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Improvement of Karl Fischer Moisture Measurements During Accelerated Aging Testing of Transformer Insulating Systems
B. Greaves, A. Levin, K. Biggie, J. Beaudoin, T. Prevost
Weidmann Electrical Technology Inc., United States of America
The preparation of solid electrical insulating material samples for accelerated aging testing of liquid-immersed transformer insulation systems per IEEE Std. C57.100™ requires a guaranteed low moisture content, which is critical to achieve and interpret test results accurately. Multiple test methods exist to determine the amount of water present in solid electrical insulating materials, such as: the oven drying method, solvent extraction method, and Karl Fischer titration method. Even though the test standards describe sample preparation, measurement procedures, and interpretation of results, there can be variation in some specific critical parameters of these tests. Thus, this situation requires the development of so-called best practices that should be followed to ensure more reliable and accurate measurements of moisture content for such accelerated aging tests. This article describes the various test methods for measuring moisture content and their deficiencies/benefits and focuses on the development of optimum test parameters for the oven extraction method of the Karl Fischer titration moisture test to improve the accuracy of lower moisture content measurements in particular.
11:00am - 11:30am
Investigating the Effects of Moisture Distribution on the Electric Field and Leakage Current of Power Transformer Bushings
M. Abouhosseini-Darzi2, E. Rahimpour1, M. Mirzaie2, A. A. Shayegani-Akmal3
1THWS, Germany; 2Department of Electrical Engineering, Babol Noshirvani University of Technology, Iran; 3University of Tehran, College of Engineering School of Electrical and Computer Engineering, Iran
Bushings are one of the most important and essential equipment of power transformers. Statistics show that one of the main and major causes of transformer failures is due to bushing problems, so it has a significant impact on the safety and reliability of the power system. One of the main reasons for bushing failures is the penetration of moisture into its internal insulation system. Moisture usually enters the insulation system of oil-impregnated paper (OIP) bushings through the flange gasket and diffuses into it over time. The moisture affects the dielectric properties and leads to an increase in its leakage current. These effects lead to changes in the electric field of the inner insulating layers of the bushings, so it is necessary to investigate these effects. In this paper, the changes of the electric field in the insulating layers of a sample bushing have been investigated with considering the different moisture distribution between the layers. This evaluation has been done during the moisture diffusion time, from the start of penetration to the time of uniformity of moisture in all layers. Also, the moisture effects on the bushing leakage current under above conditions have been studied. For this purpose, an OIP bushing is modeled in COMSOL Multiphysics software, and the simulations are carried out based on Finite Element Method (FEM) and finally the obtained results are analyzed. The results show that the moisture distribution in the bushing can have an important effect on the internal electric fields. Also, according to the results, the moisture distribution inside the bushing does not have a great effect on the leakage current and this current is only affected by the volume of the moisture penetrated inside the bushing.
