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As the voltage level continues to rise, an imperative demand arises for novel insulating papers characterized by superior electrical insulation strength and heightened thermal stability, to align with the transformative advancements in high-voltage power transformers. Nevertheless, conventional approaches relying on “trial-and-error” approaches encounter significant challenges in expeditiously developing alternative materials. Therefore, the mechanical, thermal stability and dielectric attributes of polyimide (PI)/cellulose insulating paper have been predicted through molecular dynamics (MD) simulations. Subsequently, insulating papers of the composite variety, featuring varying PI fiber content, have been fabricated and subjected to comprehensive investigations of their thermal stability and electrical characteristics. In comparison to pure cellulose insulating paper, the 6% PI/cellulose composite proves (P6) to be the most representative, exhibiting a notable 26.24% increase in tensile strength, a rise in glass transition temperature from 113.4 to 124.7 K, a reduction in permittivity from 4.22 to 3.25, a substantial 58.33% decrease in dielectric loss, and a 30.35% enhancement in breakdown strength. This study unequivocally confirms the efficacy of MD simulations in expediting the development of insulating material and establishes PI/cellulose insulating paper as an avant-garde alternative for high-voltage transformers, ushering in a new era for insulation materials.

Currently, the method of detecting methanol in transformer oil by surface-enhanced Raman spectroscopy (SERS) possesses the disadvantages of high cost, long time, and difficulty in field testing. To tackle this problem, a novel method was proposed for the combination of extraction and silver nanosubstrate to detect dissolved methanol in transformer oil. Specifically, it was determined first by Gauss view and Gaussian software that pure water and silver nanoparticles (Ag NPs) were applicable for the detection of methanol content by the Raman spectroscopy. Then, multilayer Ag NPs were synthesized on the surface of the copper sheet by a displacement reaction. The electric field distribution on the surface of Ag NPs was analyzed by COMSOL software, which further revealed that the Ag NPs could improve the Raman signal of methanol molecules. Finally, the pure water and Ag NPs were used for Raman measurement of methanol transformer oil solution with different concentrations based on the experimental platform of Raman spectroscopy. The results pinpointed that the minimum detection content of methanol in transformer oil was 1.8 mg/L. This method is simple, fast, low-cost, and applicable to the detection of trace methanol.

The frequency-domain spectrum (FDS) method can effectively evaluate the aging state of crosslinked polyethylene (XLPE) cable insulation. To more accurately achieve a quantitative analysis of information in the FDS, this article combines the concepts of fractional element (Cap-Resistor) and fractional calculus, inspired by the Debye model and the multibranch improvement method of the Cole–Cole (C–C) model, establishes an improved fractional Zener model based on the existing Cap-Resistor model, and combines the improved fractional Zener model with the elite genetic algorithm (EGA) to propose a new method for analyzing the relaxation polarization information of XLPE dielectric. Six sets of XLPE cable samples with different aging times (including a validation set) are prepared at an aging temperature of 150 °C, and the FDS of the thermal aging samples is measured. Then, the FDS is fit using a modified fractional Zener model: first, the least squares method is used to establish the optimized objective function, the characteristic parameters are extracted and preferentially selected using EGA for analysis, and the fitting equations between aging time and characteristic parameters are established, and the validation results manifest that the error of the characteristic parameters on the aging time characterization of XLPE cable insulation samples is 0.18465 %, which is excellent. The evaluation method’s accuracy has been validated. This article introduces a feasible approach for analyzing relaxation polarization information in XLPE dielectric using an improved fractional Zener model and EGA.

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.

Under the combined effect of the electric and temperature fields, bubbles will be formed on the transformer oil-paper insulation system, which will seriously endanger the insulation strength. However, the current study usually divided the formation and motion of bubbles into independent parts, lacking research on the whole process of bubble evolution. This article experimentally investigated and theoretically analyzed the whole process of the formation, deformation, and motion of bubbles in the oil-paper insulation system and explored the influence of the extremely inhomogeneous electric field (EIEF) on bubbles evolution. The results show that with the enhancement of the electric field, the bubble inception temperature (BIT) and bubble size increase significantly, while the number of bubbles decreases. Under the stretching and pushing effect of the electric field force, the bubbles will deform and move toward the low electric field region. In addition, this article studies the influence of bubbles on the transformer electric field distribution through multiphysical field simulation.