Compression behaviors of oil-immersed insulating pressed-boards made of Kraft Pulp

We report on compression behaviors of oil-immersed insulating pressed-boards used in transformers for analyzing the axial vibration of windings. Compression behaviors of oil-immersed pressed-boards depended on strain rates and temperatures, that is, viscoelastic behaviors were observed. By applying the time-temperature superposition principle to the pressed-boards' compression behaviors, we obtained the relationship between the modulus of compressive elasticity and strain rate. Based on the relationship, the pressed-boards' compression behaviors were estimated under the condition of high compression forces and high strain rates. The 20cSt silicone liquid-immersed pressed-boards showed almost the same compression behavior as the mineral oil immersed pressed-boards. The viscoelastic behavior of the oil-immersed pressed-boards was mainly decided by the properties of the cellulose fibers, and not influenced by the viscosity of the immersed oils.