Rigid Conductor Research Articles

Magnetically aligned single wall carbon nanotube films: Preferred orientation and anisotropic transport properties

Thick films of single wall carbon nanotubes (SWNT) exhibiting in-plane preferred orientation have been produced by filter deposition from suspension in strong magnetic fields. We characterize the field-induced alignment with x-ray fiber diagrams and polarized Raman scattering, using a model which includes a completely unaligned fraction. We correlate the texture parameters with resistivity and thermal conductivity measured parallel and perpendicular to the alignment direction. Results obtained with 7 and 26 T fields are compared. We find no significant field dependence of the distribution width, while the aligned fraction is slightly greater at the higher field. Anisotropy in both transport properties is modest, with ratios in the range 5–9, consistent with the measured texture parameters assuming a simple model of rigid rod conductors. We suggest that further enhancements in anisotropic properties will require optimizing the filter deposition process rather than larger magnetic fields. We show that both x-ray and Raman data are required for a complete texture analysis of oriented SWNT materials.

Improvement of Rigid Conductor Lines

Rigid conductor lines are currently used in wide ranges by subways and other railways. It is thought that the quality of current collection of rigid conductor lines is influenced by the unevenness of contact surface. Then, we developed a grinding machine to evenly smooth the contact surface. We also installed rigid conductor lines on the current collection testing equipment at the Railway Technical Research Institute, and examined the relation between contact surface and contact loss. Consequently, we confirmed that it was possible to reduce contact loss effectively by using the grinding machine.

Parametric Short-Circuit Force Analysis of Three-Phase Busbars: A Fully Automated Finite Element Approach

A three-phase busbar arrangement with straight rigid conductors carrying short-circuit currents is investigated. Calculations are made assuming steady-state ac current with a peak value equal to the peak value of the short-circuit current. The electromagnetic forces are calculated by solving the electromagnetic field diffusion equation numerically, using finite elements. The results are compared with results calculated according to IEC Standard 865/93. A large number of arrangements have been examined, covering a wide variety of cases, as used in ac indoor installations of medium and low voltage. For this purpose, the finite element procedure has been fully automated to a degree of minimal human intervention. A Let-It-Grow artificial neural network has been utilized for the automatic mesh generation. The forces calculated were in all cases in excellent agreement with IEC Standard 865/93.

Characterisation of an optimised high current MgO/Bi 2Sr 2CaCu 2O 8.21 composite conductor using pulsed transport currents with pulsed magnetic fields

High temperature superconducting conductors are already used in hybrid magnets to produce fields that enhance the performance of conventional magnets made from A-15 type low temperature superconducting wires. For such applications it is vital that the interdependence of the critical parameters such as critical current versus magnetic field can be mapped under high field and high current conditions. However these superconductors have high critical currents even at fields over 20 T, making accurate measurements difficult due to the thermal and mechanical problems. In this paper, we compare measurements on the fully optimised Bi 2Sr 2CaCu 2O 8.21 flat rigid conductors using an innovative pulsed high transport current and pulsed high field technique. We show how analysis of the voltage signal from Bi 2Sr 2CaCu 2O 8.21 tape in pulsed conditions may be used to extract the critical current under quasi-stationary conditions.

On the axi-symmetric equations of a rigid heat conductor: discontinuity waves in a non-constant state

By requiring the invariance with respect to a stretching group of transformations the non-linear system of equations governing the heat propagation in a rigid conductor is mapped in a form which has a constant state solution in terms of suitable similarity variables. It has been shown that constant state solutions become special non-constant state solutions in the original variables. In particular, we prove that the temperature dependence of the propagation of discontinuity waves along a solid in an equilibrium state well reproduces the temperature behaviour of the second sound speed.

