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991.
992.
针对零序电流互感器极性不明确导致选线失败的问题,分析了选线失败的原因,提出一种基于对地电容近似熵的选线方法。提出利用差分方法改进矩阵束,解决分量湮没问题,从而准确提取复频域极点信息。分别求取每条线路对地电容序列,由于消弧线圈补偿作用故障线路电容序列近似熵将超过阈值,则判断该条线路为故障线路。仿真实验结果验证:该方法摆脱了由于零序互感器极性不同而导致选线错误的限制,且适用于两出线系统,适应性强,选线准确率高。 相似文献
993.
为了提高通用面向对象变电站事件(GOOSE)报文的传输实时性和可靠性性能,给出一种基于现场可编程逻辑门阵列(FPGA)的GOOSE报文快速有效解析的方法。利用FPGA的并行执行机制,设计并实现了GOOSE报文解析有限状态机与订阅检验判断流程。通过对实例的行为仿真及波形捕获,验证了设计在较大网络流量下能够实现过滤并快速解析GOOSE与链路自检的功能。相对于传统CPU的顺序执行处理方式,基于FPGA的变电站实时报文解析设计具有更高的实时性及可靠性,为过程层设备的设计与开发提供了新思路。 相似文献
994.
995.
交流电网故障引发线路换相换流器高压直流(Line Commutated Converter High Voltage Direct Current, LCC-HVDC)换相失败,改变了原有交流电网工频变化量方向保护动作特性。针对这一问题,建立了由电压源换流器高压直流(Voltage Source Converter HVDC, VSC-HVDC)系统与LCC-HVDC系统组成的混合多馈入直流(bybrid multi-infeed HVDC,HMIDC)输电系统模型,并与馈入同一交流电网的单条LCC-HV 相似文献
996.
Biological Self‐Arrangement of Fiber Like Aragonite and Its Effect on Mechanical Behavior of Veined rapa whelk Shell 下载免费PDF全文
Hong‐Mei Ji Yun Jiang Wen Yang Guang‐Ping Zhang Xiao‐Wu Li 《Journal of the American Ceramic Society》2015,98(10):3319-3325
The microstructures of Veined rapa whelk shell were characterized, and a series of compression tests were carried out on the shell with the compressive loading direction making different angles (0°, 30°, 60° and 90°) with the shell spiral lines. Weibull analysis of the experiment results shows that the compressive strength is generally the highest for the sample with 0°‐orientation but the lowest for that with 60°‐orientation, which means that the strength shows an obvious anisotropy and the strongest orientation represents the direction parallel to the spiral lines of the shell. Such a phenomenon is closely related to the distinctive microscopic arrangements of different‐order aragonite lamellae. The interfaces of different‐level lamellae in the adjacent macro‐layers yield effects on the mechanical behavior of the shell in a coordinated fashion. 相似文献
997.
Guo‐Zhong Zang Huan‐Huan Liu Jian‐Fei Lei Xiao‐Fei Wang Li‐Ben Li Jing‐Xiao Cao Guo‐Rong Li 《Journal of the American Ceramic Society》2015,98(7):2112-2116
SnO2–Zn2SnO4 composite ceramics with a colossal dielectric permittivity and varistor behavior are prepared by traditional ceramic processing. By increasing bias voltage from 0 to 10 V at a low frequency (~103 Hz) and at room temperature, the relative permittivity decreased rapidly from about 20 000 to several thousand, whereas the radius of the semicircle in the complex impedance decreased and the tail gradually disappeared. However, the peak height and the position of the imaginary part of the complex modulus in the spectra were independent of the applied DC voltage. The slope deduced from the bias voltage‐dependent straight lines of the double‐logarithmic imaginary permittivity spectra were constant with a value of ?0.63 at high frequencies and they decreased to ?1 at low frequencies. The results strongly indicate that a number of weekly trapped charges existed in the ceramic bulk. From the temperature‐dependent dielectric and electric modulus spectra, the trapped charge activation energy was about 0.32 eV, which may be associated with the oxygen vacancies. Based on the results, a modified equivalent circuit related to the colossal dielectric permittivity and varistor properties was proposed, in which a Warburg impedance was added in parallel with the resistance and capacitance. 相似文献
998.
