Search results

The purpose of this paper is to carry out an analytical approximation model (heat transfer model (HTM)) for the calculation of the heat transfer coefficient at the end winding bars of large hydro generators. These coefficients are needed for lumped parameter thermal models in the design process.

The computational fluid dynamics simulation in combination with conjugate heat transfer (CHT) validates the accuracy of the HTM. The theoretical approach describes the formulation of the heat transfer coefficient and the Gauss-Newton method has been applied to find the coefficients of the approximation model.

The paper describes the new analytical approximation model for the heat transfer coefficient at the end winding bars of hydro generators and shows also the validation to simulation results.

The analytical approximation model for the heat transfer coefficient at the end winding bars has been described and a comparison with CHT results has shown a good agreement.

The purpose of this work is to propose a numerical method based on computational fluid dynamics (CFD) for reconstructing the heat transfer inside electrical machines. The used conjugate heat transfer (CHT) method takes heat convection and heat conduction into account to determine the temperature rise and the thermal losses in stator duct models of large hydro generators. Three different test cases are studied with different slot section components. The numerical models are validated with measurement data for a range of different mass flow rates.

The work presented is based on the combination of two complementary approaches, namely numerical simulation and measurements. The measured data for the air mass flow and the heat losses are used as boundary conditions for the identification of the temperature distribution in the solid and fluid domains (using a commercial software for CFD). The CHT method is an additional application of CFD and is used to solve the energy equations in the solid domains. Therefore, it is possible to define a thermal source in the solid domains.

The data obtained by the numerical computation are compared with measurement data for different mass flow rates of the cooling fluid. The quality of the computed values depending on the different mass flow rates shows a good agreement with the measured data. The temperature distribution in the solid domains depending on different material properties is also pointed out in this investigation.

The topic describes a method for solving the heat transfer in the fluid as well as the solid domains. The losses can be defined as sources in the solid domains, e.g. copper and iron, obtained by electromagnetic calculations. This boundary condition defines the situation more accurately than, for example, a constant value of the heat flux or the temperature at the walls like in common used CFD simulations. Another advantage of CFD over other approaches is the consideration of the actual wall heat transfer coefficient.

The presented investigations show relevant issues influencing the thermal behaviour of electrical machines.

The purpose of this paper is to present a new computational fluid dynamics model for large electrical machines to simulate the heat transfer at specific components to the appropriate ventilation method. The most damageable parts for overheating in generators are the end winding bars, pole windings and stator ducts.

The reduced model introduced is basically derived from the state-of-the-art pole section model (PSM) and enables faster computations for heat transfer and cooling simulations of electrical machines. The fundamentals of the two methods and the grid generation are described. Two PSMs and four different reduced models are presented and compared among each other to tune the reduced model.

As a topic of outstanding interest in large hydro generators, the heat transfer at the end winding bars is solved with the aid of the reduced model. This slot sector model (SSM) has been validated and the computation time has been reduced enormously in comparison to the state-of-the-art PSM.

The heat transfer has been carried out only for the end winding region of large hydro generators. The effect of the reduced model on the pole sections and stator ducts has not been investigated. Nevertheless, the reduced model is also valid for large motors.

This reduced model can finally be used for parametric studies with different cooling schemes and boundary conditions in the design process.

The comparison of various SSMs to PSMs shows an acceptable accuracy of the reduced model in combination with a rather low computation time. Due to modeling one slot only, the MFR-MP approach is an adequate and fast analyzing method for this kind of model structure.