Natural Ester Replacement Effect on Thermal Degradation of Cellulose Insulation From Macroscopic Behavior to Atomic-Scale Mechanism

The accelerated thermal aging test was conducted with samples composed of mineral oil (MO), FR3 natural ester, kraft insulation pressboard (KIP), and thermally upgraded paper (TUP) at 120 °C. In the middle aging period, aged MO was replaced with new FR3. Molecular dynamics was used to simulate the mechanism of delaying cellulose aging by replacing natural esters. The experimental results show that, compared to the controls, KIP and TUP impregnated in FR3 had higher degrees of polymerization (DPs) values and lower aging rates. After the FR3 replacement, the relative chain scission rate of KIP and TUP was significantly slowed. FR3 has a better aging retarding effect on TUP than KIP. Atomic scale mechanism analysis shows that FR3 natural ester could inhibit the diffusion of water and acid in the oil-paper insulation system before and after oil change, which has a significant ability to delay the acid hydrolysis of cellulose. This is the main reason why KIP and TUP exhibited a higher DP in natural ester. This article provides theoretical support for transformer replacement of natural ester.