Hai Jin

When high-voltage DC equipment is subjected to polarity-reversing voltage, the insulation performance of its internal insulation material, epoxy resin-impregnated paper (RIP), is significantly affected by low-frequency polarization. To clarify the underlying mechanisms, this study analyzes the impact of the relationship between low-frequency dielectric relaxation time and polarity-reversing time on the dynamic changes of space charges at different temperatures based on the pulsed electro-acoustic (PEA) method. Furthermore, the influence of traps at the epoxy resin (EP)/RIP interface on interfacial charge accumulation is considered. By improving the existing bipolar carrier transport model, the dynamic characteristics of interfacial space charges in RIP under different polarity-reversing times are explored. The results show that at 313K, due to the low-frequency dielectric relaxation time constant exceeding 60s, the charge distribution is not significantly affected by the reversal time; At 333K and 353K, the reduction in dielectric relaxation time leads to a decrease in interfacial charge density and maximum field strength, with the peak field strength shifting towards the epoxy layer; At 373K, influenced by space charge dissipation and enhanced relaxation effect, the electrode surface charges and the maximum field strength in the epoxy layer initially decrease and then increase with increasing reversal time. The simulation results more explicitly characterize the interfacial polarization process between EP and RIP, and together with the experimental results, elucidate the mechanism of low-frequency polarization on the dynamic characteristics of space charges in RIP under polarity-reversing voltage. The research results may provide a theoretical basis and reference for the insulation design and optimization of high-voltage DC equipment.

This study investigates the corrosion behaviour of grounding down leads in transmission towers subjected to wet–dry cycle in saline soils of Northwest China through accelerated corrosion experiments. Using saline soil from the Hexi Corridor, rich in chloride and sulphate ions, corrosion rates were assessed via weight loss, polarisation curves, scanning electron microscopy and X-ray diffraction analyses. Results demonstrate that wet–dry cycle significantly accelerates corrosion due to enhanced chloride ion diffusion and corrosion kinetics, with the highest average weight loss rate (3.08%) and corrosion current density (0.3526 mA/cm²). Scanning electron microscopy analysis revealed extensive cracking in corrosion product layers under cyclic wet–dry conditions, weakening their protective capability and further intensifying corrosion. The primary corrosion products identified were FeO and Fe ₂ O ₃ , consistent with field samples, indicating that the corrosion mechanism remains unchanged under accelerated conditions. This study provides novel insights into how cyclic moisture conditions affect grounding materials in saline environments, guiding material selection, maintenance strategies and site selection to improve transmission line reliability and safety.

The dielectric relaxation dynamics in polymer composites critically determine their functional performance in advanced electrical systems. This study systematically investigates hybrid epoxy composites comprising neat epoxy resin (EP) and paper-reinforced systems (EIP), modified with 10–50 wt% polypropylene glycol diglycidyl ether (PEGDGE) plasticizer. Through synergistic application of differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (10⁻¹–10⁶ Hz), the quantitative relationships between plasticizer content, glass transition temperature (Tg), and dielectric relaxation processes were established. DSC analysis reveals a linear Tg dependence with increasing PEGDGE content, attributed to enhanced molecular mobility. Dielectric characterization demonstrates three distinct relaxation regimes: α-relaxation below Tg, interfacial polarization at epoxy/PEGDGE boundaries, and paper/epoxy interfacial effects in EIP systems. A quantitative dielectric relaxation model was developed based on complex modulus formalism, coupled with Vogel–Fulcher–Tammann (VFT) analysis of DC conductivity. Activation energy mapping through Arrhenius decomposition reveals three characteristic values: (1) 82.01–87.80 kJ/mol for α-relaxation, (2) 55.96–64.64 kJ/mol for epoxy/PEGDGE interfaces, and (3) 30.88–44.38 kJ/mol for epoxy/paper interfaces. Crucially, the plasticizer content modulates these activation energies, demonstrating its role in tailoring interfacial dynamics.