Search Results (60)

With the shift of oil and gas exploitation to deep seas, the 35 kV high-voltage electric slip ring in Single-Point Mooring (SPM) systems faces critical challenges of insulation failure and thermal failure, threatening operational safety. This study aims to investigate its insulation strength and temperature rise characteristics. A three-dimensional electric field model and a magnetic–thermal coupling model considering the skin effect were established using the finite element method (FEM). Simulations were conducted under four high-voltage configurations and various high-current operating conditions, followed by AC breakdown tests and high-current temperature rise experiments for validation. The results show that the maximum electric field (up to 19.53 kV/mm) concentrates at the inlet polytetrafluoroethylene (PTFE) bushing, which is the insulation weak point. The maximum temperature rise at the center ring can be predicted by a power-law model. Moreover, simulation results agree well with experimental data, confirming the reliability of the computational studies. This work provides a theoretical and experimental basis for the optimal design and safe operation of high-voltage slip rings in offshore SPM systems. Full article

Quinoa (Chenopodium quinoa) is a promising source of plant proteins with the potential to produce bioactive peptides through enzymatic hydrolysis. This study aimed to extract quinoa protein and produce bioactive peptides using two microbial proteases: Alcalase (from Bacillus licheniformis) and Flavourzyme (from Aspergillus oryzae). The protein was extracted through alkaline solubilization and isoelectric precipitation, achieving a 72% yield. Hydrolysis was conducted for 4 h, and enzymatic activity was measured using the TNBS method to determine the degree of hydrolysis, while SDS-PAGE was used to analyze protein breakdown. The reaction was performed at controlled pH and temperature (Alcalase: 9.5 and 55 °C; Flavourzyme: 7 and 37 °C). Both enzymes achieved maximum hydrolysis at 60 min. Consequently, the separation and inhibitory capacity of angiotensin-converting enzyme (ACE-I) were tested at the first four time points (0, 20, 40, and 60 min). A wider variety and higher concentration of peptides smaller than 2 kDa were found in hydrolysates treated with Flavourzyme, which is associated with antihypertensive activity. The ACE-I assay showed greater activity at the end of hydrolysis. Inhibition percentages of 87.5 ± 2.11 were observed in hydrolysates with Flavourzyme, and 94.1 ± 1.11 in those with Alcalase. These findings indicate that quinoa protein, hydrolyzed with microbial proteases, is a feasible source of peptides with potential antihypertensive effects for use in functional foods and nutraceuticals. Full article

Mineral oils are increasingly being replaced by plant-based insulating liquids, known as natural esters, because of their biodegradability and high fire safety characteristic. However, their wider use in high-voltage and unsealed transformer applications is still limited due to concerns about thermo-oxidative stability and the relatively limited long-term performance data available compared to mineral oils. This study investigates improving the oxidation stability of natural esters through nanotechnology. A canola-based insulating liquid was used as the base fluid and modified with TiO₂ and SiO₂ nanoparticles of different sizes. Nanoparticle concentrations ranged from 0.05 to 0.25 wt.%, while Span 80 (sorbitan monooleate, non-ionic surfactant) served as a surfactant to ensure uniform dispersion and long-term colloidal stability. The nanofluids were subjected to accelerated aging to evaluate oxidation resistance, and key properties such as acidity, viscosity, and dissipation factor were monitored throughout the process. Dielectric performance was assessed using AC breakdown voltage testing, with results interpreted through two-parameter Weibull statistics. The TiO₂-based nanofluids demonstrated superior thermo-oxidative stability compared to both the base oil and the SiO₂-modified samples. Formulations containing smaller TiO₂ nanoparticles (5 nm) exhibited the lowest increases in viscosity, acid value, and dissipation factor, indicating strong resistance to degradation under thermal stress. In dielectric performance, SiO₂ nanofluids reached 65.8 kV, while TiO₂ nanofluids achieved a higher value of 72.4 kV, confirming their greater effectiveness. Although the nanoparticles are not biodegradable, their use at low concentrations significantly enhances the oxidative and dielectric stability of natural esters, helping extend fluid life and reduce dependence on petroleum-based insulating liquids. Full article

The reliability of magnet wire insulation is critical for the safe and efficient operation of aerospace electric machines exposed to extreme electrical and environmental conditions. Polyimide-based insulations are widely used due to their excellent thermal and dielectric properties; however, they face challenges such as space charge accumulation, partial discharge activity, and accelerated aging under combined stressors. This study investigates the dielectric breakdown behavior of MW35-C class magnet wire subjected to both AC and DC electrical stress under sub-atmospheric pressures representative of aerospace environments. Experimental measurements were performed on 13 AWG, 15 AWG, and 20 AWG wires, all sourced from the same manufacturer but differing in core conductor radius and total insulation thickness. The results were statistically analyzed using the Weibull distribution. To complement the experimental analysis, 3D finite element simulations were conducted to evaluate electric field distributions at the contact interface between wires. The results demonstrate that breakdown strength is significantly affected by ambient pressure, wire geometry (core radius and insulation thickness), and the volume effect. Among the tested wires, 20 AWG exhibited the highest breakdown strength, attributed to its favorable conductor-to-insulation ratio and reduced insulation volume, which lowers the probability of critical defects. These findings provide valuable insights for the design and qualification of robust insulation systems in all-electric and more-electric aircraft operating in low-pressure environments. Full article

In SF₆ gas-insulated equipment, solid dielectrics critically degrade insulation performance by reducing the electric field’s ability to withstand gas gaps. To investigate the critical role played by solid dielectric surfaces during the initial phase of gas–solid interface discharge phenomena, this paper experimentally measures the AC breakdown voltage (U_bd) of both dielectric surface-initiated breakdown (DIBD) and electrode surface-initiated breakdown (EIBD) across eight types of post insulator samples. Tests are conducted in 36 mm SF₆ gas gaps under pressures ranging from 0.1 to 0.4 MPa. Combined with electrostatic field simulations, the results reveal that DIBD requires substantially lower U_bd than EIBD under comparable maximum electric field (E_max) conditions. As gas pressure increases, this difference becomes more pronounced. This phenomenon can be explained by three key mechanisms: First, due to the regulatory effect of dielectric materials and shielding electrodes on the electric field distribution, the high-electric-field zone along the gas–solid interface exhibits a longer effective discharge path compared to that in a pure gas gap. This configuration creates more favorable conditions for discharge initiation and subsequent propagation toward the opposite electrode. Second, microscopic irregularities on the dielectric surface induce stronger local electric field enhancement than comparable features on metallic electrodes. Third, in high-electric-field regions adjacent to the dielectric surface, desorption processes significantly enhance electron multiplication during gas discharge, and this enhancement effect becomes more pronounced as gas pressure increases, further lowering the discharge inception threshold. As a result, discharge initiation at dielectric interfaces requires less stringent electric field conditions compared to breakdown in a gas gap, especially at high gas pressure. This conclusion not only accounts for the saturation behavior in the U_bd-p characteristic of SF₆ gas–solid interface discharges but also explains why surface contaminants/defects disproportionately degrade interfacial insulation performance relative to their impact on gas gaps. Full article

With the electrification of generator sets, electric locomotives, new energy vehicles, and other industries, AC motors subject bearings to an electric field environment, leading to galvanic corrosion due to the use of variable frequency power supply drives. The phenomenon of bearing discharge breakdown in subway traction motors is a critical issue in understanding the relationship between shaft current strength and the extent of bearing damage. This paper analyzes the mechanism of impulse discharge that leads to galvanic corrosion damage in bearings at a microscopic level and conducts electric thermal coupling simulations of the traction motor bearing discharge breakdown process. It examines the temperature rise associated with lubricant film discharge breakdown during the dynamic operation of the bearing and investigates how breakdown channel parameters and operational conditions affect the temperature rise in the micro-region of bearing lubrication. Ultimately, the results of the electric thermal coupling simulation are validated through experimental tests. This study revealed that in an electric field environment, the load-bearing area of the outer ring experiences significantly more severe corrosion damage than the inner ring, whereas non-bearing areas remain unaffected by electrolytic corrosion. When the inner ring reaches a speed of 4500_rpm, the maximum widths of electrolytic corrosion pits for the outer and inner rings are measured at 89 um and 51 um, respectively. Additionally, the highest recorded temperatures for the breakdown channels in the outer and inner rings are 932 °C and 802 °C, respectively. Furthermore, as the inner ring speed increases, both the width of the electrolytic corrosion pits and the temperature of the breakdown channels rise. Specifically, at inner ring speeds of 2500_rpm, 3500_rpm, and 4500_rpm, the widths of the electrolytic pits in the outer ring raceway load zone were measured at 34 um, 56 um, and 89 um, respectively. The highest temperatures of the lubrication film breakdown channels were recorded as 612 °C, 788 °C, and 932 °C, respectively. This study provides a theoretical basis and data support for the protective and maintenance practices of traction motor bearings. Full article

Since epoxy resin has excellent mechanical and insulating qualities, it is frequently utilized in dry transformers. Low thermal conductivity, however, has prevented it from be developed further in high-frequency and large-capacity dry transformers. This study describes the preparation of sheet boron nitride (BN)/epoxy resin composites with superior electrical, thermal, and mechanical properties through the application of varying strengths of high-frequency alternating-current (AC) electric fields. Using an optical microscope, the orienting process of BN in epoxy resin under an electric field was studied. In parallel, tests were conducted on the BN/epoxy resin composites made with varying electric field strengths. The findings indicate that the preparation using a high-frequency AC electric field decreases BN agglomeration and improves the composite’s properties. The overall performance is comparatively ideal when the applied electric field strength is 30 V/mm, the tensile strength is 48.3 MPa, the breakdown field strength is 37.65 kV/mm, and the thermal conductivity of the BN/epoxy resin composite is 0.95 W/(m·K). The thermal conductivity greatly increased and BN was organized into chains when the electric field approached 60 V/mm. The tensile strength and breakdown field strength, on the other hand, declined. Full article

Muscle atrophy, a physiological decline in muscle mass and strength due in ageing, occurs through an imbalance between protein breakdown and synthesis. The purpose of this study was to verify whether amino acid complex supplementation (ACS) can prevent and treat muscle loss in a dexamethasone (Dexa, 800 μg/kg)-induced rat model of sarcopenia. Sprague Dawley rats (6 weeks old) were assigned to seven groups: (i) normal control, (ii) positive control (high-dose ACS, 500 mg), (iii) Dexa only, (iv) Dexa + high-dose ACS (500 mg), (v) Dexa + medium-dose ACS (300 mg), (vi) Dexa + low-dose ACS (100 mg), or (vii) Dexa + liquid amino acid complex formulation (LF, 2 mL), administered orally for 4 weeks. Exercise capacity tests were performed five times using a treadmill test (TT) and forced swimming test (FST). The body weight increase in each group was less than that of the normal group. The blood biochemical indices, AST levels, and AST/ALT ratio significantly increased in the Dexa-treated medium-dose ACS group. The total muscle protein also significantly increased in all ACS groups. In the Dexa-treated LF group, CK decreased below the normal level. Exercise capacity, assessed by TT and FST, increased the most in the positive control and Dexa-treated high-dose ACS groups. In the TT, the Dexa-only group increased by about 18%, but the Dexa-treated high-dose ACS group increased by about 110%. Additionally, in the FST, Dexa-treated rats receiving a high dose of ACS demonstrated significantly increased exercise time and capacity. Electron microscopic (EM) and hematoxylin and eosin (H&E) observations of muscle tissue revealed muscle fiber atrophy in the gastrocnemius muscles of the Dexa-only group. In the EM findings of the Dexa-treated high-dose ACS group, the M-line and Z-line were clearer than in the Dexa-only group, and the mitochondria were partially preserved. In conclusion, the ACS-treated rats showed a clear recovery from muscle damage based on serum indices, total muscle protein mass, and the microscopic findings on muscle tissue. Notably, a high dose of ACS demonstrated the most effective protection and recovery of muscle tissue in the Dexa-induced sarcopenia rat model. Full article

Health assessments of high-voltage power cables are important for stable operations of power grids; however, most current health assessment model parameters lack whole cable test data, making them unable to effectively characterize the insulation aging state of whole cables. In this paper, a dielectric loss measurement device for high-voltage cables is developed. Using a high-voltage amplifier and high-precision dielectric loss measurement algorithm, the dielectric loss values of whole cables at different aging stages are measured, and the physicochemical and electrical characteristics of XLPE slice samples at each aging stage are analyzed. Through the analysis of high-voltage dielectric loss, crystallinity, carbonyl index, AC breakdown field strength, and elongation at break, aging correlation parameters are determined. The characteristic high voltage frequency domain dielectric response and delamination degree are proposed to characterize the aging state of cable insulation. The correlation between the high voltage frequency domain dielectric characteristics and cable insulation aging state is established. Finally, an assessment method of the insulation aging state of high-voltage cable is developed, providing a reference for the diagnosis and assessment of the insulation state of high-voltage XLPE cable on site. Full article

Background/Objectives: This study aimed to develop a machine learning (ML) algorithm that can predict unplanned reoperations and surgical/medical complications after vestibular schwannoma (VS) surgery. Methods: All pre- and peri-operative variables available in the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database (n = 110), except those directly related to our outcome variables, were used as input variables. A deep neural network model consisting of seven layers was developed using the Keras open-source library, with a 70:30 breakdown for training and testing. The feature importance of input variables was measured to elucidate their relative permutation effect in the ML model. Results: Of the 1783 patients with VS undergoing surgery, unplanned reoperation, surgical complications, and medical complications were seen in 8.5%, 5.2%, and 6.2% of patients, respectively. The deep neural network model had area under the curve of receiver operating characteristics (ROC-AUC) of 0.6315 (reoperation), 0.7939 (medical complications), and 0.719 (surgical complications). Accuracy, specificity, and negative predictive values of the model for all outcome variables ranged from 82.1 to 96.6%, while positive predictive values and sensitivity ranged from 16.7 to 51.5%. Variables such as the length of stay post-operation until discharge, days from operation to discharge, and the total hospital length of stay had the highest permutation importance. Conclusions: We developed an effective ML algorithm predicting unplanned reoperation and surgical/medical complications post-VS surgery. This may offer physicians guidance into potential post-surgical outcomes to allow for personalized medical care plans for VS patients. Full article

Background. Acetyl phosphate (AcP) is a microbial intermediate involved in the central bacterial metabolism. In bacteria, it also functions as a donor of acetyl and phosphoryl groups in the nonenzymatic protein acetylation and signal transduction. In host, AcP was detected as an intermediate of the pyruvate dehydrogenase complex, and its appearance in the blood was considered as an indication of mitochondrial breakdown. In vitro experiments showed that AcP is a powerful agent of nonenzymatic acetylation of proteins. The influence of AcP on isolated mitochondria has not been previously studied. Methods. In this work, we tested the influence of AcP on the opening of the mitochondrial permeability transition pore (mPTP), respiration, and succinate dehydrogenase (SDH) activity under neutral and alkaline conditions stimulating the nonenzymatic acetylation using polarographic, cation-selective, and spectrophotometric methods. Results. It was found that AcP slowed down the opening of the mPTP by calcium ions and decreased the efficiency of oxidative phosphorylation and the activity of SDH. These effects were observed only at neutral pH, whereas alkaline pH by itself caused a decrease in these functions to a much greater extent than AcP. AcP at a concentration of 0.5–1 mM decreased the respiratory control and the swelling rate by 20–30%, while alkalization decreased them twofold, thereby masking the effect of AcP. Presumably, the acetylation of adenine nucleotide translocase involved in both the opening of mPTP and oxidative phosphorylation underlies these changes. The intermediate electron carrier phenazine methosulfate (PMS), removing SDH inhibition at the ubiquinone-binding site, strongly activated SDH under alkaline conditions and, partially, in the presence of AcP. It can be assumed that AcP weakly inhibits the oxidation of succinate, while alkalization slows down the electron transfer from the substrate to the acceptor. Conclusions. The results show that both AcP and alkalization, by promoting nonmetabolic and nonenzymatic acetylation from the outside, retard mitochondrial functions. Full article

Thanks to the performance improvement introduced by micro sized functional fillers, application of epoxy composites for electrical insulation purposes has become popular. This paper investigates the dielectric properties of epoxy micro-composites filled with alumina (Al₂O₃). In particular, measurements of relative permittivity, dissipation factor, and electrical breakdown are performed, and a comprehensive statistical analysis on dielectric properties was conducted. AC breakdown strength (AC-BDS) was analyzed for normal distribution using four methods (Anderson–Darling, Shapiro–Wilk, Ryan–Joiner, and Kolmogorov–Smirnov). In addition, the AC-BDS was analyzed at risk probabilities of 1%, 5%, 10%, and 50% using Weibull distribution functions. Both normal and Weibull distributions were evaluated using the Anderson–Darling (A-D) statistic and p-value. Additionally, the log-normal, gamma, and exponential distributions of AC-BDS were examined by A-D goodness-of-fit test. The hypothesis test results of AC-BDS were fit by normal and Weibull distributions, and the compliance was evaluated by p-value and each method statistics. In addition, the experimental results of AC-BDS were fit by log-normal and gamma distributions, and the goodness-of-fit was evaluated by p-value and A-D testing. On the other hand, exponential distribution was not suitable for p-value and A-D testing. The results showed that the distributions of AC-BDS were the best using log-normal distribution. Meanwhile, statistical analysis results verified the apparent effect of temperature on dielectric properties using a paired t-test. The analysis results of this paper not only contribute to better characterization of epoxy/Al₂O₃ micro-composites but also introduce a comprehensive approach for performing statistical analysis for electrical insulation materials. Full article

