DOI:10.1049/jiee-1.1934.0180

出版商:IEE    

年代:1934

数据来源: IET

摘要:

The paper first describes the development of the use of remote-control equipment on power systems, and then outlines the constitution and duties of the staff required for operating a large load-despatching plant.The difficulties associated with the control of generation, particularly during peak-load periods, are next discussed, and the starting characteristics of various large turbo-generators installed at the stations of the Berlin municipal undertaking are given. Steam-accumulator sets, Diesel sets, and storage hydro-electric pumping plants, are relied upon in Continental practice to provide reserve power. In the operation of large systems, frequency meters are now being supplemented by remote-metering devices for use in balancing output and demand.Where a large numbner of generators feed into the network, both the individual outputs and the summated values for the various groups are transmitted to the load dispatcher by the remote-indicating equipment. This is usually operated on the impulse-frequency system, either over pilot wires or by means of carrier-current circuits.Network compensation is obtained by adjusting the earth-leakage coils so that their inductance balances the total capacitance of the interconnected system. The necessary adjustments to the coils are made of local attendants under the direction of the load dispastcher.Carrier-current telephony is commonly used for communication between the load dispatcher's office and the various control points, on account of its lower cost and greater ease of fault location as compared with other systems.Supplies to medium-sized towns, densely-populated rural areas, and electric railways, are given from secondary networks, each of which is controlled from a district load-dispatcher's office situated at a power station or substation. The results of remote control on such networks have been very satisfactory.

DOI:10.1049/jiee-1.1934.0181

出版商:IEE    

年代:1934

数据来源: IET

摘要:

Measurements of permittivity and power factor made on sheet materials with different electrodes are apt to give widely different results. The way in which these discrepancies depend on the properties of the contact film between the electrode and the sample is investigated with particular reference to tests at audio and radio frequencies, and it is shown that in certain cases electrodes consisting of graphite and brass plates in the form frequently used, give rise to very large errors. In particular cases such errors may be very large at audio frequencies and small at radio frequencies, or vice versa.Mercury electrodes are considered to be the most satisfactory for general purposes, although a film of graphite between the mercury and the sample may improve the contact slightly, as previously noted by Churcher. Thin tinfoil applied with a trace of vaseline as an adhesive is a good substitute. Graphite electrodes backed with metal plates are easy to apply, but should be used with caution at audio frequencies, and not at all at radio frequencies.

DOI:10.1049/jiee-1.1934.0183

出版商:IEE    

年代:1934

数据来源: IET

摘要:

In general, the temperature-rise of the surface of a cable, freely exposed to the air, due to the current carried, will only be a few degrees above ambient temperature, whereas if the cable is exposed to direct sunlight a substantial increase of temperature will occur. This increase may be treated as additional to that due to the load, provided it is noted, in calculating the former, that the resistance will be increased at the higher temperature reached by exposure to the sun.It is found that this rise is brought about in part by radiation, but mainly by convection. It therefore varies with the intensity of the solar radiation, the velocity of the ambient air, the diameter of the cable, its location (i.e. the extent to which it is exposed), and the nature of the surface of the cable.The maximum solar radiation in different parts of the world is known approximately, and some tabular information is given in the paper. From this the temperature-rise of a cable of given diameter can be determined for a given air velocity by means of a factorFvarying with the diameter of the cable and with the air velocity. It is found, further, that there is in practice an approximate minimum air velocity, and the maximum rise is tabulated for this figure.This maximum will be attained in about half an hour, and will be reached if the sky is clear and the cable is directly exposed normal to the sun's radiation between, say, 12 noon and 2 p.m. Summer Time.Under these conditions cables of 2 to 2½ in diameter,in this country, may show a temperature-rise of 17 deg.C. This figure must be deducted from the permissible rise of, say, 50 deg. C. above shade temperature, thus materially reducing the rating of the cable.The data given are based on results obtained in London, Milan and Buenos Aires, and are in good agreement.An account is given of the methods employed and results obtained, together with supplementary information on certain technical features that presented difficulty during the investigation.

