摘要:

The finite-element method is widely used for the solution of field problems but the method, as generally applied, suffers from the fact that it is not known how close the solution is to the actual value. This uncertainty can be reduced by providing a dual finite-element method which is so arranged that both methods together provide upper and lower bounds to the correct solution. It is found that the double approach also promises economies in the computation. The paper examines the physical basis of the dual method and applies it to Laplacian and Poissonian problems.

DOI:10.1049/ip-a-1.1983.0019

出版商:IEE    

年代:1983

数据来源: IET

摘要:

Eddy-current losses due to sinusoidal MMF are computed for square, circular, and rectangular rods using a rectangularB/Hcurve. for all sections, it is assumed that the induced currents flow on a path parallel to the sides. The results are normalised and given in a table from which many computation steps can be saved. The saturating induction is chosen as the value ofBwhich corresponds to a quarter of the applied magnetic field on the magnetisation curve. The validity of the hypothesis is confirmed by measurements made on 15 rings, constructed from mild steel, cast iron and special magnetic alloys. The power factor and losses are usually predicted within 10% for a field ranging from 200 to 70000 A/m.Résumé: Les pertes par courants de Foucault dans des tiges circulaires, carrées et rectangulaires sont analysées dans l'hypothese d'une courbe de magnétisation rectangulaire et sous I'influence d'une FMM sinusoïdale. Ceci conduit à une onde flux qui pénétre le matériau et qui y induit des courants paralléles á la surface externe. Les pertes et le facteur de puissance sont calculés et présentés sous forme de tableau. L'induction de saturation est choisie comme étant égale à I'induction correspondante au quart du champ magnétique maximum appliqué. Une série de résultats expérimentaux sur quinze noyaux montre que la théorie s'applique dans une large gamme de conditions: champs magnétiques de 200 à 70 000 A/m, pertes de 5 à 70 000W/m2et matériaux tels que la fonte et I'acier doux.

DOI:10.1049/ip-a-1.1983.0020

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The general expressions of the quasistationary electromagnetic field quantities, as well as the power loss, forces and torque, for a rotating cylindrical conductor in the proximity of a parallel straight wire carrying AC or DC, have been obtained by means of the magnetic vector potential, assuming a two-dimensional field. Specific motional field effects are shown explicitly in the DC case, when proximity factors and practical formulas of the losses, forces and torque are derived for values of motional depth of penetration large or small compared with the cylinder radius.

DOI:10.1049/ip-a-1.1983.0021

出版商:IEE    

年代:1983

数据来源: IET

摘要:

Roughly cubical specimens of about 5 mm side can be used for obtaining results which are believed to be correct within 10% For piezoelectric measurements, alternating mechanical pressure is used to produce a potential difference which is easily amplified and measured. A single specimen can be used for up to nine different measurements in compression and nine in shear; an alternative is the use of two specimens, tested only in compression. Permittivity along various axes can be measured with the same specimens. As an example, lithium niobate has been studied.

DOI:10.1049/ip-a-1.1983.0022

出版商:IEE    

年代:1983

数据来源: IET

摘要:

Lightning impuse (1.2/50 μs) and switching impulse (200/200 μs) breakdown phenomena in nitrogen and nitrogen/freon mixtures have been investigated for rod/plane gaps at total pressures up to 5 bar and spacings up to 100 mm with freon concentrations varying from 1 to 20% in the mixture. Results of breakdown voltages show that, in general, substantial improvement in breakdown strength can be achieved, particularly for negative polarities with the addition of small percentages (̃ a few per cent) of CCl2F2to N2. It is of interest to note that the characteristic ‘pressure effect’ in the positive point breakdown voltage against pressure curve observed in many strongly attaching gases is ill defined in these mixtures, and can be seen only over a limited range of experimental conditions. The corresponding effect for negative point breakdown is observed in these mixtures at the relatively low pressures of 2 to 4 bar for long gaps (>40 mm). The breakdown voltages for a 100 mm gap with the switching impulse at pressures greater than 2 bar are generally 20% lower than the corresponding lightning impulse data.

DOI:10.1049/ip-a-1.1983.0024

出版商:IEE    

年代:1983

数据来源: IET

摘要:

In the paper, a new method for the analysis and design of lightning protection systems for constructions and buildings against direct strokes is presented. while the theory of the method is discussed in the paper, its applications are presented in a companion paper with the same heading: ‘Part 2: Applications’. The theory is based on the study of the critical field strength values in nonuniform fields, and its applications to an electromagnetics model of the lightning stroke. The main goal of the paper is to give the electrical engineer a tool for the determination of the parts of the structure and its vicinity, which are exposed to lightning strokes. The probability of strokes which may hit the structure is valuable information in the design of a reliable lightning protection system.

DOI:10.1049/ip-a-1.1983.0025

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The behaviour of pressboard plates of 1 mm and 2 mm thicknesses immersed in mineral oil and stressed in the highly inhomogeneous electric field of a rod-plane gap under alternating voltages of the industrial frequency of 50 Hz is described. First, the partial discharges inception and breakdown voltages of the plates, measured under continuously increasing applied voltages, are given. Then the characteristic phases of the discharge development under applied voltages of each time-constant effective value are described in detail and conclusions are drawn as to the position in the test object, and the kind of partial discharges which appear with time. Also, the measured values of the discharge quantities are given. Finally, the measured relationships between life duration of the insulating plates and the relevant applied voltages of constant value are presented and some conclusions are drawn on the overall behaviour of the plates.

DOI:10.1049/ip-a-1.1983.0026

出版商:IEE    

年代:1983

数据来源: IET

摘要:

A simple general approach for the noise-loading analysis using more realistic nonlinear system modelling is presented. The memoryless bandpass nonlinear system is assumed to have both amplitude nonlinearity and AM/PM conversion, and the noise band is simulated by a set of equispaced equal-amplitude and randomly phased sinusoids.

DOI:10.1049/ip-a-1.1983.0028

出版商:IEE    

年代:1983

数据来源: IET