Flat Conductor Research Articles

Effect of temperature on the breakdown voltage of paper-covered conductor impregnated with various liquids

Lengths of flat copper conductor insulated with aromatic polyamid (aramid) tape or cellulose tape were bent into rings and secured around the edge of discs. Two discs were placed edge-to-edge in one plane and breakdown voltages were measured between the conductors. The conductor assemblies were dried under vacuum, impregnated and immersed in several low-flammability liquids at temperatures up to 180 degrees C under air. Comparisons were made with mineral oil which was tested up to 130 degrees C under nitrogen. With the discs set to provide a 1-mm liquid gap between the insulated conductors, the variation of breakdown voltage with temperature is limited to a few percent and values tend to their highest at 80 degrees C for both AC and lightning impulse. With the conductors in contact, alternating breakdown voltages vary little, whereas impulse voltages fall appreciably with temperature rise, especially for cellulose.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Computer Power: Part 1: Distribution of Power (and Communications)

Power and communications wiring can be brought to computers and computer terminals in a variety of ways. Each method has its strengths and weaknesses; some that are ideal for one library may be forbidden another. Options include use of extension cords, perimeter raceway (such as conduit, wiremold, and armored cable), and interior raceway (such as underfloor duct, flat conductor cable, and power poles). Three sidebars discuss 1) the National Electrical Code; 2) volts, amps, watts, etc.; and‐3) transformers, circuit breakers, and circuits.

Twisted coil geometry in plasma confinement devices

Twisted coils, ie., coils for which windings do not lie in a plane, are used widely in plasma confinement devices, especially those in the general class of stellerator-type devices. In the design of these devicesad hoc expressions for the positions of turns and the outer envelope of the windings are usually assumed. However, these expressions do not correctly represent the true shape taken by windings as successive turns and layers of turns are applied to a curved surface. In the present work, the techniques of differential geometry are used to determine the actual location of turns as they are wound on arbitrary surfaces. In the process, a set of natural winding coordinates is derived; the Biot Savart law for calculation of magnetic fields is expressed in terms of these natural coordinates. Next, the advantages of using a class of surfaces, called developables, for winding surfaces are discussed. A particular developable, called the rectifying developable, offers the additional advantages that the turns on it are geodesies and that wide flat conductors can be wound on it to minimize bending strains. Finally, the problem of windings with conductors of finite thickness is briefly discussed.

Electro-ceramic stack

A transducer of acoustic energy through a water medium is fabricated in a manner which assures high reliability yet significantly reduces cost per unit by including modified conductive elements. A pair of flat conductors are interleaved sinuously through a ferroelectric stack in a mutually orthogonal relationship. The conductors are so interleaved as to electrically couple the elements of the ferroelectric stack in parallel in accordance with proven transducer design. At least one rod axially extends through the sandwiched ferroelectric elements and conductors to hold them in compression and to assure a reliable electrical connection for producing an integral hydroacoustically cooperating structure.

Current distribution in conductors in the vicinity of magnetic bodies

Magnetic bodies in the vicinity of current carrying conductors influence the distribution of currents. This paper presents an exact solution of the current distribution in a wide flat conductor in the presence of periodically spaced magnetic rectangular bars. The magnetic bars are placed at an arbitrary distance from both sides of the conductor. The solution clearly defines the distances where magnetic bodies have considerable influence on the distribution of current and on the conductor impedance. Experimental results closely confirm the theory.

The influence of magnetic materials on the distribution of currents in conductors

The use of magnetic materials near the surface of current carrying conductors is of interest. A very noticeable change in the current distribution in flat conductors is found using rectangular magnetic bars. The current tends to concentrate at the air-gaps between the magnetic bars. Experimental results closely confirm the theory.

Redistribution of current in flat conductors using magnetic bars

Current carrying conductors, partially covered with magnetic materials, exhibit interesting properties and have a number of possible applications. This paper investigates the very noticeable change in the current distribution in flat conductors when using rectangular magnetic bars close to their surfaces. The current tends to concentrate at the air gaps between the magnetic bars. The theoretical solution is obtained by separation of variables. The effect of different parameters on the current distribution and conductor impedance is determined. Different approximations are compared with the exact solution.

