Temperature Calculation And Analysis For Stator Transposition Bar Of Hydro-generator Based On The Thermal Network Method

The efficiency and the effective material utilization of generator will improve with the increase of the generator capacity.However,temperature is an important factor limiting the increase of generator capacity.Therefore the accurate analysis and calculation of temperature field distribution are very important for temperature monitoring,forecasting and improving the life of the generator.During the process of motor design,the transposition technique is often used to reduce the circulating loss between the strands for the purpose of reducing the temperature.As the complex structure of the stator transposition bar,when the numerical method is used to calculate the temperature field,it is difficult to mesh the solving domain and the calculation period is extended.In this paper,a thermal network method which can consider the actual transposition structure of stator bars is proposed to calculate the stator temperature field.Taking a 250 MW Hydro-generator as an example,the temperature field distribution of stator transposition bar is obtained.According to the structural characteristics of the stator transposition bar of250 MW hydro-generator,a thermal network model considering the actual transposition structure of strands is established,and the matrix form of the network node temperature field equation for solving the thermal network model of stator transposition bar is given.The finite volume method is used to calculate the distribution of fluid velocity in the radial ventilation groove.On the basis of empirical formula,the heat transfer coefficient of each convective heat transfer surfaces are obtained,the analytical method and finite element method are used to calculate the thermal conductivity between different types of nodes in the radial,the circumference and the axialdirection.By considering the actual structure of stator transposition bar,the copper loss of transposition strand is calculated by the 3D finite element method.Based on the calculated thermal network parameters,the temperature field calculation and analysis for the stator bar without considering the transposition structure and considering the 360 degree transposition type are completed,the maximum and minimum temperature values for each part of the solving domain are presented.the distribution of node temperature along the radial and axial direction under the above two cases are analyzed.The calculation results of the stator temperature field with the 360 degree transposition type are compared with the numerical results and the experimental values,and the validity of the thermal network method is verified.The influence of the current phase between upper bar and lower bar,and the transposition type of the stator bar on the temperature field in the stator are studied.The temperature field distribution of the transposition bar with void transposition type and less than 360 degree transposition type are calculated,and the temperature field of the stator with 360 degree transposition type is compared and analyzed with above cases.