现代高压直流输电技术及直流阀技术

在最近20年内高压直流晶闸管阀和高压直流输电技术的发展,使得用高压直流输电更经济、更可靠。越来越多的输电线路使用高压直流进行电力传输。现代的高压直流晶闸管阀以组件式结构、大功率和水冷晶闸管、智能晶闸管控制单元、全面的计算机阀控制和严格的试验为特征。容性换流技术、数字式光纤互感器、有源直流滤波器和连续可调交流滤波器的使用,有效地提高了高压直流输电的质量,产生了更健全的高压直流输电系统。作为新一代高压直流换流器的电压控制型换流器,使得小容量电力传输经济可行。     

Methods of quantitative matrix analysis of Zircaloy-2

The zirconium-based alloy Zircaloy-2 contains small amounts of iron, chromium and nickel dissolved in the matrix. Several attempts to measure these amounts have been made in the past, but the results are conflicting and inconclusive. The advent of wide angle, laser pulsed atom probe tomography motivates a new attempt to analyze the matrix. Large datasets are now easily obtained using laser pulsing but quantification is not straightforward due to rather complex mass spectra. Zircaloy-2 contains about 1 wt% tin, 0.1 wt% oxygen and trace amounts of Si, C and Al. Severe overlaps make quantification of any Fe⁺, Cr⁺ and Ni⁺ ions impossible. Quantification of Fe, Cr and Ni therefore requires that they appear as doubly charged ions only, and consequently the field must be kept high enough. In addition, adsorbed CO⁺ may appear at the main peak of Fe²⁺. In the paper a method is reported, which gives what we believe an accurate quantitative analysis of at least iron and chromium in the matrix.     

Quantitative atom probe analysis of carbides

Compared to atom probe analysis of metallic materials, the analysis of carbide phases results in an enhanced formation of molecular ions and multiple events. In addition, many multiple events appear to consist of two or more ions originating from adjacent sites in the material. Due to limitations of the ion detectors measurements generally underestimate the carbon concentration. Analyses using laser-pulsed atom probe tomography have been performed on SiC, WC, Ti(C,N) and Ti₂AlC grains in different materials as well as on large M₂₃C₆ precipitates in steel. Using standard evaluation methods, the obtained carbon concentration was 6-24% lower than expected from the known stoichiometry. The results improved remarkably by using only the ¹³C isotope, and calculating the concentration of ¹²C from the natural isotope abundance. This confirms that the main reason for obtaining a too low carbon concentration is the dead time of the detector, mainly affecting carbon since it is more frequently evaporated as multiple ions. In the case of Ti(C,N) and Ti₂AlC an additional difficulty arises from the overlap between C₂⁺, C₄²⁺ and Ti²⁺ at the mass-to-charge 24 Da.     

使用合成试验回路对三峡—常州HVDC晶闸管阀进行运行试验

三峡―常州(3G)HVDC晶闸管阀使用的是高额定容量的晶闸管,若用传统的背靠背回路进行试验,需要巨大的投资。为此,开发了一合成试验回路,并成功用于试验三峡晶闸管阀。该回路使用常规的背靠背试验回路作电流源,用振荡回路作电压源,能够充分再现HVDC晶闸管阀的4种运行状态。所产生的试验电应力大于或等于运行条件下的预计电应力。型式试验结果表明,三峡HVDC晶闸管阀完全满足要求。由于试验参数普遍高于设计要求,表明晶闸管阀的设计裕度较大。     

Quantitative APT analysis of Ti(C,N)

A specially produced Ti(C,N) standard material, with a known nominal composition, was investigated with laser assisted atom probe tomography. The occurrence of molecular ions and single/multiple events was found to be influenced by the laser pulse energy, and especially C related events were affected. Primarily two issues were considered when the composition of Ti(C,N) was determined. The first one is connected to detector efficiency, due to the detector dead-time. The second one is connected to peak overlap in the mass spectrum. A method is proposed for quantification of the C content in order to establish the C/N ratio. A correction was made to the major C peaks, C at 6 and 12 Da, with the ¹³C isotopes, at 6.5 and 13 Da, according to the known natural abundance. In addition, a correction of the peak at 24 Da, where C and Ti overlap, is proposed based on the occurrence of single/multiple events for respective element. The results were compared to the results from other techniques such as electron energy loss spectroscopy, chemical analysis and X-ray diffraction. After applying the corrections, atom probe tomography results were satisfactory. Furthermore, the content of dissolved O in Ti(C,N) was successfully quantified.     

用于HVDC晶闸管模块运行试验的新合成试验回路

现代晶闸管阀的高额定容量使其难以在试验室用背靠背试验回路进行试验,用合成试验回路对晶闸管阀的设计进行验证是一种替代方法。设计合成试验回路的核心在于,如何正确地再现作用在晶闸管阀上的负荷。为此,重点描述了换流阀在4种运行状态下的电压和电流负荷。ABBPowerSystems开发了一种新的合成试验回路,正确地再现了运行中施加在HVDC晶闸管阀上的电压和电流负荷。验证试验表明,该回路的设计是成功的。