Stability Of Coil Research Articles

Dynamic stability of helical and barrel coils in transformers against axial short - circuit forces

The axial instability of winding conductors is one of the frequent modes of short-circuit failures in power transformers. This paper throws a new light on this failure mode for helical and barrel coils and takes important steps forward in three ways:(i) recognising a new mode of possible failure.(ii) accounting for the dynamic considerations leading to the formula for calculating the mechanical resonance frequency which one must avoid in the design.(iii) calculating the critical strength of winding conductors which should not be exceeded.The conclusions here will help the design engineer to keep the transformer windings stable under short-circuit forces.

A 10 tesla toroidal field magnet system for general atomic's PGFR concept

General Atomic's concept for a reactor compatible superconducting toroidal field coil is presented. The concept employs bath cooled, copper stabilized NbTi conductor to generate 10 tesla at a nominal temperature of 4.4 K. The emphasis of this paper is upon the coil configuration, stability criterion, cryodynamic performance, and support of magnetic loads. The guiding principles of the design are fabrication economy, reactor compatibility, and operational reliability.

Magnet design of toroidal field coils for the UWMAK-Tokamak systems

The design of toroidal field coils for the UWMAK series of Tokamak reactor designs is described. These are cryogenically stable coils cooled in liquid helium to 4.2 K. Each individual turn of composite conductor of TiNb plus matrix conductor is epoxied into a groove in a thin disk structure. The magnet is divided into 12, 18 or 24 sectors; each sector is comprised of 15–20 thin disks which are spaced and bolted together to form a rigid structure with all disk surfaces exposed to cooling. The overall shape of each ‘D’ magnet sector is chosen so that only constant tension forces are present. Bending forces do occur but only near transition sections from the D to the central straight section of each coil. This method of rigid mounting should be compared with loose ‘jelly-roll’ windings on a central coil form, a more typical magnet fabrication technique. The design procedure is for the composite conductor TiNb plus copper (or aluminum) to be mounted in stainless steel (or aluminum alloy) disks. Full stability is obtained for strains less than 0.2% for steel support and less than 0.4% for aluminum supports based on stress-strain resistivity experiments in progress. The use of high purity aluminum conductor and high strength aluminum alloy structure reduces costs significantly dependent only on the orderly development of new aluminum TiNb composite conductors. The amount of TiNb is conservatively chosen to carry full current at 5.2 K although operation at 4.2 K is planned and full recovery to the superconducting state could be obtained with full current wire quantities selected at 4.3 K. This conservative choice doubles the amount of TiNb used at 8 tesla but provides an extra temperature rise of ΔT = 0.9 K above expected usual temperature excursions. Magnet safety and protection is based on the natural mutual coupling of many coils which are closely coupled to each other. If one coil loses current, the other coils increase their currents to keep the flux as constant as possible. The uncoupled flux and companion field energy would be discharged by a high voltage power supply temporarily set to discharge the one bad coil. Such sub-division and partial energy removal requires that there be substantial subdivision of coils into many separate dewars, so that problems can be isolated. An expression for the magnetic forces on sectioned toroidal field coils is given in closed form and is used to compute the shape of a specific coil. Data obtained here are shown to be in good agreement with those given by more complex procedures. The most severe structural design requirement is based on simultaneous loss of current in two adjacent sectors. The remaining sectors attempt to straighten out into a solenoid which compresses the structure between coils except beside the bad coil or coils where tension might exist. Such current loss in two adjacent sectors is considered an extremely unlikely occurrence since the discharge procedure mentioned above takes place in less than 1 min so that simultaneous refers to a 1 min overlap. Because of such rapid amelioration of the causes of current change and flux motion, no temperatures can exceed room temperature during the orderly shutdown of one or two coils. In general, the study illustrates that fully stable magnets using composite conductors should be engineered without major uncertainties according to straightforward scientific concepts. While subsequent designs will undoubtedly include improvements there is no reason to expect that superconductivity implies venturesome unknown TF coil performance.

Calorimetric measurement of enthalpy change in the isothermal helix-coil transition of poly(L-ornithine) in aqueous solution.

AbstractThe enthalpy change associated with the isothermal pH‐induced uncharged coil‐to‐helix transition ΔHh° in poly(L‐ornithine) in 0.1 N KCl has been determnined calorimetrically to be −1530 ± 210 and −1270 ± 530 cal/mol at 10° and 25°C, respectively. Titration data provided information about the state of charge of the polymer in the calorimetric experiments, and optical rotatory dispersion data about its conformation. In order to compute ΔHh°, the observed calorimetric heat was corrected for the heat of breaking the sample cell, the heat of dilution of HCl, the heat of neutralization of the OH− ion, and the heat of ionization of the δ‐amino group in the random coil. The latter was obtained from similar calorimetric measurements on poly(D,L‐ornithine). Since it was discovered that poly(L‐ornithine) undergoes chain cleavage at high pH, the calorimetric measurements were carried out under conditions where no degradation occurred. From the thermally induced uncharged helix–coil transition curve for poly(L‐ornithine) at pH 11.68 in 0.1 N KCl in the 0°–40°C region, the transition temperature Ttr and the quantity (∂θh/∂T)Ttr have been obtained. From these values, together with the measured values of ΔHh°, the changes in the standard free energy ΔGh° and entropy ΔGh°, associated with the uncharged coil‐to‐helix transition at 10°C have been calculated to be −33 cal/mol and −5.3 cal/mol deg, respectively. The value of the Zimm–Bragg helix–coil stability constant σ has been calculated to be 1.4 × 10−2 and the value of s calculated to be 1.06 at 10°C, and between 0.60 and 0.92 at 25°C.

