Compared with conventional power plants, wind power plants (WPP) have their own characteristic, which are more vulnerable to transient overvoltages. Transient overvoltages may contribute to insulation failures of step-up transformers. In WPPs, the transient overvoltage is mainly caused by switching operations of vacuum circuit breakers. In this paper, suitable models for the simulation of transient overvoltages are developed. A detailed model of vacuum circuit breaker, which is required to simulate both the capability of high-frequency current interruption and the withstand capability of transient recovery voltage, is developed. Input parameters for cable models are calculated on the basis of the parameters of actual cables. A wide band transformer model is also proposed for studying the transient behaviors in WPPs. Simulations of transient overvoltages during circuit breaker switching operations in WPP have been carried out in PSCAD/EMTDC. In case studies, it considers some influence factors of transient overvoltages, such as the length of cable feeders and the collector system topology adopted in WPPs. The results obtained from this research can be used as a reference for the insulation level designation of electrical components in WPPs.
Carbon nanotubes (CNTs) were shortened from 5 to 15 μm to ca. 200 nm using ball milling with ethanol as the milling aid agent, and a platinum catalyst with these shortened carbon nanotubes (SCNTs) as the support was prepared by a high‐pressure colloidal method. It was found that this catalyst with SCNTs showed much higher activity than a platinum catalyst with normal CNTs as support; for methanol anodic oxidation, the activity of the Pt/SCNTs was 50% higher than that of the Pt/CNTs, and the Pt/SCNTs also showed higher activity for the cathodic reduction of oxygen. The Pt/SCNTs were characterised by X‐ray diffraction scanning and transmission electron microscropy. It is suggested that the significant performance enhancement when SCNTs are used as support might result from the generation of new surfaces and defects, the opening of closed nanotubes in the process of milling, higher platinum dispersion on the shortened nanotubes and the interaction of platinum nanoparticles with the SCNTs.
IEC 61850-9-2 proposes the process bus communication for protection and automation within substations. The actual performance of process bus such as real-time, security and reliability are of concern, when transmission of sample values and trip signals over the same network. This paper presents the establishment of a dynamic simulation test platform, in order to facilitate the test of protection schemes over the process bus. An example is given to demonstrate that incorrect switch configuration, message priority tagging, and the volumes of traffic on the network may have an impact on the real time and reliability of the signals to be delivered.
Using the designed multi-tooth tool, a novel porous metal fiber sintered felt (PMFSF) with three-dimensional reticulated structure has been produced by solid-state sintering of copper fibers. The copper fibers were fabricated using the cutting method. According to the SEM results, it was found that there were two kinds of sintering joints of surface contact and crossing fiber meshing among the fibers in the PMFSF. The coarser sintering joints will help to enhance the mechanical strength of PMFSF. Based on the structure characteristic, a three-dimensional model with the cubic pore cell structure was established to describe the structure of PMFSF. In addition, the effectiveness of geometric model was verified by the test results of specific surface area of PMFSF.
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