The synchronous machine Solution

Pagina 1

EXERCISES FOR ELECTRIC POWER SYSTEMS COURSE ENERGY DEPARTMENT, Electrical section 1 Class 6 - solution The Synchronous Machine Exercise 1 1. From the open-circuit characteristic of the synchronous machine one can get the value of the magnitude of emf /g1831 /g2868 for any value of the excitation current /g1835/g3032/g3051/g3030 . Moreover, from the short-circuit characteristic of the synchronous machine one can get the value of the magnitude of the current in the stator windings of the machine when the terminals of the machine are short-circuited, /g1835/g3046/g3030 , for any value of the excitation current /g1835/g3032/g3051/g3030 . Considering the synchronous machine single-phase circuit in short-circuit conditions the magnitude of the phase impedance of the synchronous machine is, according to Ohm’s law: |/g1852 /g3046/g3364/g3364/g3364|/g3404 /g1852/g3046/g3404/g1831/g2868 /g1835/g3046/g3030 Using the above equation one can compute, point by point, the impedance characteristic of the synchronous machine, for example: /g2165/g2187/g2206/g2185 /g2161/g2777 /g2165/g2201/g2185 /g2182/g2201 [A] [A] [A] [/g2743] 40 210 1750 0.12 80 315 3500 0.09 120 360 5260 0.06844 etc. etc. etc. etc. 2. In normal operating conditions, the equivalent single-phase circuit of the synchronous machine operating as a generator is: E0 Isc RsjX s Zs EXERCISES FOR ELECTRIC POWER SYSTEMS COURSE ENERGY DEPARTMENT, Electrical section 2 and the equation that characterizes the circuit is: /g1831 /g2868/g3364/g3364/g3364/g3404 /g1848/g3364/g33c7 /g1862/g1852/g3046/g3364/g3364/g3364/g1835̅ (1) In our case, in the above equation the synchronous impedance is assumed constant and equal to the nominal value. This corresponds to the machine operating at nominal excitation current, or nominal emf: /g1831…