{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

10_article_transfaging - F E A T U R E A R T I C L E...

Info icon This preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
26 IEEE Electrical Insulation Magazine F E A T U R E A R T I C L E 0883-7554/07/$25/©2010IEEE Pilot dielectric response analysis (DRA) measurements, using sinusoi- dal, triangular and square applied voltage wave-forms, and PD mea- surements, were carried out at ambi- ent and elevated temperature in or- der to investigate ageing in oil-filled transformers. Possible Indicators of Aging in Oil-Filled Transformers Part 1: Measurements Key words: aging, condition indicator, transformer, degradation model, failure rate, expected life, degree of polymerization, conduction and displacement currents, partial discharge Introduction Degradation model development using basic research, and remaining life estimation, are essential for modern electrical engineering aging-asset management programs [1]. A CIGRE report [2] presents in detail the different aging factors and models, mechanisms of failure, condition-assessment and diagnostic techniques, and life assessment and extension methods. Aging in cellulose paper insulation can be related to a decrease in tensile strength [3]. A correlation between tensile strength and degree of polymerization (DP), as observed by many researchers, is shown in Figure 1. The DP of the paper is reduced from its starting value (DP 0 ) as a result of molecular cellulose chains being cut by hydrolysis, oxidation, and pyrolysis in the transformer. Aging depends on temperature according to Montsinger’s rule [3], [4], which predicts that the lifetime of many insulating materials shortens by 50% for every 6–10°C increase in operating temperature. It has been found in postfailure inspections that the DP value of paper samples taken from transformers can vary with sample location and ambient climatic conditions [3]. Laboratory studies have shown that the furane compound concentration increases with decreasing DP of pressboard insulation (Figure 2). The rate of furane formation varies with aging temperature and initial moisture content of the pressboard [5]. However, field experience has shown that the correlation of furane concentration with transformer aging and remaining lifetime has limitations. Furane concentration is sensitive to operating temperature, transformer loading, transformer design, and the concentration of moisture and oxygen in contact with the cellulose. No firm correlation between furane concentration and age or remaining lifetime was established by CIGRE [3]. It should also be noted that furanes generated at hot spots may diffuse to the sampling location. It is recommended that the relationship between DP and furane content be recalibrated whenever the oil is replaced or filtered. Other degradation products in the oil such as acids, sludge, dissolved gases, water, and other polar and phenolic compounds are also being investigated as possible indicators of aging. These can alter the permittivity and conductivity of the paper (cellulose) insulation. Consequently, asset managers are also using dielectric methods, such as polarization index, dielectric response analysis (DRA), tan δ
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern