Feipeng Wang

Developing environmentally sustainable and resource-saving ester coolants is essential because these fluids reduce our reliance on traditional energy. To meet the massive cooling demands of data center servers and electric vehicle (EV) batteries, this study uses coconut fatty acid distillate (CFAD)—a waste material full of saturated fatty acids—to synthesize a neopentyl glycol diester (CNE0). We used response surface methodology (RSM) to find the best synthesis conditions, reaching a 97% conversion rate and a pour point of -4 ℃. We ran molecular dynamics (MD) simulations to understand how molecular structure affects low-temperature flow, and the results showed that odd-carbon chains, ethyl branches at the C2 position, and central double bonds effectively lower the pour point. Based on these findings, we added undecenoic acid and cost-effective castor oil fatty acids to improve the feedstock. The optimized sample (CNE7) performed very well, exhibiting a pour point as low as -27 ℃ and a fire point as high as 272 ℃. This study offers a practical way to make the coolant at a 50–60% lower cost than commercial natural esters. Ultimately, its low cost and high safety fit perfectly with the needs of the EV industry and large-scale data centers, while the research clearly explains how to use structural changes to develop high-performance coolants

Poly (vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) is a strongly promising fluoropolymer because of outstanding flexibility, electrochemical consistency, and excellent dielectric property, making it promising material for dielectric and electronic applications. Nanocomposite films composed of P(VDF-HFP) and varying-concentration of 2D Co₃O₄ nano mesh are synthesized via spin-coating process. Mechanical, structural, morphological, dielectric, electrical characteristics of the nanocomposites are comprehensively studied. The FTIR and XRD analysis confirms the retention of electroactive β-phase and successful incorporation of Co₃O₄ nano mesh into polymer matrix with strong interfacial interactions. SEM study reveals a uniform dispersion at lower loadings and agglomeration at higher loadings. Mechanical testing shows that Young’s modulus increases from 123.05 MPa (0.0 wt.%) to 959.92 MPA (4.0 wt.%). Dielectric analysis reveals significant enhanced permittivity as the temperature increases for all nanocomposite films. AC conductivity also improves significantly with filler content, frequency and temperature. At 30 °C σ_ac rises from 1.65 x 10^-8 S/cm for 0.0 wt.% to 6.99 x10^-3 S/cm for 7.0 wt.% composite at 107 Hz. The 4.0 wt.% sample shows a peak σ_ac of 1.11 x 10^-2 S/cm, indicating enhanced charge transport due to interfacial polarization and filler-induced conduction pathways. These results indicate that Co₃O₄ nanomesh effectively tunes the mechanical and dielectric response of P(VDF-HFP), although excessive loading leads to aggregation and higher dielectric loss.

Self-healing (SH) is a critical feature of metallized film capacitors (MFCs), since it ensures MFCs’ operational stability under extreme conditions. While SH depends not only on applied voltage and environmental factors but also strongly on the dielectric material. Despite this, current research on SH behaviors primarily examines metallized dielectric films rather than complete MFC devices, there remains a lack of systematic device-level comparative analyses for different dielectrics. Therefore, this paper investigates the SH probability of polypropylene (PP) and polyethylene terephthalate (PET) MFCs at the device level under varying voltage ramp rates. Results reveal that PET exhibits higher SH propensity, with SH probability exceeding 90% across all rates—nearly twice that of PP. SH process becomes less severe with rising ramp rates for both materials, but PET remains higher SH severity: it more readily triggers related-SH (RSH) events with peak energies up to 1080.44 mJ (vs. PP’s 769.92 mJ), causing greater damage and inferior voltage withstand level. Density functional theory (DFT) analysis explains these disparities by identifying differences in polarization and conductivity between them. PET demonstrates a higher molecular polarity index (MPI), along with broader electrostatic potentials and narrower orbital energy gaps. These attributes facilitate charge accumulation and enhance the severity of SH events in PET relative to non-polar PP.

The ageing of insulating paper escalates the peril of insulation failure in oil‐impregnated‐paper power equipment. Consequently, the real‐time monitoring and non‐destructive assessment of insulating paper condition assume paramount significance. This paper proposes a residual life prediction method of insulating paper based on Fourier transform infrared (FTIR) spectroscopy. The windowed wave feature (WWF) extraction method is designed and the WWF‐bagging model is established to assess the tensile strength (TS) of insulating paper. Combined with the shapley additive explanations (SHAP) algorithm, we propose that kurtosis and skewness of infrared spectrum are the pivotal parameters for insulating paper life prediction. Additionally, a consistent correlation is observed between the infrared spectral band of aldehyde band and the ageing time. The experimental results evince that the proposed model surpasses classical methods evaluating the residual life of ageing insulating paper.

