稀释气体对镁熔体在HFC-134a气氛中高温氧化行为的影响

对镁熔体在HFC-134a/空气混合气体中和HFC-134a/CO2混合气体中的氧化行为进行了比较研究.结果发现,镁熔体在这2种混合气体中的氧化行为存在差异,而且这种差异与HFC-134a的浓度有关.当混合气体中HFC-134a浓度较高时,镁熔体在HFC-134a/CO2混合气体中的氧化速度小于HFC-134a/空气混合气体,差别不是很大;然而,当混合气体中HFC-134a浓度较低时,镁熔体在HFC-134a/CO2混合气体中的氧化速度远小于HFC-134a/空气混合气体中的氧化速度.产生差异的原因可能与氧化膜中MgF2和MgO的相对含量有关,也可能与单质的C含量有关.这一结果表明,在HFC-134a浓度保持不变的情况下,把与HFC-134a混合的稀释气体由空气改变为CO2,可提高混合气体的保护效果,尤其是在HFC-134a浓度较低的情况下.     

A new method for discrimination of ground faults causes in distribution lines

Since most problems in distribution lines are ground faults, the technology to distinguish the causes in the distribution lines will be very useful in preventing faults beforehand or, at least finding any problems at an early stage. The waveforms of ground faults which were collected from data concerning problems in the distribution lines and ground fault experiment are analyzed. The technology which could predict classified groups drawn from the scale of I₀ (the waveform of ground fault current) and V₀ (the waveform of ground fault voltage), and both of them in the ground faults is studied. The results demonstrated that I₀ could be classified into three groups, that is, leaking ground faults are sine curve shaped, gap discharge ground faults are triangular, and intermittent discharge ground faults are needle shaped. Also, simulated equivalent impedance of the causes of ground faults by EMTP is calculated. Furthermore, the influence caused by the condition of the distribution lines is investigated. With these results, a technique is proposed which could predict the cause of problems in ground faults.     

The protective surface film formed on molten ZK60 magnesium alloy in 1,1,1,2-tetrafluoroethane/air atmospheres

The composition, microstructure and growth kinetics of the surface film formed on molten ZK60 magnesium alloy in 1,1,1,2-tetrafluoroethane/air mixture were investigated by using SEM, EDS, XRD, XPS and TG. The results show that the film formed in 0.01% 1,1,1,2-tetrafluoroethane/air was non-protective, and its phase composition changed with melt temperature. At 760 °C, the film was mainly composed of MgO and some MgF₂ and ZrO₂, whereas at 660 °C it consisted mainly of MgO and Mg₃N₂. The film formed in air containing 0.1% 1,1,1,2-tetrafluoroethane or higher was comprised of MgF₂ and C with small amounts of MgO, and it was protective.     

SVC对风电机组暂态特性的影响

在电力系统仿真软件PSASP 6.8中建立了基于静止无功补偿器(SVC)补偿型发电机组的模型,仿真计算1个由6台风电机组构成的风电系统中异步风电机组的暂态特性。分析了风电场升压变压器低压侧10 kV母线在第5 s出现三相短路故障且在5.12s故障切除时,SVC对系统暂态电压的影响。结果表明,SVC补偿型机组具有快速调节无功功率的能力,SVC装置对机端电压都有一定的支撑能力,风电场升压变压器低压侧装SVC,可以减轻风电机组并网过程中对系统的冲击,电压从并网到稳定所经历的时间较不加装SVC短,实现了恒速风力发电机组的柔性并网。     

熔炼镁及镁合金用坩埚材料化学稳定性的热力学分析

通过建立热力学可能的反应模犁，分别计算了高温下镁及镁合金与一些金属氧化物和非氧化物反应的自由能变化，并用自由能判据分析了这些反应发牛的可能性。结果表明，非氧化物SiC和ZrB2对镁及镁合金液具有良好的化学稳定性，可以作为熔炼镁及镁合金的坩埚材料使用，并用实验对这种材料在镁及镁合金液中的化学稳定性进行了验证。     

Oxidation behavior of molten magnesium in air/HFC-134a atmospheres

The oxidation behavior of molten magnesium in the atmosphere of air containing HFC-134a has been investigated in the temperature range of 660–760 °C. The oxidation rates and kinetics have been measured by the weight gain method and oxidation products have been characterized by XRD, SEM, EDS, XPS and AES. The results show that the oxidation kinetics is complex which cannot be described by simple equations. The rate of oxidation of molten magnesium in air/HFC-134a covering gas mixtures varies with the concentration of HFC-134a and molten temperature. Increasing the concentration of HFC-134a and decreasing the temperature can slow down the oxidation rate of molten magnesium. The film formed +on the surface of molten magnesium is mainly composed of MgF₂, MgO and C. MgF₂ is predominant product at the top layer and decreased gradually with the depth while MgO and C remain almost constant with relatively low content. The mechanisms of the oxidation of molten magnesium in air containing HFC-134a have also been discussed based on the experimental results.     

农药中间体2—氯—5—氨甲基吡啶的合成研究

农药重要中间体２－氯－５－氨甲基吡啶是由Ｎ－（２－氯代吡啶－５－甲基）－邻苯二甲酰亚胺先在碱水溶液中水解,再在稀酸中水解而制得的高收率产品,讨论了反应条件对合成反应的影响。产品总收率为８２％以上。     

带静止无功补偿的异步风电机组的特性分析

在电力系统仿真软件Matlab／simulink中建立了静止无功补偿型发电机组的模型,仿真计算在一个由5台风电机组构成的风电系统中进行。风电机组是带有静止无功补偿（英文简称SVC）的异步风电机组,SVC装置对电机端电压有一定的支撑能力。风电场升压变压器的低压侧装SVC,可以减轻风电机组并网过程中对系统的冲击,电压从并网到稳定所经历的时间较不加装SVC者短,实现了恒速风力发电机组的柔性并网。