Haren, 8th of July, 2020 – The demands placed on oil-filled transformers are constantly increasing. Ever greater efficiency and operational reliability are desired, even at high operating temperatures and heavy electrical load. Especially for the construction of modern transformers, Röchling Industrial has further developed the properties of its’ premium insulating material, Trafoboard®. Trafoboard® has been subjected to comprehensive testing by the University of Applied Sciences Osnabrück.
Since 2010, Röchling has been offering an insulation material made of high-quality laminated pressboard for the highest demands on electrical properties in the form of Trafoboard®. Trafoboard® HD-PH consists of high-density pressboard layers, made from pure cellulose according to IEC 60641, bonded together using a phenol-based resin matrix.
Röchling has several decades of experience with the phenolic resin for use in oil-filled transformers, thanks to the high-voltage insulation material Lignostone® Transformerwood®, which is also part of the company’s product range. The properties of phenolic resin remain constant in oil-filled transformers even over a very long period of time and thus offer very good conditions for the construction of transformers. Against this background, Röchling developed the phenolic-glued pressboard, Trafoboard® HD-PH
The very low moisture content and the very good drying behaviour characterise the material. Trafoboard® HD-PH meets the mechanical and electrical requirements for laminated pressboard according to IEC 60763-3 type 3.1 A.2 and in part clearly exceeds them. Unlike polyester-glued laminated pressboard, this material does not release styrene during machining. This avoids an unpleasant smell and a possible health hazard for the employees.
Röchling has been cooperating closely with the University of Applied Sciences in Osnabrück for years in the development of insulating materials for transformer construction. This also applies to Trafoboard® HD-PH, which has been approved for many years by renowned manufacturers of oil-filled transformers after thorough examinations of the properties and has been successfully used worldwide as insulating parts, such as rings, platform and fasteners.
To enable transformer manufacturers to make allowance for the requirements for increasingly powerful transformers, Röchling has now further optimised the electrical properties of the material and had them tested in the modern high voltage laboratory of the University of Applied Sciences in Osnabrück. A high partial discharge inception field strength in the bonded seam between the laminated pressboard layers is the greatest challenge for the electrical properties. Consequently, Röchling has further optimised the manufacturing process of Trafoboard® and once again improved the bonded seam of the premium insulating material.
The University of Applied Sciences in Osnabrück tested 40 samples parallel to the lamination in mineral oil for partial discharge with a measurement precision of <1 pC up to a voltage of 200 kV. The results on Trafoboard® show no continuous partial and only two samples broke down. All the other tested samples were stopped due to a flashover at the sample surface or a breakdown of the test sample. These events occur mainly by the surrounding mineral oil rather than by the sample, since the average event voltage corresponds to the electric strength of the oil. The samples did not show any partial discharge within the material at an average maximum field strength of 10 kV/mm. (See diagram)