Saturation Functions for Synchronous Generators from Finite Elements

Under EPRI sponsorship, a steady-state turbogenerator saturation algorithm suitable for inclusion in power system stability codes has been devised. The algorithm was constructed to fit reactances resulting from nonlinear finite-element calculations of steady-state load points covering the operating range (V,P,Q) of the generator. Saturation functions were derived for two generators: Cholla 4, owned by the Arizona Public Service Company, and Bull Run (HP unit), owned by the Tennessee Valley Authority. The owners of these generators measured steady-state load data for these machines, and the measured load angles and excitation currents were compared with those calculated using the algorithm. Agreement within 2 degrees in angle (max. 3 degrees), and 2 percent in excitation was obtained. This paper describes the fitting process and the comparisons of the results to test data. A companion paper describes increases in power transfer found from coding the algorithm into an existing stability program, and testing the prototype code on an 1100 bus stability study.