摘要:

The British Electrical and Allied Industries Research Association have undertaken a comprehensive research into the problems arising in the construction and uses of overhead electric lines. The research has been productive of valuable results.The present paper deals with two sections of the work: (1) as to the strength of wooden poles, single and compound, and (2) as to the intensity of wind pressures on wires and cables such as are used for overhead power lines and on the poles and lattice structures for supporting them.The tests on wooden poles disclosed a fundamental weakness in the usual design of compound poles and led ultimately to the development of a much improved design. Accurate figures were also obtained of the rupturing strength of red fir poles. The improved design of compound pole is described and the weakness of existing designs is pointed out.The wooden poles were tested under practical conditions. The information gained was supplemented by a series of tests on small-scale models, which confirmed the claims made for the greatly increased strength of the new designs of compound poles.The tests of wind pressures were made on wires of various sizes, on cylindrical sections corresponding to those of wooden poles and on angle bars and a lattice framework. Definite values of the coefficient relating wind pressure with velocity have been recorded by these tests, the figures being of considerable value to designers. Sufficient data have been obtained to enable, for the first time, a proper allowance to be made by the designer for wind pressures on wires and cylindrical poles of the sizes commonly used for electric power lines.A series of experiments to determine the wind pressure on angle bars is described. The results indicate that the wind pressure on a fabricated frame may be estimated from the data obtained by tests on standard sections.The work of the Association described has produced valuable results and the researches are being continued.

DOI:10.1049/jiee-1.1929.0016

出版商:IEE    

年代:1929

数据来源: IET

DOI:10.1049/jiee-1.1929.0017

出版商:IEE    

年代:1929

数据来源: IET

摘要:

This paper is supplementary to the paper on “The Attenuation of Wireless Waves over Land” which was read a year ago before the Wireless Section. It describes an experimental and theoretical investigation of the absorption of wireless waves produced by their passage over a town. In the course of the work the polar curve of signal intensity of 2LO was obtained and this curve was utilized to provide a revised signal-strength contour map of 2LO.Important differences between town attenuation and country attenuation are disclosed by the experiments. In particular, the absorption over the dense part of the town is found to increase extremely rapidly with the frequency of the waves.Aerials tuned for the reception of broadcasting in suburban districts are found to produce a critical effect on the attenuation in the neighbourhood of the common wave-length to which they are all tuned.Confirmatory experiments on short waves are described in an appendix, which also emphasizes the difficulty of calculating the resultant field strength in a region influenced by re-radiation from one or more receiving aerials.

DOI:10.1049/jiee-1.1929.0020

出版商:IEE    

年代:1929

数据来源: IET

摘要:

This report covers a research on the phenomena of so-called “contact resistance”. The research was carried out, on the suggestion of the E.R.A., by the Metropolitan-Vickers Electrical Co., Ltd., and the results show the nature and importance of contact phenomena, also their true bearing on resistivity and dielectric-loss measurements, and that certain conclusions reached by a previous investigator were exaggerated.The authors give a detailed account of a series of experimental investigations and describe the development of methods for the determination of the actual resistance and capacitance of the interface between electrodes and dielectrics.Section (I) of the report deals with two methods which demonstrate the existence of a potential drop across the contact face but which do not lend themselves to accurate quantitative work. A third method is described in which the potential distribution along a cylindrical specimen, subjected to a known d.c. voltage, is ascertained by means of exploring electrodes, and the contact voltage-drops deduced. From these, and the known resistance of the specimen, the contact resistances at each electrode are obtained in ohms per cm2. In the case of slate this was found to be 0.8 to 0.9 × 106, and fibre 5 to 9 × 106.Since the contact voltage-drop with direct current is not affected by direct-contact capacitance effect, a fourth method was developed in which the current and watt-loss were measured for a given a.c. stress of known frequency. From these measurements the equivalent series resistance and capacitance of the specimen can be calculated. The specimen was then machined down to a different thickness and similar calculations were made for a range of thicknesses. These factors plotted against thickness and extrapolated to zero thickness revealed the residual quantities attributable to the interface. In Table 6 it is shown that, over a wide range of power factors, the contact resistance does not vary greatly, it being of the same order as already determined.Ultimately the potential distribution method, previously adopted for direct current was modified for a.c. determinations and a large number of tests were carried out on slate, fibre and bakelite. Table 9 gives a complete summary of the results of 75 tests, including a number of check tests to ascertain the effect of frequency, voltage stress, humidity, temperature, surface leakage, roughness of surface and dirty mercury. Tests 53 to 69 were carried out with electrodes other than mercury. The results are important in that they reveal methods of obtaining better contact than can be obtained by the use of a simple mercury electrode.For comparative purposes the authors give in Table 11 the maximum, minimum and mean values of contact resistance and capacitance for normal conditions at 50 cycles and show that the agreement obtained between the two a.c. methods mentioned above is as good as the agreement obtained in different tests by any one method.The significance of the contact effect in relation to measurements on dielectrics is discussed, certain typical conditions being postulated and the percentage error in power factor and permittivity shown to be negligible except in the case of thin specimens of low-grade material. In the extreme case of a hypothetical material 1 mm thick, having a power factor of 80 per cent, the error attributable to contact impedance is shown to be 18 per cent, while in a more normal case where the power factor is 5 per cent and the thickness 1 cm, the error is appreciably less than 1 per cent.

DOI:10.1049/jiee-1.1929.0022

出版商:IEE    

年代:1929

数据来源: IET

摘要:

In this paper it is the author's endeavour to show not only that metering methods have played an important part in load-levelling, but that the load-levelling relay in connection with simple metering is a solution of the load-levelling problem.A considerable amount of attention and energy has been devoted to the ways and means of bringing about an improvement in the load factors of the various electricity supply undertakings; and as the load-levelling of the future will concern the distributing mains and consumers' supply services, the author suggests that it will be a problem for the mains and meter engineers rather than for the power station engineers.In order not to delve too deeply into the very complex metering problems, the paper has been limited to the following six considerations:—(1) Load-levelling by metering, with various tariff methods.(2) Load-levelling control at the generating station and substations.(3) Some attractive off-peak loads.(4) Load-levelling relays on consumers' premises.(5) General description of load-levelling relays.(6) Where load-levelling relays can be usefully employed.

DOI:10.1049/jiee-1.1929.0025

出版商:IEE    

年代:1929

数据来源: IET