Determination of high power synchronous generator subtransient reactances based on the waveforms for a steady state two-phase short-circuit

Abstract

In the paper, there is presented an analysis of the waveforms at the stator winding terminals of a high power synchronous generator for a steady state two-phase short-circuit. The analysis was performed by the finite element method based on a 2D generator model taking into account higher spatial and time harmonics of the magnetic field as well as the impact of eddy currents in the rotor damping circuits. The used FE model was experimentally verified. For the steady state two-phase short-circuit, the waveforms determined by the FE method were compared with the approximated waveforms calculated using analytical formulas. The analytical formulas were derived from the machine equations written in the stator fixed coordinate system (α, β, 0), using normalized transformation of coordinates and the Heaviside operational calculus. The higher time harmonics obtained based on the FFT analysis of the waveforms of the short-circuit current and open phase voltage were used for determining subtransient reactances in the d and q axes of a 200MW generator. The thus determined generator reactances were compared with the values determined by other methods.