Experiments Research on the Deterioration of Inverter Transformer Insulation Paper Mechanical Properties With Mechanical-thermal Synergy

Oil-paper insulation system of converter transformer lies in a combination environment under which strong mechanical vibration and thermal are coupling, but the deterioration characteristics of insulation paper has not been paid enough attention. To study the mechanical-thermal synergy on the deterioration of insulation paper mechanical properties, thermal-vibration ageing box was designed. A series of accelerated ageing experiments were carried out under conditions of 130℃ thermal aging, added with vibration amplitude of 0, 1.99mm and 2.64mm at frequency 10 Hz, and ageing duration was 48h, 96h and 144h respectively. The tensile strength (TS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis and the degree of polymerization (DP) were measured for the specimen. The results show that the promotion of mechanical-thermal synergy is sharper than that of thermal ageing, and the higher the amplitude, the more obvious the decrease of TS and DP of the insulation paper. Orientation of cellulose macromolecule chain makes the fiber axial mechanical strength is far superior to the radial one, and the perpendicular component of the applied force is higher than the one along to the surface of the insulation paper, the above two factors play a key synergy role to accelerate the deterioration of the insulation paper mechanical properties. XRD and SEM analysis indicate that, from a microstructure point, the relative crystallinity and microcrystal size of the cellulose fiber become smaller, which indicates the type of microcrystalline doesn't change with ageing conditions. At the same time, the phenomena of refinement, bifurcation and breakage of fiber, and appearance, increase and development of holes, were found and they promoted the mechanical properties deterioration of the insulation paper. The study can provide a reference for the deterioration mechanism research of converter transformer insulation paper under the complex mechanical-thermal condition. © 2019 Chin. Soc. for Elec. Eng.