Search Results (31)

Insulation failure in aviation generator windings is one of the most common faults. Modern aircraft winding materials often employ polyimide enameled wire, making research on its reliability and health monitoring particularly important. Based on the relationship between temperature and aging rate described by the Arrhenius law, this study designed accelerated thermal aging experiments, testing twisted-pair, coil, and winding samples made of copper-core polyimide enameled wire. The variation in multiple parameters was visualized using B-spline fitting, ultimately identifying parallel equivalent capacitance as the most suitable parameter for monitoring generator winding insulation. It was also indicated that aging of the winding insulation coating has almost no effect on the performance of the electrical system. Finally, experimental data were processed using Bayesian nonlinear regression, where prior data were updated with new data to obtain posterior aging curves. When the IC ($C_p$) value reaches 1.2009 and 1.4089 times its initial value, the sample is considered to have reached 50% and 100% of its lifespan, respectively. This provides a reference approach and quantitative indicators for predicting the lifespan of polyimide enameled wire windings. Full article

Wide-bandgap power devices, particularly silicon carbide (SiC) MOSFETs, have seen widespread adoption in electric vehicle (EV) motor drive systems due to their superior switching characteristics, including high switching speeds and high switching frequencies. However, these advantages exacerbate motor terminal overvoltage, with peaks reaching twice the inverter output voltage, causing insulation breakdown in windings and bearing electro-corrosion, which shorten motor lifespan. Traditional overvoltage prediction methods, such as distributed parameter models or detailed ladder network approaches, require extensive system parameters and involve high computational loads, while simplified models lack generality. To address these issues, this paper proposes a simplified prediction method based on a lumped ladder network model combined with frequency scanning. The approach uses impedance analysis to identify anti-resonance frequencies, enabling direct estimation of overvoltage amplitudes without prior knowledge of cable or motor specifics. Experimental validation on a SiC-based drive system demonstrates prediction errors below 10% and a reduction in computational time compared to conventional methods. Full article

Grafted polypropylene (PPG) has demonstrated significant potential as a recyclable insulation material for high-voltage cables. While its fundamental electrical, mechanical and thermal properties have been widely studied, research on its long-term performance remains insufficient. This study comparatively investigates the thermo-oxidative ageing performance of PPG and traditional cross-linked polyethylene (XLPE) to evaluate the expected lifespan of cable insulation. The evolution of mechanical and electrical properties of PPG and XLPE was monitored during accelerated thermo-oxidative ageing experiments conducted at their respective maximum allowable operating temperatures, and the most sensitive ageing parameter was identified. Furthermore, the influence of thickness on the insulation ageing process was examined through experiments on samples of different thicknesses. Results indicate that the estimated thermo-oxidative ageing lifespan of XLPE at its maximum operating temperatures of 90 °C is 37.75 years, while that of PPG at 110 °C is 45.65 years. This work offers a practical methodology for polymer ageing lifespan analysis and provides valuable insights for assessing the long-term performance of PPG cables in high-voltage applications. Full article

This study explores the feasibility of constructing a microwave kiln for artisanal ceramics using accessible materials and homemade susceptors. Two modified microwave ovens (18 L and 50 L) were equipped with insulation and susceptors to achieve temperatures up to 1280 °C. Susceptors were fabricated from silicon carbide (SiC) and magnetite (Fe₃O₄) powders via microwave-assisted reactive sintering. Magnetite-poor susceptors (SiC/Fe₃O₄ > 2 by weight) demonstrated excellent durability, maintaining stable thermal performance over multiple cycles. In contrast, magnetite-rich susceptors (SiC/Fe₃O₄ ∼ 1) exhibited high initial efficiency and the ability to control redox conditions but degraded significantly after 10–15 cycles due to partial melting. The microwave kiln achieved significant time savings, completing the ramp-up of the firing cycles in 1 h, compared to 8–10 h in conventional kilns. Energy consumption per litre was comparable to large electric kilns but significantly lower than small ones. The fired ceramics, including porcelain and earthenware, showed excellent mechanical and aesthetic qualities, with glazes performing well even at lower temperatures than recommended. The study highlights the advantages of microwave heating, such as faster processing, energy efficiency, and the ability to control redox conditions, which mimic traditional gas-fired kilns. The developed susceptors are cost-effective and easy to manufacture, making this approach accessible to craftspeople and amateurs. While magnetite-rich susceptors enable redox control, their limited lifespan requires further optimisation. This work demonstrates the potential of microwave kilns for artisanal ceramics, offering flexibility, efficiency, and quality comparable to traditional methods, with promising applications for unique or small-scale production. Future research should focus on refining susceptors durability and validating redox control effects on ceramic glazes. Full article