To assess the insulation withstand characteristics of insulating fluids in cold environments, this study examines the negative lightning impulse characteristics of 45# mineral oil and Midel 7131 synthetic ester within a temperature range of 10 °C to −30 °C. Experimental results show that the breakdown voltage of both oils increases as the temperature decreases, with the synthetic ester exhibiting greater sensitivity to low-temperatures. A significant linear correlation is observed between the breakdown voltage and the logarithm of kinematic viscosity. A specialized observation system is developed to capture the dynamic streamer evolution in insulating oils at low-temperatures. Streamer images at different temperatures reveal that low-temperatures significantly suppress the initial streamer development and reduce the overall propagation speed. To further analyze streamer morphology, a novel image processing method combining CLAHE (Contrast-Limited Adaptive Histogram Equalization) enhancement and dynamic threshold extraction is proposed, yielding pseudo-color images that retain both grayscale and structural information. Quantitative analysis of streamer grayscale distribution at 0 °C and −30 °C indicates that low-temperatures increase the branching density and overall brightness of the streamer channel. These findings provide valuable insights for the selection of insulating oils and the design of high-voltage equipment in cold and high-altitude regions.

Metallized polypropylene film capacitors (MPPFCs) are pivotal components utilized across a spectrum of applications, including electromagnetic ejection, aerospace, and DC power transmission. Understanding the self-healing (SH) mechanism of MPPFCs is challenging, necessitating a comprehensive grasp of the physicochemical processes involved in SH, alongside a deep understanding of the impact of MPPFCs’ multilayer winding structure on SH. In this paper, we present an analysis of the voltage-dependent characteristics of the SH mode of MPPFCs under DC voltage. We substantiated our findings through experimentation and proposed a voltage-dependent multi-stage consecutive self-healing (CSH) model based on MPPFCs’ SH behavior at varying voltage levels. Our investigation reveals that as the SH voltage increases, the SH mode transitions from single SH to multi-stage CSH. In the CSH mode, sub-SH events are temporally and physically coupled through arc plasma and energy transfer, with notably stronger coupling between the first two sub-SHs observed in the three-stage CSH compared to the two-stage CSH. This heightened coupling leads to more breakdown layers with a significant increase in SH time, SH energy, and electrode removal area, albeit accompanied by a substantial decrease in insulation resistance. This paper offers direct evidence that multi-stage CSH is identified as the dominant mechanism driving insulation resistance decay and structural damage under high voltage. This understanding serves as a crucial basis for condition monitoring and structural optimization of MPPFCs.

Natural ester dielectric fluids are increasingly favored as sustainable alternatives to mineral oils; however, their susceptibility to oxidation remains a major challenge. Conventional stabilization methods using synthetic antioxidants often pose health and environmental concerns. This study explores the use of methyl carnosate (MC), a bio-based antioxidant, to enhance the oxidation stability of soybean oil (SO). The addition of MC increases the oxidation onset temperature of SO by nearly 20 °C and effectively mitigates the rise in kinematic viscosity and soluble acidity during accelerated aging at 120 °C. These parameters remain significantly lower compared to neat SO and the commercial product FR3^® fluid. Mechanistic investigations reveal that MC effectively inhibits the transfer of allylic and bisallylic hydrogens, thereby delaying the formation of aldehydes generated from peroxide decomposition. This study underscores the potential of MC as a sustainable and effective additive for enhancing the oxidation stability of natural ester dielectric fluids.

With increasing demands for fire safety and environmental friendliness, retrofilling transformers with alternative insulating liquids has become a growing trend. However, retrofilling power transformers remains uncertain, as more residual mineral oil compromises K‐class flame retardancy, and its impact on environmental performance has yet to be clarified. Meanwhile, there is a lack of evaluation methodology and retrofilling procedure for power transformers. This paper presents a synthetic ester retrofilling conducted on a 20 MVA/110 kV transformer. Kerosene vapour‐phase drying was implemented to supplement traditional oil draining, and the insulating liquid achieved a fire point of 304°C, meeting K‐class flame retardancy after retrofilling. The estimated residual mineral oil content was less than 0.8 wt%, significantly lower than the typically reported value (e.g., 3 wt%–5 wt%). Standardised testing confirmed that the synthetic ester containing 3.5% mineral oil maintained its environmental performance, achieving 82.6% biodegradability. Additionally, the evaluation methodology and recommended procedure for retrofilling power transformers are proposed in this study. The performance changes of the retrofilled transformer were discussed in detail. A significant decrease in lightning impulse insulation margin and insulation resistance was observed, which should be given particular attention.