Phase Wires Research Articles

Formation of micromeshes by nickel silicide

Nanoscale mesh structures of nickel silicides have been grown on Si(001) surfaces. After cleaning the Si(001) surfaces in an ultra-high vacuum (UHV), nickel measuring approximately seven to eight monolayers in thickness is deposited on the surfaces. On gradually heating the surface above 760 °C, nickel silicides are grown on the surface, accompanied by highly dense etch pits. Self-assembled nano-scale meshes in the NiSi phase (wire size c.a. 20 nm) are nested over the etch pits having an average area of 1μm 2.

Power flow in four-wire distribution networks-general approach

The neutral wire in most power flow software is usually merged into phase wires using Kron's reduction. Since the neutral wire and the ground are not explicitly represented, neutral wire and ground currents and voltages remain unknown. In some applications, like power quality and safety analyses, loss analysis, etc., knowing the neutral wire and ground currents and voltages could be of special interest. In this paper, a general power flow algorithm for three-phase four-wire radial distribution networks, considering neutral grounding, based on backward-forward technique, is proposed. In this novel use of the technique, both the neutral wire and ground are explicitly represented. A problem of three-phase distribution system with earth return, as a special case of a four-wire network, is also elucidated. Results obtained from several case studies using medium- and low-voltage test feeders with unbalanced load, are presented and discussed.

超狭開先ＧＭＡ溶接プロセスの開発 ４ 位相制御型ＧＭＡ溶接プロセスによる開先内でのアーク入熱分布制御

GMA welding process with synchronized control system consisting of a pulsed arc current waveform with cyclical variation of wire feed rate has been developed on the base of computer simulation. In the ultra-narrow gap (less than 5 mm gap) welding process, as the welding wire melting behavior is controlled by low frequency pulsated arc current waveform, the arc generating at the wire tip can be widely oscillated in the direction of thickness. The arc heat pole is dominated by wire melting tip position in consumable electrode welding process, and the arc heat distribution can be changed by this wire tip behavior. The wire melting tip position is represented by wire extension which is a function of wire feed rate and wire melting rate. In order to more-adequately control the arc heat distribution, this report describes synchronized control process between wire feed rate and pulse current waveform in the ultra-narrow gap GMA welding. The important control factor in the newly proposed process is phase shift θ between pulse current waveform and wire feed rate pattern. Firstly, the non-steady state simulation of the wire melting behavior is developed in the case that both arc current and wire feed rate change periodically with low frequency. From simulation results of wire tip behavior under various phase sifts and wire feed rates and pulse conditions, the adaptive welding conditions can be found effectively. Secondly, the synchronized control of welding was carried out under adaptive welding conditions. From the experimental results, it was verified that the arc heat distribution was effectively controlled with the phase shift method expected by numerical simulation thus adequate penetration shapes were obtained in the proposed welding process.

Front Cover

For a specific susceptibility of end-user equipment, the impact of disturbances can be mitigated by design modifications of circuit layout, grounding system design, overvoltage protection, filters, use of steel conduit, use of additional transformers, etc. The effectiveness of these design options on power quality can be analyzed with specialized analysis software. These analysis methods should be able to model systems with three phase wires, four wires (three phase and a neutral/or ground wire), five wires (three phase wires, a neutral wire, and a ground wire), single and double phase circuits, grounding and bonding points, grounding systems, etc. This article presents a method with these capabilities. An additional feature of the method is that the power system component models are physically based, i.e., the model retains the physical construction of the component as opposed to being represented with an abstract mathematical equivalent. A physically based model and analysis procedure provides the means to expose the interrelationship between the physical parameters (i.e., grounding system design, size of neutral, etc.) and power quality. Typical results are presented in this article. In addition, the model is utilized for a statistical assessment of the effects of specific designs on power quality.

