超高压变压器油中酸类物质的生成规律和变压器热老化状况分析

为了防止变压器突发性恶性事故发生,探寻更为准确地评估超高压变压器油纸绝缘老化状态和预测变压器剩余寿命的方法意义重大。为此,在130℃下进行了变压器油纸绝缘加速热老化实验,同时跟踪测定变压器油中的酸值、糠醛含量和介质损耗因数,分析模拟老化条件下生成酸类物质的规律,并与变压器老化特征量糠醛和油介质损耗因数的变化规律进行了对比分析。实验结果表明:在变压器油纸绝缘热老化过程中,老化生成酸性物质的反应分为反应诱导阶段和反应发展阶段。在老化反应进入诱导阶段后期,油中糠醛的含量下降,此后,油中的糠醛含量便不能正确反映变压器纸绝缘的老化状况。在老化反应的发展阶段,其反应速率常数是诱导阶段的约5~11倍。老化过程中变压器油中酸值的变化和介质损耗因数的变化具有良好的相关性,生成酸类物质反应速率的快速增加,与变压器油的绝缘性快速下降相一致。结果初步表明跟踪测定变压器老化过程油中酸值的变化,可更为准确地评估变压器油纸绝缘的老化。     

An efficient small‐delay faults simulator based on critical path tracing

Testing for small‐delay defects (SDDs) has become an important component of integrated circuit testing. In this paper, an efficient small‐delay fault simulator, a hybrid method combining forward serial simulation and backward critical path tracing simulation for SDDs is proposed, which aims to determine the coverage of small‐delay defects for a given test set fast and accurately. In our proposed method, a unit delay model is employed, and reconvergent sensitization as well as hazard‐based detection is considered. Signal waveforms are expressed by bitmap data forms. In addition to providing an accurate result for fault simulation, the proposed simulator can well assist test generation. Experimental results demonstrate that the proposed simulator can further accelerate the simulation by one or two orders of magnitude compared with previous works. Copyright © 2014 John Wiley & Sons, Ltd.     

Mechanistic insights into the structure‐dependent selectivity of catalytic furfural conversion on platinum catalysts

The effects of surface structures on the selectivity of catalytic furfural conversion over platinum (Pt) catalysts in the presence of hydrogen have been studied using first principles density functional theory (DFT) calculations and microkinetic modeling. Three Pt model surface structures, that is, flat Pt(111), stepped Pt(211), and Pt₅₅ cluster are chosen to represent the terrace, step, and corner sites of Pt nanoparticle. DFT results show that the dominant reaction route (hydrogenation or decarbonylation) in furfural conversion depends strongly on the structures (or reactive sites). Using the size‐dependent site distribution rule, our microkinetic modeling results indicate the decarbonylation route prevails over smaller Pt particles less than 1.4 nm while the hydrogenation is the dominant reaction route over larger Pt catalyst particles at T = 473 K and = 93 kPa. This is in good agreement with the reported experimental observations. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3812–3824, 2015     

火电厂SCR脱硝系统运行中存在的问题及解决措施

火电厂是最主要的NOx排放源,选择性催化还原(SCR)脱硝技术是目前的主流工艺,它是目前效率最高,最为成熟的脱硝技术。阐述火电厂脱硝工艺技术特点、催化剂选型,分析了脱硝系统运行中存在的共性问题,并提出相应的处理措施,对提高脱硝系统运行可靠性、安全性和经济性有一定的指导意义。     

500kV变电站断路器W相无电流原因分析与处理

内蒙古电网某500 kV变电站内5022断路器在运行过程中W相出现无电流的情况,通过测量断路器端子箱电流互感器二次电流、保护装置电流,统计并分析断路器电流变化历史数据,检查一次设备等手段,确定故障原因为5022-1隔离开关因长时间运行导致动、静触头间产生了较大的接触电阻.对此,在5022断路器停电检修期间,打磨5022-1隔离开关W相接点处,清除表面氧化物,有效降低了接触电阻.送电后,测试5022断路器三相电流均已恢复平衡,保证了电网安全稳定运行.同时,分别从技术、管理角度提出了防范措施.     

Enhanced Ferroelectric Phase Stability and High Temperature Piezoelectricity in PN Ceramics via Multisite Co‐Doping

The tungsten bronze‐type lead metaniobate (PbNb₂O₆, PN) is a promising material for high‐temperature piezoelectric devices, while its application is limited by the difficulty in fabrication. In this study, the microstructure and electrical properties of Ca‐doped PN and Ca, Mn‐co‐doped PN ceramics sintered at different temperatures were investigated. Doping promoted the formation of the originally metastable ferroelectric orthorhombic phase. This might be partly attributed to the increased lattice distortion of the orthorhombic phase in the doped samples compared to that reported for pure PN. However, in single A‐site Ca‐doped PN the ferroelectric orthorhombic structure showed a low stability and started to transform to paraelectric phase far below 300°C, resulting in unstable high temperature piezoelectric properties. Interestingly, such a phase transition was completely depressed by A‐site Ca and multisite Mn‐co‐doping, which also improved the piezoelectric performance (d₃₃ = 71 pC/N) and thermal stability in both structure and piezoelectricity. The better stability and performance of the co‐doped samples were explained by the improved sintering behavior and poling efficiency as well as its ability to occupy different sites in the TTB lattice.     

