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NUMERICAL STUDY OF HEAT TRANSFER INSIDE A COOLING FLUID IN A POWER TRANSFORMER

Nelu-Cristian Chereches
Gheorghe Asachi Technical University

Nadim El Wakil
Laboratoire de Thermomécanique - UTAP Moulin de la housse, Faculté des Sciences, Université de Reims Champagne Ardenne, B.P. 1039, 51687 Reims cedex 2, France

Alina Marinescu
Laboratoire de Thermomécanique - UTAP Moulin de la housse, Faculté des Sciences, Université de Reims Champagne Ardenne, B.P. 1039, 51687 Reims cedex 2, France

Jacques Padet
Laboratoire de Thermomécanique - UTAP Moulin de la housse, Faculté des Sciences, Université de Reims Champagne Ardenne, B.P. 1039, 51687 Reims cedex 2, France

Abstract

In this paper we study the heat transfer and fluid flow in a step-down 3-phase power transformer. In order to simplify the study we choose an element composed of two windings wound around a core. The Joule effect and the Foucault currents produce an undesirable heat in the different components of the transformer. From an economical and security point of view, there is a need to cool the transformer to preserve it from destruction. Our main objective is the cooling optimization of the power transformer. A numerical study has been conducted for six different geometric configurations with six different flow rates of the cooling oil at the entrance. The physical properties of the fluid are supposed to be function of the temperature. The control volume method has been used to resolve the continuity, the momentum and the energy equations in the steady state. The obtained results show that the structure of the flow is somehow complex and according to the case some rolls appear at the top and the bottom of the windings; these rolls contribute to a good mixing of the fluid leading to a nearly homogenous temperature. The hot temperature is located inside the cooling channels crossing the primary and the secondary windings. These channels are very narrow ones, and the fluid has a difficulty to flow through them, so its preference goes to those separating the different elements. To reduce these high temperatures, there is a need to force the fluid to go in these narrow channels by using a directed flow.

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