Conductor Configurations Research Articles

Simulation models of a dissipative transmission line above a lossy ground for a wide-frequency range. II. Multiconductor configuration

For pt. I see ibid., vol.38, no.2, p.127, 1996. The simulation model of a multiconductor dissipative line above a lossy ground, based on the exact formulation of the Maxwell equations, is proposed for a wide frequency range. The procedure is an extension of the analysis of single conductor configurations. The exact expression of the matrix modal equation of the line is first proposed, assuming that in the system there are as many dominant discrete modes of propagation as there are conductors. New expressions of the distributed series-impedance and shunt-admittance matrices are proposed, with reference to the definition of the wire-to-ground voltage. Moreover, an easy-to-implement simulation model is proposed for use in computer codes, based on the logarithmic approximation of the Sommerfeld integrals and Bessel functions. Applications are carried out in order to compare the results of the proposed procedure and of the Carson (1926) theory, with reference to a three-conductor line above a lossy ground.

A new numerical grid truncation scheme for the finite difference of Laplace's equation

A modified form of Laplace's equation, based on coordinate stretching, is proposed, that lends itself to a new convenient numerical grid truncation methodology for the solution of Laplace's equation in open regions. The proposed method eliminates the need for approximate local boundary conditions the truncation boundary of the numerical grid. Thus, it provides for a simple, robust, computationally efficient and very accurate grid truncation scheme. First, an analytic justification of the proposed grid truncation methodology is presented. Next, its numerical implementation is discussed in conjunction with the numerical solution of Laplace's equation in unbounded two-dimensional regions. Numerical studies are used to illustrate the choice of the parameters used in the numerical implementation of this new truncation scheme, and quantify their impact on solution accuracy. A separable boundary value problem is used to motivate the proposed truncation scheme. The numerical studies and associated numerical results emphasize the calculation of per-unit-length capacitances for two-dimensional conductor configurations of the type used for unshielded planar transmission lines.

Effects of conductor edge profile on transmission properties of conductor-backed coplanar waveguides

A boundary integral equation method is applied to the full-wave analysis of conductor-backed coplanar waveguides with a rectangular or trapezoidal conductor cross-section. Due to a particular choice of Green's functions for each subregion defined in a given cross-section, electromagnetic fields in each subregion are analytically expressed in terms of equivalent magnetic currents on apertures and resulting integration contours are defined only on aperture surfaces. Consequently, this approach can overcome relative convergence problems even in the case of largely different aperture widths among subregions. Numerical data show that this approach has a stable convergence property and requires a short computation time. Numerical results obtained with this approach are in excellent agreement with other available theoretical data. A series of calculated data for some rectangular and trapezoidal conductor configurations are provided to show the effects of conductor edge profile on transmission properties of conductor-backed coplanar waveguides.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A model to predict current distributions in heavy current parallel conductor configurations

This paper presents a model for predicting the current distribution in high current cables consisting of relatively widely spaced parallel conductors. These cables are typically used in electric glass melters to interconnect the power transformers and the melter secondary bus installations. Due to mutual inductive coupling between the conductors, electromagnetic forces will cause a nonuniform current distribution. The proposed model has been developed to account for these forces in specified parallel conductor configurations. The model also takes into account the skin effect impact on the individual conductor resistances and self inductances. The model is coded in a simple computer program which can be used to predict current distributions in electric glass melters and similar heavy current applications. Results obtained using the proposed model for a Scott-T transformer system with a variety of multiconductor cable configurations are presented in the paper for demonstration purposes. >

A research for application of HTSC to high magnetic field at 4.2 K

Some high-temperature oxide superconductors (HTSCs) exhibit their best electromagnetic transport property at 4.2 K, which can be applied to produce high magnetic fields. The adiabatic stability of Bi-2212 at 4.2 K is analyzed. A configuration of the composite Bi-2212 conductors which can be used in a high magnetic field magnet is suggested. The stability performance of bi-2212 silver-sheathed tape was studied experimentally. By using composite conductors, a 10 T HTSC coil which can be inserted into a NbTi-Nb/sub 3/Sn magnet of 15 T was designed, and the possibility of the application of HTSC to 30-40 T superconducting magnets is discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effects of meal and its electrolytes on bioelectrical impedance.

Bioelectrical impedance analysis (BIA) is a simple, reproducible and indirectly validated technique for the assessment of body composition1–3. It is based on the physical principle that the impedance (or conductivity) of a geometrical system is related to the conductor length and configuration, its cross-sectional area, and signal frequency4. Assuming a constant conductor configuration and using a fixed signal, the impedance becomes a function of conductor (body) volume. The conductive pathway is directly related to the water content of the body. Therefore, the conductivity is minimal in the less hydrated fat tissue and far greater in the fat—free body mass which contains virtually all the water and conducting electrolytes. In other words, the BIA is an index of total body water and evidently affected by the alterations in the concentration of conductive electrolytes5.