DOI:10.1049/jiee-1.1934.0184

出版商:IEE    

年代:1934

数据来源: IET

摘要:

A direct and very important method of designing band pass filters has been given by Zobel, who finds that there are eight types of filter sections of special importance. In a later paper, Zobel gives methods for computing the attenuation of these sections: but these methods are fairly lengthly and it is very inconvenient to apply them to the various types of sections that are tried before a final design is achieved.This paper gives a method for calculating the attenuation of the eight types of sections by means of a nomogram, so that the preliminary calculations can be made very quickly and easily and then the detailed calculation of Zobel can be applied to the final structure. The method employed simplifies the problem of design considerably.

DOI:10.1049/jiee-1.1934.0185

出版商:IEE    

年代:1934

数据来源: IET

摘要:

The paper first outlines the results obtained over a period of 10 years with oiled sapphire-steel bearings on a single type of meter used by a large supply undertaking, and describes tests carried out on new and worn pivots and jewels with various lubricants and abrasives. The results indicate that oil greately increases the life of a bearing, but that, even when oiled or greasy jewels are used, the presence of rust or debris is the major cause of wear and consequent errors in the reading of the meter.A series of wear tests on various pivot materials, both oiled and dry, is next described. The results show that materials of all hardnesses give comparatively good results when oiled. No conclusive evidence is obtained of the validity of Stott's theory that oxygen is set free from sapphire under the influence of the large cohesive forces which operate in meter bearings.The cause of surface cracking in sapphire jewels is then investigated, by means of a device which initiates impacts at the rate of 18 per minute between the pivot and the jewel of a meter bearing.Finally, an account is given of apparatus designed for the rotational testing of meter bearings in air and inert atmospheres, providing special facilities for the microscopical examination of jewels. The results of tests in nitrogen, argon, neon, hydrogen, and a vacuum, are discussed, and it is concluded that further experimental work is necessary in order to confirm or disprove the sapphire-oxygen theory.

DOI:10.1049/jiee-1.1934.0186

出版商:IEE    

年代:1934

数据来源: IET

摘要:

If a rod of iron, steel or nickel is placed axially in a solenoid which is excited by direct current, and if the rod is caused to vibraste longitudinally with its natural frequency, the changes of mechanical stress will produce corresponding changes of flux in the rod, so that an e.m.f. of the same frequency will be induced in a search coil which embraces the masgnetized part of the rod. The frequency of this e.m.f. is measured by means of oscillograms, from which the value of Young's modulus is easily found.

DOI:10.1049/jiee-1.1934.0188

出版商:IEE    

年代:1934

数据来源: IET

摘要:

It has been found that in both normal and incremental permeability measurements the values obtained at low flux densities are increased by the application of a large magnetizing force, such as is involved in the demagnetization of a specimen, this increase then disappearing approximately exponentially with time. This effect, which occurs whether d.c. or a.c. methods of measurement are used, is termed the “time-decrease of permeability.”. It appears to be due to a disturbance of the material from its equilibrium condition by a strong magnetizing force, the time-decrease representing a gradual return to its equilibrium state, which may require several days or even weeks to be effectively completed. A similar disturbance can be produced by severe mechanical treatment.The time-decrease is only considerable below aboutB= 1000, and within that range varies greatly with the magnetizing force. It also depends enormously on the nature of the material tested, being much greater in highsilicon alloys than in any other type of material. Except at vanishingly small magnetizations, the magnetizing force applied in making the measurements itself exerts a disturbing influence and affects the magnitude of the time-decrease. The effects of a polarizing magnetization and of high temperature have also been examined.Some correlation appears to exist between the magnitude of the time-decrease and the shape of the μ/Hcurve. but it has not been found possible to establish a quantitative correspondence with any function derived from the μ/Hcurve. A good mathematical representation of the variation of the permeability with time is given by an expression of the form δ =Kepsilon−Atn, whereK,A, andnare constants.The time-decrease is shown to be distinct from ordinary ageing, although the results obtained by Wild and Perrier indicate a close relation between the two phenomena. The practical significance of the effect is discussed in relation to the constancy of inductance of iron-cored coils and to the standardization of the conditions of permeability measurements at low flux densities.

DOI:10.1049/jiee-1.1934.0189

出版商:IEE    

年代:1934

数据来源: IET

DOI:10.1049/jiee-1.1934.0190

出版商:IEE    

年代:1934

数据来源: IET

DOI:10.1049/jiee-1.1934.0193

出版商:IEE    

年代:1934

数据来源: IET