DOI:10.1049/pi-2.1949.0001

出版商:IEE    

年代:1949

数据来源: IET

DOI:10.1049/pi-2.1949.0002

出版商:IEE    

年代:1949

数据来源: IET

DOI:10.1049/pi-2.1949.0003

出版商:IEE    

年代:1949

数据来源: IET

摘要:

The theoretical investigation of an earlier paper has been extended by a study of the effect of the shape of the demagnetization curve of a permanent magnet on its performance. This has been carried out in terms of the reduced co-ordinates, i.e. the ratio ofBandHto their values at the remanence and coercive points respectively. It is shown that the performance can then be determined entirely by the curve factor and the magnet's dimensions. In particular, all magnets of the same curve factor will give the same output in a given construction, providing that the quantitiesABrandLHcare maintained constant.There are only three different curve factors to cover all the alloys which are commercially available. The smallest of these (0.42) applies to all the isotropic materials. Curve factors must lie between the values of 0.25 and 1.0, but the extreme values can only be reached when the ratio of coercive force to remanence is infinity or zero. The maximum curve factor obtainable when this ratio is known has been calculated.The use of remanence factor is preferable to curve factor in computation; so the four cases of magnet utilization have been evaluated in terms of the former, and the leakage coefficient. Curves have been plotted to illustrate these relationships. Apart from the case of static flux with full recoil, increases of remanence factor (or curve factor) produce increased useful energy when measured in terms of the product of remanence and coercive force. The exception gives a minimum for a remanence factor of 0.7, the value corresponding to the isotropic alloys. On the other hand, the utilization factor (useful energy in terms ofBHmax) always decreases steadily for increases in remanence factor.Families of curves have been plotted for all four cases of magnet utilization and for each practical alloy. An example is given of the uses of these curves in a design problem.

DOI:10.1049/pi-2.1949.0004

出版商:IEE    

年代:1949

数据来源: IET

摘要:

The paper deals with the magnitude and distribution of harmonic currents flowing in a.c. networks. The various sources of harmonics are discussed in general, and harmonics arising from the use of mercury-arc rectifiers and in h.v. transmission are dealt with in greater detail.The flow of harmonics arising from these sources is considered from a theoretical aspect, using equivalent networks, experimental verification of these theories being given for certain simple cases. The possibility of a complete theoretical solution is shown, and certain probable practical conclusions are drawn.Various methods of reducing harmonics are discussed, and the relative importance of the various sources is considered in the light of modern trends in harmonic suppression.

DOI:10.1049/pi-2.1949.0009

出版商:IEE    

年代:1949

数据来源: IET

DOI:10.1049/pi-2.1949.0010

出版商:IEE    

年代:1949

数据来源: IET

摘要:

In designing machines and apparatus with solid or partly solid magnetic circuits, such as eddy-current brakes, clutches, impact exciters, and rolling-mill motors, flux/time curves have often to be predetermined to secure a desired rapidity of response. The prediction has hitherto been uncertain, especially in the absence of test results on similar machines, and expensive changes of design, introducing laminated poles and yokes have sometimes been resorted to where the standard design or a simple modification of solid sections would have sufficed.The paper considers the rise of the total flux as retarded by eddy currents and shows that for this purpose all eddy-current paths can be represented by a single fictitious damping-ring whose resistance and leakage reactance are calculated from first principles. Simple expressions for the usual shapes of iron section are developed, and the test results which are given provide agreement between theory and experiment.For magnetic circuits which consist of solid iron in parts only and with fairly large air-gaps as in d.c. machines and alternators, it will generally suffice to take account only of the resistance of the fictitious damping-ring and to ignore its leakage reactance. A graphical procedure may then be used for obtaining the flux/time curve very rapidly. The error thus introduced makes the response appear rather less rapid than it is in reality.Where greater accuracy is needed, the leakage reactance of the substitute damping-ring has to be introduced and the solution found by solving transformer equations for successive parts of the characteristic.The substitute damping-ring, as a theoretical device, should prove helpful in solving other problems involving eddy currents by converting the system into a transformer with short-circuited secondary.

DOI:10.1049/pi-2.1949.0015

出版商:IEE    

年代:1949

数据来源: IET

摘要:

The paper describes two new direct-reading methods which have been developed for the measurement of dielectric power factor, with particular reference to the field and works testing of high-voltage insulation. The two methods to some extent resemble the Schering bridge in that they incorporate a low-loss condenser of known capacitance and negligible loss angle, as the standard with which the insulator under test is compared, but differ radically from the bridge in the manner in which the comparison is effected.The essential feature of the first method is the production of a series of unidirectional voltage pulses of rectangular waveform and constant amplitude, and of the same frequency as the supply. The circuit is so arranged that the duration of each pulse, and, in consequence, the mean value of the resulting voltage, is directly proportional to the insulator loss angle δ. The final indication of loss angle (or, what is virtually the same thing since δ is small, the power factor sin δ), is either given directly on a calibrated voltmeter, or estimated approximately by visual examination of the pulse waveform on an oscillograph screen.The second method consists essentially in using the difference between two voltages, of equal amplitude but with a mutual phase difference equal to the insulator loss angle, as a measure of the power factor, the latter being indicated directly on a calibrated voltmeter. The particular point of interest about this method lies in the means adopted for the preliminary adjustment, which must be made to ensure that the amplitudes of the two voltages are exactly equal.

DOI:10.1049/pi-2.1949.0021

出版商:IEE    

年代:1949

数据来源: IET

摘要:

A review of the literature of the subject shows the wide acceptance of the view that slot ripples in the open-circuit e.m.f. waveform of salient-pole synchronous machines are caused by the interaction of rotor permeance harmonics with those set up by the stator slot-openings. It is shown in the paper that this is usually only a secondary cause and that these ripples are due primarily to stator slot-frequency currents flowing in secondary circuits on the rotor; as a consequence the ripples may be generated with either a smooth or salient-pole rotor. It is further shown that e.m.f. ripples may be generated not only when the stator slots per pole-pair are even but also when they are odd or fractional. These e.m.f. ripples may correspond to the fundamental or a higher harmonic of the flux-density variation due to the stator slot-opening.Expressions are derived for the frequencies of the ripples in the special cases, such as turbo-alternators and synchronous motors with smooth-slotted rotors, where the squirrel-cage winding is placed in uniformly-indexed slots.Various methods for reducing or suppressing these ripples are discussed and corresponding formulae derived.The paper concludes with a detailed examination of a number of oscillograms and the appropriate data of the machines to which they refer.

DOI:10.1049/pi-2.1949.0024

出版商:IEE    

年代:1949

数据来源: IET

DOI:10.1049/pi-2.1949.0059

出版商:IEE    

年代:1949

数据来源: IET