Seismic Interaction of Interconnected Electrical Substation Equipment

This paper investigates experimentally the dynamic interaction between components of electrical substation equipment interconnected by rigid bus conductors. Specific tests conducted in this study were (1) quasi-static tests of three different types of rigid bus with spring connectors; (2) quasi-static tests of one rigid bus slider; and (3) shake table tests of five different pairs of generic substation equipment specimens interconnected by three different rigid bus assemblies. All connectors tested exhibit stable hysteretic behavior with various degrees of energy dissipation capacity. The spring connectors dissipate energy through yielding and generated the highest forces among the connector tested and generally caused an amplification of the dynamic response of one of the interconnected equipment components. The bus slider dissipated energy through friction and generated lower forces than those of the spring connectors. Its high damping capacity, however, systematically reduced the dynamic response of interconnected equipment components. Finally, a special seismic connector that incorporates three flexural vertical aluminum cables generated the lowest forces. Its minimal damping capacity, however, resulted in higher equipment dynamic response than with the bus slider.

Development of long-span-type overhead rigid-conductor line of a catenary system

An overhead rigid conductor line in a tunnel is free from the fear of disconnection because the contact wire is not tensioned, and it is superior in maintenance saving. In order to introduce this in open sections, we have developed “a long-span-type overhead rigid conductor line of catenary system.” This contact line structure consists of a contact wire of no tension attached to a supporter that has a small drag coefficient suspended from the messenger wire. We have now developed a “square supporter” to make the drag smaller and have put it to various tests with support point intervals of 50 and 10 m. As the testing results show, the contact loss is 1 to 2% at 130 km/h, and this overhead rigid conductor line can collect the current with a stability equal to that of the normal catenary system. © 2000 Scripta Technica, Electr Eng Jpn, 131(1): 94–102, 2000

Consequences of a generalized Ohm's law for magnetic transport in conducting media

The consequences for magnetic transport of a generalized Ohm's law that includes the inertia of electrons are explored. For metals, this law coincides with the Drude model for electronic conduction. A formula for the absorption coefficient in a rigid conductor is derived. It is found that the stronger the inertial effects the higher the attenuation of the field in the conductor. Also, in the low-frequency limit the decay time of the field inside a conductor is found to be larger than the one obtained with the ordinary Ohm's law. The case of an ionized gas is also briefly discussed.

Pressure-induced percolation transitions in composites

In physical experiments the percolation threshold for conductivity of conductor-insulator mixtures can be achieved by addition of conductive inclusions to the insulating embedding matrix, keeping the volume of the cell constant, or by compression of a mixture containing an initially nonpercolating quantity of conducting inclusions. The latter case we define as a pressure-induced percolation transition (PIPT). Two limiting cases of PIPT may be envisioned, namely rigid conducting particles in a deformable insulator and deformable conducting particles in a less deformable insulator. In both cases the percolation state is achieved at some critical pressure (strain) which depends on the initial concentration of the conducting phase. The experimental results on conductivity of powder conductor-insulator mixtures show that pressure-driven percolation differs substantially from the usual percolation model: even in the simplest case of a rigid conductor in a deformable insulator the critical index of conductivity close to the critical strain is much less than the expected value . The value is achieved at larger strains. The low value of close to the percolation threshold can be explained by considering the competition of processes of destruction and creation of contacts between conductive inclusions and clusters under the applied stress. In the case of deformable conductive inclusions interpretation of the PIPT is rather complicated. The strain sensitivity of the conductivity is maximal close to the percolation threshold; we consider some practical implications of anomalous strain sensitivity.

Development of Long Span Type Overhead Rigid Conductor Line of Catenary System

Overhead rigid conductor line in tunnel is free from the fear of disconnection because the contact wire is not tensioned, and it is superior in maintenance saving. In order to introduce this in open section, we have developed “a long span type overhead rigid conductor line of catenary system”. This contact line structure consists of contact wire of no tension attached to the supporter which has a small drag coefficient hanged by the messenger wire. In this time, we have developed “square supporter” to make the drag smaller and put it to various tests with support point interval 50m and 10m. As the testing results, the contact loss is 1_??_2% at 130km/h, and this overhead rigid conductor line can collect the current with stability equal to the normal catenary system.

