直流真空断路器换流频率对开断特性影响研究

直流断路器作为提高直流输电可靠性、灵活性的重要环节, 是一项极具研究意义的关键技术。为给机械式直流断路器的振荡回路参数设计提供指导, 有必要研究换流频率不同时的介质恢复过程以及开断特性。本文对真空断路器弧后介质恢复过程分阶段进行分析, 提出了鞘层预备阶段的概念, 给出了鞘层预备阶段持续时间的计算方法, 进一步发展了鞘层发展理论, 在此基础上通过理论分析和仿真来研究真空断路器换流频率对开断能力的影响, 得到换流频率对开断极限电流的影响规律。     

Involvement of Clostridium gasigenes and C. algidicarnis in 'blown pack' spoilage of Brazilian vacuum-packed beef

The objectives of this study were to isolate psychrotrophic clostridia from Brazilian vacuum-packed beef cuts (spoiled or not) and to identify the isolates by using 16S rRNA gene sequencing. Anaerobic psychrotrophic microorganisms were also enumerated and samples were collected to verify the incidence of psychrotrophic clostridia in the abattoir environment. Vacuum-packed beef cuts (n = 8 grossly distended and n = 5 non-spoiled) and environmental samples were obtained from a beef packing plant located in the state of São Paulo, Brazil. Each sample was divided in three subsamples (exudate, beef surface and beef core) that were analyzed for vegetative forms, total spore-forming, and sulfide reducing spore-forming, both activated by alcohol and heat. Biochemical profiles of the isolates were obtained using API20A, with further identification using 16S rRNA gene sequencing. The growth temperature and the pH range were also assessed. Populations of psychrotrophic anaerobic vegetative microorganisms of up to 10¹⁰ CFU/(g, mL or 100 cm²) were found in ‘blown pack’ samples, while in non-spoiled samples populations of 10⁵ CFU/(g, CFU/mL or CFU/100cm²) was found. Overall, a higher population of total spores and sulfide reducing spores activated by heat in spoiled samples was found. Clostridium gasigenes (n = 10) and C. algidicarnis (n = 2) were identified using 16S rRNA gene sequencing. Among the ten C. gasigenes isolates, six were from spoiled samples (C1, C2 and C9), two were isolated from non-spoiled samples (C4 and C5) and two were isolated from the hide and the abattoir corridor/beef cut conveyor belt. C. algidicarnis was recovered from spoiled beef packs (C2). Although some samples (C3, C7, C10 and C14) presented signs of ‘blown pack’ spoilage, Clostridium was not recovered. C. algidicarnis (n = 1) and C. gasigenes (n = 9) isolates have shown a psychrotrophic behavior, grew in the range 6.2-8.2. This is the first report on the isolation of psychrotrophic Clostridium (C. gasigenes and C. algidicarnis) in Brazil. This study shows that psychrotrophic Clostridium may pose a risk for the stability of vacuum-packed beef produced in tropical countries during shelf-life and highlights the need of adopting control measures to reduce their incidence in abattoir and the occurrence of ‘blown pack’ spoilage.     

Rehydration of air-dried Shiitake mushroom (Lentinus edodes) caps: Comparison of conventional and vacuum water immersion processes

Air-dried Shiitake mushroom (Lentinus edodes) caps were rehydrated using conventional and vacuum techniques, at different temperatures (30, 40, 50 and 80 °C) and times (1, 2, 3, 6, 9, 12, 15, 18, 21, 120, 150 and 210 min). Three empirical models were used to model the rehydration process: 1st order kinetics, Peleg’s model and the Weibull distribution function. To determine the effects of temperature and pressure on the mushroom caps, the texture of the rehydrated material was determined, evaluating peak shear force and microstructure using cold-stage scanning electron microscopy (cryo-SEM). The rehydration of the mushrooms was found to be temperature and pressure-dependant. The speed of vacuum rehydration was faster compared to conventional rehydration. When rehydrated at 80 °C, a loss in rehydration capacity was observed in both cases, which can be explained by the structural damage and cell shrinkage which occurred during air-drying. Also, the vacuum rehydrated samples had the lowest toughness values. It was concluded that vacuum rehydration of dried Shiitake mushroom caps could be a feasible alternative to the conventional rehydration process, resulting in a lower immersion time and in a desirable texture.     

微波技术在分析化学中的应用进展

综述了近10年来微波技术在分析化学领域中的应用,详细介绍了微波消解和微波萃取在分析化学中的应用进展。     

126kV真空断路器的运动建模与优化设计

根据对真空断路器运动原理的分析,建立了126kV真空断路器的动力学模型.提出了一种新的方法来设计真空断路器产品的运动特性,该方法利用多体动力学仿真软件ADAMS 建立真空断路器产品的虚拟样机模型,对真空断路器的分、合闸过程进行仿真分析,通过对样机模型结构和力学等参数的修改,最终实现产品的优化设计.仿真结果也验证了该方法的有效性.     

碳纤维复合芯铝绞线投运后的电晕异常分析

基于河慈4P67、河溪4P68碳纤维复合芯铝绞线(ACCC)在雨天和晴天的不同电晕放电情况,进行了实验室模拟试验,试验结果表明:在干燥情况下,相同截面的ACCC导线比普通钢芯铝绞线(ACSR)的起晕电压高;湿润状态下,相同截面的新ACCC导线比ACSR导线的起晕电压低。     

冷凝器、抽气器铜管腐蚀穿孔的原因分析与解决办法

针对冷凝器、抽气器铜管腐蚀穿孔的现状,分析产生原因及解决方法,相应提高了汽轮机出力。     

高压真空断路器缺相故障分析研究

针对一起电动机过电流保护动作故障,采用理论分析计算和实际检查分析验证相结合的方法进行分析研究,得出了结论。     

光束线超高真空阀多参数状态监测系统设计

光束线良好的运行状态是用户正常实验和存储环安全运行的重要保障。为提高光束线的关键设备超高真空阀故障的诊断能力与运维水平,在合肥光源现有光束线控制系统的基础上,开展了超高真空阀门的状态监测研究。本文给出了超高真空阀的多参数状态监测实现方法,获取了超高真空阀门开关动作的数据波形,同时在实验物理和工业控制系统(EPICS)平台下建立了阀门的状态数据库,实现了数据的远程共享。     

脉冲技术在离子镀膜中的应用机理和展望

脉冲电源技术因在等离子体镀膜中表现出增强离化、强附着、高效沉积和涂层光滑致密等特性而日益应用广泛。本文简述了脉冲电源技术在引弧、弧源和基体偏压等镀膜应用,从等离子体产生、传输过程及粒子沉积等全局出发,阐述了脉冲参数与弧斑运动、靶材利用率、离化状态(能量、比例和密度)以及涂层性能等因素间的作用机制,对比分析了脉冲与直流技术在电弧等离子镀膜中的优势和差异点。同时,提出了对现有脉冲技术仍需攻破批量稳定、弧源和偏压源参数匹配以及高能电磁干扰等技术应用难点,为拓展脉冲电源技术更广更深的应用提供较有益的理论依据和工艺参考方向。