DOI:10.1049/ji-2.1948.0094

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The many methods so far developed for predetermining the regulation of alternators all depend on a theoretical approximation to the m.m.f. and flux distributions occurring under full-load conditions. In general, the better the approximation the more accurate (and more complicated) is the method. Estimation of the flux distribution is difficult owing to the different reluctances of the magnetic paths, and to saturation and leakage.The paper shows that a simple test may be carried out on an alternator at low speeds under such conditions that the m.m.f. and flux distributions of a given full-load case are reproduced exactly. The necessary conditions are readily calculated for any given machine, and only a relatively small output is needed from the prime mover.The method described in the paper is applicable to both single-phase and polyphase alternators an to cylindrical, salient-pole and inductor types. It may also be used to predetermine other alternator load-characteristics.The results obtained by the method, when compared with those of direct load tests, indicate that the errors are of the same order as the possible experimental errors.

DOI:10.1049/ji-2.1948.0095

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The paper is concerned with assessing the suitability of spark-gaps for the measurement of the amplitude of short-duration recurrent impulses. Measurements are described which were made on a range of gaps between 2-cm diameter spheres, using recurrent impulses of from 4 to about 1/10 microsec duration, at recurrence rates from 3 000 to 100 per second.The breakdown voltage of the gaps tested was found to be independent of both impulse duration and recurrence rate within the limits of experimental error, and the calibration data obtained agree with the corresponding data given in B.S. 358 : 1939 for gap lengths greater than 0.2 cm. In obtaining these results it was necessary to irradiate the gap by means of 0.2 mg of radium.Measurements were also made on a range of gaps between parallel-plate electrodes with 1.0 microsec impulses repeated 400 times per second. For gaps greater than 0.2 cm in length, irradiation by 0.2 mg of radium produced no effect on the breakdown voltage, and did not appear to be essential for the satisfactory use of such gaps.

DOI:10.1049/ji-2.1948.0096

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The paper gives a practical explanation of the behaviour of power transformer windings subjected to incoming lightning and switching surges.A method of analysis is developed covering practical transformer windings, of various types and ratings, subjected to applied surges of various shapes. Stress distribution, and the ultimate breakdown strength of the complete transformer, are determined.This analysis leads to conclusions concerning methods of improving the surge strength, such as by electrostatic shielding or by stress control. These conclusions are substantiated by low-voltage surge-distribution tests, and by full-scale tests to destruction. Examples are described.Finally, so that the results of this work may be realized in practice, certain changes in purchasing specifications for transformers are suggested

DOI:10.1049/ji-2.1948.0101

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The construction is described of a voltmeter circuit suitable for the measurement of d.c. 50-c/s peak, and 50-c/s r.m.s. voltages. This circuit has a range of 200–1000 volts, and can be used with a reistance potential divider for measurements up to 120 kV. It consists essentially of an electrostatic instrument in combination with a diode rectifier and a reservoir capacitor. With the present apparatus the accuracy of measurement is estimated to be within ± 2% for d.c. voltages and ± 3% for 50-c/s voltages. Peak factors should be measurable to ± 1%, and ripple voltages on d.c. supplies to within 10% of the ripple, i.e. to 1% of the full voltage for 10% ripple.

DOI:10.1049/ji-2.1948.0105

出版商:IEE    

年代:1948

数据来源: IET

摘要:

Motors with solid-iron secondaries include both induction motors and, during their starting period, synchronous motors with solid poleshoes. They have peculiar characteristics arising from the fact that the secondary impedance values alter according to the slip; moreover, their relationship to slip is a complicated one owing to large variations in permeability. The object of the paper is to provide a theoretical treatment leading to the equivalent secondary impedance at any stated value of slip. The starting and running performance of the motor can then be calculated by known methods. The effects of using secondary material of higher or lower permeability and resistivity are considered, and the ideal combination of these values is established. This leads to an examination of the effects produced by adding copper to the solid iron, either as bars or end-rings, and the method of calculating the performance of such machines. The running characteristics are compared, and equivalent circuits and current locus diagrams are given.The most important application of the work is to salient-pole motors with solid pole-shoes, where equivalent pole-face impedance values must be determined for both direct and quadrature axes. These quantities are modified by the addition of copper end-rings or by the milling of grooves in the pole face, and the method of obtaining the modified values is developed.

DOI:10.1049/ji-2.1948.0107

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The scale of growing covered by commercial market-gardening and nursery production, and by amateur gardening, offers wide scope for the application of electricity in ways which contribute materially to the prosecution of these activities. Such applications are regarded in two main categories: those concerned with actual growth processes, e.g. soil warming, space heating and illumination, and those for ancillary purposes such as soil sterilization, pest destruction and water pumping.Soil warming is now largely effected by the low-voltage transformerfed system and is applied to hotbeds, propagating beds and benches, to cloches, and to beds and borders in glasshouses. It provides an economical way of producing localized warmth in such particular cases and by so doing can sometimes result in other economies, e.g. in space heating.Electrical space heating of glasshouses must be handled very carefully and at present can be applied with justification only in certain classes of glasshouse work, principally in the high-grade propagating house and the amateur's greenhouse.Electrical methods are already improving the technique and simplifying the operation of various sterilizing processes, both of soil and of plants, and certain possibilities of future developments are discussed. Electricity also offers considerable mechanical aid in the form of water pumping, ventilation, lawn-mowing, etc., and there is a distinct possibility that methods will be developed for the successful operation of small-plot cultivating appliances.

DOI:10.1049/ji-2.1948.0111

出版商:IEE    

年代:1948

数据来源: IET

摘要:

Modern contactor design is reviewed and reference is made to the influence which various applications of contactor type control gear have had on design and development.After a general survey the special considerations appertaining to motor-control duty are examined in detail, having due regard to the extreme cases which frequently occur in practice. Arc control and contact developments are mentioned, and a short discussion of the oil-immersed contactor follows with particular reference to its use in chemical plants and for high voltage. Some special contactor designs are discussed, as well as the problems arising in connection with the control of electric furnaces. A short résumé of the desirable features of contactor auxiliary switches concludes the paper.

DOI:10.1049/ji-2.1948.0114

出版商:IEE    

年代:1948

数据来源: IET