High Voltage最新文献

Insulation systems in high-voltage electric machines play a pivotal role in the reliable operation and longevity of the equipment. Mica-based insulation materials have proven to possess and maintain excellent dielectric properties in the long run and prevent premature insulation degradation. Numerous qualifications tests, such as voltage endurance, are outlined in IEC and IEEE standards. The authors, however, take a different parametric approach, opting for reliability assessment of insulation systems using derived three-parameter Weibull models. Therefore, instead of simple pass–fail criteria, empirical data is employed to determine failure rate probabilities quantitatively and objectively. Experimental data, including breakdown, dissipation factor, and partial discharge measurements, are used to construct the Weibull distribution model to predict fault and failure rates and calculate hazard functions. The rigorous examinations interpreted through the analytical model help assess insulation system resilience and particularly the impact of electrical field stress and mica content. Variation of electrical stress from 66.75 to 71.20 V/mil demonstrated how the mean time to failure of the system changed from 146.4 to 85.1 at 3 U_n, hence identifying opportunities for design improvement and uncovering performance boundaries. Ultimately, the developed framework enhances comprehension of insulation system failure probabilities, guiding design decisions and ensuring a secure and reliable operation of electrical machines across applications.

Line-commuted converter (LCC)–voltage source converter (VSC) hybrid high voltage direct current (HVDC) transmission system is an innovative technology, the existing LCC and VSC protection require setting, and it is difficult to be directly applied in the LCC–VSC hybrid HVDC, which is a serious problem in practical engineering. A novel linear regression density peak clustering (LRDPC) approach is introduced for transmission line protection. LRDPC employs Least Squares linear regression to compute the fault current slope, followed by density peak clustering for fault type identification. The proposed protection structure is straightforward and setting-less, eliminating the need for fault pole selection elements and classification thresholds. Validation on the Kun-Liu-Long LCC–VSC HVDC RTDS system demonstrates the method's effectiveness in identifying diverse faults under varying conditions, including fault types, locations, resistances, and signal-to-noise ratios. Notably, it remains robust against fault impedance (600 Ω) and noise interference (20 dB).

When some new-type sensors are subjected electromagnetic interference (EMI), the traditional standard can no longer serve as the guidance for their EMI protection. Therefore, it is necessary to evaluate the complexity of the new sensing equipment's suffering from electromagnetic interference. A hybrid method of feature extraction and complexity evaluation of Electromagnetic Interference signals based on generalised correntropy criterion (GCC) is proposed. First, a variational mode decomposition algorithm for adaptive extraction of decomposed signals is constructed using GCC, and Generalised S-transform is used for processing and reorganisation. Then, according to the time-frequency space model, a new quantitative evaluation criterion interference factor is proposed, which overcomes the shortcomings of the traditional qualitative classification and the inability to solve the cross classification of indicators. Then, the Gated Recurrent Unit is introduced, and the GCC-GRU evaluation model with GCC as the loss function is derived. The authors conduct EMI tests and measured signal evaluation with Medium Voltage and High Voltage switches, and the results show that the method proposed is correct and effective.

C₆F₁₂O is proposed to be one potential eco-friendly insulation gas to replace SF₆. However, the assessment of its decomposition properties and the compatibility with metal electrodes in discharge faults is still challenging, which greatly hinders the development of its insulation and arc-extinction applications. Herein, a theoretical method is proposed to reasonably address the discharge effects on C₆F₁₂O decomposition over typical Cu and Al electrodes at atomic scale. The results show that both the external electric field and the excess electrons could affect the activation of C₆F₁₂O by changing the electron acceptance of C₆F₁₂O and the orbital hybridisation during the surface bonding. On metal surfaces, the C-F single bond in adsorbed C₆F₁₂O is the weakest position to decompose, and its cleavage could be promoted by the discharge effects. After the C-F breaking, the C-C cleavage remains unfavourable on Cu (111), but it is significantly promoted on Al (111), indicating a higher corrosion risk on the Al surface via continuous C₆F₁₂O decompositions. The proposed method as a valid supplement to the experiment reveals the discharge effects and the decomposition tendency of C₆F₁₂O on metal electrodes in discharge faults, which broadens the means for insulation gas evaluation.

The influences of thermal cycling ageing on structures and insulation performances of polypropylene (PP)/elastomer/boron nitride (BN) nanocomposites are investigated. The Melt blending method was used to prepare the nanocomposites, in which propylene-based elastomer (PBE) or ethylene-octene copolymer elastomer (EOC) was contained for comparison. Then, the samples were treated using a thermal cycling process with a temperature range from −30 to 150°C, and the number of thermal cycles was set from 0 to 15. Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry and X-ray diffraction measurements were taken to facilitate the comprehension of structural changes. Additionally, measurements were taken to assess the trap distribution and direct current (DC) breakdown strength of the samples. The obtained results revealed that following thermal cycling ageing, the morphology and crystallinity of PP/PBE/BN remained almost unchanged. In contrast, PP/EOC/BN exhibited substantial microstructural damage accompanied by a significant reduction in crystallinity. As the number of thermal cycles increased, the trap level and DC breakdown strength of PP/PBE/BN were maintained at high levels, while those of PP/EOC/BN initially remained stable but then experienced a sharp decline. It is suggested that the addition of BN nanoparticles enhances the thermal cycling ageing resistance of the PP/PBE blend, whereas it weakens this resistance of the PP/EOC blend.