Further development of aluminum clad superconductors

A high-volume fabrication technique has been developed to clad conventional NbTi/Cu composite conductors with high-purity aluminum. A variety of sizes and shapes of practical superconductors has been clad using aluminum of initial residual resistance ratios ranging from 200 to 3000. In some of the conductor configurations a strengthening element in the form of a stainless steel wire or an aluminum alloy has been incorporated. The various conductor types investigated and their mechanical and electrical characteristics are presented. The advanced conductors developed will be particularly suitable for large magnet applications such as high-energy physics particle detectors, high-field MRI, and magnetic energy storage.

Specifying dry-type distribution transformers for solid-state applications

Existing theories, specification, and standards relating to the application of dry-type distribution transformers for solid-state applications are discussed. The criteria for selecting the proper transformer for several types of solid-state loads, such as UPSs, rectifiers, variable-speed drive systems, etc. are discussed. A significant set of computer-generated calculations that show the behavior of dry-type distribution transformers of various sizes and conductor configurations under both sinusoidal and nonsinusoidal conditions is presented. It is readily seen that improper selection of a transformer for a solid-state application may result in a serious reduction in efficiency as well as a large increase in temperature rises with detrimental effect on the expected life span of the transformer. A few experimental results from tests carried out on several transformers are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

TEM wave current distribution on two coaxial arc strips

The longitudinal current density in two coaxial arc-strip conductors surrounded by homogeneous dielectric is derived. The current density is found by converting a set of two coupled integral equations into a set of nonhomogeneous linear equations whose solution can be approximated by a single closed-form function. In the limiting case, corresponding to a two-conductor parallel-plate transmission line, a good agreement with previously published results has been verified. The method presented can also be used for treating other configurations of cylindrical conductors in the form of arc-sectors forming two- and multiconductor transmission lines.

Asymmetric, multi-conductor low-coupling structures for high-speed, high-density digital interconnects

Small inter-line spacings and high switching speeds emphasize the problems of crosstalk and coupling distortion in high-speed, high-density digital interconnects. The use of substrate compensation allows the design of structures in which crosstalk and coupling can be essentially eliminated, even for inter-line spacings of less than one center conductor width. Characteristics of this novel method are presented for both symmetric and asymmetric multiline geometries. Pulse distortion and crosstalk on a four-line, symmetric structure are analyzed, showing how crosstalk and coupling distortion are reduced by substrate compensation. Pulse distortion on symmetric coupled lines is studied, showing that it is possible to choose a substrate combination which significantly reduces coupling and crosstalk for a wide range of conductor configurations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A configuration-oriented SPICE model for multiconductor transmission lines with homogeneous dielectrics

Using the SPICE circuit analysis computer program to simulate a lossless multiconductor transmission line is investigated. It is demonstrated that for the case of a homogeneous dielectric, the multiconductor line can be represented by a system of standard two-wire lines which is not based on modal decomposition. This system is readily modeled with SPICE. While restricted to situations where the dielectric constant can be assumed uniform, the present method has the advantage of an intuitive relationship to the conductor configuration, simpler SPICE input data requirements, and an improvement in computer run time over other methods. >

Equivalent capacitances of coplanar waveguide discontinuities and interdigitated capacitors using a three-dimensional finite difference method

Equivalent capacitances of coplanar waveguide discontinuities on multilayered substrates are calculated using a three-dimensional finite-different method. The application of the method is demonstrated for open ends and gaps in microstrip and coplanar waveguides, as well as for more complicated structures such as interdigitated capacitors. The main advantage of the method is its flexibility in treating multilayered substrates and different conductor configurations. It can therefore be applied to more complicated structures such as interdigitated capacitors, air bridges, and waveguide transitions. The effect of conductor metallization thickness and shielding walls is also taken into account. Good agreement between the calculated data and measurements up to 25 GHz in the case of coplanar structures indicates the validity of the static analysis even for high frequencies. >

Results from AC transmission line audible noise studies at the Anneberg EHV test station

Results from single-phase test line audible noise measurements on various conductor configurations for transmission lines in the 400 kV range are presented. The predicted L50 audible noise levels are given as functions of the rain rate. After single-phase to three-phase conversion, a comparison is made with results from long-term measurements on an operating 400 kV line. It is shown that the long-term L50 audible noise level in rain can be predicted with sufficient accuracy from the test line measurements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Impact of high temperature superconductors on pulsed power systems

Some recent parametric analyses conducted on a series of alternative baseline designs of 5-50-MVA pulsed AC generators with low-temperature-superconductor, high-temperature superconductor, and cryocooled windings are discussed with emphasis of the influence of operating temperature from liquid helium to liquid nitrogen coolant system design, conductor configuration, and consequent energy economics of the machine. These are related to the projected performance of a novel conductor concept presently under development.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Lightweight power bus for a baseload nuclear reactor in space

