摘要:

If the fullest advantage is to be gained from the rapid developments which have taken place in connection with radiant and high-frequency methods of heating, care must be exercised in the selection of the applications for which they are recommended. Although many processes can be carried out more effectively by the new methods, there is still a very real place for contact and convective heating. The purpose of the paper is to facilitate this selection.The paper first reviews the various methods of heating, indicating the physical laws and practical considerations by which they are governed and the rates of heating which may be obtained. An endeavour is then made to classify, in terms of their technical requirements, the types of application for which each process is best suited. Finally, several specific applications are considered in some detail, and it is shown that processes having a superficial similarity may never-theless possess features which are of sufficient importance to warrant the use of different methods of heating.

DOI:10.1049/ji-2.1945.0092

出版商:IEE    

年代:1945

数据来源: IET

摘要:

After giving an outline of the purpose which moisture meters are intended to serve, and of the various types which have already been described, the paper describes the development and construction of a new type of meter that has already been put to good use in several industries.A constant alternating voltage is applied to a sample of the material contained in a small vessel, which may be regarded as a fixed air condenser, or in some instances as a conductivity cell. The current passing through the material is measured by means of a sensitive thermionic ammeter of special construction, which can be adjusted to read the capacitance current, proportional to the dielectric constant of the material; the conductance current, proportional to its a.c. conductivity; or some function of both these currents. The current selected is that which shows the most favourable variation with moisture content.The use of the meter for testing seeds and grain, dried foods and flax straw is discussed, and typical results are given. Other applications are briefly outlined.

DOI:10.1049/ji-2.1945.0095

出版商:IEE    

年代:1945

数据来源: IET

摘要:

The paper reviews the problems of excess and fault current protection in so far as they may be solved by the use of h.r.c. fuses, or by developments based on these fuses. Following a brief commentary on two types of fuse (non-tripping and tripping) and on the fault-clearance ability of the cartridge fuse, consideration is given to the various forms of protection afforded. A survey is made of future possibilities, with special reference to a scheme for open-circuit protection, a new time-limit fuse with an accuracy equal to the h.r.c. cartridge fuse which may supersede the overload coil with a fuse in shunt, and a solution of the earth-fault protective problem. Consideration is also given to the selection of fuses for different duties, to the economics of fused switchgear, and to the need for fuse designers to attempt a greater measure of standardization.

DOI:10.1049/ji-2.1945.0101

出版商:IEE    

年代:1945

数据来源: IET

摘要:

The paper reviews existing methods of protection from excess load current in medium-voltage circuits, and outlines problems encountered with the wide variation of industrial applications. The need is stressed for full co-operation between engineers, and also between engineers and the user, in the control-gear, motor and distribution fields. B.S. Specifications dealing with excess current are considered, suggestions are made to correlate them, and a review is made of the main factors which determine the protection required. Motor starting loads, starting times, and various duty cycles, are mentioned, coupled with faults which can be caused by the inherent characteristics of some electrical equipment. Existing basic designs of overload relays, and some of the difficulties experienced with them, are dealt with. The effect of temperature variation on thermal and oil devices is outlined; also excess current due to lost-phase faults, with suggestions for the type of protection required to meet various circuit conditions. General design points are reviewed in the light of past experience and recent developments. The relation of equipment to both excess load-current capacity and short-circuit rupturing capacity is considered; also the correlation of fuses and overload relay design with the thermal rating of electrical gear in the protected circuit.

DOI:10.1049/ji-2.1945.0102

出版商:IEE    

年代:1945

数据来源: IET

DOI:10.1049/ji-2.1945.0107

出版商:IEE    

年代:1945

数据来源: IET

摘要:

The paper deals with steel-tank mercury-arc rectifier equipments developed and built in this country in recent years for the supply of high-voltage direct current for radio transmitters. The arrangements adopted, and the reasons for them, are described in detail; and an account is given of certain problems encountered in the development of these sets. The effect of the circuit adopted on some of the factors affecting backfire at high voltages is briefly discussed.

DOI:10.1049/ji-2.1945.0108

出版商:IEE    

年代:1945

数据来源: IET

摘要:

The paper describes the types of high-voltage steel-tank rectifier used in the higher-power radio stations constructed by the British Broadcasting Corporation, including a recent type of pumpless air-cooled equipment, and gives a review of their performance in service.Appendices contain some analytical and design data for the various types of rectifier connection used in practice, smoothing circuits, and grid-control features, with particular reference to stations in which rectifiers form the bulk of the load, and in which, owing to Class B modulation, the load on the rectifier fluctuates over wide limits at syllabic frequency.

DOI:10.1049/ji-2.1945.0109

出版商:IEE    

年代:1945

数据来源: IET

摘要:

The paper gives methods by which the principal performance characteristics of mercury-arc rectifier or inverter equipments that are likely to be of interest to operating engineers, e.g. regulation, power factor, magnitudes of harmonics, etc., can be quickly determined. The methods given are suitable for practical use, and can be applied without expert knowledge of rectifier circuit theory.

DOI:10.1049/ji-2.1945.0112

出版商:IEE    

年代:1945

数据来源: IET