The cross-linked polyethylene insulated cables with corrugated aluminium-sheathed are widely used in urban power systems. Recently, a new type of power cable fault has emerged, primarily due to defects in the buffer layer. However, there is a notable lack of effective evaluation methods for these defects in high-voltage (HV) cables. Initially, a theoretical analysis of the gas generation mechanism in the cable buffer layer was conducted, identifying distinct gas products at different stages. Subsequently, the diffusion kinetics of gas within the cable was studied, highlighting the importance of gas in determining the state of the buffer layer. The authors then collected and analysed 60 sets of buffer layer gases from two operational 110 kV HV cables using gas chromatography technology. Combining these results with the findings from on-site inspections, the characteristic gas components and concentration distribution under various defect conditions were summarised. The results found higher concentrations of CH₄ in normal cables and defective cables, while there are higher concentrations of H₂, CO and CO₂ in defective cables, and the oxygen content decreases. The discoveries made in this research may offer a new approach for assessing the state of the cable buffer layer.

The potential of using eco-friendly thermoplastic polypropylene (PP)-based insulation for high voltage direct current (HVDC) cable has been widely investigated but much less work on the PP-based semiconducting screen (SC). Considering a long service life (>30 years) under high temperature and high electrical stress is required for typical HVDC cables, and investigations on the effect of antioxidant (AO) concentration and thermal oxidative stability, mechanical, and electrical properties of PP-based SCs have been conducted. It has been demonstrated that an appropriate combination and amounts of AOs are critical for achieving high thermal stability and maintaining the mechanical properties of SC after ageing in a harsh environment (150°C, with Cu, in air, 7 days). Although higher amounts of space charges have been observed in SC/PP/SC samples with higher AO concentrations, the impact on space charge behaviours is less after ageing, suggesting that ageing (or operating at high temperature) leads to microstructure evolution in SC and can potentially mitigate space accumulation in PP-based insulating materials.

Long-term exposure to moisture leads to a gradual deterioration of performance and reduced service life of glass fibre-reinforced epoxy resin (GFRP) material in composite insulators. Therefore, it is necessary to analyse the moisture absorption characteristics of GFRP material and the evolution of damage to their internal interface properties. Moisture absorption tests on GFRP rod material used in composite insulators to obtain their three-dimensional diffusion coefficients are conducted. Atomic force microscopy was then employed to obtain the composite material system's fibre/matrix interfacial phase parameters. Furthermore, a finite element model incorporating representative volume elements with interfacial phases and a mesoscale transient moisture absorption finite element model for the composite material was established. Finally, the moisture absorption characteristics of GFRP material and the evolution of damage to the interfacial phase under thermal-humidity cycling conditions were investigated. The results showed that the diffusion coefficient along the fibre direction in GFRP material was higher than that in the perpendicular direction. The moisture diffusion finite element model, incorporating an anisotropic interfacial phase, fitted the anisotropic diffusion coefficients of GFRP material more accurately. As moisture invaded the GFRP material, the mismatch stresses continuously increased during the moisture absorption. Moreover, the non-uniform arrangement of fibres resulted in uneven distribution of moisture-induced stresses inside the material, leading to higher mismatch stresses in areas with dense fibre arrangements in the matrix. Prolonged high and low humidity cycles led to the development of micro-cracks, micro-porosity, and interface debonding along the fibre direction at the GFRP material interfaces, thereby affecting the anisotropic moisture absorption characteristics of the material. The findings of this study provide valuable insights into the mechanisms underlying the deterioration of GFRP material in composite insulator rods due to moisture degradation.

Understanding the impulse discharge behaviour of natural ester (NE) is crucial for its safe application in high-voltage transformers. The ionisation potential (IP) of triglycerides plays a significant role in the process of molecular ionisation during impulse discharge for NE. The correlation coefficients between molecular size, frontier orbital, electrostatic potential, polarity, and IP were analysed. And the quantitative microstructure-IP model for triglycerides were built, which revealed that IP is strongly related to the highest occupied molecular orbital (HOMO) energy E_HM, as well as the average value of positive electrostatic potential V_p(+), the average value of negative electrostatic potential V_p(−), and the surface area of negative electrostatic potential S(−). The HOMO and negative electrostatic potentials of saturated triglycerides are predominantly linked to the carbonyl O atoms. Conversely, in unsaturated triglycerides, the influence of C=C double bonds on HOMO and negative electrostatic potentials is more pronounced. Therefore, the IP of unsaturated NE with C=C bonds is lower than that of saturated NE, rendering it more susceptible to ionisation under a strong electric field which is unfavourable for impulse breakdown voltage. The structure-property correlation analysis is valuable for understanding ionisation mechanism during the impulse discharge breakdown of NE at the microscopic level.