FINITE‐ELEMENT SOLUTION OF STEADY‐STATE SKIN‐EFFECT PROBLEMS IN STRAIGHT FLAT CONDUCTORS

Using an integrodifferential approach to steady‐state skin effect problems, the current density distribution in straight flat conductors is solved by the finite‐element method. The approach takes into account a combination of one‐dimensional finite elements corresponding to the flat conductors and triangular finite elements for the remaining domain outside conductors. The results obtained for a flat conductor placed inside a ferromagnetic medium are compared with analytical solutions provided by finite Fourier transforms. As a final output, besides current density distribution, one can calculate parameters useful to designers such a a.c. resistance and reactance of the straight flat conductors.

Critical current behavior in bending and tensile stressed Nb&amp;lt;inf&amp;gt;3&amp;lt;/inf&amp;gt;Sn composites at temperatures below 4.2 K

Critical current measurements were obtained on bronze-diffused reacted Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn multifilamentary conductors as a function of mechanical stress loads and applied transverse magnet fields up to 13 T for temperatures in the range between 4.2 K and 1.9 K. To simulate the winding handling of reacted Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn wires for superconducting magnets, operated in normal or superfluid helium the effects of room temperature bend strain on current carrying capacities of monolithic and flat cable conductors were investigated by controlled winding processes using mandrels with various diameters. The results show a field-dependent degradation in critical current with increasing bend strain for both conductor types. Only a very small precompression effect (< 0.5%) on critical current is observed. At higher strain, beginning at 0.4%, the critical current decreased rapidly, reaching at 13 T by more than 50% at a bending strain of 0.9% calculated on overall conductor cross section. Both optical and scanning electron microscopy were used to examine the samples before and after testing. Additional data on the mechanical properties (tensile stress-strain diagrams) of Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn samples are presented, along with some preliminary critical current versus uniaxial tensile stress measurements at 2.2 K and 4.2 K, respectively. First results indicate that the increase in critical current at 2.2 K is relatively larger (about 25%) than that at 4.2 K. This fact is interesting for Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn magnets cooled with superfluid helium to obtain a broad strain tolerance.

Elimination of the Skin Effect Error in Heavy-Current Shunts

A mathematical analysis of the transient skin effect in tubular and flat conductors has led to the development of a theory of ideal heavy-current shunts immune to the measuring error caused by this effect. A general expression was derived for calculating a profile of the measuring circuit laid inside the shunt wall that would give a step response undistorted by the skin effect. A model of the new shunt ws examined with a current step; the recorded response followed the applied pulse form.

New magnetic command system for a 200-kA circuit breaker with 10-μs current transfer time

We present improvements of the previously described command system of a 200-kA circuit breaker with 10-mus current transfer time. It uses the magnetic pressure produced by a high-current pulse sent through two flat conductors instead of a coaxial circuit. The necessary command current is cut in half and the standoff voltage is higher.

A new model for the flat conductor electromagnetic SAW transducer

Previous models for Rayleigh- and Lamb-wave electromagnetic transducers have been based on the assumption that the current distribution in each transducer conductor is uniform. We present solutions for the dynamic magnetic fields surrounding an array of flat conductors above a ground plane in which the current distribution is allowed to vary. The resulting solutions are used to calculate space-harmonic curves and to derive a new transducer model including electrical inductance, eddy current resistance, acoustic impedance, and transducer efficiency. A direct analogy to the interdigital transducer is established. For fundamental frequency operation, this model is nearly equivalent to previous flat field models, provided the conductor width/spacing ratio is 1/2 or less. For harmonic transducer operation, the present analysis is substantially different from other models and it matches data more accurately. A method for measuring the individual insertion loss of dissimilar transducers in a lossy medium is presented.

Fields of Flat Conductor Electromagnetic Surface Acoustic Wave Transducers

Fields of Flat Conductor Electromagnetic Surface Acoustic Wave Transducers

Frequency-dependent inductance and resistance of foil conductor loops

For both economic and technical reasons, flat thin conductors are of increasing interest in coil-winding. A problem is that at relatively low frequencies the current flow may may be nonuniform over the conductor cross-section. Both inductance and resistance of coils become frequency dependent. We have developed a new and general calculation of these effects, using a circuital model, for a single turn of a foil coil. The nonuniform current flow is described. We show that the extra losses due to this increase with the square of frequency, and that there is a small fall of inductance with increasing frequency.

