油纸绝缘状态评价模型的改进(英文)

Identification of the aging condition and the failure probability of oil-paper insulation in transformer is important for improving the reliability of electric power transmission system and applying life cycle cost (LCC) management to electrical equipment. Based on data obtained in a series of multi-accelerated-aging experiments, two approaches for calculating failure probability of oil-paper insulation were compared in aspects of degree of polymerization (DP) and condition ranking. In the experiments, mineral oil and cellulose paper are sub- jected to electrical and thermal stresses, and several parameters, including dissolved gases’ volume fraction, furfural content, moisture content, and degree of polymerization, are measured after the aging process. Results show that weight of carbon oxide, which has a close relationship with cellulose paper degradation, is much higher in DP model than in condition ranking model. Moreover, it is concluded that DP model is more practically accurate than condition ranking model, because aging of cellulose paper rather than mineral oil is the key and critical factor of oil-paper insulation aging.     

Gas entrainment in an evaporating spray jet

Gas entrainment induced by a spray jet can be significantly affected by the spray evaporation rate. In this study, we have directly measured the air entrainment induced by a liquid nitrogen spray jet into an unbounded and stagnant room air. It is realized that the air entrainment is proportional to the axial gradient of oxygen mass flow in a pure nitrogen spray jet. Hence, the air entrainment can be determined by a combined measurement of local cross-sectional distributions of oxygen concentration, gas temperature and gas velocity along the jet path. These measurements are directly obtained using an in situ oxygen concentration analyzer, a thermocouple system, and a Laser Doppler Velocimeter. In order to evaluate the effect of evaporation rate, direct measurements and numerical simulations of the air entrainment by a cold gaseous jet of nitrogen (at a temperature slightly above that of liquid nitrogen) into room air are also performed. Measurements of the entrainment rate and flow similarity of the gaseous jets without droplets compared very well against those from the single-phase jet theories and numerical simulation, which validates our experimental approach and analysis method. Our experimental results indicate rough flow similarities exist in evaporating spray jets with round nozzles. Although the air entrainment by the liquid nitrogen spray is found significantly increased, as compared to that by the cold gaseous jet of nitrogen from the same nozzle and at the same jetting velocity, the increased ratio is far less than the equivalent momentum ratio of the liquid nitrogen spray to the gas nitrogen jet. This experimental finding suggests that the evaporation of spray markedly weakens the gas entrainment. In this study, a parametric model is also developed to provide a theoretical basis of the data analysis for the cross-section averaged spray evaporation rate within the spray jet region.     

基于DSP的壁纸印刷花纹涂层厚度在线检测

在壁纸生产过程中,尤其是在花纹印刷过程中,有效地在线测量花纹涂层厚度,对于减少壁纸生产的次品率和提高生产效率至关重要。本课题针对壁纸印刷花纹涂层厚度在线检测问题进行了研究,利用激光传感器测厚原理,基于TI公司生产的TMS320F2812DSP芯片为硬件核心处理器,完成了花纹涂层厚度的非接触在线测量。     

异型波电压下气隙缺陷的局部放电检测方法设计

设计了三种异型波,将其应用于含气隙缺陷的交联聚乙烯绝缘材料局部放电检测试验中,旨在探索一种便捷、无损、准确、可靠的针对气隙缺陷进行局部放电检测的方法.首先,制作了含气隙缺陷的绝缘试样模型,在工频交流电压下对气隙缺陷试样进行局部放电试验;其次,设计并制作了三种异型波,利用所设计的异型波对相同的试样进行局部放电试验;最后,...     

Grain size tailoring and enhanced energy storage properties of two-step sintered Nd3+-doped AgNbO3

AgNbO₃ as a lead-free antiferroelectric material, has received widespread attention in recent years due to its promising application in the aspects of energy storage devices. However, the high remnant polarization and low breakdown strength limits its energy storage properties. In this work, Nd³⁺-doped AgNbO₃ (Ag_1−3xNd_xNbO₃, x=0−0.015) ceramics were prepared and a two-step sintering method was employed. The introduction of Nd³⁺ leads to the enhanced stability of the antiferroelectric phase, refined grain size and increased resistivity. Furthermore, by adjusting the pre-heating temperature in the two-step sintering, the homogeneity of microstructure is improved and the resistance of pre-heated samples increases by one order of magnitude compared with normally sintered samples, leading to the enhanced breakdown strength. Ag_0.97Nd_0.01NbO₃ pre-heated at 1100 °C for 2 h exhibits promising energy storage properties, with a recoverable energy storage density of 3.2 J/cm³ and energy efficiency of 52 % under an applied electric field of 210 kV/cm.     