Phase transformation behavior and wire drawing properties of Ti-Ni-Mo shape memory alloys

Transformation behavior and wire drawing properties of Ti-Ni-Mo shape memory alloys have been investigated by means of differential scanning calorimetry (DSC) measurements, X-ray diffraction, electron microscopy, tensile tests and wire drawing tests. Mo addition to a Ti-Ni binary alloy induced the R phase transformation, and consequently Ti-Ni-Mo alloys showed two stage transformation, i.e., from the B2(cubic) parent phase to the R(rhombohedral) phase, and then from the R phase to B19′(monoclinic) phase. In the thermo-mechanically treated 51Ti-48.3Ni-0.7Mo alloy, reverse transformation temperature, Af, kept constant, irrespective of thermo-mechanical treatment conditions, while it changed in the thermo-mechanically treated 51Ti-49Ni and 51Ti-48.5Ni-0.5Mo alloys. Mo addition to Ti-Ni binary alloy decreased wire drawing stress. Wire drawing stress decreased with raising intermediate annealing temperature monotonously when the annealing treatment was made in vacuum. When the annealing treatment was made in air, however, it decreased with raising annealing temperature up to 923 K, and then increased. Optimum intermediate annealing temperature of Ti-Ni-Mo alloys for wire drawing was 823 K, above which a thick oxide film which reduced the drawability of the alloys was formed on the surface of alloy wires.

98/03000 A general-purpose transmission line model and its interface with an electromagnetic transients programme

The present paper describes a lightning surge calculation including the wave deformation due to corona. The corona wave deformation is represented by a linear corona model consisting of R-C parallel circuits with diodes, which is easily achieved by the electromagnetic transients program, EMTP. This simple corona model gives satisfactory accuracy compared with field test results. The lightning surge calculation was carried out using a two-conductor model consisting of a phase wire from which a back-flash occurs, and an equivalent ground wire. The two-conductor model gives almost the same accuracy as that using a multiconductor full representation model, for example an eight-conductor model for a twin-circuit line with two ground wires, with a computation time and memory less than a half those of the full representation model.It is observed from calculated results that the corona, in general, reduces voltages at towers and substations by more than 10%. The wave deformation due to the frequency-dependent effect of a transmission line generally has no significant effect on a lightning surge, and thus may be neglected in a lightning surge calculation.

Role of an overhead ground wire in the generation of lightning-induced voltage over lossy ground

The role of an overhead ground wire on the generation for lightning-induced voltage on a multiconductor line associated with a vertical return-stroke channel is studied based on numerical calculation. The induced voltage is calculated by a method in which the tangential component of the electric field to the wire is looked upon as an inducing source. The analyzed multiconductor line consists of three phase wires and an overhead ground wire having one or two earthing points. The influence of the overhead ground wire on the induced voltage is dependent on the direction of a return stroke, as well as the ground conductivity. When a return stroke is on the side of a power distribution line, the induced voltage decreases with a decrease in the earthing resistance of the overhead ground wire, irrespective of the ground conductivity. When a return stroke is close to an end of a distribution line, the influence of the overhead ground wire is dependent on the ground conductivity. In this case, the voltage induced on overhead wires over lossy ground sometimes increases with the presence of an overhead ground wire having only one earthing point. This effect can be avoided by adding earthing points to the overhead ground wire. © 1998 Scripta Technica. Electr Eng Jpn, 121(4): 18–27, 1997

Role of an overhead ground wire in the generation of lightning‐induced voltage over lossy ground

The role of an overhead ground wire on the generation for lightning-induced voltage on a multiconductor line associated with a vertical return-stroke channel is studied based on numerical calculation. The induced voltage is calculated by a method in which the tangential component of the electric field to the wire is looked upon as an inducing source. The analyzed multiconductor line consists of three phase wires and an overhead ground wire having one or two earthing points. The influence of the overhead ground wire on the induced voltage is dependent on the direction of a return stroke, as well as the ground conductivity. When a return stroke is on the side of a power distribution line, the induced voltage decreases with a decrease in the earthing resistance of the overhead ground wire, irrespective of the ground conductivity. When a return stroke is close to an end of a distribution line, the influence of the overhead ground wire is dependent on the ground conductivity. In this case, the voltage induced on overhead wires over lossy ground sometimes increases with the presence of an overhead ground wire having only one earthing point. This effect can be avoided by adding earthing points to the overhead ground wire. © 1998 Scripta Technica. Electr Eng Jpn, 121(4): 18–27, 1997