Rigid line inclusions under anti-plane deformation and in-plane electric field in piezoelectric materials

The problems of the rigid line inclusions under anti-plane deformation and in-plane electric field in piezoelectric materials are studied by using the complex variable method of Muskhelishvili. The rigid line inclusions are considered, respectively, as a dielectric and conductor. A square-root singularity of the field variables is identified. The singularity exists only if the shear loading is acting perpendicular to the rigid lines and the electric loading is parallel to them. For the rigid dielectric line inclusion, the singularity coefficients of both stress and electric field depend on the material properties, and the mechanical and electrical loads applied at infinity, whereas the electric displacement is a constant on the entire plane. The values of the J-integral are always negative. For the rigid conductor line inclusion, the field singularity coefficients corresponding to the field variables applied at infinity become independent of the material properties and other respective loading parameters. The values of the J-integral can be either positive or negative.

Electromagnetic forces in three-phase rigid busbars with rectangular cross-sections

A three-phase busbar arrangement with straight rigid conductors carrying short-circuit currents is investigated. Calculations are made assuming steady-state AC current with a peak value equal to the peak value of the short-circuit current. This assumption is used in the related IEC Standards 865/92. In this paper, the electromagnetic forces and current densities are calculated by solving the electromagnetic field diffusion equation numerically, using finite elements. The results are compared with results calculated according to the IEC Standards 865/86, as well as with the corresponding technical revision IEC 865/92. The comparison involves arrangements with rectangular cross-sections, as used in AC indoor installations of medium and low voltage. The forces calculated, especially in cases of multiple sub-conductors per main conductor, were greater than those calculated according to the above Standards. In older Standards this difference is up to fifty per cent, while in the revision this difference is smaller. The differences are probably due to proximity effects.

Global existence and singularity formation in solutions of a modified Fourier law

The aim of this paper is the analysis of formation of singularities from smooth initial data, for rigid conductors. The modified Fourier law used asserts that the governing second-order equation is hyperbolic with first-order dissipation. Global existence for small initial data is also examined.

The effect of tendon on muscle force in dynamic isometric contractions: A simulation study

Recently, Baratta and Solomonow J. Biomechanics 24, 109–116 (1991) studied the effect of tendon on muscle-tendon complex behavior in cat tibialis anterior (TA) muscle. This was done by determining the relation between neural stimulation and muscle force in a dynamic isometric experiment, both before and after the removal of the distal tendon. From their results, Baratta and Solomonow concluded that in isometric and concentric contractions at mid-range force levels, tendon behaves as a rigid force conductor. This conclusion is in conflict with literature in which several functions are attributed to the elastic behavior of the series elastic element (SEE), of which tendon is the major part. The present study investigates the expected generalizability of their findings, by simulating the experiments using a straight-forward Hill-type muscle model. First, model predictions are shown to be in line with the experimental results on cat TA: in dynamic isometric experiments at mid-range force levels, the effect of SEE removal is indeed negligible. Second, the effect of SEE removal is predicted to vary largely among muscles. Third, the most important determinants of the effect of SEE removal in dynamic isometric contractions are shown to be maximum fiber shortening velocity and the ratio of SEE slack length to fibre optimum length.

On the Interaction of Two Piezoelectric Fibers Embedded in an Intelligent Material

In this paper we are concerned with the problem of two circular piezoelectric fibers of different radii and distinct material properties, perfectly bonded to a host intelligent material, of infinite extent. The matrix material may be piezoelectric or nonpiezoelectric but, together with the fibers' materials, it possesses the symmetry of a hexagonal crystal in the 6 mm class. The system is subjected to electromechanical loadings (singularities) which produce out-of-plane displacement and in-plane electric fields, but are otherwise arbitrary. Within the framework of the procedure of heterogenization, recently developed by the authors, the solution is sought as a transformation applied to the solution of the corresponding homogeneous problem (i.e., the problem of the host material occupying the full space and subjected to the same sources). The solution is formulated in a manner which leads to some exact results. Universal formulae are derived for the electromechanical field at the point of contact of two piezoelectric fibers. Some quantities which are invariant under the transformation, i.e., quantities which take the same values in the heterogeneous as in the corresponding homogeneous problems, are also discovered. The ramifications of this discovery are investigated. Moreover, the asymptotic behavior of the electromechanical field at the closest points of two plated circular holes or rigid conductors, approaching each other in an intelligent matrix material is also studied and given by universal formulae, i.e., formulae which are independent of the electromechanical sources. The interaction of the fibers with host-material microdefects, such as dislocations, electric line charges and microvoids, is scrutinized. The possibility of manipulating the electrical potential to reduce the high stress level is also discussed.

