EPS 2021 01

Pagina 1

Electric Power Systems Exam #1: 29/06/2021 1° Part The nameplate data of a three-phase synchronous generator is: Nominal Power 180 MVA Maximum mechanical power of turbine 160 MW Nominal voltage (line-to-line) 10 kV Nominal frequency 50 Hz Synchronous reactance 1.5  Number of poles 4 - Maximum emf, EE (phase-to-ground) 12.5 kV Winding connections Triangle (D) - In normal operating conditions the synchronous generator is injecting a line current of 7000 + 250∙N A to the external grid with a leading power factor of cos𝜑 =0.94; the synchronous generator is operating at its nominal voltage. The power losses in the machine are neglected. In these conditions: 1. determine the real (𝑃𝐺) and reactive power (𝑄𝐺) produced by the generator, the emf (𝐸𝐸) and the load angle (𝛿); 2. draw the voltage phasor diagram corresponding the previously calculated operating conditions; 2. determine the mechanical torque at the shaft of the generator in the given operating conditions; 3. considering a change in the operating conditions of the generator described by an increase in the operating voltage at the external terminals of the generator of +1 ∙N % and an increase of the emf of +20 %, while the real power produced remains constant, determine the new value of the reactive power produced by the generator (𝑄𝐺), the magnitude of the line current injected by the generator to the external grid and the power factor; 4. draw the voltage phasor diagram corresponding the previously calculated operating conditions; 5. check the capability limits of the generator for the operating conditions described at question 3. 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…