摘要:

In many problems the resultant of a number of equal and equally spaced vectors is required in terms of their simple scalar sum. This relation is usually expressed in the form of a ratiof(Θ) = sin Θ/qsin (Θ/q),whereqis the number of vectors spaced over an angle 20.The vectors may be those of the electromotive or the magnetomotive force of the coils of an armature winding; the quantityf(Θ) is then called the distribution factor, and is of frequent occurrence in the theory and design of armature windings.The object of this paper is to discuss the principal mathematical properties of the distribution factor, and to give a complete series of curves exhibiting these properties in a form suitable for practical application.

DOI:10.1049/jiee-1.1922.0063

出版商:IEE    

年代:1922

数据来源: IET

摘要:

The calculation of the resistances of the sections of a starting rheostat for a series motor requires a knowledge of the magnetization curve of the motor, as well as a determination of two “grading” coefficients (of which one depends on the variation of flux, and the other on the variation of current, during starting). A number of graphical and analytical methods of calculation have been proposed, but these give the solution only for a particular number of sections. The method presented in this paper has the same order of accuracy as analytical methods, but it enables the grading coefficients corresponding to several numbers of sections to be obtained simultaneously from a single set of preliminary calculations, which are considerably simpler than those required with other analytical methods. The basis of the method is the use of charts of grading coefficients which are calculated for various numbers of sections, definite values of the percentage pressure-drop in the motor at full load, and given starting conditions. The grading coefficients for any particular motor are obtained by plotting on the appropriate chart a magnetization characteristic of the motor and determining the intersection of this curve with the appropriate curves on the chart. The complete calculation of a starter can be carried out in a few minutes. The method is particularly suitable for rheostat design departments, as the charts are of universal application. Charts of grading coefficients are given for all practical requirements for industrial control and also for seriesparallel control. A number of worked examples are included, illustrating the application of the method.

DOI:10.1049/jiee-1.1922.0064

出版商:IEE    

年代:1922

数据来源: IET

DOI:10.1049/jiee-1.1922.0066

出版商:IEE    

年代:1922

数据来源: IET

摘要:

The object of the investigation was to determine the amount of the contact resistance between the surfaces of an overlapping joint in rectangular straight busbar conductors of copper and aluminium under various conditions of surface preparation and pressure, and hence to ascertain the efficiency of such joints. An efficient joint was regarded as one in which the total resistance, which includes effects due to stream-line distortion, does not exceed that of an equal length of continuous conductor on either side of the joint. As a preliminary it was necessary to determine and allow for the effect of stream-line distortion under various conditions of overlap. Generally full-sized models were investigated, and the two surfaces with varying amounts of overlap were pressed together by means of an hydraulic ram or by bolts or special clamps. Numerical results are deduced and tables and graphs given for the contact resistance per unit of surface area under various conditions of pressure and amount of overlap, and after various modes of cleaning and preparing the surface, including the interposition of tinfoil or the soldering of the two bars together. A series of graphs are given which show the efficiency of copper and aluminium joints in terms of the above defined standard for a wide range of values of busbar sizes and for any value of specific contact resistance likely to occur under practical conditions, and hence the amount of overlap required to obtain an efficient joint. The efficiency of making joints by means of clamps and bolts was also considered and the pressure occurring at such joints estimated by comparison of the contact resistance obtained when the same joint was held together in the hydraulic press. The effect of modifying the numbers, size and position of the bolts used was also investigated.

DOI:10.1049/jiee-1.1922.0068

出版商:IEE    

年代:1922

数据来源: IET

DOI:10.1049/jiee-1.1922.0070

出版商:IEE    

年代:1922

数据来源: IET

摘要:

The paper deals with an examination, by means of the oscillograph, of the details of the current-changes in the auxiliary and line circuits of the Gulstad high-speed vibrating relay. The results include:—(1) Variation of the current in the two branches of the auxiliary circuit.(2) Resultant of the auxiliary currents determining the magnetization of the relay cores.(3) Influence of leak circuits.(4) Effect of a closed line circuit and operation of the line currents.The circuit connections used in the tests are given and a new type of frequency meter devised by the author is describe

DOI:10.1049/jiee-1.1922.0071

出版商:IEE    

年代:1922

数据来源: IET

DOI:10.1049/jiee-1.1922.0073

出版商:IEE    

年代:1922

数据来源: IET

DOI:10.1049/jiee-1.1922.0075

出版商:IEE    

年代:1922

数据来源: IET

摘要:

The paper deals with the performance of a commercial type of l½-kW spark transmitter. The electrical quantities in the various circuits are discussed, and experimental results are given which enable a complete analysis of the losses to be arrived at. Particulars of the performance of this type of installation under traffic conditions show that the type of signal emitted gives high commercial efficiency.

DOI:10.1049/jiee-1.1922.0077

出版商:IEE    

年代:1922

数据来源: IET

DOI:10.1049/jiee-1.1922.0079

出版商:IEE    

年代:1922

数据来源: IET