Microstructural features and thermal stability of alumina-bonded nano-polycrystalline diamond synthesized by detonation sintering

In this work, alumina-bonded nano-polycrystalline diamond (NPD) was synthesized by detonation sintering in the temperature range of 3000–3500 K and pressure range of 15–25 GPa. The microstructures and thermal stability of the NPD detonation sintered at 3255.05 K and 24.51 GPa were studied, and are described herein. Transmission electron microscopy and electron diffraction revealed that the polycrystalline diamond has a unique formation process and no graphitization. Scanning electron microscopy indicated that the size of polycrystalline particles increased in samples 2, 3, and 4. And thermogravimetric analysis indicated that the thermal stability of the diamond particles was enhanced. The 18% mass loss of specimen corresponded to the oxidation and decomposition of the amorphous carbon and carbon-containing compounds synthesized by detonation. Finally, graphitization calculations showed that the graphitization probability of polycrystalline diamond produced at the temperature of 3255.05 K and pressure of 24.51 GPa was 15.04%.     

Structure,spectral analysis and microwave dielectric properties of novel x(NaBi)0.5MoO4-(1-x)Bi2/3MoO4 (x = 0.2 ∼ 0.8) ceramics with low sintering temperatures

Herein, the x(NaBi)_0.5MoO₄-(1-x)Bi_2/3MoO₄ (xNBM-(1-x)BMO, x = 0.2 ∼ 0.8) microwave dielectric ceramics with low sintering temperatures were prepared via the traditional solid-state method to adjust the τ_f value and dielectric constant. The crystal structure was determined using X-Ray diffraction and Raman spectroscopy, the microstructure was investigated using scanning electron micrograph and energy disperse spectroscopy, and the dielectric properties were studied using a network analyser and infrared spectroscopy. For the xNBM-(1-x)BMO composite ceramics, the (NaBi)_0.5MoO₄ tetragonal phase coexisted with the Bi_2/3MoO₄ monoclinic phase. With the rise of x value, the permittivity increased from 23.7–29.8, and the τ_f value shifited from -53.3 ppm/°C to -13.7 ppm/°C. The 0.8NBM-0.2BMO ceramic sintered at 680 °C possessed excellent microwave dielectric properties with a ε_r = 29.8 (6.7 GHz), a Qf = 11,800 GHz, and a τ_f = -13.7 ppm/°C. These results made the xNBM-(1-x)BMO composite ceramics great candidates in low temperature co-fired ceramics technology.     

Yarn-dyed shirt piece defect detection based on an unsupervised reconstruction model of the U-shaped denoising convolutional auto-encoder

Due to the scarcity of defective yarn-dyed fabric samples in the textile industry,the imbalance of defect types and the high cost to manually design defect features gained the poor generalization,and the supervised model solves the problem of yarn-dyed fabric defect detection with difficulty.Therefore,an unsupervised reconstruction model is proposed based on the denoising U-shaped convolutional auto-encoder,and a residual analysis method ispresented to inspect yarn-dyed shirt piece defects.First,normal samples are collected for a specific fabric in the training phase.Second,an unsupervised reconstruction model is trained based on the denoising U-shaped deep convolutional auto-encoder,which is employed to reconstruct new test samples.Finally,calculating the residual map between the original image and correspondingly reconstructed image is used to inspect and locate areas of fabric defects.Experimental results show that the proposed method can inspect and locate many types of yarn-dyed fabric defects without any defective fabric samples.     

分层土壤短距离放线下接地电阻测试方法研究

当土壤不均匀,如土壤为双层甚至三层时,采用传统补偿法测量接地电阻往往会带来较大测量误差。研究提出了短距离放线方式下接地电阻测试方法。分析了工频接地电阻与电流注入点的位置关系,研究了不同电流注入点对接地电阻测量偏差的影响规律,验证了短电流极引线法在工频接地阻抗测试中的可行性。针对不同的土壤结构,研究了电流引线布线长度对电压补偿点位置的影响。提出不同土壤结构下电流引线长度的选取规律,实现了短电流引线下接地阻抗的准确测量。