Reduced model for the thermo-fluid dynamic analysis of a power transformer radiator working in ONAF mode

Abstract This work introduces an extension of the semi-analytical reduced model presented in Rios Rodriguez et al. (2016), with the aim of analyzing the thermo-fluid dynamic behavior of a power transformer radiator working in ONAF (Oil Natural Air Forced) mode, considering vertical blowing of the fans. The objective of this research paper is the development of a numerical tool to be used during the design process of power transformers in order to obtain more detailed information about the radiators performance, either they are working in ONAF or ONAN (Oil Natural Air Natural) mode. Since it is observed both in the experimental measurements and in the numerical simulations that not all the radiator panels are blown by a single fan, the reduced model here presented considers a mixed situation wherein the heat is removed by natural convection in a fraction of the radiator while in the rest the heat is removed by forced convection. As a consequence, besides adding to the set of conservation equations introduced in Rios Rodriguez et al. (2016) those corresponding to the momentum and energy balance for considering forced heat convection transfer, there appears the need of introducing additional equations for coupling the natural and forced heat convection transfer models. The reduced model developed in this work is applied to estimate different characteristic parameters of a power transformer radiator working in ONAF mode, like the oil flow rate, dissipated power, outlet and inlet oil temperatures, among others. The computed results are compared to those obtained by CFD simulations and experimental measurements carried out on an ad-hoc workbench for validation purposes. It is found that the reduced model reproduces with acceptable accuracy the values of the most important design variables at a very low computation cost. In this manner, it can be considered as a reliable and valuable tool in the design of power transformers, allowing to carry out parametric studies.

[1]  N. E. Wakil,et al.  Numerical study of heat transfer and fluid flow in a power transformer , 2006 .

[2]  Weeratunge Malalasekera,et al.  An introduction to computational fluid dynamics - the finite volume method , 2007 .

[3]  Bertrand Poulin,et al.  Transformer Design Principles: With Applications to Core-Form Power Transformers , 2001 .

[4]  R. B. Dean.  Reynolds Number Dependence of Skin Friction and Other Bulk Flow Variables in Two-Dimensional Rectangular Duct Flow , 1978 .

[5]  Stephan Freytag.  An Introduction To Splines For Use In Computer Graphics And Geometric Modeling , 2016 .

[6]  Juan Carlos Ramos,et al.  Numerical modelling of natural convection of oil inside distribution transformers , 2011 .

[7]  James A. Fay,et al.  Introduction to Fluid Mechanics , 1994 .

[8]  Min-gu Kim,et al.  Prediction and evaluation of the cooling performance of radiators used in oil-filled power transformer applications with non-direct and direct-oil-forced flow , 2013 .

[9]  Sachin B. Paramane,et al.  A coupled internal–external flow and conjugate heat transfer simulations and experiments on radiators of a transformer , 2016 .

[10]  Hamid Nabati,et al.  Heat Transfer and Fluid Flow Analysis of Power Transformer's Cooling System Using CFD Approach , 2009 .

[11]  S. Churchill,et al.  Correlating equations for laminar and turbulent free convection from a vertical plate , 1975 .

[12]  M. Darwish,et al.  The Finite Volume Method in Computational Fluid Dynamics: An Advanced Introduction with OpenFOAM® and Matlab , 2015 .

[13]  P. Sagaut.  BOOK REVIEW: Large Eddy Simulation for Incompressible Flows. An Introduction , 2001 .

[14]  P. Moin,et al.  Turbulence statistics in fully developed channel flow at low Reynolds number , 1987, Journal of Fluid Mechanics.

[15]  Sachin B. Paramane,et al.  CFD Study on Thermal Performance of Radiators in a Power Transformer: Effect of Blowing Direction and Offset of Fans , 2014, IEEE Transactions on Power Delivery.

[16]  F. Archambeau,et al.  Code Saturne: A Finite Volume Code for the computation of turbulent incompressible flows - Industrial Applications , 2004 .

[17]  S. Acharya,et al.  Comparison of the Piso, Simpler, and Simplec Algorithms for the Treatment of the Pressure-Velocity Coupling in Steady Flow Problems , 1986 .

[18]  P. Moin,et al.  A dynamic subgrid‐scale eddy viscosity model , 1990 .

[19]  J. Smagorinsky,et al.  GENERAL CIRCULATION EXPERIMENTS WITH THE PRIMITIVE EQUATIONS , 1963 .

[20]  Stuart W. Churchill,et al.  A comprehensive correlating equation for forced convection from flat plates , 1976 .

[21]  F. Torriano,et al.  Numerical investigation of 3D flow and thermal effects in a disc-type transformer winding , 2012 .

[22]  László Kiss,et al.  Large Power Transformers , 1987 .

[23]  Antonios G. Kladas,et al.  Power transformer thermal analysis by using an advanced coupled 3D heat transfer and fluid flow FEM model , 2012 .

[24]  Mario Alberto Storti,et al.  Numerical and experimental thermo-fluid dynamic analysis of a power transformer working in ONAN mode , 2017 .

[25]  P Sagaut,et al.  Large Eddy Simulation for Incompressible Flows: An Introduction. Scientific Computation Series , 2002 .

[26]  Eduardo W. V. Chaves,et al.  Introduction to Fluids , 2013 .