Nikola Tesla Institute
Dr. Draginja Mihajlović
3PINT and related innovative technologies as permanent solution to mitigate corrosive sulphur in power transformers / Aging Tests of Alternative Insulating Liquids
ABSTRACT: 3PINT and related innovative technologies as permanent solution to mitigate corrosive sulphur in power transformers
Focus of 3PINT project is to upgrade readiness level of the innovative technology for the removal of corrosive sulphur, PCB and aging product from transformer oils. Technology itself includes chemical conversion process to refine transformer oils in eco-frendly manner. Used technology is environmentally closed with no toxic emissions and waste released into environment. In addition, innovative solution for corroded silver-plated contacts cleaning, effectively removes silver sulphide deposits from OLTC contacts, ensuring long-term reliability and complete power transformer corrosive sulphur mitigation.
Keywords: 3PINT, innovative technology, environmentally closed technology, power transformer, complete corrosive sulphur mitigation
Abstract: Aging Tests of Alternative Insulating Liquids
Using alternative insulation liquids as a replacement of mineral oil took place since decades. Until now there is no regulation in the standards to identify the degradation of solid or liquid insulation under the application of alternative liquids. Most of investigations rely on the guidance known and used for mineral oil, which leads mostly to confusion and are misleading. Determination of aging and end of life for transformers filled with mineral oil is based on huge amount of information and experience gathered since oil transformers were built. The limits of key properties and DGA analysis are well defined for reconditioning, reclaiming and replacement of mineral oil as well as for fault detection in transformers. Efforts of research community were focused to extract these rules and modify them to fit to alternative liquids, however, until now there is no real success in this area. In this study, comparative laboratory aging tests of two natural esters of the same base were performed. Tests were conducted at 180 °C in stainless steel vessels with two different types of paper and four different metallic components in defined ratios corresponding to real power transformers. After several aging periods up to 28 days was finished, the key properties of insulating liquids were measured, such as: gasses dissolved in the oil, acidity, breakdown voltage, water content, interfacial tension, viscosity, antioxidant content, as well as degree of polymerization of the paper and water content in the paper. The aging results provided valuable insights into the differences in aging and gas emission patterns of the tested liquids, which varied depending on the type of paper used and the antioxidants present in the liquids. Additionally, the study demonstrated the interrelationship of liquid properties at various stages of paper degradation. The findings highlighted the importance of performing compatibility tests between insulating liquids and other materials intended for use before their application in power transformers.
Keywords: Aging Test, Compatibility, Lifetime, Natural Ester, Power Transformer
Biography of the presenter
Draginja Mihajlović, PhD in Chemical Engineering, is an associate research engineer in the Laboratory for Insulating Oil and Paper Testing, Nikola Tesla Institute of Electrical Engineering, Belgrade, Serbia. She is engaged in analysis of oil and paper insulation, power transformers condition assessment and fault diagnostics. She was also engaged in research activities in the field of: moisture distribution in paper/oil insulation, method for light alcohols dissolve in the insulating oils (methanol, ethanol) and elemental sulphur detection and quantification and aging of cellulose insulation impregnated with mineral and alternative liquids. She was involved in number of domestic and international projects related to PCB decontamination and sulphur corrosion phenomena as leading engineer.