Enhancement of the critical current density in Chevrel phase superconducting wires

The critical current densities Jc of Chevrel phase wires with niobium as an antidiffusion barrier were measured in magnetic fields up to 24 T. At 20 T and 1.9 K, Jc reaches 5.4×108 A/m2 and decreases slightly down to 3.1×108 A/m2 at 24 T. A wire with a 20% superconducting cross section has been successfully drawn and its overall critical current density Jcov exceeds 100 A/mm2 at 1.9 K up to a magnetic field slightly above 20 T. This demonstrates the ability of Chevrel phase wires to be used in high magnetic field applications. Moreover, some parts of the coil have certainly higher Jc, since Jc is very often limited by a thermal excursion of the entire coil. The effective upper critical field μ0Hc2*, deduced from the magnetic field dependence of Jc, is too low compared to the expected bulk value, indicating that superconducting properties at the grain boundaries are still degraded. If the bulk μ0Hc2 can be restored at the grain surfaces, Jcov should be higher than 100 A/mm2 up to at least 30 T.

Conditions of aerodynamic instability of airfoil equilibrium positions

where C~ and C~ are the stationary aerodynamic lift and drag coefficients; the dash stands for the derivative with respect to the angle of attack a. The conclusions of [1] were verified on the experimental data published in [2]. Large vibrations (with amplitudes greater than a meter) of phase wires, mainly in the vertical direction along the O Y axis (Fig. 1), were observed repeatedly in high-voltage power lines. In the special literature such motions are called a dance or galloping of a single wire of a power line. Condition (1) was obtained by Den-Hartog [3] in studies of one-dimensional motion of a mechanical model of a wire as a necessary condition of self-excited vibrations in the vertical plane. Thus, the consideration of one-dimensional self-excited vibrations of an airfoil led to condition (1), which may rightfully be called the Glauert-Den-Hartog condition. It is interesting to note that , in our opinion, Russian researchers are not familiar with the paper of Glauert [1]. Thus, for example, there are no references to [1] in [4], although stability questions are considered, and other papers of Glauert are cited. Fedyaevskii and Blyumina [5] studied the conditions of loss of aerodynamic damping by an angle airfoil rotating about a fixed axis. They obtained a rather complex inequality containing moment aerodynamic coefficients and came to the conclusion (from experimental data) that condition (1), which they call DenHartog's condition, can also be used as a criterion. Therefore, in our opinion, it would be useful for researchers to know that the book-stacks of the Russian State Public Library of Scientific and Technical Literature contain rather complete sets of the Proceedings of the British Advisory Committee for Aeronautics for 1909-1980. Condition (1) was confirmed experimentally [5, 6] and has been applied in civil engineering. In designing skyscrapers, which are subjected to wind loads, the cross section of the building must be oriented so that the angles of attack with respect to the direction of prevailing winds are beyond the interval in which inequality (1) holds [71. In simulating the behavior of a power-line wire under the action of wind, Van'ko [8] considered motion of an airfoil with three degrees of freedom: motion along the O X and O Y axes and rotation about the center of mass (Fig. 1). The conditions of existence of static solutions of the system of equations of motion were established: if the airfoil is lifting and the lift Y ~ 0, equilibrium positions exist for any wind (air flow) velocity V > 0. In studies of the Lyapunov stability of possible equilibrium positions, the following results were obtained:

Possible mechanism of lightning strokes to extra-high-voltage power transmission lines

The possible mechanism of lightning strokes to extra-high-voltage power transmission lines is discussed. It has been theoretically shown in the case of 1150 kV transmission lines that the interaction between the charges of a thunderstorm cloud and the downward leader from one side and the charges induced by them on the transmission line wires from the other side can cause swinging and dancing of the wires which leads to the possibility of disruptive discharges from the phase wire. Using a charged aerosol cloud it has been experimentally found that the appearence of discharges is accompanied with swinging of the wires. Some recommendations for lightning protection improvement are made.

