Flow and temperature distributions in a disc type winding-part I: Forced and directed cooling modes

© 2019 The Authors The thermal design of a power transformer determines its lifetime and loading capability, so correct modelling of liquid flow and temperature distributions in the winding is of vital importance. Existing standards and widely used simple calculation models can seriously under/overestimate winding hotspot temperatures under certain circumstances. In this paper, liquid flow and temperature distributions in a physical model representing a disc-type winding in a liquid forced and directed cooling mode are investigated experimentally using Particle Image Velocimetry (PIV) and a temperature measurement system and numerically using Computational Fluid Dynamics (CFD). Dimensional analysis is used to generalise the results into a form useful for design review. The operating conditions investigated include different liquid inlet velocities, inlet temperatures, power losses in individual disc segments, and the effect of alternative liquids. It is shown that hotspot temperature and position within the winding are a non-linear function of liquid inlet velocity, with stagnation and reverse flow demonstrated in both experiments and CFD models. Comparisons of liquid flow and temperature distributions between measurements and CFD simulation results show that 2D CFD results are representative when there are no reverse flows and 3D CFD simulations are needed when reverse flows occur. The results are presented first in dimensional forms to show the effect of each parameter, and then in non-dimensional forms to provide a generalised insight into transformer thermal design

Techniques of variational analysis

Variational arguments are classical techniques whose use can be traced back to the early development of the calculus of variations and further. Rooted in the physical principle of least action they have wide applications in diverse fields. This book provides a concise account of the essential tools of infinite-dimensional first-order variational analysis illustrated by applications in many areas of analysis, optimization and approximation, dynamical systems, mathematical economics and elsewhere

Evaluation of Bubble Formation in Transformer Insulation Systems - a Step Forward

Bubble formation in transformers could result in severe consequences leading to power outages and huge financial losses. There is an increased risk of bubble formation in the future due to increasing load demand and much higher loading fluctuations. The bubble formation process in transformer insulation has been studied for decades and the water content in the paper has been addressed as the most influential impact parameter. However, results from the most common insulating material combination of Kraft paper and mineral oil vary widely and a meaningful comparison for other parameters or insulating material combinations is challenging. This paper presents the development and verification of a simple test setup that can be used to study various impact factors on the bubble formation process with a high degree of confidence.</p