Ultra high-current superconducting cables for a 2.2-tesla, 300-kilojoule energy storage magnet

We have built and tested two types of superconducting cables to be used in pulsed energy storage magnets for the LASL Magnetic Energy Transfer and Storage (METS) program. These 2.2-T, 300-kJ magnets are to operate at 10 to 12 kA with a safety factor in critical current of about 50% at 10 kA. The conductor must exhibit low losses in addition to being stable. Magnetic Corporation of America (MCA) designed a flat conductor using 1224 copper-matrix, monofilament wires combined in two stages of cabling followed by two stages of flat braiding. Two of these conductors were constructed, one with wire already on hand and the second using wire made specifically for this application. Intermagnetics General Corporation (IGC) designed two rectangular conductors using 315 and 319 mixed-matrix multifilament wires combined in three stages of cabling followed by compaction in a Turk's head. The maximum transport current capabilities (I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</inf> ) of these cables were measured in hairpin shaped samples with the straight section under test in perpendicularly applied fields. The measured results at 2.5 T for the two MCA cables were 11.7 kA and 15.4 kA, and for the IGC cables were 18.2 kA and 19.3 kA (extrapolated). In addition, samples of the compacted and uncompacted major strands from the IGC cables were tested. The results of these measurements are compared with values of I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</inf> calculated from the single-wire critical currents taking into account the adjacent conductor fields and the cable self-fields. Several causes of degradation of I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</inf> in the compacted cable are discussed including those due to experimental factors.

Magnet coil tests with multiple soldered niobium-tin filament conductors

Flat conductors with Nb 3Sn/Nb filaments, prepared by the solid state diffusion process were investigated for degradation after bending and tensile loading. Proportionality was found between the critical bending diameter and the distance of the filaments from the neutral zone. Four conductors with rectangular cross-section were stabilized by soldering in parallel to copper foil; coils were then wound and tested in the magnetic field of a niobium-titanium magnet. Measurement of the quench currents confirmed that the conductors were not damaged by the manipulations required. The 5% decrease in currentcarrying capacity compared with short sample measurements is ascribed to the more unfavourable cooling conditions in the coil. Individual conductors with a larger number of filaments now available for further tests are reported.

Limiting currents in the compression of magnetic flux between flat and coaxial conductors

Experiments are described on magnetic flux compression by flat and coaxial conductors. As the initial current I0 is increased the final current I1 obtained as a result of flux compression at first increases proportionally to I0 and then reaches a maximum and remains constant for further increases in I0. Analysis of the experiments shows that in coaxial structures when a small explosive charge accelerates the conductors the limiting current is determined by the maximum work which a conductor can perform in compressing the magnetic field. In experiments with flat busbars and large explosive charges the limiting currents appear to be determined by the flux losses in short-circuited voids formed in the linking of irregular surfaces of the busbars. This assumption is shown to be in qualitative agreement with experiment.

Temperature-dependent resistivity of a flat conductor and the temperature, current, and electric field patterns

Characteristic physical quantities have been determined as functions of the nonlinearity criterion and the frequency criterion for a flat conductor heated by a current having stationary and current distributions but temperature-dependent conductivity.

Mutual coupling in a finite planar array of circular apertures

Equations are presented for the calculation of the interelement mutual coupling in a finite size planar array of waveguide-fed apertures in an infinite flat conductor. The general mutual admittance expression is evaluated for circular apertures and the mutual coupling calculations are verified experimentally for two <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TE_{11}</tex> mode excited apertures. Qualitative agreement between calculations for a 183 element array and an infinite array establishes the validity of the finite array theoretical model.

High-frequency wave propagation between parallel surfaces very close together

In a dielectric medium between parallel flat conductors it is usual to consider high-frequency wave propagation in terms of TEM theory, and this is certainly applicable with good accuracy when the separation between the surfaces exceeds about one-thousandth of an inch. For smaller separations the surface-wave content of the field becomes a significant factor, even for smooth, bare metal boundaries. Ultimately the transverse field decay across the width of the slot becomes dominant and causes a rapid increase in both the attenuation and phase-change coefficients. The situation may be interpreted physically as a direct consequence of the need to maintain, within a very small space, the electric field in the direction of propagation of the wave. This behaviour is examined, and illustrated by considering specific examples.