Zhicheng Su

Cellulose-based insulation paper is widely used in high-voltage equipment, but its limited thermal conductivity and dielectric strength restrict reliable performance under elevated temperatures and strong electric fields. In this work, a dual-phase composite paper is developed by incorporating nano-ZnO and polyimide (PI) into a cellulose matrix, guided by molecular dynamics (MD) simulations. The combined fillers improve interfacial compatibility, suppress void defects, and establish continuous thermal pathways together with stable insulating barriers. Simulation predictions of enhanced thermal transport, charge suppression, and mechanical reinforcement are verified by experiments. The optimized formulation containing 3 wt% nano-ZnO and 6 wt% PI achieves a thermal conductivity of 0.294 W·m⁻¹·K⁻¹, a tensile strength of 72.12 MPa, corresponding to 87.26% and 41.02% improvements over pure cellulose (P0). Meanwhile, the breakdown strength increases from 60.22 to 73.51 kV·mm⁻¹ (+22.07%), and the relative permittivity and dielectric loss tangent decrease to 2.49 (−40.86%) and 0.46% (−43.21%). These results demonstrate that the dual-filler strategy provides a structurally compact and functionally stable composite architecture, enabling simultaneous enhancement of thermal, mechanical, and dielectric properties. This study confirms the effectiveness of simulation-guided design in accelerating the development of multifunctional cellulose-based insulating materials and highlights their potential for application in next-generation high-voltage power systems.

Nano-modified insulating oils have great potential to enhance the dielectric and thermal performance of offshore wind transformers, but nanoparticles are affected by temperature fluctuations to change the oil properties and microstructure, which restricts their large-scale application in offshore wind power equipment. In this study, γ-aminopropyltriethoxysilane (APTES) modified graphene oxide/natural ester composite insulating oil is developed through a surface functionalization strategy. The thermal conductivity and dielectric loss characteristics are systematically evaluated within a wide temperature range, revealing temperature-nanoparticle synergistic interaction mechanisms. Additionally, a model of natural ester insulating oil doped with nanoparticles is constructed based on molecular dynamics (MD) to elucidate the performance enhancement mechanisms, and the performance enhancement mechanism is clarified by calculating the mean square displacement (MSD), free volume (FFV), and radial distribution function (RDF) of the model. Results show that when the temperature rises, the modified nanoparticles can efficiently suppress the diffusion behavior of molecules in the oil, significantly reduce the free volume fraction by filling the gaps between oil molecules, and form hydrogen bonds with water to maintain the number of hydrogen bonds. This work provides theoretical foundations and design guidelines for developing high-temperature-resistant nanocomposite insulating oils.

Frequency-domain spectroscopy (FDS) is a nondestructive technique for moisture status evaluation of oil-impregnated paper (OIP) bushings; however, due to the lack of effective models to predict the FDS curve of OIP bushings under nonuniform moisture, it is difficult to establish a large database for FDS characteristics analysis and heterogeneous moisture status assessment. To address this issue, this article established a bushing finite element method (FEM) model and an improved X model based on the FEM and dielectric theory, respectively, for FDS prediction of nonuniformly damped OIP bushings. Comparing the FDS curves predicted by the bushing FEM model and the improved X model, it was found that the average relative errors are less than 1.25%. Finally, FDS measurements were conducted on the nonuniformly damped bushings in the laboratory to verify the accuracy of the proposed models. The experimental results indicated that the average relative errors of the bushing FEM model and improved X model in FDS prediction are less than 9.29% and 10.21%, respectively. This proves that the proposed models are highly accurate. The innovation of this article lies in establishing a bushing FEM model and an improved X model to predict the FDS curve of OIP bushings under nonuniform moisture.

The moisture intrusion of high-voltage oil-immersed paper (OIP) bushing may cause insulation deterioration. Polarization and depolarization current (PDC) technology is an effective and nondestructive method to evaluate the moisture state of OIP bushings’ insulation. However, the current PDC assessment methods are difficult to evaluate the nonuniform moisture status of OIP bushings. To address this issue, this article studies the PDC characteristics of OIP bushings under radial nonuniform moisture distribution. Initially, by combining with the laboratory PDC measurements and finite element method (FEM) simulation, the influence laws of the dampest insulation layer’s moisture content and position on the overall PDC curve of OIP bushings are explored. The results show that the moisture content and position of the dampest insulation layer have a significant influence on the overall polarization current curve. The peak value, steady-state value, and integral value of the polarization current are negatively correlated to the position and positively correlated to the moisture content of the dampest insulation layer. The moistest layer’s position of the radial nonuniformly damped bushing can be determined by polarization current integral difference under positive and negative PDC link-wire ways. This research provides the theoretical basis and technical support for the nonuniform moisture state evaluation of OIP bushing insulation.