Thermal Modelling of a Power Transformer Disc Type Winding Immersed in Mineral and Ester-Based Oils Using Network Models and CFD

Agustin Santisteban,Alfredo Ortiz,Fernando Delgado,Felix Ortiz,Alejandro Piquero

doi:10.1109/access.2019.2957171

Agustin Santisteban, Alfredo Ortiz + Show 3 more

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https://doi.org/10.1109/access.2019.2957171

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Abstract

This contribution presents the early results of a R&D collaboration established between the University of Cantabria and the Power Transformer Manufacturer EFACEC. This paper tests two different techniques of steady state thermal modelling applied to power transformer windings, Computational Fluid Dynamics (CFD) and Thermal-Hydraulic Network Modelling (THNM). The state of the art of thermal modelling demonstrates that these techniques have been used to calculate both average and hotspot winding temperatures by solving the winding temperature and flows profiles within the winding. THNM models have worse accuracy than CFD in the predicted results. The improvement of these THNM models is a topic of study in transformer thermal modelling. The first goal of this paper is to test the accuracy of a new calibrated THNM model of a disc-type winding immersed in mineral oil. Then, this THNM model is tested with ester-based liquids, such as a natural ester and a synthetic ester, to determine if it can be applied to these liquids without further calibrations. Finally, the cooling performance of both type of liquids is compared using only the THNM model results. The results of this work show that the THNM model developed herein gives good estimations of temperatures compared to those obtained with CFD for both types of liquids. Also, the use of alternative fluids leads to lower temperatures when considering the same oil flow rate and temperature as inlet boundary condition.

Highlights

Oil-immersed power transformers are one of the most expensive and critical components of an electrical system
While in Computational Fluid Dynamics (CFD), the governing principles of both fluid flow and heat transfer are written in the form of partial differential equations, that are replaced by algebraic equations and solved at discrete elements in time and space, in Thermal Hydraulic Network Modelling (THNM), those same governing principles are mostly written in the form of simpler algebraic equations that rely on analytical and/or empirical coefficients, in particular in the fluid domain, where the flow profile is not solved, and singular phenomena such as hot streaks or flow
The first technique, CFD, computes in detail the temperature and velocity fields arising in the transformer winding and its accuracy has been proved for years

Summary

INTRODUCTION

Oil-immersed power transformers are one of the most expensive and critical components of an electrical system. In 2008, Zhang et al determined experimentally two Nusselt correlations that were later used to calculate the convective heat transfer coefficients for zigzag cooled power transformer windings, [37] Despite this advancement, some authors have pointed out that these networks were based on expressions obtained from a limited number of experimental cases with relatively simple flows, such as in papers [36]–[38]. To obtain more robust expressions, Wu et al, [36], [38], and Coddé et al [39], have used CFD to extend the numbers of cases considered, by creating a large set of two-dimensional junction/elbow models In this contribution, a THNM model of a disc-type winding, previously developed for mineral oil, was used to perform thermal-hydraulic calculations with alternative liquids, namely a natural ester-based oil and a synthetic ester-based oil.

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