𝑙); 4. Draw the phasor diagrams that represent the operating conditions of SG1 and SG2 described at question 3; 5. considering the operating conditions identified at question 3 check the capability limits (curves) for both synchronous machines (SG1 and SG2). In the above data, N is the last number of the student’s Person Code/Codice Persona (e.g. if Person Code is 10381486 then N = 6);…