Promising critical current density in the Chevrel phase superconducting wires

Chevrel phase wires with high quality powder were made under very careful conditions. Small coils of about 1 m wire length, treated under hot isostatic pressing conditions, were measured in a magnetic field up to 15 T. We have obtained a critical current density of 5.0 Ø 10 8 A/m 2 at 15 T and 4.2 K. This represents an improvement of 35% with respect to the best reported results to date. We show that these J c values are still extrinsically limited by a few defects responsible for the thermal quench of the coils. When it was possible to localise the defects, holes in the anit-diffusion barrier were observed.

Hot isostatic pressing of Chevrel phase bulk and hydrostatically extruded wire samples

In order to lower final sintering temperatures for Chevrel phase (CP) wires, we have investigated low-temperature hot isostatic pressing (HIP'ing) of both bulk and wire samples. We have fabricated (Pb,Sn)-based Chevrel phase (CP) monofilament and 61 filament wires by hydrostatic extrusion of (Cu or Cu-Ni)/(Nb or V)/CP composites, followed by cold drawing. We have investigated the CP/barrier reaction during heat treatment, finding V is unsuitable, but Nb is suitable at these lower temperatures for prereacted Pb/sub 1-x/Sn/sub x/Mo/sub 6/S/sub 8/ cores. We prepared powders of the binary Chevrel phase Mo/sub 6/S/sub 8/ by acid leaching of Li/sub x/Mo/sub 6/S/sub 8/ and Ni/sub x/Mo/sub 6/S/sub 8/. We prepared bulk samples of PbMo/sub 6/S/sub 8/ and Pb/sub 1-x/Sn/sub x/Mo/sub 6/S/sub 8/ by HIP'ing mixtures of "Pb+Mo/sub 6/S/sub 8/" powders (in situ route) or by prereacting Pb, Sn and Mo/sub 6/S/sub 8/ powders before HIP'ing (prereacted route). The in situ powders were HIP'ed under different time-temperature-pressure conditions up to 12 h/600/spl deg/C/200 MPa, producing partially consolidated PbMo/sub 6/S/sub 8/ samples. Further HIP'ing of all samples at temperatures of 700, 800 and 1000/spl deg/C, 200 MPa pressure and times of 8 and 80 hours produced additional consolidation, up to 95% of full density. As the aggressiveness (temperature and time under pressure) of the HIP process increased, the density, hardness, critical temperature, and magnetization critical current density increased.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of sintering time and temperature on superconducting properties of Chevrel phase wires made with micron-sized powder

A systematic study of inductively measured T c, transport critical current density (J c) and the field (B max) at which pinning force density is maximum has been made on newly developed Chevrel phase superconducting (CPS) wires. At fixed sintering temperatures, B max(4.2 K) increases monotonically to values ≥ 0.16 B c2 with increasing sintering times (t s). Simultaneously, the deterioration of J c(4.2 K, 7.5 T) values and the inductive transition show a degradation of the CPS core. The emerging picture lends support to the evolution of well comnected paths in a granular CPS core, however, limited by degradation due to Pb/ S losses.

J c investigations in Chevrel phase wires

Two-step heat treatments have been carried on ceramic-route precursor wires and lead to the optimization of critical current density. J c curves as a function of heat treatment time show a maximum value at any temperature, corresponding to a compromise between the fabrication and the degradation of the superconducting Chevrel phase.

