摘要:

The theoretical considerations in the choice of number of breaks are analysed and it is shown that, while for plain breakers multi-break construction may have its advantages, the more efficient the arc-control devices employed the less the advantages of additional breaks become with normal designs. In particular, it is shown that for a metalclad and cable system, the duty on one break of a multi-break controlled- arc breaker is almost as great as for that of a singlebreak unit. Experimental evidence in support of the theory advanced, obtained with cathode-ray equipment, is given.The development of a single-break 66-kV metalclad equipment is described, with particular reference to the interrupting ability, and test-results are given, obtained on four different short-circuit plants, showing consistent operation. The advantages to the user of the single-break oil circuit-breaker are shown by comparison with double-break designs of similar rating, and single-break layouts are described for different switching schemes and system voltages.In the Appendix an analysis is made of 3-phase cathode-ray films, showing that no leakage current is carried and that in consequence the observed reliable operation is to be expected.

DOI:10.1049/jiee-1.1936.0131

出版商:IEE    

年代:1936

数据来源: IET

摘要:

This paper contains an account of the advances in design and theory of the screened hot-wire ammeters described in 1930. The design has been improved both mechanically and electrically, leading to more compact instruments of lower impedance. These improvements have arisen from a more careful consideration of the temperature distribution in the hot wire, the behaviour of the magnifying system, and the corrections necessary at high frequencies. The results of experience with a number of experimental instruments are given and constitute a basis for any further designs that may be required.

DOI:10.1049/jiee-1.1936.0137

出版商:IEE    

年代:1936

数据来源: IET

摘要:

The paper describes a combination of beat-frequency oscillator and cathode-ray oscillograph so arranged that the oscillator output is rapidly varied in frequency over a limited range without appreciable change in amplitude, and, after passing through the apparatus whose response curve is to be measured, is applied to the vertical deflector plates of the oscillograph, the horizontal deflection being proportional to the frequency.A frequency scale is obtained on the oscillograph by means of piezo-electric crystals, so that the calibration of the instrument is unaffected by variations in supply voltages, etc.The variation of frequency is obtained by electrical means instead of by the usual rotating condenser, and the absence of mechanically moving parts renders the apparatus compact and portable.

DOI:10.1049/jiee-1.1936.0138

出版商:IEE    

年代:1936

数据来源: IET

DOI:10.1049/jiee-1.1936.0141

出版商:IEE    

年代:1936

数据来源: IET

摘要:

The magnetic properties of thin mumetal and permalloy “ C ” laminations have been determined with sinusoidal alternating magnetizing forces, and it has been found that for magnetizing forces of the order for which the d.c. permeability is a maximum, the a.c. permeability at, say, 50 cycles per sec. may be less than a tenth of the corresponding value with direct current; whereas for comparatively large magnetizing forces the a.c. and d.c. permeabilities are practically identical.The a.c. flux densities were determined by (a) a mechanical rectifier, (b) a cathode-ray oscillograph, and (c) the Maxwell and the Campbell bridges. Also, by means of the cathode-ray oscillograph, B—H loops were obtained at various frequencies up to 75 cycles per sec. It is shown that these loops become more elliptical as the frequency is increased; but it is pointed out that this is not due to the flux at a given point of the lamination becoming more sinusoidal, but to the average effect of a flux varying enormously in density and in phase over the section of the lamination.The method given in textbooks for calculating the mean flux density in thick iron laminations due to an alternating magnetizing force assumes the permeability to remain constant at a value equal to the maximum d.c. permeability. It is shown in this paper that such a method accounts for only a small fraction of the difference between the densities obtained with alternating and direct current; and it is suggested that a much closer estimate of the a.c. flux density may be made by using the differential permeability derived from the d.c. hysteresis loops instead of the maximum d.c. permeability.A peculiar dissymmetry was observed in the B—H loops obtained with alternating magnetization, this dissymmetry being most marked when the maximum magnetizing force was in the neighbourhood of that corresponding to maximum d.c. permeability. The dissymmetry was perfectly stable but could be reversed by the momentary application of a comparatively large magnetizing force. It could not be reversed by reducing the flux to zero and increasing it again to the original value. No explanation has been found for this phenomenon.The iron loss at 50 cycles per sec. was measured by the Maxwell and the Campbell bridges, and was found to vary approximately as the 1.7th power of the maximum flux density over a very considerable range of the latter.It is shown that although the impedance of an iron-cored choke may be balanced by a resistance and inductance in series in the Maxwell bridge, the flux linkages per ampere and, therefore, the maximum flux density for the same number of turns, may be far smaller for the equivalent inductance than for the actual choke; and the method usually given for calculating the maximum flux density for iron-cored chokes from Maxwell-bridge tests may be in considerable error. It is also shown that values of maximum flux density based upon the equivalent impedance, instead of the equivalent reactance, are in “reasonably close” agreement with those determined with the cathode-ray oscillograph. Further, the values thus calculated from the Maxwell-bridge results are in agreement with those obtained with the Campbell bridge.

DOI:10.1049/jiee-1.1936.0142

出版商:IEE    

年代:1936

数据来源: IET

DOI:10.1049/jiee-1.1936.0148

出版商:IEE    

年代:1936

数据来源: IET