Improved calculation of iron losses in large salient-pole synchronous hydro-generators

To bridge the existing gap between the calculated and the actually measured iron losses in low loss electrical steel parts of electrical machines, one of the possible improvements is to incorporate the effect of punching into the loss modelling. Therefore, within the finite element analysis the electrical steel parts geometry is divided into different sub-regions, and affected local magnetisation curves and magnetic loss parameters are attributed to each of these regions. Both these local magnetic properties are deduced from measurements on industrially punched samples of different widths. In this paper such improved iron loss calculation methodology is carried out on two large synchronous hydro-generators. The additional losses due to punching occur mainly at the punched edge and are of both hysteretic and excess loss nature, but also in the unaffected bulk of the geometry all iron loss components increase due to a magnetic flux re-distribution from the edge to the bulk of the stator tooth geometry. Another finding is that the higher harmonic dynamical losses in the stator teeth increase due to the punching. As a conclusion, at least part of the unexplained measured total losses of large hydro-generators can be attributed to the punching effect on the iron losses, which enables more accurate design of such generators.