DOI:10.1049/pi-a.1955.0012

出版商:IEE    

年代:1955

数据来源: IET

DOI:10.1049/pi-a.1955.0013

出版商:IEE    

年代:1955

数据来源: IET

DOI:10.1049/pi-a.1955.0014

出版商:IEE    

年代:1955

数据来源: IET

DOI:10.1049/pi-a.1955.0015

出版商:IEE    

年代:1955

数据来源: IET

DOI:10.1049/pi-a.1955.0016

出版商:IEE    

年代:1955

数据来源: IET

DOI:10.1049/pi-a.1955.0017

出版商:IEE    

年代:1955

数据来源: IET

摘要:

In actual operation, when a fault occurs on a fused circuit, this circuit will probably be carrying a load current, so that the fuse element will be at some temperature above ambient, and this will affect its operating characteristics under the fault conditions. Standard specifications of test do not take this into account, so that fuses are tested when initially at ambient temperature. Tests carried out on fuses with single-wire elements over a wide range of load and fault currents are described. These have shown the range and amount of the reduction in pre-arcing time caused by preloading; allowances for this reduction suggested previously do not appear to have been complete. The arcing time is also affected, and the transient voltage produced by the fuse when interrupting the circuit is reduced by pre-loading. Tests at a constant prospective current, with the instant of circuit closure varied throughout a half-cycle, have shown large variations in pre-arcing times and in transient voltages, both for pre-loaded and unloaded fuses. The temperature rise of the element centre for any load current has been calculated and verified by tests using temperature-sensitive paints. With a knowledge of this temperature, the reduction in the current-heat integral with pre-loading has been calculated and checked experimentally.

DOI:10.1049/pi-a.1955.0018

出版商:IEE    

年代:1955

数据来源: IET

摘要:

The arc melting of metals such as molybdenum, using the consumable-electrode process, is described. After a discussion of the nature, the shape and the stability of the arc, consideration is given to its behaviour inside a water-cooled copper mould when using a.c. and d.c. power supplies both under vacuum and in an argon atmosphere. The effect these factors have on ingot quality and on mould life is also discussed. The cause and detrimental effects of an unintentional electrical discharge which occurred in a prototype melting-plant are described in detail, and suggestions are made for minimizing the occurrence of the phenomenon. Experiments have been conducted to determine certain relationships between arc voltage, gas pressure and arc length for the high-intensity low-pressure molybdenum-depositing arc. The shapes of burn-offs are related to the current supply used: electrode-negative burn-offs are of two principal types, one conical and the other characterized by two drip-points; electrode-positive burn-offs have hemispherical ends; and a.c. burn-offs have almost flat ends. A theory is suggested to explain the configurations. The relationship between burn-off rate and current has been determined over a wide range of conditions; globule size was found to be related to the type of power supply used, and an explanation of this is included.

DOI:10.1049/pi-a.1955.0019

出版商:IEE    

年代:1955

数据来源: IET

摘要:

A variable-speed squirrel-cage motor has been a desirable aim since the general acceptance of a.c. supplies. The paper contains a description of a suitable and practically proved system of variable-frequency control for this and other purposes provided by a self-contained rotating frequency convertor, called the Speedmaster. The theory and application of this frequency convertor and some variants to a.c. variable-speed single- and multi-motor drives, utilizing different types of a.c. motors, are presented. Selected examples of actual equipments are included.

DOI:10.1049/pi-a.1955.0020

出版商:IEE    

年代:1955

数据来源: IET

摘要:

The operation of an induction motor at one-half normal speed against appreciable load, by means of unbalanced impedance in the secondary circuit, is shown to be a practicable possibility with accurately predictable characteristics. Precautions must be taken to prevent saturation of the main magnetic circuit of the machine, and in some cases it may be essential to limit the injection of low-frequency currents into the supply system. Simple solutions to these problems are described, and it is concluded that the method has sufficient merits to justify its use in certain applications where a speed reduction to about one-half the normal value is required.

DOI:10.1049/pi-a.1955.0022

出版商:IEE    

年代:1955

数据来源: IET