Use of Cottonseed Meal for Producing Eicosapentaenoic Acid by Pythium irregulare

Cottonseed meal (CSM), a common agricultural by‐product, was used as a nutrient source for the production of eicosapentaenoic acid (EPA) by Pythium irregulare. CSM can support good cell growth performance, as can yeast extract (YE). In terms of the maximum EPA content and EPA yield, CSM is superior to YE. Low concentrations of CSM are beneficial to lipid synthesis, and high concentrations favor the EPA content. Utilizing response surface methodology (RSM) analysis, the optimum contents of glucose and CSM in the fermentation medium were determined to be 40.2 and 16.1 g/l, respectively. After 6 days of fermentation at 25 °C and optimal conditions, the EPA yield and productivity were 245.3 and 40.9 mg/l day, respectively. Particle size of CSM was found to affect the EPA production, and a finely ground CSM (100 mesh) was determined to be best for EPA production. The variation in the fatty acid content of total fatty acid (TFA) indicates that EPA was synthesized through the n‐6 route in P. irregulare and Δ12 desaturase was the key enzyme for EPA biosynthesis. Sodium carbonate was determined to be notably good at removing free gossypol attached to biomass. After fungal biomass from each flask had been harvested from Na₂CO₃‐supplemented medium, 1 % (w/v) Na₂CO₃ solution was used to wash the mycelia three times; free gossypol (FG) was not detected (detection limit 0.0018 %). This work provides a new approach using cottonseed meal to produce EPA through fungal fermentation.     

Preparation and properties of epoxy‐modified tung oil waterborne insulation varnish

This work aimed to develop a novel epoxy‐modified tung oil waterborne insulation varnish with blocked hexamethylene diisocyanate as a curing agent. The Diels–Alder reaction between tung oil and maleic anhydride, and the ring‐opening esterification reaction of epoxy resin were confirmed. The conversion rate of epoxy was explored as a function of reaction time and temperature. The effects of epoxy resin content on the thermal stability, water absorption and insulation properties (insulation strength, volume resistivity, and surface resistivity) of films were investigated, and the resistances of films to salted water were evaluated. The increase in epoxy resin contents could improve the thermal stability and insulation properties of films, and decreased the water adsorption of films, but when the epoxy resin content reached 30% and above, the water solubility of resin became poor. After being immersed in 3.5 wt % NaCl solution, the electrical insulation strength of films were lower than that in dry state, and decreased as the immersed time prolonged. In particular, the electrical insulation strength loss of films increased significantly for epoxy resin content at 15% and below. Furthermore, the increase of epoxy resin content could improve the hardness and adhesion of films, but the flexibility of films became worse. On the basis of experimental, the epoxy resin content at 25% was appropriate to prepare waterborne epoxy‐modified tung oil resin. The resulting varnish may have potential as an immersing insulation varnish for the spindle of electric motor. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42755.     

Design and Synthesis of CdWO4:Sb3+ Phosphor Based on sp Energy Level Regularities of Sb3+ Ion

Sb³⁺‐activated CdWO₄ phosphors were designed according to sp energy levels regularities of Sb³⁺ ion in some inorganic compounds. The sp energy levels regularities of Sb³⁺ in dozens of compounds were established with the aid of the dielectric theory of the chemical bond for complex crystals: E_A = 6.2187?1.7584h_e, E_B = 7.019?1.957h_e, E_C = 7.259?1.964h_e. Environmental factor h_e of Cd site was calculated to be 1.6583 with the refined crystal structure and refractive index of CdWO₄:Sb³⁺. Sb³⁺‐doped CdWO₄ was synthesized through a precipitation method and its structure was refined with the General Structure Analysis System. The transition energy of A band of Sb³⁺ in CdWO₄ can be predicted to be 3.312 eV (374 nm), according to the relationship equation between E_A and environmental factor h_e. By monitoring the 521 nm emission band, the excitation spectrum gives a weak excitation band peaking at 355 nm, which was assigned to the ¹S₀–³P₁ transition of Sb³⁺ according to our prediction. Thus, Sb³⁺‐doped CdWO₄ phosphor was designed and synthesized successfully based on sp energy levels regularities of Sb³⁺ ion. This work is a great help to understand the spectroscopy of Sb³⁺ ion and will be useful for the design and development of Sb³⁺‐doped phosphors for applications.     

永磁扰动检测有限元分析及优化设计

永磁扰动检测是一种新型无损检测技术,通过永磁扰动传感器在铁磁构件表面扫查并拾取受缺陷影响下静磁场变化情况来判别缺陷尺寸大小。本文深入分析了永磁体与缺陷的扰动机制,并针对传感器设计理论不足、永磁扰动检测信号微弱等问题,提出了采用环绕式体线圈探测永磁体内产生的磁扰动及采用螺旋线圈探测永磁体与缺陷间的外磁扰动,并在此基础上探究感应线圈及永磁体的几何参数对永磁扰动检测效率的影响。通过有限元模型多参数化扫描及正交试验设计方法对永磁扰动传感器进行了优化设计,该方法能够有效地提高永磁扰动内、外感应电压的幅值。