Recent progress in chevrel phase syntheses: A new low temperature synthesis of the superconducting lead compound

This paper reviews recent progress in the synthesis of Chevrel phases. The objective was to produce better microscopic homogeneity of the elements and/or precursors required to form the phase. Among these new processes, the one dealing with insertion of lead into the binary Mo 6S 8 compound is particularly attractive for the development of Chevrel phase wire since the phase formation occurs at temperature as low as 440°C. To achieve good microscopic homogeneity of PbMo 6S 8 (PMS), PbS is used and the extra sulfur is removed under a hydrogen gas flow. Basic superconducting properties, like a.c. susceptibility transition and specific heat anomaly at T c, demonstrate extremely fine super-conducting particles. Further annealing at the moderate temperature of 600°C improves the homogeneity and/or the crystallinity of the powder.

Considerations for practical conductor design of Chevrel phase wires

It is noticed that the application of PbMo/sub 6/S/sub 8/ (PMS) wires for the generation of steady-state magnetic fields in excess of 20 T requires that several conditions be fulfilled in order to be realistic. Practical design considerations for PbMo/sub 6/S/sub 8/ wires are reported. Besides the availability of wires with sufficient lengths and uniform high critical current density J/sub c/, thermal and mechanical stability have to be achieved. The most severe criterion for thermal stability is based on the prevention of flux jumps in the presence of screening currents in the adiabatic limit. This results in filament diameters between 710 mu m and 90 mu m for critical current densities of 5*10/sup 8/ A/m/sup 2/ and 2*10/sup 9/ A/m/sup 2/, respectively. A dynamic stabilization of a PMS wire in an epoxy-impregnated coil is not very efficient. The behavior of the J/sub c/ of PbMo/sub 6/S/sub 8/ wires under tensile and compressive stress is discussed.

Power line tower models above 1000 kHz in the standard broadcast band

It is shown that the resonant behavior of power lines at higher frequencies is quite dependent on the geometry of the crossarms that the tower uses to carry the phase wires. Tower models (including crossarm detail) which can reproduce the Thornhill measurements at 1605 kHz and the scale-model measurements from 1000 to 1900 kHz are developed. One such tower model is simple enough to allow the analysis of long runs of power line. Such models are useful in estimating scattering from power lines across the entire AM broadcast band. >

ChemInform Abstract: Status and Prospects of Superconducting Chevrel Phase Wires for High Magnetic Field Applications

Abstract In spite of the recently discovered high Tc superconductivity, Chevrel phase superconductors still remain interesting for very high field applications. For example, PbMo6S8 (PMS) with an upper critical field above 50T at 4.2K can now be prepared either as bulk or a wire with critical current densities near that of commercial Nb3Sn conductors. In this paper we give a review of the present situation of the development of Chevrel phase wires. Based on investigations on bulk samples, we also discuss the important potential for further improvements on this material.

Influence of transverse compressive and axial tensile stress on the superconductivity of PbMo 6S 8 and SnMo 6S 8 wires

The behaviour of the critical current density, J c, of PbMo 6S 8 and SnMo 6S 8 monofilamentary wires with external transverse compressive stress, σ t, and axial tensile stress, σ a, was investigated. Varying the reinforcing steel content in the wire matrix, different axial prestress states, e.g. the compressive, tensile and unstressed state were realized. The observed variation of J c, versus σ a was significantly smaller compared with that of Nb 3Sn wires, which is explained by the higher upper critical magnetic field, B c2, of the Chevrel phase. The elastic strain range of 0.6–0.8% (with 0.2% compressive prestrain of the filament) fulfils the requirements for future technical applications of this type of wire material. The effect of transverse applied compressive stress, σ t, on I c and B c2 ∗ of the Chevrel phase wires was investigated in magnetic fields up to B = 22 T and T = 4.2 K. Analogous to Nb 3Sn wires, a strong degradation of the critical current density with σ t was observed. As for the axial tensile stress, the influence of σ t on J c is found to increase with the applied magnetic field. At 20 T the transverse compressive stress effects reduce J c about twice as much as the axial tensile stress. At present externally steel reinforced PbMo 6S 8 wires can be compared with Nb 3Sn wires, the effect of transverse stress appears to be considerably smaller in the Chevrel phase wire, possibly as a consequence of the higher upper critical field with respect to Nb 3Sn.