Modeling of effects of laminations on steep fronted surge propagation in large AC motor coils

The modeling of machine windings for steep-fronted surge propagation has been based on an assumption that the slot walls act as flux barriers at the frequencies of interest (1 to 10 MHz). The assumption is valid for a solid slot environment, because the magnetic flux cannot penetrate beyond the skin depth, delta , which is of the order of 10/sup -6/ m for the frequencies concerned. However, this is not the case for a laminated slot environment, which can allow magnetic flux penetration on steep-fronted surge propagation in large AC motor coils are examined. Experimental data are reported showing that solid-slot models cannot accurately replace the laminated environments. Maximum interturn voltages observed for the solid slot model are smaller (by a factor of about 2/3) than those for the laminated slot environment. The differences between solid and laminated environments is attributed to the effect of laminations, which can be approximately modeled using the concept of surface impedance.<<ETX>>