摘要:

An attempt has been made to develop the theory progressively. The relay is first considered as a simple coil. This leads to Helmholtz's law. The inclusion of a slug, ignoring flux leakage, increases the time-constant of the relay. It is shown that time-constants add up arithmetically. This is felt to be important: it simplifies calculation. With flux leakage, the rise of flux no longer obeys Helmholtz's law, a rough treatment giving two exponential terms in place of one.The release of slugged relays is complicated by saturation. A graphical method of dealing with this has been evolved.The impulse relay is treated at some length on account of its great practical importance and because of the interesting oscillations produced by the condenser at the dial.In order to examine the effect of flux leakage a little more thoroughly, the relay core has been viewed as a transmission line with “heelpiece return.” The slug becomes distributed inductance, and the resulting telegraph equations have been solved by Heaviside's “expansion theorem.” In no case is the actual motion of the armature considered in this paper.

DOI:10.1049/jiee-1.1928.0032

出版商:IEE    

年代:1928

数据来源: IET

摘要:

The paper investigates by the method of conformal transformation the distribution of electrical stress round certain systems of conductors which are important in high-tension practice. In particular the effect of rounding the edges of the conductors in reducing the high stresses at the edges is found quantitatively.The methods used are applied to calculate the variation of breakdown voltage with spacing distance between the electrodes. The two-thirds power law is derived as a limiting case for some of the electrodes, and the effect of variation of electrode shape and of physical assumptions is shown. The theoretical results are compared with such experimental data as are available.Approximate formulae are derived for the capacity of coaxial rectangular cylinders, which are an extension of the well-known correction for the corner of a Leyden jar, and their application to heat conduction problems is pointed out. The results are reduced to graphical form.

DOI:10.1049/jiee-1.1928.0033

出版商:IEE    

年代:1928

数据来源: IET

摘要:

In this paper the principal features of an electric motor are discussed and the characteristics of the squirrel-cage machine are considered in relation to them. The disadvantages of the squirrel-cage motor are then examined and their importance on certain types of drive is considered. These disadvantages are mainly connected with the poor starting performance of the motor, and various methods of over coming the starting difficulties are dealt with. A centrifugal clutch is described which enables a motor with a star-delta startor to start heavy loads with comparatively small starting currents. The characteristics of high-resistance rotors for both continuously-rated and short-rated motors are discussed, and various other devices for the improvement of starting performance are reviewed. The advantages of the double-squirrel-cage rotor over many of the alternative proposals are then described.A close examination of the starting currents drawn by squirrel-cage motors under various conditions of starting is made and the subject is considered from the point of view of the supply engineer. Records of the current peaks on various feeders are given, the characteristics of every motor on each feeder being known. Additional records show the effect of the diversity factor for these current peaks on the current of the transformer supplying several feeders, and on a complete substation. Finally, the regulations of certain supply undertakings for the installation of squirrel-cage motors are examined and the following general regulation is evolved:-The starting current of any of the induction motors in an installation, when expressed in terms of full-load current, must not exceed ¾+total installed h.p./4×motor h.p.

DOI:10.1049/jiee-1.1928.0034

出版商:IEE    

年代:1928

数据来源: IET

DOI:10.1049/jiee-1.1928.0039

出版商:IEE    

年代:1928

数据来源: IET