The air-cored linear synchronous motor (ACLSM), characterized by high precision and stability, is widely applied in high-precision manufacturing. However, due to the absence of an iron core, the windings must be fixed with low thermal conductivity epoxy-based potting adhesive, leading to poor heat dissipation and significant temperature rise, which risks the motor’s lifespan and accuracy. To improve heat dissipation in ACLSM, this research proposes a multi-scale filler-based strategy to enhance the thermal conductivity of the adhesive. A series of comprehensive characterizations and thermal tests demonstrates the effectiveness of this approach. The results demonstrate that the BN-AlN sample exhibits superior thermal conductivity of 1.182 W/m·K at 25 wt% filler loading, a 48.7% enhancement over commercially adhesive 381-4DZ, with only a 38% increase in cost. Meanwhile, it possesses superior electrical insulation properties and appropriate hardness, making it highly suitable for the potting of ACLSM windings. The winding encapsulating with the modified adhesive achieves a maximum temperature reduction of 8.82 °C, while improving temperature uniformity by 29.8%, confirming its exceptional thermal management capability. Full article

This article introduces a novel, cost-effective, noninvasive sensing mechanism for measuring water flow rate. It employs two tunneling magnetoresistance (TMR) sensors (analog and bi-polar), a magnet, and a stainless-steel cantilever. The TMR sensors are installed outside the insulating water pipe. A magnet is fixed at the free end of the cantilever and integrated into the pipe system. The cantilever’s deflection corresponds to the flow rate, with an analog TMR sensor measuring the bending angle. This bending angle, in either direction of the cantilever’s deflection, is captured through the analog voltage from the TMR sensor. The output from the analog TMR sensor is an analog voltage that directly reflects the strength of the magnetic field. An ESP32 microcontroller records the voltage from the analog TMR sensor, converts it to flow rates, and utilizes the bi-polar TMR sensor to ascertain the flow direction. A prototype sensor was developed and tested in a laboratory-scale setup to validate the effectiveness of the sensing mechanism. This prototype demonstrated a worst-case accuracy of 1.0% across flow rates of 0 to 1.5 m³/h for both the forward and reverse flow directions. The response and recovery times of the sensor are approximately 470 ms and 592 ms for forward and 487 ms and 625 ms for reverse direction flow. Also, hysteresis errors of 1.84% and 2.06% have been calculated for both flow directions. Notably, the sensing element does not contain any rotating components or require electrical connections to the cantilever for measurement. These attributes potentially lead to lower maintenance requirements and a longer lifespan for the sensor. Full article

As the global push for renewable energy intensifies, the materials used in the generation, transmission, and storage of renewable energy systems have come under scrutiny due to their environmental impact. In particular, crosslinked polymers are extensively utilized in these systems because of their excellent thermal, mechanical, and electrical properties. However, their non-recyclable nature and significant waste generation at the end of their service life present severe sustainability challenges. This review employs a citation network-based methodology to analyze the role of crosslinked polymers in renewable energy systems, with a focus mainly on two critical applications: (1) production, specifically in the manufacturing of wind turbine blades; and (2) transmission, where they are integral to high-voltage cable insulation. Our complex network analysis reveals the major themes within the field of sustainability, providing a structured approach to understanding the lifecycle challenges of crosslinked polymers. The first part explores the primary polymers used, their typical lifespans, and the environmental burden of generated waste. We then describe both traditional recycling strategies and innovative approaches, such as supercritical water processing and thermoplasticizing technologies, which offer potential solutions to mitigate these impacts. Finally, we highlight emerging reprocessable materials, including vitrimers, ionomers, and specialty thermoplastic alternatives, which provide recyclability while maintaining performance. This comprehensive assessment emphasizes the urgent need for innovation in polymer science to achieve a circular economy for renewable energy systems. Full article

Turbine generators are essential for power generation, but the presence of shaft voltages and currents poses significant challenges to their reliability, efficiency, and operational lifespan. These phenomena, arising from electromagnetic induction, poor shaft grounding, rotor excitation systems, and varying operational conditions, can lead to severe damage to bearings and rotors, resulting in costly downtime and maintenance. This study reviews the mechanisms behind shaft voltage and current generation, their impact on turbine generators, and the effectiveness of various mitigation strategies, including shaft earthing brushes, bearing insulation, and advanced health monitoring systems. Furthermore, it explores emerging techniques for measuring and diagnosing shaft voltage and current, as well as advancements in predictive maintenance and condition monitoring. This study further explores the integration of artificial intelligence and machine learning in predictive maintenance, leveraging real-time condition monitoring and fault diagnostics. By analyzing existing and emerging mitigation strategies, this study provides a comprehensive evaluation of solutions aimed at minimizing these electrical effects. The findings underscore the importance of proactive management strategies to enhance generator reliability, optimize maintenance practices, and improve overall power system stability. This research serves as a foundation for future advancements in shaft voltage mitigation, contributing to the long-term sustainability of power generation infrastructure. Full article

This paper presents the issues related to aging studies of electrical insulation in winding wires, which are widely used in electrical machines. Insulating materials in electrical machines are subjected to various stress factors, particularly electrical stress. The proper design of such insulation systems requires an understanding of the behavior of individual system components under specific operating conditions. This knowledge enables the optimization of insulation design, which can contribute to extending the operational lifespan of electrical machines. In this study, the results of experimental investigations on twisted-pair winding wires with different geometric dimensions, subjected to electrical stress (a square voltage waveform in the kilohertz frequency range) under different pressure conditions, are presented. The experimental research is supplemented by simulation-based calculations of the electric field intensity in the examined twisted-pair winding wire samples. Full article

Single-family residential buildings represent the highest share of building sector in Romania. Their operation emits the most CO₂ into Earth’s atmosphere, as most of them are not energy efficient. A life cycle assessment is performed for a case study building, built in 2019 in Romania, establishing its carbon footprint. For this building CO₂ emissions are 177.55 tCO₂ for the construction stage, 76.19 tCO₂ for the operation stage, 3.55 tCO₂ for the demolition stage, and a total of 129.76 tCO₂ after reducing with the carbon sequestration from vegetation 127.53 tCO₂. The main purpose of this study is to analyse the carbon footprint for a typical single-family Romanian household, with an emphasis on the operational stage. The study compares the results and extrapolates them to all single-family residential buildings in Romania regarding CO₂ emissions, with an emphasis on the operational stage. The results illustrate a considerable reduction in CO₂ emissions from old, high energy consumption buildings to new, low energy consumption buildings. The highest operational stage emissions for old buildings in Romania are 962.94 tCO₂ for firewood heating and 573.69 tCO₂ for gas boiler heating, as those buildings are not insulated and don’t use a heat pump. Additionally, considering the use of photovoltaic panels for the entire lifespan, the CO₂ emissions for the operational stage decrease for the case study building from 76.18 tCO₂ to 19.90 tCO₂. Moreover, using a heat pump detriments firewood or gas boilers, decreasing CO₂ emissions for the operational stage by up to 34% and 26%, respectively. Due to the higher cost of electrical energy compared to natural gas in Romania, gas boilers are more cost-effective than heat pumps. Because of this, and the higher implementation costs, the tendency is towards natural gas. This will in turn result in an increase of CO₂ emission for the entire life cycle of the building by approximate 32% for new buildings and 86% for old, high-energy-consumption buildings. Full article

In most industrialized countries, power transformers built several decades ago are approaching the end of their operational lifespan. The ongoing energy transition, focused on developing 100% renewable energy sources and accelerating global transportation electrification, further exacerbates these assets. Combined with rising electricity demand, there is an increasing risk of critical transformers’ degradation acceleration. In this context, understanding the aging mechanisms of the insulation system inside these essential assets, which form the core of every energy network, becomes paramount for today’s managers and engineers responsible for their operations. The acids generated through oil oxidation can be classified into two categories: low molecular weight acids (LMAs), which are inherently more hydrophilic and consequently have a greater impact on the degradation rate of solid insulation through hydrolysis, and high molecular weight acids (HMAs), which do not significantly contribute to the degradation of paper insulation. This study specifically addresses the impact of acids generated through oil oxidation—focusing on LMAs. New oil samples were infused with different ratios of LMAs before impregnation. The impregnated paper samples underwent thermal aging at 115 °C. Different physicochemical and dielectric properties were investigated. The investigations revealed that oils blended with formic acid exhibited more adverse effects on the insulation system compared to other LMAs. This information is essential for industry professionals seeking to mitigate the risks associated with transformer degradation and extend the lifespan of these critical assets during the energy transition. Full article

During their lifespan, high-voltage (HV) electrical systems are subjected to operating conditions in which electrical, mechanical, thermal and environmental-related stresses occur. These conditions over time lead to unforeseen failures caused by various types of defects. For this reason, there are several technologies for measuring and monitoring the electrical systems, with the aim of minimizing the number of faults. The early detection of defects, preferably in their incipient state, will enable the necessary corrective actions to be taken in order to avoid unforeseen failures. These failures generally lead to human risks and material damage, lack of power supply and significant economic losses. An efficient maintenance technique for the early detection of defects consists of the supervision of the dielectrics status in the installations by means of on-line partial discharge (PD) measurement. Nowadays, there are numerous systems in the market for the measurement of PD in HV installations. The most efficient with a reasonable cost will be those that offer greater security guarantees and the best positioned in the market. Currently, technology developers and users of PD measuring systems face difficulties related to the lack of reference procedures for their complete characterization and to the technical and economic drawback of performing the characterization tests on site or in laboratory installations. To deal with the previous difficulties, in this paper a novel method for the complete and standardized characterization of PD measuring systems is presented. The applicability of this method is mainly adapted for the characterization of systems operating in on-line applications using high-frequency current transformer (HFCT) sensors. For the appropriate application of the method, an associated and necessary scale modular test platform is used. In the test platform, the real on-site measuring conditions of an HV insulated distribution line are simulated in a controlled way. Practical characterizations, showing the convenience and advantages of applying the method using the modular test platform, are also presented. Full article

The lifespan of an electrical transformer, primarily determined by the condition of its solid insulation, is well known under various operating conditions when mineral oil is the coolant in these machines. However, there is a trend toward replacing this oil with biodegradable fluids, especially esters; therefore, an understanding of the ageing of solid insulation with these fluids is essential. Currently available data do not allow for the selection of the best ester among those available on the market, as each study applies different conditions, making it impossible to compare results. Thus, this paper analyses the degradation of Kraft and Thermally Upgraded Kraft papers with the following five most promising commercial esters: sunflower, rapeseed, soybean, palm, and synthetic. The materials underwent accelerated thermal ageing at 130, 150, and 170 °C, and the integrity of the papers was evaluated through their polymerisation degree and the obtaining of the degradation kinetic models. The wide range of materials studied in this work, which were subjected to the same treatments, allows for a comparison of the esters, revealing significant differences in the impact of the alternative fluids. Sunflower, rapeseed, and soybean esters provided the best paper protection, i.e., the degree of polymerisation of Kraft paper in the tests at 150 °C decreased by 71% with these fluids, compared to the 83% reduction with mineral oil, 79% reduction with palm ester, and 75% reduction with synthetic ester. Furthermore, different kinetic models were obtained to predict the degradation; it was concluded that the Emsley model provides the best fit. Additionally, it was found that the behaviour of a dielectric fluid with one type of paper cannot be extrapolated, which is only noticeable in broad-scope studies. Full article

Mineral oil has been used for many years in various electrical equipment, including transformers, as a cooling and insulation medium. However, its low biodegradability and poor performance in terms of fire protection have prompted the search for fluids to replace it, with vegetable oils being prominently considered. In this study, the dielectric, chemical, and physical properties of four vegetable oils obtained from different seeds (sunflower, rapeseed, soybean, and palm) and a biodegradable synthetic fluid are analysed throughout their lifespan in transformers. Their performances are compared with a traditional mineral oil to assess which one is more suitable for use in transformers employing this type of paper. To achieve this, the fluids were subjected to thermal ageing in combination with copper and a thermally upgraded kraft (TUK) paper, with its degradation controlled by measuring the degree of polymerisation. The results demonstrate that the origin of the vegetable oils affects their properties and degradation rates. It was found that most of the alternative fluids are suitable for use in transformers with the TUK paper and that they can increase their lifespan. Full article

Superhydrophobic coatings can be a suitable solution for protecting vulnerable electrical infrastructures in regions with severe meteorological conditions. Regenerative superhydrophobicity, the ability to regain superhydrophobicity after being compromised or degraded, could address the issue of the low durability of these coatings. In this study, we fabricated a superhydrophobic coating comprising hydrophobic aerogel microparticles and polydimethylsiloxane (PDMS)-modified silica nanoparticles within a PDMS matrix containing trifluoropropyl POSS (F-POSS) and XIAMETER PMX-series silicone oil as superhydrophobicity-regenerating agents. The fabricated coating exhibited a static contact angle of 169.5° and a contact angle hysteresis of 6°. This coating was capable of regaining its superhydrophobicity after various pH immersion and plasma deterioration tests. The developed coating demonstrated ice adhesion as low as 71.2 kPa, which remained relatively unchanged even after several icing/de-icing cycles. Furthermore, the coating exhibited a higher flashover voltage than the reference samples and maintained a minimal drop in flashover voltage after consecutive testing cycles. Given this performance, this developed coating can be an ideal choice for enhancing the lifespan of electrical insulators. Full article