摘要:

The paper gives a general survey of the present stage of development of power rectifiers. Recent innovations in the design of rectifier types are described, and some of the limitations arediscussed.The subject matter mainly concerns rectifiers of the mercury-arc type, including water-cooled rectifiers, glass-bulb rectifiers, pumpless air-cooled steel-tank rectifiers, and igniter types. Thesevarious rectifiers represent a voltage range from 200 volts to 50 kV (d. c), and currents up to about 10 000 amperes. Reference is also made to some of the leading non-vacuum rectifiers, such as jet-wave rectifiers, gas-cooled arc types, and electrolytic and mechanical types. Most of these are still in course of development, and an indication of the progress achieved is given. The more direct methods of controlling the output of the mercury-arc rectifiers by means of control grids are mentioned, and in this connection voltage regulation, inversion, and arc suppression, are discussed.General features of rectifier equipment are considered, together with some aspects of rectifier auxiliaries. The scope and performance of rectifier installations are also indicated, special reference being made to railway electrification, highvoltage working, and the applications of grid control.Finally, some suggestion of the possible trend of future developments is given.

DOI:10.1049/jiee-1.1938.0161

出版商:IEE    

年代:1938

数据来源: IET

摘要:

The paper is submitted to a joint meeting of plastics chemists and electrical engineersas a contribution to a general survey of the field in which their activities meet. It consists of the following parts:—(i) A brief discussion of dielectrics and the factors which represent their value to the electrical engineer.(ii) A discussion of the essential nature of plasticity, and of the characteristics which the chemist has to produce when synthesizing plastics for the moulding industry.(iii) An experimental investigation of the properties of synthetic resins of the bakelite type, and the way in which their electrical properties may be affected by chemical and physical factors.(iv) A brief discussion of the various synthetic plastics now available, and of such of their properties as are of importance in electrical practice, with some general conclusions as to lines of research which may be expected to yield results profitable to both the industrial chemist and the electrical engineer.

DOI:10.1049/jiee-1.1938.0167

出版商:IEE    

年代:1938

数据来源: IET

摘要:

An account is given of the investigations on which were based much of the revision and, in particular, the new rating and voltage-drop tables, with Appendix 5, of the Tenth Edition of the I.E.E. Regulations for the Electrical Equipment of Buildings. The results of these investigations will, subject to the approval of the I.E.E. Council, be embodied in the next edition of the Regulations for the Electrical Equipment of Ships. This work, carried out partly at the National Physical Laboratory and partly at the E.R.A. auxiliary laboratory, dealt mainly with the effect of alternating current instead of direct current; of new modes of installation such as heavy cables in cleats, large groups of cables in conduits, ducts, chases, and surface wiring systems; the use of bare copper rods, long vertical runs in chases or shafts, etc.; and with the effect of steel bulkheads or steel-reinforced concrete structures in proximity to a. c. systems. While the earlier figures of the Ninth Edition were largely confirmed as general averages for certain conditions, a large number of new circumstances were investigated in detail, and the values observed were theoretically substantiated to the accuracy permitted by the conditions. The main purpose of the paper is to indicate the more accurate figures on which the necessarily condensed average tables of the Regulations are based, but the detailed results have also other applications.The experimental work is classified broadly in three sections, as follows:—(a) The current-carrying capacities of large cables run in air in various configurations.(b) Effects due to proximity of large cables to steel structures. In this section of the research, cables were run parallel to a steel plate, through holes in a steel plate, and through a steel-rod structure (to simulate reinforced concrete). Tests were made on both singlephase and 3-phase systems.(c) The properties of small rubber-insulated cables (sizes up to 0.5 sq. in. were included in some conditions of test) installed in a variety of methods such as in conduits, ducts, etc.The results of the investigations show that the reduction in current-carrying capacity due to skin effect and sheath losses is only serious in cables of 0.5 sq. in. conductor section and above. The increase in current rating due to better cooling conditions when cables are spaced farther apart may be partially or wholly counterbalanced in lead-covered cables by increase in sheath losses. In the case of bare copper rods run vertically, the temperature of which may be higher than that of insulated cables, it was found that excessive heating of rubber-insulated cables connected to the rods occurred near the joints.When cables carrying alternating current are run close to a steel plate the impedance is increased, and in some cases the effect on the voltage-drop may be sufficient to necessitate reducing the current rating of the cable below that based on the permissible temperature-rise. Also, in the case of a reihforced-concrete building, steelwork may be so heated owing to heavy currents in large cables as to cause serious expansion.

DOI:10.1049/jiee-1.1938.0169

出版商:IEE    

年代:1938

数据来源: IET

摘要:

The developments in cable practice since the previous rating tables were issued are treated from the aspect of their effect on current rating or carrying capacity, and the basis of the new rating tables is described. These tables are given, together with means for calculating the rating of cables installed in any of the usual modes.

DOI:10.1049/jiee-1.1938.0170

出版商:IEE    

年代:1938

数据来源: IET

摘要:

The paper describes how rotational hysteresis loss in small disc samples of sheet steel may be measured in a simple manner a new method, the loss being determined directly without the inclusion of eddy-current losses. The difficulty in the way making measurements on a single disc, due to the magnetic anisotropy of the material, is indicated. The magnetic anisotropy in commercial electrical sheet materials is then briefly discussed, and it is shown how by use of a sample made up of three similar discs the experimental difficulty may be overcome.The observed results on four electrical sheet materials are then given.The loss, plotted against flux density, is seen to fall rapidly towards zero near saturation, as has been found for various ferromagnetics by other investigators, but a sharp increase in loss, hitherto unreported, is shown to occur, for all four materials, at a point near the “knee” of the magnetization curve. A qualitative explanation of this phenomenon and of the general form of the loss curve is given on the basis of the “domain” theory of ferromagnetism.

DOI:10.1049/jiee-1.1938.0172

出版商:IEE    

年代:1938

数据来源: IET