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Loss calculation and thermal calculation

In a low speed generator, typically more than 80 % of the losses are resistive losses in the stator winding, hysteresis and eddy-current losses in the stator core can be almost neglected. These losses produced by the stator current lead to a temperature rise in the generator which must not exceed the maximum allowed temperatures of the winding insulation (typically Class B, 130°C) due to the danger of increased ageing and destruction. Moreover, in a permanent-magnet machine, high magnet temperatures enhance the risk of irreversible demagnetization of the permanent magnets. These aspects emphasize the necessity of detailed temperature calculations in order to design the generator as small as possible by applying the thermal limit rating.

wind-direct uses the following approaches for thermal calculations:

  •  analytical approximations using well-known lumped networks
  •  2D FE analysis of slots and laminated stack geometry
  •  3D FE analysis of the complete model to find out the temperature “hot spot” in the end windings

Main results: maximum stator current loading and magnet temperatures as functions of the cooling system for given slot geometry.

thermal calculations
If very compact generator designs should be considered, it is usually not possible to rely upon natural wind to cool the generator. Instead, wind-direct recommends to consider active cooling by water or air.