Study on bubble evolution in oil-paper insulation during dynamic rating in power transformers

Solid insulation tended to absorb moisture during the operation and maintenance of oil-immersed transformers, which could be dangerous to the apparatus especially under rated conditions. As had been researched, wet insulation could lead to bubble effect in turn-to-turn insulation when the temperature in transformer increased rapidly. Primarily, this paper investigated the degradation of dielectric strength caused by gas bubbles generated from oil-paper insulation. This paper mainly focused on clarifying the evolution of thermal bubble formation. The experimental platform consisted of an oil-paper insulation system, and an adjustable heating system was established to study the influence of water and gas content on bubble evolution temperature. Results showed that the gas content and moisture content in the paper could significantly affect inception temperature of bubble formation, which could well explain the high probability of bubble evolution in old and wet oil-impregnated transformers. Then, a mathematical model was founded to calculate the bubble evolution temperature considering the solubility of gas and moisture in transformer oil at a certain temperature. Finally, based on the above results, this paper provided a strategy for managing the risk of insulation failures in oil-immersed transformers caused by thermal bubbles in dynamic rating conditions.

[2]  T. Karayiannis,et al.  Modelling of the growth and detachment of a vapour bubble and the effect of an electric field in the nucleate boiling regime , 2006 .

[3]  Z. Nadolny,et al.  Bubble effect as a consequence of dielectric losses in cellulose insulation , 2010, IEEE Transactions on Dielectrics and Electrical Insulation.

[5]  K. Walczak,et al.  Can the bubble effect occur in an oil impregnated paper bushing? , 2012, IEEE Transactions on Dielectrics and Electrical Insulation.

[6]  Wolfgang Wagner,et al.  International Equations for the Saturation Properties of Ordinary Water Substance , 1987 .

[7]  Huaizhi Li,et al.  Modified model of bubble formation in non-Newtonian fluids , 2009 .

[8]  M. Hara,et al.  Effect of thermally induced bubbles on the electrical breakdown characteristics of liquid nitrogen , 1990 .

[9]  M. Koch,et al.  A new method for on-line monitoring of bushings and partial discharges of power transformers , 2012, 2012 IEEE International Conference on Condition Monitoring and Diagnosis.

[10]  S. R. Lindgren,et al.  Bubble evolution from transformer overload , 2001, 2001 IEEE/PES Transmission and Distribution Conference and Exposition. Developing New Perspectives (Cat. No.01CH37294).

[11]  F. Heinrichs,et al.  Bubble Formation in Power Transformer Windings at Overload Temperatures , 1979, IEEE Transactions on Power Apparatus and Systems.

[12]  R. J. Ringlee,et al.  An Improved Method of Oil Preservation and its Effect on Gas Evolution , 1958, Transactions of the American Institute of Electrical Engineers. Part III: Power Apparatus and Systems.

[13]  T. Saha,et al.  Moisture-bubbling of vegetable oil impregnated paper at transformer overload temperatures , 2015, 2015 IEEE 11th International Conference on the Properties and Applications of Dielectric Materials (ICPADM).

[14]  M. Noe,et al.  Withstand alternating voltage of liquid nitrogen in the presence of gas bubbles , 2014, 2014 IEEE 18th International Conference on Dielectric Liquids (ICDL).

[15]  Stefan Tenbohlen,et al.  Evolution of bubbles in oil-paper insulation influenced by material quality and ageing , 2011 .

[16]  P Przybylek,et al.  The influence of cellulose insulation aging degree on its water sorption properties and bubble evolution , 2010, IEEE Transactions on Dielectrics and Electrical Insulation.