一种用于线阵列系统极性测试的可靠方法

一组线阵列系统的性能在很大程度上取决于其扬声器的正确安装。例如,一个极性错误的单体扬声器可能会明显地影响整个系统的声压和指向性。然而,这种错误的鉴定非常耗时。因此,这就需要一种快速同时又可靠的方法来找出这样的线阵元素。介绍了一种怎样一步一步来检查一个完整的线阵列系统的方法,同时,还能找出引起极性问题的原因。除了理论背景,还描述了一个实际应用的成功案例。     

Novel three‐phase current‐regulated digital PWM and its behavioral analysis

There have been various studies of PWM algorithms for a three‐phase voltage‐source AC/DC power converter since the analog modulation scheme based on a triangular carrier wave was proposed in the 1960s. The PWM algorithm can be considered the heart of electronic power conversion. With progress in digital technology, there is an increasing need for gate signals to be generated directly by digital ICs, such as MPU, DSP, or FPGA/CPLD. This paper analyzes quantitatively the precision of current control of digital PWM taking account of both the sampling period and the delay time (the latter is inevitably accompanied by a digital procedure). The delay time is shown to have a double effect on the current error. In addition, the paper theoretically derives the conditions for digital PWM to meet the PPCR (Pulse Polarity Consistency Rule, that is, the next gate command moves only to the adjacent ones or commands). So far as the authors know, no paper has presented the mathematical requirements for PPCR taking account of the effect of the delay time of digital PWM. The derived theoretical results are summarized as digital PWM design criteria for a three‐phase PWM converter in order to facilitate practical implementation of the theory, guaranteeing PPCR behavior as well as quantitative accuracy of current regulation. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(2): 62–77, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10330     

WMZ-41A型微机母线保护装置的探索与应用

根据WMZ-41A型微机母线保护装置的工作原理,结合胜利油田电力管理总公司九分场变电站220 kV微机母线保护改造施工中遇到的问题,介绍了WMZ-41A型微机母线保护装置的功能及特点,具体分析了单元极性和失灵判据存在的缺陷和原因,提出了改进技术方案,不但提高了施工调试的技术水平,而且在保护的准确性、系统的稳定性和供电的可靠性上都有了质的飞跃。     

Types as Graphs: Continuations in Type Logical Grammar

Using the programming-language concept of continuations, we propose a new, multimodal analysis of quantification in Type Logical Grammar. Our approach provides a geometric view of in-situ quantification in terms of graphs, and motivates the limited use of empty antecedents in derivations. Just as continuations are the tool of choice for reasoning about evaluation order and side effects in programming languages, our system provides a principled, type-logical way to model evaluation order and side effects in natural language. We illustrate with an improved account of quantificational binding, weak crossover, wh-questions, superiority, and polarity licensing.     

Geometrical Characteristics and Surface Polarity of Inclined Crystallographic Planes of the Wurtzite and Zincblende Structures

Inclined crystallographic planes of the wurtzite structure were investigated in comparison with the zincblende structure in terms of surface geometry characteristics. The ball–stick model indicates that the semipolar surface possesses a surface polarity resembling the anion polarity, which agrees with the common experimental observations of epitaxial growth preference for the cation-polarity surface over the surface. The wurtzite surface was found to share geometrical similarities with the zincblende {100} surface uniquely among the possible semipolar planes. This finding encourages epitaxial growth on the plane of wurtzite semiconductors, e.g., GaN, with the potential of avoiding atomic step formations typically associated with off-axis crystallographic planes.     

极性反转试验中,±800kV换流变压器套管尾部的电场分布研究

±800 kV换流变压器出线套管,是一个结构复杂的绝缘系统。在试验与运行中,套管要承受不同形式电压的作用。特别在直流极性反转的情况下,套管尾部结构复杂,电场十分集中,易发生油中闪络或击穿放电,严重威胁特高压换流变压器的安全运行。应用有限元法,仿真计算了±800 kV换流变压器出线套管尾部的电场分布,计算结果表明:在极性反转试验中,套管尾部电场分布不均匀,且不同时刻、套管尾部电场分布及各关键位置的场强变化呈现线性特性。进一步分析得知:在套管设计中,不仅要考虑正负极性反转试验电压下的稳态电场分布,还应重视极性反转过程中暂态电场与界面空间电荷效应,以便留有足够的裕度,避免在极性反转试验时套管损坏。     

Research on the characteristics of atmospheric air dielectric barrier discharge under different square wave pulse polarities

Energy efficiency limits the application of atmospheric pressure dielectric barrier discharge(DBD),such as air purification,water treatment and material surface modification.This article focuses on the electrical and optical effects of the DBD under three square wave pulses polarities-positive,negative and bipolar.The result shows that under the same voltage with the quartz glass medium,the discharge efficiency of bipolar polarity pulse is the highest due to the influence of deposited charge.With the increase of air gap distance from 0.5 to 1.5 mm,average power consumed by the discharge air gap and discharge efficiency decrease obviously under alumina,and increase,and then decrease under quartz glass and polymethyl methacrylate(PMMA).Through spectrum diagnosis,in the quartz glass medium,the vibration temperature is the highest under negative polarity pulse excitation.Under bipolar pulse,the vibration temperature does not change significantly with the change of air gap distance.For the three dielectric materials of quartz glass,alumina and PMMA,the molecular vibration temperature is the highest under the quartz glass medium with the same voltage.When the gap spacing,pulse polarity or dielectric material are changed,the rotational temperature does not change significantly.     

馈电开关漏电保护不兼容故障的处理

介绍了一起综采工作面馈电开关漏电保护不兼容故障的处理,从馈电开关附加电源极性、直流电压等级、保护器及馈电设置等方面分析了故障的原因,并对馈电开关生产厂家提出几点建议。     

换流变压器极性反转非线性电场分析

换流变压器绝缘材料电导率受电场强度、温度和压力等因素影响,即呈现非线性特性。为了考查非线性对换流变压器极性反转电场分布的影响,针对电导率对电场强度的非线性,对绝缘纸板和油的电导率非线性特性进行了数值拟合,并用于分析1台±500kV换流变压器的非线性极性反转电场。线性和非线性媒质条件下的计算结果表明,考虑1min极性反转的过程时,线性媒质中反转完成时刻的油中最大电场强度值同瞬间完成极性反转的数值结果几乎相同,而非线性条件下反转完成时刻的油中最大电场强度值要比瞬间完成极性反转的数值结果小50%。针对这一现象,进一步对非线性条件下空间电荷加速重新分布的过程进行了分析。     

换流变压器阀侧绕组端部瞬态电场分析

为了研究换流变压器阀侧绕组区域的瞬态电场分布规律,即在长时直流电压和极性反转电压作用下的电场分布规律,建立了2个典型的油纸绝缘模型和1个±500kV换流变压器绕组端部简化模型,并利用有限元软件ANSYS对上述模型进行了长时直流电场和极性反转电场分析,主要分析了模型结构、材料属性和试验时间对上述电场分布的影响,得到了直流电场趋于稳态所需时间的影响因素以及极性反转电场的一些特点。最后重点分析了±500kV换流变压器绕组端部的极性反转电场,同时考虑了绝缘纸板的正交各向异性。结果表明,直流电场趋于稳态所需时间的长短与模型结构及绝缘材料的电阻率有关;合理地设置极性反转时间才能保证对变压器油的有效考核。这些结论可为换流变压器绝缘结构的设计及绝缘试验提供参考依据。