摘要:

The review covers the two principal classes of technique for working on live, high-voltage power lines, respectively, ‘hot stick’ and ‘bare hand’. Developments to meet conditions in the UK are emphasised. The basic principles, to avoid flashover and to prevent the passage of undesirable currents in the workmen's bodies, are illustrated by descriptions of actual operations. The history of live working, which is largely North American in conception, covers its progressive application from relatively low-voltage distribution systems to UHV transmission. The levels of atmospheric pollution and humidity in places like the UK pose special problems of leakage and flashover which have necessitated research. Some of the results are described. The questions of exposure to electric fields and the need for protective measures such as conducting suits are considered. The long-established rule of thumb about currents in humans, that perception, local paralysis and possible fatality occur at about 1, 10 and 100 mA, is contrasted with the recent furore about the alleged consequences of imperceptible induction. Future developments towards live working at the highest voltages and in adverse climatic conditions are foreseen.

DOI:10.1049/ip-a-1.1981.0012

出版商:IEE    

年代:1981

数据来源: IET

摘要:

There have been two major engineering conferences in London which have covered the span of development of postal mechanisation in which the British Post Office has taken a leading part. This review gives the background to the decisions taken which have determined the course of postal mechanisation in the UK. It also comments on the world scene against which these developments have taken place and have been recorded by the papers and discussions at those two conferences spanning a decade of progress.

DOI:10.1049/ip-a-1.1981.0013

出版商:IEE    

年代:1981

数据来源: IET

摘要:

It has previously been shown that when arcs rotate over a copper cathode the erosion rate of this electrode rises and falls as the arc velocity is increased. In the paper it is shown that it is the magnitude of the transverse magnetic field and not the arc velocity, which determines the successive minima and maxima in the erosion rate. The erosion rates of cathodes of a number of materials are examined and for each the factor of increase in magnetic field strength is determined which is sufficient to cause successive minima and maxima in erosion rate. It is suggested that these variations, and similar variations found when the cathode-cooling-water flow rate is increased, arise from related phenomena in the oxide film on the cathode surface.

DOI:10.1049/ip-a-1.1981.0014

出版商:IEE    

年代:1981

数据来源: IET

摘要:

A description is given of the build up of polarisation charges at the interface of dissimilar media in a dielectric system, resulting from the sudden application of a DC electric field. The process is experimentally investigated by detecting the ponderomotive force acting on a solid dielectric located between the plates of an air-insulated parallel-plate capacitor. Measurements of such force, the variations of which take place in time scale ranging up to 105s, are presented and discussed. Based on a simplified model of the multilayer system composed of the solid dielectric and air, analytical solutions are given for the time dependence of surface charge densities as well as of ponderomotive force. The theoretical results of the analysis are compared with the corresponding experimental data for a few solid dielectrics.

DOI:10.1049/ip-a-1.1981.0015

出版商:IEE    

年代:1981

数据来源: IET

摘要:

With the increasing nonavailability of naphthenic crudes, attention is being turned to the manufacture of transformer oils from mixed-base Middle-East crudes, which incidentally happen to be rich in sulphur, and to present problems in producing oils with satisfactory electrical and oxidation characteristics. The Darius stocks, with relatively low sulphur plus CA(the proportion of aromatic carbon atoms in the oil molecule), possess excellent electrical properties while the oxidation stability needs upgrading. On the other hand the Arabian-mix stocks, with comparatively high sulphur plus CA, exhibit better oxidation stability. But since their electrical properties fall below the specified values, they require severe acid treatment which in turn adversely affects oxidation behaviour. In both cases, the oxidation stability can be improved by the use of antioxidants.

DOI:10.1049/ip-a-1.1981.0016

出版商:IEE    

年代:1981

数据来源: IET

摘要:

A counter has been used for the estimation of the mobility spectrum of positive large ions in the atmosphere of a laboratory containing high-voltage equipment producing positive corona. The form of the mobility spectrum is changed relative to that under natural conditions. The densities of ions of all mobilities, of the same polarity as the equipment, are increased. In conjunction with a small-ion counter, measurements have shown a saturation in the total density of large and intermediate ion mobilities, as a function of increasing corona voltage, in the presence of an increasing density of small ions. Measurements of the decay and recovery of ions of, respectively, the same and opposite polarity to the corona voltage, have shown that after corona ceases, densities of ions of opposite polarity which are initially very low, are very slow to recover, especially in the case of small ions. It is concluded that atmospheric ionisation conditions are disturbed for at least 1 h after operation of high-voltage equipment. Parallel experiments in the presence of negative corona show similar trends.

DOI:10.1049/ip-a-1.1981.0017

出版商:IEE    

年代:1981

数据来源: IET

DOI:10.1049/ip-a-1.1981.0018

出版商:IEE    

年代:1981

数据来源: IET

DOI:10.1049/ip-a-1.1981.0019

出版商:IEE    

年代:1981

数据来源: IET

DOI:10.1049/ip-a-1.1981.0020

出版商:IEE    

年代:1981

数据来源: IET

DOI:10.1049/ip-a-1.1981.0021

出版商:IEE    

年代:1981

数据来源: IET