EPS 2021 03

Pagina 1

Electric Power Systems Exam #3: 09/09/2021 1° Part Exercise 1 In the figure bellow a three -phase demand (D) is supplied by a three -phase synchronous generator ( SG) through the electric line L. The demand absorbs 𝑃𝐷 =400+20∙𝑵 [MW] with a lagging power factor cos𝜑𝐷 =0.95. The electric transformer T nameplate specifies the following data: Nominal electrical power 600 MVA Nominal ideal transformer ratio 20/132 kV/kV Short-circuit voltage 10 % The synchronous generator SG nameplate specifies the following data: Nominal electrical power 700 MVA Nominal line-to-line voltage 20 kV Maximum phase-to-ground emf 24 kV Maximum turbine power 650 MW Stator winding resistance 0.2 Ω Synchronous reactance 0.03 Ω Stator phases connection D The demand is supplied at line-to-line voltage of 𝑉𝑠𝑢𝑝𝑝𝑙𝑦 =(95+𝑵) % of the nominal voltage at the secondary (high) voltage side of the transformer T. Determine: 1. the real and reactive power supplied by the synchronous generator to the grid (𝑃𝐺,𝑄𝐺) and the line-to-line voltage at the synchronous generator’s terminals (𝑉𝐺); 2. the emf 𝐸𝐸 and the load angle (𝛿) of the synchronous generator; 3. check the capability curve of the synchronous generator in the given operating conditions; NOTE: 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. P su P Exercise 2 Consider the following electric network Line xl [p.u.] L1 0.1 L2 0.2 + 0.01∙N L3 0.05 Generator Real power output: PG Voltage set- point: VG [p.u] [p.u] G 4.0 1.06 Demand Absorbed real power: PD Power factor [p.u] [-] D 5 + 0.2∙N 0.93 – lagging Knowing that the inductive reactor I is characterized by a reactance 𝑋𝐼 = 2 p.u. and that the External Grid (Ext Grid) is modeled as an infinite…