摘要:

The mining industry is one of the largest producers and users of electric power in this country. It is generally assumed that the methods of production and utilization are not as economical as they might be. The following notes of some efforts to achieve efficiency and increase reliability, together with results of tests made with this end in view, may be of general interest.For the purpose of reference the paper is divided into three parts:—Part 1 deals with the general problem of power production at mines, giving briefly the essential differences between a colliery power plant and a normal power plant.Part 2 deals with the modern methods of supplying the four main power-consuming units at mines, with particular reference in each case to the question of the utilization of synchronous motors, and also discusses the advantages and disadvantages of alternating-current and Ward-Leonard control for electric winders.Part 3 gives the results of progressive conversion of several mines from steam to electric drive for the various main units and also the effect of supplying compressed-air power from a central station in a similar way to electric power.

DOI:10.1049/jiee-1.1925.0066

出版商:IEE    

年代:1925

数据来源: IET

摘要:

This paper analyses the form of various waves to be expected in rectified circuits, and by the general method of treatment the analysis could be applied to a pronounced commutator ripple. A specialized form of wave-form, due to a rectifier where a sharp cut-off of the current is to be expected, is also considered.

DOI:10.1049/jiee-1.1925.0078

出版商:IEE    

年代:1925

数据来源: IET

摘要:

In Part 1, it is shown that the problem of constructing a network the impedance of which shall be equal to the impedance of an infinite uniform telephone line, can be solved exactly by the use of a number of sections of simple artificial lines. The artificial lines described are intended entirely for use in this way, and since their propagation constants are widely different from that of the uniform line, they cannot be used as “artificial transmission lines” to which any terminal apparatus might be added.Some of the artificial lines can be used for attenuation correction.In Part 2, it is shown that related networks can be obtained such that when placed in series or in parallel with the infinite uniform line, the impedance of the combination is a pure resistance

DOI:10.1049/jiee-1.1925.0079

出版商:IEE    

年代:1925

数据来源: IET

摘要:

A method is outlined whereby known, small radio-frequency voltages may be produced. The method consists of an arrangement of a current transformer, across the secondary of which is a suitable resistance of known value. A thermo-junction or other device serves to measure or to set the primary current. Voltages from a few microvolts to a few tenths of a volt may be conveniently produced. The nature and extent of the errors of the method are discussed, and the precautions necessary to reduce these to a negligible amount are indicated. Various uses of the method are touched upon and the limitations of the method are given.An appendix gives a simple analytical treatment of the iron losses in the core of a current transformer at radio frequencies, in so far as these affect the ratio of the transformer. The phase displacement of the currents is, however, not discussed.

DOI:10.1049/jiee-1.1925.0080

出版商:IEE    

年代:1925

数据来源: IET