摘要:

The paper is based on an investigation of the degree of variation of results obtained in repeat tests in the simplest case of a single-break circuit breaker and fixed conditions of supply.It is shown that the difficulty of rating a circuit breaker is closely analogous to the difficulty a student would have if asked to determine the tensile strength of a specimen on a testing machine in which a concealed fulcrum of the lever system was moving in an unknown manner and varying the leverage over a range of the order of, say, 1 to 50.Curves are given, based on a large mass of data, showing the variations which occur in the individual maxima and the means of arc energy in groups of repeat tests, and startling conclusions are drawn as to the prohibitively large number of tests necessary to establish a rating with any reasonable degree of accuracy by the generally accepted commercial methods of testing.The investigation also throws light on the probable cause of some of the mysterious failures of circuit breakers that have been reported from time to time.On three-phase testing a slight reduction in the number of tests may be allowed, but this does not materially affect the general conclusion that the number necessary would be prohibitively large.A thorough investigation of all possible causes of variation, the development of formulæ and the determination of constants by test, appears to be the only way of solving the important and pressing problem of the rating of oil circuit-breakers.

DOI:10.1049/jiee-1.1927.0102

出版商:IEE    

年代:1927

数据来源: IET

摘要:

It is the usual practice to make the ratio of the radial thickness to the mean diameter of a ring about 1/10 to 1/15, so as to limit the error due to non-uniform flux distribution. The adoption of a ratio of this order is apparently based upon the work of M. G. Lloyd, who calculated the errors involved in the determination of the magnetization curve and of the hysteresis loss for various ratios of radial thickness to mean diameter. His calculations, however, were based on the assumption of constant permeability. It is shown in this paper that, when the variation of permeability is taken into account, the errors involved in the determination of the above-mentioned quantities are almost invariably either smaller or larger than those calculated by Lloyd.The paper discusses the influence of the ratio of radial thickness to mean diameter, and of reluctivity, upon:-(a) The relationship between the average flux density in the ring and the flux density corresponding to the average magnetizing force.(b) The relationship between the actual hysteresis loss in the ring and the hysteresis loss in the same volume of iron owing to the flux density corresponding to the average magnetizing force. The influence of the exponent ofBupon this relationship is also considered.(c) The relationship between the true hysteresis coefficient and that determined from a test performed with (1) an alternating-current supply, (2) a ballistic galvanometer.Reference is made to the desirability—under certain conditions—of using a higher ratio of radial thickness to mean diameter than is customary, in order that any error due to mechanical strain produced by punching, etc., may be reduced.

DOI:10.1049/jiee-1.1927.0106

出版商:IEE    

年代:1927

数据来源: IET

摘要:

The paper first gives a brief outline of the general conditions required and the means adopted for making the fullest possible use of the power available. Then follows a general survey of the actual conditions existing in the various parts of the Empire.The benefits derived from the use of hydro-electric resources are pointed out, and finally the way in which the productive efficiency and the general standard of living of the community may be raised is indicated.Maps have not been included in the paper, as the reproductions would have to be on too small a scale to be of much value. Readers are therefore advised to follow the paper with any good, large-scale atlas which may be available.

DOI:10.1049/jiee-1.1927.0107

出版商:IEE    

年代:1927

数据来源: IET

DOI:10.1049/jiee-1.1927.0115

出版商:IEE    

年代:1927

数据来源: IET