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Description
In automatically wound machines, the actual position of each single conductor in the slot is usually unknown. However, depending on the individual placement in the slot, parallel-connected strands can lead to differing circulating currents. Since the flux-linkage due to leakage flux in the slot varies in radial direction, increasing towards the slot opening, the induced voltage also differs in parallel strands that are aligned in radial direction, resulting in circulating currents and thus additional copper loss in the stator winding. The circulating currents itself cannot be seen in standard phase current measurements, but manifest in a change of the phase resistance. Analysis of AC effects, such as skin and proximity effect as well as the circulating currents and corresponding losses are usually done by finite element analysis (FEA), while mostly only a single slot is considered, neglecting the influence of neighboring slots on the flux density of the stator iron and thus the resulting slot leakage flux. This work compares different levels of detail of 2D FE models, e.g. single slot, single pole and pole pair model, and investigates the impact of the modelling depth on the resulting copper loss. Moreover, the potential increase of AC-losses is assessed for two machines that are identical except for the stator winding, i.e. one and the same machine is investigated at two different voltage levels, namely 400 V and 800 V. The reference machine is a 160 kW nominal power and 9000 rpm maximum speed permanent magnet synchronous machine already running in various applications. Since the magnetic circuit has to remain constant, both designs share the same overall winding scheme and total number of strands per slot but differ in the number of parallel and serial connected strands. As described above, this will lead to different circulating currents and therefore also different losses.
| Submitters Country | Germany |
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