| In order to optimize the design of large air-cooled hydro-generators, and improve the efficiency of large air-cooled hydro-generators, the stator bar transposition technique should be chiefly considered. The optimal transposition method of stator bar can effectively reduce the circulating current loss between windings, which achieve the effect of preventing the local overheating of windings and improving the efficiency of hydro-generators. In addition, with the growth of unit capacity of hydro-generators, it leads to increase electromagnetic load and thermal load, which would seriously affect the operation safety and stability of hydro-generators. Under normal condition, it is difficult to calculate the loss of transposition structure and measuring the temperature of transposition strands. Therefore, the accurate calculation of partial hot spots of transposition strands, it will provide a reasonable basis for reasonable forecast of insulation life and improvement the capacity of the generator. So, the calculation of temperature and determination of the local overheating point per strand are particularly crucial, which becomes a key issues. In this paper, the numerical calculation for the fluid field and temperature field of a 250 MW air-cooled hydro-generator is carried out.Firstly, based on ventilation system structure of 250 MW hydro-generator,three-dimensional solving model of the fluid field in radial ventilation groove is established. The fluid flow characteristics and distribution is calculated and analyzed in radial ventilation groove. The fluid velocity distribution and surface heat transfer coefficients are compared and analyzed on the different angles of incidence, from which the distributions of velocity and heat transfer coefficients are obtained.Secondly, considering transposition strand, the three-dimensional solving model of the temperature field is established. Based on the calculation results of the fluid field in radial ventilation groove, boundary conditions of temperature field model is determined,and then the calculation model of stator temperature field is analyzed by finite volume method(FVM) under rated load condition. The temperature distribution of each transposition strand is obtained, and the numerical results of model with transposition strand structure and baseline model without transposition are compared with tested values.Finally, the influence of different strand transposition types on the stator temperature field is discussed. The temperatures of 360° transposition and less than 360°transposition of the generator stator windings are respectively analyzed and calculated on the various stator parts by FVM. |
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