Superconducting coils impregnated with Wood's metal

This report describes the stability of superconducting coils wound with fine multi-filamentary wires and impregnated with Wood's metal.The training effect and current degradation observed before impregnation are remarkably improved after impregnation. The instability of superconductin coils seems to originate in “wire movement” in the winding. In comparison with organic impregnants, low melting point-metals such as Wood's metal are effective impregnants in suppressing “wire movement” in the winding and in elevating the stability of superconductin coils, because cracks and voids do not exist in the winding owing to good osmosis in the melting state and coils are well cooled owing to good thermal conductivity.

Superconducting Coils impregnated with Wood's Metal

This report describes the stability of superconducting coils wound with fine multi-filamentary wires and impregnated with Wood's metal.The training effect and current degradation observed before impregnation are remarkably improved after impregnation. The instability of superconductin coils seems to originate in “wire movement” in the winding. In comparison with organic impregnants, low melting point-metals such as Wood's metal are effective impregnants in suppressing “wire movement” in the winding and in elevating the stability of superconductin coils, because cracks and voids do not exist in the winding owing to good osmosis in the melting state and coils are well cooled owing to good thermal conductivity.

HIGH-FIELD Nb3Sn SUPERCONDUCTING MAGNETS BY MAGNETIC-FIELD STABILIZATION

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The optical rotation and molecular configuration of synthetic polypeptides in dilute solution

The optical rotations of a number of synthetic polypeptides have been measured in a variety of solvents. For each polypeptide species, a number of copolymers of different D:L compositions have been examined. Several distinct types of behaviour have been found, which may readily be interpreted in terms of the relative stability of left-handed helices, right-handed helices, and random coils. In solvents that are not too polar (even for quite considerable departures from the enantiomorph) predominantly L polymers exist entirely as right-handed helices. The rotation of a right-handed helical form of several meso polypeptides has been deduced; this rotation varies somewhat from polymer to polymer but is not markedly dependent on the solvent. It appears that the solvated D and I residues on a meso helical polypeptide largely cancel out each other’s contributions to the rotation. The dispersion of the right-handed helical form of poly-DL-leucine has been derived.

The electrical stability of tubular inductance coils with deposited conductors

The electrical stability of tubular inductance coils with deposited conductors

The electrical stability of tubular inductance coils with deposited conductors

The electrical stability of tubular inductance coils with deposited conductors

Discussion on the two papers “The stability of inductance coils for radio frequencies” and “The electrical stability of condensers”, by Mr. Thomas, before the Wireless Section, 6th May, 1936

Discussion on the two papers “The stability of inductance coils for radio frequencies” and “The electrical stability of condensers”, by Mr. Thomas, before the Wireless Section, 6th May, 1936

Discussion on the two papers “The stability of inductance coils for radio frequencies” and “The electrical stability of condensers”, by Mr. Thomas, before the Wireless Section, 6th May, 1936

Discussion on the two papers “The stability of inductance coils for radio frequencies” and “The electrical stability of condensers”, by Mr. Thomas, before the Wireless Section, 6th May, 1936

The stability of inductance coils for radio frequencies

The paper gives an account of an investigation into the stability of inductance of coils used in radio transmitters and valve oscillators. It is shown that variation of temperature is chiefly responsible for instability, and data are obtained showing the value of the temperature coefficient of inductance for a number of modern coils of representative types, from which it is observed that this coefficient differs appreciably from the coefficient of expansion of the metal conductor. A theoretical investigation is made of the inductance variation produced by small changes in self-capacitance and in dimensions, together with an examination of the causes of mechanical distortion with temperature change. A critical study of existing methods of temperature compensation is presented and conditions for stability are established. As a result of the investigation, an experimental coil is described in which high stability is obtained by the application of these principles.

The stability of inductance coils for radio frequencies

The paper gives an account of an investigation into the stability of inductance of coils used in radio transmitters and valve oscillators. It is shown that variation of temperature is chiefly responsible for instability, and data are obtained showing the value of the temperature coefficient of inductance for a number of modern coils of representative types, from which it is observed that this coefficient differs appreciably from the coefficient of expansion of the metal conductor.A theoretical investigation is made of the inductance variation produced by small changes in self-capacitance and in dimensions, together with an examination of the causes of mechanical distortion with temperature change. A critical study of existing methods of temperature compensation is presented and conditions for stability are established.As a result of the investigation, an experimental coil is described in which high stability is obtained by the application of these principles.