3D heating hazard assessment on transformer covers. Arrangement decisions

Abstract

Purpose -The purpose of this paper is to apply a 3D methodology to assess the heating hazard on transformer covers and present a practical tool to design amagnetic inserts arrangement. Design/methodology/approach -A practical 3D methodology linking an electromagnetic analytical formulation with thermal finite element method is used for computation. Such methodology allows the evaluation of the temperature on metallic device elements heated by electromagnetic induction. This is a 3D problem which in the case of power transformers becomes especially difficult to apply due to the discretization requirement into the thin skin depth penetration compared to big machine dimensions. Findings -From the numerical solution of the temperature field, decisions on dimensions and different amagnetic inserts arrangements can be taken to avoid hot spots on transformer covers. Research limitations/implications -Some parameters presented in the model as heat exchange coefficients and material properties are difficult to determine from formulae or from the literature. The accuracy of the results strongly depends on the proper identification of those parameters, which the authors adjust based on measurements. Originality/value -Differing from previous works found in the literature, which focus their results in power loss computation methods, this paper evaluates losses in terms of temperature distribution, which is easier to measure and validate over transformer covers. Moreover, an experimental work is presented where the temperature distribution is measured over a steel cover plate and a cover plate with amagnetic insert.

Electromagnetic and thermal parameter identification method for best prediction of temperature distribution on transformer tank covers

“…Figure 6(b) shows the temperature distribution if the flat cover base is made from mild steel and the bushing turrets are instead made from a magnetic material. Stainless steel material properties might be determined from experiments (Penabad-Duran et al, 2012) applying the parameter identification technique presented in this paper. It can be seen how due to the proper combination of materials, the temperature is reduced to permitted values.…”

“…Most of the related works focus their results on loss prediction (Kulkarni et al, 2004;Milagre et al, 2012) to ensure their total values, however the thermal problem for hot spot localization has become more significant in recent years (Cranganu-Cretu and Schneider, 2009;Glotic et al, 2009). It allows the effective design of the structural transformer elements guaranteeing total losses, maximum permitted temperature rise and considering also material cost (Penabad-Duran et al, 2012;Di Barba et al, 2005) which has acquired importance among designers and manufacturers imposed by the severe competitive market situation.…”

Reduction of stray losses in Tertiary Voltage Bushings in power transformer tanks

“…These cables are connected to bushings mounted in the tank walls or cover. High currents produce high stray fields in the vicinity of the bushing holes and this can produce high stray losses and hot spots in these parts of the tank [1]- [5]. In this paper authors analyze the case of tertiary voltage bushings placed in the tank cover.…”

Numerical verification of Turowski’s coefficient

“…This is because a very fine mesh is required in the thin skin depth of leakage flux penetration of about one millimeter against the dimensions of a few meters of the volume of the device (Lopez-Fernandez et al , 2012a, b, c). Nevertheless, analytical methods are being used as they still offer advantages in terms of fast calculation, in certain applications, when the non-linearity of magnetic characteristics is properly incorporated into the formulation (Penabad-Duran et al , 2012; Lopez-Fernandez et al , 2012a, b, c). The assessment of stray losses was an early concern, where, the classical solution was to adopt a losses correction factor.…”