Preparation of M@BiFeO3 Nanocomposites (M = Ag,Au) Bowl Arrays with Enhanced Visible Light Photocatalytic Activity 下载免费PDF全文
Xingang Zhang Bo Wang Xiuzhang Wang Xiangheng Xiao Zhigao Dai Wei Wu Junfeng Zheng Feng Ren Changzhong Jiang 《Journal of the American Ceramic Society》2015,98(7):2255-2263
High surface area BiFeO3 (BFO) bowl arrays photocatalyst loaded with different size noble metal nanoparticles were successfully prepared by combining templates method and thermal evaporation followed by heating. The structural and optical properties of the BiFeO3 bowl arrays and the composite M@BFO bowl arrays (M = Ag, Au) were comparatively characterized. The composite M@BFO bowl arrays showed much higher photocatalytic performance than the pure BFO bowl arrays. The enhanced photocatalytic property of the composite structure could be ascribed to the enhanced near‐field amplitudes of localized surface plasmon of the noble metal nanoparticles which boost the separation of electron–hole pairs and the transfer mechanism of electrons. 相似文献
999.
Investigations on Radiation Tolerance of Mn+1AXn Phases: Study of Ti3SiC2, Ti3AlC2, Cr2AlC,Cr2GeC,Ti2AlC,and Ti2AlN 下载免费PDF全文
Jingren Xiao Tengfei Yang Chenxu Wang Jianming Xue Yugang Wang 《Journal of the American Ceramic Society》2015,98(4):1323-1331
Nanolaminated Mn+1AXn phases as candidate materials for next generation nuclear reactor applications show great potential in tolerating radiation damage. However, different Mn+1AXn materials behave very differently when exposed to energetic neutron and ion irradiations. Based on first‐principle calculations, the radiation tolerance of two M3AX2 and four M2AX phases were studied in this work, covering all the Mn+1AXn phases previously investigated with experiments. We have calculated the formation energies of Frenkel pairs and antisite pairs in these materials. The improved radiation tolerance from Ti3AlC2 to Ti2AlC observed by experiments can be understood in terms of different Al/TiC layer ratio as the A atomic plane in the nanolaminated crystal Mn+1AXn accommodates radiation‐induced point defects. The formation of MA–AM antisite pair in Mn+1AXn materials would provide an alternative way to accommodate the defects resulted from radiation damage cascades, whereas this ideal substitution channel does not exist for Cr2GeC due to its pronouncedly higher MA–AM antisite pair formation energy. To further elucidate their radiation damage tolerance mechanism, we have made a detailed analysis on their interatomic M–X, M–A, and X–A bonding characters. Criteria based on the bonding analysis are proposed to assess the radiation tolerance of the six Mn+1AXn materials, which can be further applied to explore other Mn+1AXn phases with respect to their performances under radiation environment. 相似文献
1000.
Mingwen Bai Eleni Sarakinou Ying Chen Ali Daad Chandio Xiaofeng Zhao Michael Preuss Ping Xiao 《Journal of the American Ceramic Society》2015,98(12):3639-3642
Transmission electron microscopy‐based grain orientation mapping method was employed to investigate the microtexture of the alumina scale formed in commercial thermal barrier coatings (TBCs) with two standard types of Pt‐enriched bond coats. Reliable orientation/phase maps with a spatial resolution down to 2 nm were acquired on the alumina grains. It was observed that the alumina scale on the Pt‐aluminide β‐phase bond coat has a stronger c‐axis texture normal to the bond coat surface, in comparison with that on the Pt‐diffused γ/γ′‐phase bond coat. The microtexture of the alumina scale could affect its effective coefficient of thermal expansion, which is a contributor to the severity of the bond coat rumpling mechanism of TBCs failure. 相似文献