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Insulation
Published in Fang Zhu, Baitun Yang, Power Transformer Design Practices, 2021
Kraft paper is widely used in power transformers due to its high dielectric strength, lower power factor and being free from conducing particles. Its main electric properties are listed in Table 4.3. As wire conductor insulation, thermal upgraded Kraft paper is widely used to achieve 120°C insulation temperature in normal service condition.
Quality Control of Packaging Materials
Published in Morton E. Bader, Practical Quality Management in the Chemical Process Industry, 2020
When referring to paper the term basis weight is used and a paper ply is usually between 40-70 1bs. This is the weight of a ream of 500 sheets of paper of standard dimensions (3,000 sq. ft.). Paper used in bags must meet certain tear and tensile strengths. The most widely referred to documents for paper tests are Uniform Freight Classification and Federal Specifications UUS48. Commonly used paper plies are designated as follows: Natural Kraft - Untreated paperExtensible Kraft - Same as natural but paper has more strengthNatural Wet Strength Kraft - Paper is treated with melamine resin to provide moisture resistance.Extensible Wet Strength Kraft - Same as above but utilizing extensible KraftBleached Kraft - Paper which is white or colored. Most often used as outermost ply of a bag for aesthetic and printability reasons Vapor barrier and protective inner plies are available. Glassine papers and certain plastic laminations provide protection against grease.
Insulating Media
Published in Leonard L. Grigsby, Electric Power Transformer Engineering, 2017
Thomas A. Prevost, David L. Hanson, Leo J. Savio, Ted Haupert
Electrical-grade paper and pressboard are mostly made from wood pulp processed by the kraft chemical process, hence known as kraft paper and kraft board (kraft is German for strong). The starting material is wood, both soft wood and hard wood. Wood is a natural composite material that is made up of flexible tubes of cellulose bound together by lignin, a brownish aromatic polymer that is mostly removed during the pulping process. A schematic representation of the fine structure of wood pulp is shown in Figure 12.3.1
Performance Analysis of Alternative Solid Dielectrics of Power Transformers with a Blend of Mineral and Silicon Oils
Published in IETE Technical Review, 2018
Chilaka Ranga, Ashwani Kumar Chandel, Rajeevan Chandel
For the last ten decades, cellulose-based Kraft insulating papers have been generally used in liquid-filled transformers [13]. Though the degradation rate of Kraft paper is high, it has been preferred by the utilities and consumers because of its low cost and reasonably good performance [14,15]. In 1950s, thermally upgraded Kraft (TUK), which is an updated version of Kraft, was introduced [9]. The development process of TUK is to chemically treat the paper with a nitrogen-based compound such as dicyandiamide [16]. Such chemical treatments stabilize the cellulose molecule hydroxyl radicals. As a result, the tendency of insulating paper towards hydrolysis is achieved. Also, the thermal upgradation process was widened for the operating temperatures of the paper from 95 to 110 °C, as mentioned in the IEEE C57.91 [17]. Further developments in improving the operating performance of transformer solid dielectrics have been achieved by using synthetic materials [18,19]. These synthetic papers and films can operate even at temperatures higher than 220 °C [20].