Analysis of air-gap influence on a large hydro generator´s parameters using sudden symmetrical short-circuit test

Accurate alternator´s parameters are important for driving, simulating, planning and protecting power systems. These parameters are related to the geometry of the machines and depend on many factors. One of the most important is the effective air gap. In this paper, the influence of the variation of the latter on transient parameters is analysed. To this end, a sudden three-phase short circuit is simulated using a 3D FEM approach coupled to the electric circuit elements and the classical lumped parameters are determined for a variation of the air gap up to 20% of the manufacturer given value. The methodology, from modeling of the short-circuit test to the processing of the waveforms, in relation to previous works, is exposed.