Study on the Change Rule of Electro-Optical Frequency Dielectric Characteristics in Epoxy Resin Insulation Systems Under Multifactorial Combined Aging

Epoxy resin insulating materials are widely utilized in dry-type electrical equipment. Prolonged exposure to complex operational conditions induces aging phenomena in these materials, leading to significant degradation of their dielectric strength. This deterioration critically compromises the operational reliability of equipment, making it imperative to clarify the change law of aging characteristics of epoxy resin insulation materials under multiple stresses. In this study, an electrical-thermal-mechanical multifactorial combined aging test platform was established under laboratory conditions. Accelerated aging tests were conducted on epoxy resin insulation samples under both single-factor and combined multifactorial conditions, with the following parameters: thermal aging at 150°C, electrical aging under $4 \text{kV} / \text{mm}$ field strength, mechanical aging with vibration frequency of 100 Hz and acceleration of 8g, over a 30-day aging cycle. Dielectric characterization was performed using Frequency Domain Spectroscopy (FDS) across $10^{-3} \sim 10^{3} \text{Hz}$ and Terahertz TimeDomain Spectroscopy (THz-TDS) spanning $0.1 \sim 3 \text{THz}$, The variation curves of dielectric characteristics for epoxy resin insulating materials were obtained across two characteristic frequency bands. Explored the influence of different aging stresses on the changes in dielectric parameters. The experimental results demonstrate that throughout the experimental aging cycle, the loss tangent curves of epoxy resin insulation consistently exhibited a characteristic pattern of initial decline followed by subsequent elevation. Notably, during advanced aging stages, a marked increase in dielectric loss was observed with progressive accumulation of aging factors. As the experimental aging progressed, both the absorption coefficient and extinction coefficient exhibited a progressive increase within the terahertz frequency range, while the transmittance curve initially demonstrated a significant decline before gradually stabilizing to a plateau. The two non-destructive testing (NDT) methods employed in this study significantly broaden the spectral coverage of dielectric response characterization for insulating materials. These findings provide critical datasets and theoretical foundations for non-destructive evaluation (NDE) of aging progression in epoxy resin insulation systems.