Measurements of inductive charges during drop breakup in horizontal electric fields

Waterdrop pairs with initial diameters of 2.1 and 1.7 mm were collided at inclinations < 3° from the vertical after attaining fall speeds of 3.4 and 2.1 m s−1, respectively, and broke up in either negligible or strong electric fields (50 k V m−1). The colliding waterdrops had initial charges < 0.1 pC. In a horizontal electric field of < 100 V m−1 the fragments were not charged measurably by noninductive processes (< 0.05 pC). However, at 50 kV m−1 the waterdrops acquired charges up to 5 pC by induction. All breakups observed between the drop pairs resulted in “disjection”, that is a separation with the largest fragment staying below the other(s). The results, based mainly on filament breakup, over mechanically limited disjection angles from 69° to 111° (given by the connecting line between the centers of the two largest fragments at the moment of separation and the horizontal) provide experimental evidence of a cosine dependence of inductive charging in the presence of horizontal electric fields. They also support application of a theoretical equation developed by Latham and Mason (1962) for rebounding rigid spherical conductors. The results can be generalized to include all raindrop‐raindrop collision/breakups involving drop pairs with diameters > (1.8;0.4 mm) and to all electrical field directions because fields up to 50 kV m−1 do not affect the breakup configurations. A particular conclusion is that breakups of colliding raindrops, in the size and voltage ranges quoted, aid in the dissipation of vertical electric fields in the atmosphere.

A one-dimensional, linear model of rigid thermal conductors exhibiting phonon viscosity: A numerical example

We investigate one-dimensional heat propagation in a rigid thermal conductor on the basis of a linearized model. It is assumed that the free energy of the medium depends on the temperature and heat flux as well as on their first-order spatial derivatives. The model includes dissipation accounting for phonon viscosity. The basic set of equations is reduced to two coupled partial differential equations for the temperature and heat flux. It is shown that the model leads in a special case to the well-known form of Fourier's law for heat conduction proposed by Guyer and Krumhansl. An example is considered and solved by using a numerical technique based on the method of finite differences. The stability and accuracy of the algorithm are checked numerically, and the obtained results are analyzed to determine the influence of the different material constants involved in the model.

Global external magnetohydrodynamic instabilities in straight noncircular Z pinches

The straight EXTRAP experiment [Phys. Scr. 16, 147 (1977); Nucl. Instrum. Methods 207, 223 (1983)] is modeled as a magnetohydrostatic equilibrium with cylindrical symmetry and a plane magnetic field. The plasma is surrounded by a vacuum that extends to infinity, and in which four axial rod currents are placed symmetrically. The plasma current density is either parallel or antiparallel to the rod currents, thus having one sign throughout. In the stability analysis, the configuration is assumed to have a finite axial length (the boundary conditions appropriate to a rigid perfect conductor are imposed at the two ends), and the rods are assumed to be permeable to the magnetic field. According to ideal magnetohydrodynamics, such an equilibrium is globally unstable to flute modes and/or slip modes unless the rod currents vanish (circular Z pinch). This is due to the increase away from the center of the octupole field of the rods.

A heat conduction equation with three relaxation times. Particular solutions

A one-dimensional, linear heat conduction equation involving three relaxation times is derived for a rigid thermal conductor. Form preserving and plane wave solutions are investigated. Attention is focused on the influence on wave propagation of a dissipation term involving the time derivative of temperature in the expression for entropy. Some numerical results are presented.

Non-linear motion of a rigid conductor in a magnetic multipole field

The non-linear motion of an ideally conducting current-carrying rigid cylinder in a magnetic multipole field is analyzed. It is found that non-linear stability is achieved provided the current in the external conductor rods is sufficiently large. Since the results agree qualitatively with experimental observations of the Extrap z-pinch, it is suggested that the so far unexplained stability of this configuration is due to non-linear effects.