The Most Important Insulation Component Material in Oil-Immersed Transformers
Insulating paper fiber material is the most important insulation component material in oil-immersed transformers. Paper fibers are the basic solid tissue components of plants. The atoms that make up the material molecule have positively charged nuclei and negatively charged electrons that run around the nuclei. Unlike metal conductors, there is almost no free electrons in the insulating material. The extremely small electrically conductive current in the insulator is primarily derived from the ionic conductance. Cellulose is composed of carbon, hydrogen and oxygen. Thus, due to the presence of hydroxide in the molecular structure of the cellulose, there is a potential for water formation, which imparts water-containing properties to the paper fibers.
In addition, these hydroxides can be considered to be centers surrounded by various polar molecules such as acid and water, which are combined by hydrogen bonding, making the fibers susceptible to damage. At the same time, the fiber often contains a certain proportion (about 7%) of impurities, including a certain amount of water. Due to the colloidal nature of the fibers, these moistures are not completely removed. This also affects the performance of the paper fiber.
Polar fibers are not only easy to absorb moisture (moisture makes strong polar media). Further, when the paper fibers absorb water, the interaction force between the hydroxides is weakened, and the mechanical strength is drastically deteriorated under the condition that the fiber structure is unstable. Therefore, paper insulation parts are generally used after drying or vacuum drying and oil immersion or insulating varnish. The purpose of the varnish is to keep the fibers moist. It is guaranteed to have high insulation and chemical stability and high mechanical strength.
At the same time, after the paper is sealed by paint, it can reduce the absorption of moisture by the paper, prevent the oxidation of the material, and fill the gaps with the town to reduce the bubbles which may affect the insulation performance, cause partial discharge and electric breakdown. However, some people think that after immersion in the paint, there may be some paint that will slowly dissolve in the oil and affect the performance of the oil. The application of such paint should be fully taken care of.