摘要:

Examinations of ferromagnetic behaviour under conditions likely on power systems show that eddy currents may be allowed for by including an appropriate linear resistor in mathematical models. They also show that hysteresis paths depend on the previous history of a core but are hardly affected by the time derivative of the flux. Current-transformer studies are described to illustrate a computational method in which discrete points on a number of hysteresis paths are specified. An extrapolation technique is used, and consideration is given to points at which flux reversals occur. It is shown that highly-accurate representation may be achieved.

DOI:10.1049/piee.1974.0326

出版商:IEE    

年代:1974

数据来源: IET

摘要:

A previous paper outlined the principles of a new method for dynamically varying the shape of polarised quadrilateral relay characteristics for the protection of e.h.v. transmission lines. The present paper extends these methods to the protection of double-circuit lines. Consideration is given to the compensation of earth-fault relays, and it is shown that compensation schemes which ignore the effect of mutual coupling between circuits are desirable. Digital-computer application studies of a typical double-circuit 400kV transmission line of earthed construction indicate that, from the point of view of accuracy and fault coverage, there is little advantage in the use of variable devices in zone 1. However, they enable a greater proportion of the protected feeder to be covered with minimum fault-detection time. Emphasis is placed on the response of relays connected to healthy conductors, and the possibility of avoiding unwanted tripping emerges. A high degree of immunity to maloperation during heavy-circuit loading and power swings is achieved.

DOI:10.1049/piee.1974.0327

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The paper describes a scheme in which a fuzzy algorithm is used to control plant, in this case, a laboratory-built steam engine. The algorithm is implemented as an interpreter of a set of rules expressed as fuzzy conditional statements. This implementation on a digital computer is used online, to control the plant. The merit of such a controller is discussed in the light of the results obtained.

DOI:10.1049/piee.1974.0328

出版商:IEE    

年代:1974

数据来源: IET

摘要:

Part of the winding near its middle is often omitted when the volume about the centre of a solenoid over which the magnetic field is relatively uniform is to be extended. Field distributions are considered, and optimum gap lengths computed. The volume of specified field uniformity is compared with hat of uniform solenoids. The use of solenoids with a gap makes certain precautions essential.

DOI:10.1049/piee.1974.0329

出版商:IEE    

年代:1974

数据来源: IET

摘要:

A model is proposed for the mechanisms by which multiple emitting sites are formed and material is lost from a nonrefractory arc cathode with an oxide layer more than about 10−8m thick, when an arc is rotated magnetically over its surface for long times. Using measured copper cathode erosion rates and scanning-electron-microscope photographs of the size and number of craters on cathode arcing surfaces, results have been obtained which seem to support the model. Average lifetimes of emitting sites have been estimated to be considerably greater than those on cathodes with very thin oxide films. The model suggests that it is important to keep the oxide layer from becoming too thick, to obtain low cathod erosion rates.

DOI:10.1049/piee.1974.0330

出版商:IEE    

年代:1974

数据来源: IET

摘要:

Measurements are presented of the decrease of loss tangent with time of application of a high alternating stress and its return on removal of the stress. Measurements were made at an elevated temperature, as well as at ambient conditions. An explanation of the phenomena in terms of the movement of charge carriers into the polymer and their recombination within the polymer is attempted.

DOI:10.1049/piee.1974.0331

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The phonopore and the phonoplex were both systems introduced in 1885 for providing additional telegraph channels (or, alternatively, in the phonopore system, a telephone channel) in the frequency range above that of the ordinary d.c. or Morse channels. The phonopore, developed by Charles Langdon-Davies in England, used a special kind of coupling transformer/condenser, which is here analysed but shown to have had few useful special properties, and used a ‘harmonic’ telegraph channel, i.e. a keyed oscillatory signal. Edison's phonoplex used, for the highpass channel, signals derived from the transients produced by an induction coil. Both systems were made commercially, and had a certain success on railways. The Phonopore Syndicate (later Company) had an interesting but not successful history, here partially unravelled; from 1893, its managing director was C.E. Spagnoletti, F.R.S., Past-President of the Society of Telegraph Engineers, and newly-retired telegraph superintendent of the Great Western Railway. Although the company had, by 1895, raised around £100 000 of capital, it was in that year effectively purchased by the New Phonopore Telephone Co. for £2000. The new company continued in existence, with an issued capital reaching no more than about £8000, until it was purchased for £175 in 1916 by the Phonopore Construction Co., which finally ceased operations soon after 1920.

DOI:10.1049/piee.1974.0332

出版商:IEE    

年代:1974

数据来源: IET