Space environmental interactions with the power distribution/power processing subsystem can become a serious problem for power systems rated at tens to hundreds of kilowatts. Utilization of ceramic superconductors at 1000 A/cm/sup 2/, which has already been demonstrated at 77 K, in a conductor configuration may eliminate both bus mass and distribution voltage problems in a high-power satellite. The analytical results presented demonstrate that a superconducting coaxial power transmission bus offers significant benefits in reduced distribution voltage and mass. >

Application of air-break switches for de-energizing transmission lines

Results of an extensive evaluation and recommendations are presented for the application of air-break switches equipped with fast interrupting mechanical devices for line dropping on a 115 kV system. A computer study as well as field tests indicated that parallel lines have negligible effect on charging current. However, the current is affected significantly by conductor configurations. It was also found that high tip speed and minimum bounce of quick-break devices significantly increase the charging current interruption capability.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Self-consistent computations of the geometries of magnetically confined liquid metal columns.

In this paper, a modeling methodology is described which permits the computation of the cross-sectional geometry of a two dimensional column of perfectly conducting liquid in the presence of a magnetic field imposed by specified configurations of source conductors. The description is self-consistent in the sense that the column geometry results from a magnetic pressure corresponding to a magnetic field determined by the column geometry. Solutions are obained by iteratively calculating the magnetic field structure for a given column geometry and source conductors, and then calculating a new column geometry based on the magnetic stresses, surface tension, and pressure jump at the liquid-air interface. This loop is continued until a self-consistent solution is obtained. A quadrupole source magnetic shaping problem solved by Shercliff ushing conformal mapping is duplicated using the methodology described in this paper. The results obtained are in good agreement with those published by Shercliff. In addition, results are shown for arbitrary shaping problems, including levitation of horizontal columns, that are too complex for analytic solutions.

Energy Loss Mechanisms of Superconductors Used in Alternating-Current Power Transmission Systems

The intrinsic hysteretic loss of superconductors carrying alternating current has been derived from simple models and verified experimentally. In practical cable designs the losses are increased by surface roughness, conductor configuration, and added metallic components. When possible applications by electric utility companies are being considered, such losses are only one of many factors that must be adjusted in an optimization that produces the lowest cost(including both capital and operating expenses) during the lifetime of the system.

Analysis and design of single-pole transmission structures

The unguyed single-pole transmission structure is widely used to support transmission lines of up to 345 kV capacity. Most such structures are wood poles, although prestressed concrete poles and tubular steel poles are sometimes used in high decay or high load situations. A number of features combine to make this type of structure an interesting structural analysis and design problem. Whether naturally grown or manufactured, the pole structure is almost always nonprismatic. Wind, ice and snow loads acting alone or in combination are variable and occasionally severe in nature. Poles are slender and the combination of transverse wind load with vertical dead and ice loads often leads to behavior which is geometrically highly nonlinear. The continuous exposure to weather, fungi, accidents, etc. results in structures with capacities that often deteriorate very significantly with time in service. The material properties (strength, stiffness), especially of wood, are highly variable, as are the soil conditions. The configurations of conductors, davit and cross arms, and attachments that are in use vary widely. This large variety of structural shapes plus the necessity of changing the configurations of in situ structures to meet new conductor and clearance requirements prevents the use of only a few designs. Thus rapid ways to assess existing structures and to design new structures are required. Since there are more than 130,000,000 poles currently in use in single-pole and H-frame transmission structures and several million new poles are put into service each year, the design effort related to poles is large. As part of an eight-year effort to develop reliability-based design methods for transmission structures, a correct procedure for analyzing and designing single-pole transmission structures was established. Implemented in program POLEDA (POLE Design and Analysis), this procedure enables unguyed planar single-pole structures of virtually any material and configuration to be rapidly analyzed or designed. The analysis is based on the Newmark numerical technique which, it is shown, in the limit provides an exact solution to the differential equation for large deflections of transversely loaded beams. The four design options provided in POLEDA use the load and resistance factor design (LRFD) format. This permits the user to use current, deterministic, design procedures or to use load and resistance factors based on reliability studies. The program provides the necessary high-quality analysis capability which forms an integral part of reliability-based design. It is being widely adopted by the electric utility industry.

Application of Levinson algorithm for fault calculations in high phase order transmission systems

Ever increasing pressures against the construction of new high voltage transmission lines are forcing electric utilities to seek new ways of augmenting the power transmission capabilities of existing rights-of-way. One of the alternatives being contemplated is high phase order transmission, where the number of phases is raised from three to six, twelve or higher. In order to make full utilization of the idea, transmission line design with the phase conductors being located on the circumference of a circle is advocated. The primitive impedance matrix of such a configuration of phase conductors is a Toeplitz matrix and is also symmetric. A generalized approach based on the application of Levinson algorithm is developed in the present paper for the calculation of fault currents in an arbitrary N-phase transmission line. The fault currents due to faults involving any number of phases to ground are calculated using the algorithm. Results for six and twelve phase systems obtained using the method are included in the paper.