摘要:

Some analysis of the probable performance of a power system has always been a necessary preliminary to the detailed design of the apparatus. Such analysis has become increasingly important as the complexity of systems has grown, and is more vital than ever to-day, in the interests of economy as well as those of technical adequacy.For some years it has been the practice in the United States to test the soundness of proposals for new construction upon circuit models. Elsewhere, reliance has mostly been placed upon analytical methods, but it has often been found impossible to make a comprehensive study without a prohibitive amount of work.After reviewing briefly the kinds of analysis which may be needed, and the methods of solution available, the paper describes a British a.c. network analyser and discusses some examples of studies made with its aid. Details are given of a procedure which has been found satisfactory.

DOI:10.1049/pi-2.1950.0199

出版商:IEE    

年代:1950

数据来源: IET

摘要:

The ratio of a current transformer having appreciable capacitance between windings is dependent upon whether and how the windings are connected together. There are five ratios which may be defined without a knowledge of the external circuits, one of them without any direct link between windings and four with a low-resistance link between one primary terminal and one secondary terminal; only two of these ratios may be measured directly by a simple bridge. Formulae are developed in the paper by means of which all the ratios may be deduced from simple bridge measurements; the adequacy of the formulae is tested by experimental measurements.A simple test is developed for determining quickly whether the effect of capacitance is appreciable in a transformer of unknown characteristics, and methods of construction of low-capacitance transformers are discussed.

DOI:10.1049/pi-2.1950.0204

出版商:IEE    

年代:1950

数据来源: IET

摘要:

The general principles on which the voltage distribution in a transformer winding is dependent are outlined. The effects of different impulse voltage waveshapes on the voltage distribution in core-type transformers are described and discussed.Breakdown/time-lag curves for insulation across coils and between turns are given, and from these and the distribution measurements it is shown that the impulse voltage which would give rise to an inter-turn breakdown is very much higher, in general, than that required to give a breakdown across coils. The problem of obtaining adequate insulation across coils to meet the impulse-voltage level required for transformers for installation on the highest-voltage systems is emphasized.A new type of winding is described of relatively simple construction which has been developed to solve this problem. The voltage distribution in a typical example is compared with the conventional core type of winding already discussed. The oscillograms of the voltages in this winding due to a chopped wave show that, unlike the conventional winding, the chopped wave does not give rise to more severe conditions than full-wave tests.It is concluded that by better utilization of insulation it is possible to obtain a very much higher impulse level with the new type of winding than can be obtained with a conventional winding using the same amount of axial insulation.

DOI:10.1049/pi-2.1950.0209

出版商:IEE    

年代:1950

数据来源: IET

摘要:

The theory of the series transductor with natural excitation is discussed and general equations for load and control current are derived. The effect of phase shift between the supply voltage and that across the transductor is taken into account, and the transient changes which occur at the moment of transductor cut-off are explained. The effect on the transductor characteristic of the shape of theB/Hcurve for the core material is considered, and the analysis is extended to enable an experimentalB/Hcurve to be used in the derivation of the transductor characteristic. It is shown that, with 100% self-excitation, the transductor characteristic approximates in shape to the upper part of theB/Hcurve.

DOI:10.1049/pi-2.1950.0212

出版商:IEE    

年代:1950

数据来源: IET

摘要:

A polyphase induction-motor, fed with balanced supply-voltages, can be represented as a single-phase transformer having a variable load-resistance connected to the secondary terminals. The exact practical theory of the transformer that has previously been described1can therefore be utilized to provide an exact practical theory of the induction motor; this is done in the paper.The method consists essentially in an application of Thévenin's theorem, and the theory is ranked as “practical” because the few parameters used can all be measured experimentally. A development beyond the corresponding transformer-theory is required for the induction motor, because the fact that the rotor can be turned with respect to the stator renders indeterminate the phase relationship between the primary voltage and the secondary open-circuit standstill voltage. A technique for measuring the correct phase-shift for the voltage ratio is described.The relationship between the open-circuit voltage-ratio and the locus of the stator current is demonstrated by tests on a wound-rotor induction-motor; these tests also illustrate the effect of saturation in the leakage-flux paths. Tests on a squirrel-cage induction-motor are also described. The voltage ratio of a squirrel-cage induction motor cannot be measured on open-circuit, but the phase shift of the voltage ratio can be inferred from the stator-current locus. Dynamometer tests are described which confirm the torque/speed characteristic calculated from the circle diagram. The influence of saturation of the main flux-path upon the characteristics is explained in the light of the theory.

DOI:10.1049/pi-2.1950.0222

出版商:IEE    

年代:1950

数据来源: IET

摘要:

The paper describes the application of television techniques to highspeed photography. The system described uses an iconoscope tube in which the photo-emission is controlled by the application of suitable potentials to the collector electrode. The charge image, formed during a chosen interval, is stored on the mosaic and subsequently scanned. Examples of exposures of various duration down to 2 × 10−5sec are shown. The mechanisms of spurious image formation during the “shutter-closed” period are discussed. The performance of the system is compared with that of the Kerr cell.

DOI:10.1049/pi-2.1950.0232

出版商:IEE    

年代:1950

数据来源: IET

摘要:

The design of high-accuracy current-transformers for operation at rated currents of less than five amperes or at frequencies higher than 50 c/s should include consideration of the effects of capacitance. The performance of transformers is shown to be dependent not only on the magnitudes of the self-capacitances of the windings and the mutual capacitance between the windings, but also upon the distribution of the capacitance between windings. With the normal method of winding a transformer layer by layer, the capacitance between windings is concentrated between the outer turns of the inner winding and the inner turns of the outer winding. This is shown to be an unsatisfactory distribution, and the performance is improved if the capacitance between windings is symmetrical and distributed as much as possible.A satisfactory distribution of capacitance between windings and also low self-capacitances are obtained by adopting a winding technique well known in radio work, in which the order of winding the turns is such that adjacent turns are as nearly as possible consecutive turns.Further improvement of the transformer performance may be obtained by increasing the thickness of insulation between windings and using insulation of low permittivity. It is shown that the thickness of this insulation may, with advantage, be about one-eighth of the mean depth of the secondary winding.Formulae are given for estimating the capacitances and leakage reactances of the transformer. It is shown that the leakage reactance of the secondary, when both windings are uniformly distributed round the core, is negative.The performance of multi-ratio transformers, especially of the tapped primary type, is necessarily less satisfactory than that of single-ratio transformers, but considerable improvements may be made by adopting an arrangement of the winding which is symmetrical with regard to the secondary for all ratios. Good winding arrangements for multi-ratio transformers with primary windings of the series-parallel type or with secondary windings of the tapped type are also suggested.

DOI:10.1049/pi-2.1950.0233

出版商:IEE    

年代:1950

数据来源: IET

摘要:

In the design of transformers, the prediction of the amount of waveform distortion from a knowledge of the properties of the core material becomes complicated if the preceding circuit has a high impedance. A theorem is given showing that, if suitable distortion and other measurements are made on a sample core of the material to be used and the distortion factor plotted as a function of two suitably chosen variables, then this information is sufficient to enable the distortion arising from any transformer in any resistive circuit to be calculated exactly.

DOI:10.1049/pi-2.1950.0234

出版商:IEE    

年代:1950

数据来源: IET