EPS 2019 2020 02

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Electric Power Systems Exam #2: 21/07/2020 1° Part Exercise 1 The nameplate data of a three-phase synchronous generator is: Nominal Power 200 MVA Nominal voltage (line-to-line) 10 kV Nominal frequency 50 Hz Synchronous reactance 1  Number of poles 8 - Maximum no-load emf, E0 (phase-to-ground) 13.5 kV Winding connections Triangle (D) - In normal operating conditions the synchronous generator is supplying a load of 35 + 0.5∙N MVA with a lagging power factor of cos𝜑 =0.92; the synchronous generator is operating at nominal voltage. Neglect the power losses in the machine and consider the terminal voltage of the generator always constant. In these conditions: 1. determine the phasor of the current supplied by the generator to the load (𝐼̅), the emf (𝐸0) and the power angle (𝛿; 2. determine the mechanical torque at the shaft of the generator in the given operating conditions; 3. considering the emf 𝐸0 constant and fixed to the value previously determined (constant excitation current) and considering an increase in the mechanical power at the shaft of the machine of 4 (four) times the previous value determine the phasor of the current supplied by the generator to the load (𝐼̅), and the power angle (𝛿); 4. determine the maximum reactive power ( 𝑄𝑔max ) that the machine can produce when operat ed at the mechanical power indicated in the previous point. 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); Please substitute accordingly. Exercise 2 Consider the following electric network Line xl [p.u.] L1 0.2 L2 0.1 L3 0.05 + 0.01∙N Generator Real power output: PG Operating voltage: VG [p.u.] [p.u.] G 12 1.08 Demand Absorbed apparent power: AD Power factor [p.u.] D1 5 0.92 - lagging D2 1 0.90 - leading…