DOI:10.1049/ji-2.1948.0001

出版商:IEE    

年代:1948

数据来源: IET

摘要:

A rayon factory being essentially a chemical works, a brief description is given of the chemical process of making rayon. The manufacture of rayon is a steadily developing enterprise of comparatively recent times, and the electrical equipment used is treated historically as well as from technical and practical aspects.

DOI:10.1049/ji-2.1948.0002

出版商:IEE    

年代:1948

数据来源: IET

摘要:

Formulae are deduced for evaluating the increase in m.m.f. and power due to the presence of overlapping joints in a magnetic core under a.c. magnetization conditions, assuming that the magnetic material is homogeneous, and that its permeability is a constant quantity. The effect of hysteresis is considered, and the formulae appear to be applicable at frequencies in, at least, the power- and audio-frequency ranges.The investigation shows that a certain value of mean flux density exists, under constant-frequency conditions, for which the percentage increase of both the m.m.f. and the power loss attains a maximum value. The maximum value and the values of mean flux density at which it occurs increase as the frequency is reduced.Experimental results for both Mumetal and 4% silicon-steel have been obtained, and they serve to verify the general validity of the formulae which have been derived in the theoretical investigation.

DOI:10.1049/ji-2.1948.0005

出版商:IEE    

年代:1948

数据来源: IET

摘要:

In order to explain the discrepancies which exist between results obtained experimentally and those determined from the classical solution of the behaviour of ferromagnetic laminae when subjected to a.c. magnetization, a more rigorous solution has been obtained by taking account of the variation of both the permeability and hysteresis loop, with changes in the maximum flux density, throughout the thickness of the lamination.A method of harmonic analysis has been utilized to represent the relationship which exists, at any instant of time, between the m.m.f. and flux density across the section of the lamination, in order that the quantities of fundamental and harmonic frequency may be separately investigated. Calculations to determine the total iron loss have shown that, for the range of frequency and flux density covered, only the quantities of fundamental frequency need be considered in the more usual practical case of sinusoidal waveform of applied voltage, or alternatively, of sinusoidal excitation current.Contrary to the classical solution, it is shown that the m.m.f. and flux density at any point in the lamination are not necessarily in phase, even when the usual hysteresis effect is negligible. In consequence, an energy loss occurs which is additional to the usual conception of eddy-current and hysteresis loss. The physical explanation of the existence of the additional loss suggests that it may conveniently be designated as the “differential hysteresis loss.” The range of application of the theoretical expression for the iron loss is subject to an upper limit, corresponding approximately with the knee of the magnetization curve. An alternative solution is put forward for values of magnetizing force beyond this point.Tests have been carried out on samples of both Mumetal and silicon steel, to cover a wide range of frequencies and flux densities. The theoretical value of loss calculated from the new formulae accounts for the greater part of the measured value without introducing a fictitious value for the permeability. A comparison of the measured and calculated values gives a useful indication of the inhomogeneity of the material.It is noted that a reduction in lamination thickness results in an increase of the hysteresis loss and a reduction of the permeability, the latter effect tending to increase the eddy-current loss. This is of particular importance at low audio-frequency operation, where a reduction of lamination thickness can result in an appreciably higher total loss.

DOI:10.1049/ji-2.1948.0006

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The well-known discrepancy between the calculated value of the eddy-current losses in electrical sheet steels at supply frequencies and the experimentally observed value is discussed. The effect of the flux waveform distortion due to magnetic non-uniformity of laminations is examined experimentally and found to be small. It is shown, however, from experiments on a model, that inside each lamination the flux waveform distortion with alternating magnetization is severe, and is sufficient to cause the hysteresis loss per cycle to be strongly frequency-dependent. On the other hand, the discrepancy which occurs with alternating magnetization is found to be absent with a pure rotational flux where there are no waveform effects. It is concluded that, without having recourse to more elaborate explanations, the observed anomaly might be largely accounted for by the increased hysteresis loss brought about by internal flux waveform distortion, the true eddy-current loss being, in fact, not appreciably different from its calculated value.

DOI:10.1049/ji-2.1948.0007

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The paper gives the results of the authors' statistical analysis of tests made by the Safety in Mines Research Board (S.M.R.B.) to establish conditions of flameproofness of flange gaps for electrical gear for use in hazardous atmospheres. The chance of occurrence of an ignition of an external explosive atmosphere when an explosion occurs inside the flanged vessel, is found to increase approximately linearly with the size of the gap at the flanges. From a study of this variation of chance of ignition with flange gap, it has been possible to determine a gap which is safe within a certain approximately known risk, both for the case of a linear increase of chance with gap, and for the more accurate empirical law of variation of chance with gap deduced from the experimental data. Thus values of the statistical maximum safe gap are given for a number of hazardous atmospheres; these are such that, so far as can be determined, there is only a chance of the order of 1 in 1012that the true maximum safe gap is actually less than the value given.These data afforded a basis for the determination of the maximum permissible gaps given in B.S. 229: 1946.

DOI:10.1049/ji-2.1948.0008

出版商:IEE    

年代:1948

数据来源: IET

摘要:

This paper concerns the behaviour of earth resistances under h.v. currents. The author has tried to contribute to the explanation of the phenomena causing the decrease of the earth resistance and to check the effectiveness of giving to the earth electrodes the properties of edges or points. An explanation is given for the “breakdown” of the soil, based on the results obtained from the theoretical treatment of model earths. The analysis of the experimental results obtained on model earths leads to favourable conclusions as regards the use in practice of electrodes having the properties stated above. The direct discharges on the ground surface during lightning strokes and falls of overhead h.v. line conductors are considered and the corresponding resistances and currents are estimated. The results obtained lead to the suggestion that in some cases the special earthing of h.v. line poles is not necessary, either for the protection of these lines against lightning strokes or for the operation of the line-disconnecting devices during short-circuits to earth.

DOI:10.1049/ji-2.1948.0009

出版商:IEE    

年代:1948

数据来源: IET

摘要:

Voltage transformers having two secondary windings for connection to dual instrument burdens are discussed. After considering the vector diagrams under no-load and under load conditions, expressions are derived which enable the performance to be predetermined from the design data of the transformer. The influence of the burden on one of the secondary windings in modifying the errors at the terminals of the other secondary winding is investigated. From the analytical equations, further expressions are deduced to facilitate the estimation of the performance of a transformer when the results of standard tests are given. Finally, the calculated and measured errors of two transformers under various loading conditions are compared and are shown to agree.

DOI:10.1049/ji-2.1948.0010

出版商:IEE    

年代:1948

数据来源: IET

摘要:

After briefly dealing with train braking in general, the electrical characteristics of the regenerative brake are developed. The stabilizing line is introduced, giving the relationship between the armature current and the field current (regulation curve) to give stable regenerative braking into a receptive contact wire. Regenerative braking circuits employed in traction systems are indicated. By means of the stabilizing line theory their characteristics can be deduced, thus enabling their suitability to be judged.The requirements for good load-sharing in multiple-unit operation are dealt with and a method is described based on the theory outlined in the earlier part, which enables the matching of different locomotives of multiple-unit groups even when their excitation circuits differ.Results of service tests carried out on the 3 000-volt electrification in Natal, during which loads up to 1 600 tons were handled exclusively by the multiple-unit regenerative brake with regenerated outputs up to 5 000 kW, are briefly shown in a number of figures.

DOI:10.1049/ji-2.1948.0018

出版商:IEE    

年代:1948

数据来源: IET