This study examines and compares the breakdown and aging properties of five insulating liquids. Additionally, the influence of different voltage polarities on these properties was analyzed to investigate the effect of aging on polarity behavior under lightning impulse voltage in a semi-uniform field. The results were compared to standardized AC breakdown tests. After 2330 h and 4350 h of aging, changes were observed in key aging indicators such as water content (both absolute and relative), total acid number, and color across all liquids. Viscosity increased by up to 10% in natural esters. Notably, the rise in water content due to aging was concerning only for mineral oil, exceeding 20%. The impact of aging on breakdown voltage varied depending on the voltage type and polarity. Aging had the least effect under negative lightning impulse voltage, while the synthetic ester MIDEL 7131 exhibited the most significant reduction in breakdown voltage under positive lightning impulse voltage, dropping by over 24%, from more than 560 kV to 428 kV. In contrast, mineral oil showed only a 3% decrease. For the other liquids, the most pronounced reduction in breakdown voltage due to aging occurred under AC voltage, with natural esters showing a 17% decline, synthetic esters 26%, and mineral oil experiencing a 38% reduction. Full article

The effect of temperature on the localized corrosion resistance and passive film characteristics of laser powder-bed fusion (LPBF) 316L (UNS S31603) was studied in a buffered 3.5 wt% NaCl solution at 25, 50, and 75 °C. DC techniques such as cyclic potentiodynamic polarization showed lower passive current densities, high breakdown potentials, and a higher resistance to initial breakdown compared with wrought 316L samples at all temperatures. However, LPBF 316L was more susceptible to metastable pitting at potentials before film breakdown and higher damage accumulation post film breakdown. AC techniques, such as Mott–Schottky analysis and electrochemical impedance spectroscopy, showed that the formed passive film was more robust on the LPBF 316L samples at all temperatures, accounting for the higher initial resistance to pitting. However, with increasing temperatures, the film formed had an increasing concentration of defect density. Passive compositions at the various test temperatures studied using X-ray photoelectron spectroscopy (XPS) showed that the LPBF samples showed higher amounts of Cr and Fe oxides and hydroxides compared with the wrought samples, which made the passive films on the LPBF samples more compact and protective. Investigation of the pits formed on the LPBF showed the preferential regions of attack were the melt-pool boundaries and cell interiors due to their being depleted of Cr and Mo when compared with the boundaries and matrix. Full article

In this paper, the aging characterization of a kind of insulating paper modified by magnetron sputtering MgO particles based on a microstrip resonant sensor was presented. Firstly, the modified insulating paper with 0, 15 and 30 min MgO particle sputtering times was prepared by a magnetron sputtering device. After that, the properties of the modified insulating paper with different sputtering times were analyzed through microscopic characterization, infrared spectrum, polymerization degree, dielectric constant, AC breakdown strength and thermal aging experiments. The results show that the dielectric constant of the modified insulating paper decreased obviously, the AC breakdown strength increased and the thermal aging resistance was better after 15 min of sputtering. The overall performance of the modified insulating paper after 30 min of sputtering is reduced due to excessive sputtering. In addition, microstrip resonant sensors are introduced to characterize the thermal aging degree of the modified insulating paper, and two microstrip resonant sensors are prepared: a complementary split ring resonator (CSRR) and an interdigital-capacitor-shaped defected ground structure resonator (IDCS-DGS). The resonance frequency deviation of the modified insulating paper samples after aging was measured by microstrip resonance sensors to show the influence of aging temperature on aging degree. The experimental results show that the test results of the microstrip resonance sensors are in good agreement with the traditional characterization methods and can characterize the various aging stages of the modified insulating paper to a certain extent, which proves the feasibility of the characterization method. Full article