An Overview of Circulating Currents in Salient-Pole Synchronous Hydrogenerators

The competition among large hydrogenerators to achieve the highest efficiencies leads to increased interest in circulating current losses in salient-pole synchronous machines. Based on an experimentally validated computational model, this paper studies the impact of several classical transpositions on the circulating current losses for typical MVA-sized machines. It showcases that the circulating currents are mainly due to the stator bar itself (so-called "self-field") and the stator winding, while the rotor winding has only a marginal impact. Classical transpositions, such as 450 deg and 540 deg, produce interesting impacts but have limited practical application due to the short iron length. The major reduction in circulating current is achieved with a transposition in the winding overhang (30-60 deg) combined with an incomplete transposition in the overhang. This result has also led to a recent patent application [1].