摘要:

Appreciable developments in the design and application of ripple-control equipments have taken place during the past ten years. The paper reviews the progress made and indicates the modern requirements of such systems in view of their proved value to the supply authority and their anticipated widespread use.Basic requirements for a system of ripple control are described, followed by a method of network analysis for predetermining the ripple power required to give a desired signal strength, and for evaluating its degree of uniformity, on a known supply network.Limitations in the practical and economic application of series-injection methods for superimposing the signalling power on the supply system have led to the parallel-injection method being more usually adopted. The modern injection circuits described and methods of connecting them to the electricity supply networks show that appreciable improvements have been made in injection efficiency, with corresponding reductions in size of plant required.The need for ensuring that a ripple-control system should not be liable to mal-operation owing to “spillover” signals is shown to be an important factor governing its principle of operation. The present trend of the art is to use a single ripple frequency as a “carrier” for each supply area, and to use some form of coding as the discriminating factor for affording separate control channels. The principle of various forms of coding suitable for ripple control, and receiving relays to suit such codes, are discussed.The economics of centralized ripple control for off-peak loads, and as a means of improving the domestic load factor, are reviewed.

DOI:10.1049/ji-2.1948.0126

出版商:IEE    

年代:1948

数据来源: IET

摘要:

A comparison is made of traffic conditions in the Warsaw Railway Junction before and after its electrification between 1933 and 1938 by a group of British firms.The paper gives a survey of the equipments used and describes the reasons which led to the selection of a voltage of 3 000 volts d.c. for this scheme. A summary of the improvements achieved by the electrification of the suburban service is given and maintenance troubles experienced in the early stages of the electrification are described.

DOI:10.1049/ji-2.1948.0142

出版商:IEE    

年代:1948

数据来源: IET

摘要:

A description is given of the conditions discovered when high-voltage solid-type cable accessories have been dismantled after many years of service. In several instances compound migration had occurred, followed by secondary effects such as collapse of lead sleeves and ingress of moisture.A reconditioning technique used successfully to prolong the useful life of installed joints and sealing ends exhibiting these defects is described.An explanation of the phenomenon of compound migration is also suggested.The basic principles for new designs, together with typical illustrations of cable joints and end terminations, are given, which in the authors' opinion should prevent compound migration occurring in future installations.

DOI:10.1049/ji-2.1948.0145

出版商:IEE    

年代:1948

数据来源: IET

摘要:

For electric cables, as used for indoor wiring, the only standard of reference now existing in this country is B.S.7, which covers only rubber insulants; for lack of any other specification, the dimensions therein specified for rubber compounds are being misapplied to other insulating materials, without taking into account the different properties of the latter.A new “basic specification” is proposed, composed of a series of electrical, physical, thermal, mechanical and chemical tests; and the author suggests the use of such an agreed basic specification for the determination of minimum dimensions of any approved materials of which the cable may be composed.Following out this suggestion, the author deals with such test requirements under the two headings: (a) electrical specification, which covers the primary purpose of the cable to transmit electrical power, and (b) mechanical specification, which covers the adequate protection of the cable in service.Under the electrical specification some calculations and graphs of interest are given as illustrations only of the more comprehensive survey that is necessary.The author further deals with practical and economic considerations, which may have some bearing on purely echnical conclusions, e.g.:(a) The lack of importance of eccentric insulation, provided the required minimum thickness is used.(b) The incorrectness of stipulating an average thickness with a plus and minus tolerance as against the correct method of specifying either a minimum thickness or a maximum, or both.(c) The increase of cable costs, basically as the square of the radial thicknesses imposed.In particular, the properties of pre-war rubber, reclaimed rubber, p.v.c. compounds and polythene are compared.

DOI:10.1049/ji-2.1948.0152

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The paper gives a brief critical review of some of the more important contributions to this subject. All of these develop methods of calculating surface losses which are largely empirical and give no clear picture of the flux-density variations in the air-gap, due to the presence of slot-openings, which are the sources of surface losses.The paper applies Carter's field equations to the determination of the wave shape and amplitude of the flux ripples produced by the slot openings. The fundamentals of these non-sinusoidal ripples are resolved into rotating flux-density fields so that the losses produced by these harmonic fields in the iron and winding circuits traversed by them may be calculated.It is further shown that the currents produced in a squirrel-cage rotor by the stator slot-openings are at stator slot frequency and that these currents produce rotating fields whose frequency at the stator is a function of the number of rotor slots.The list of references includes a representative selection of the papers published on the subject.

DOI:10.1049/ji-2.1948.0170

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The paper, which is an attempt to survey the present position, opens with a discussion of the limitations of the dynamometer wattmeter. Compensation for voltage circuit phase angle and for eddy current and voltage circuit losses is discussed. The effect of the iron circuit is noted, the influence of leakage flux being pointed out. The effects of distortion are noted, and attention is drawn to some hitherto unformulated rules relating the distortion in the current and voltage waves. Null methods of using the wattmeter are briefly described, and a new circuit is proposed. The concept of complex permeability is introduced as an approach to bridge measurements, and an equivalent circuit for a test transformer is deduced. It is shown how this may be used in a novel circuit in such a way as to eliminate copper losses. The limitations of the bridge method are briefly discussed, and the relation between bridge and wattmeter methods is shown to lead to the concept of “distortion coefficient,” a new characteristic property of the iron, which can be determined experimentally and which may provide a succinct approach to distortion problems.

DOI:10.1049/ji-2.1948.0171

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The paper describes a method of localizing sustained earth-faults on systems protected by Petersen coils. The method is based on the measurement of variations of electrostatic field strength in the vicinity of the overhead line. A description is given of the apparatus used and of results of tests made. The practical applications of the method are explained. An additional use of the apparatus is indicated as a voltage detector on overhead high-voltage lines.

DOI:10.1049/ji-2.1948.0172

出版商:IEE    

年代:1948

数据来源: IET

摘要:

Measurements of magnetostriction and permeability of samples of hot-and cold-rolled silicon steels are given before and after abrasion in different directions relative to the applied field. It is shown that surface abrasion of electrical sheet steel produces high internal strains of a markedly directional nature which affect the magnetic properties. The results are interpreted in terms of the domain theory of ferromagnetism.

DOI:10.1049/ji-2.1948.0173

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The mathematical results of Butler and Mangl are utilized to determine the distribution of the flux density in ferromagnetic laminae at various instants. The manner in which the phenomenon of polarization in opposite directions occurs at the outer and inner parts of nickel-iron laminae is clearly demonstrated for power-and audio-frequency operation.The mathematics is extended to enable the distribution of harmonic magnetization in the laminae to be determined. It is shown that harmonic magnetization occurs in the laminae even when the total flux does not contain harmonics.The calculated results afford an explanation of the difficulties encountered in attempts to demagnetize nickel-iron alloys completely, and assist the development of a reliable method of demagnetization. It is shown that methods that have been applied successfully to silicon-iron alloys, and tacitly accepted for nickel-iron alloys, possess inherent defects in the latter case.

DOI:10.1049/ji-2.1948.0174

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The general theory of absolute high-voltage r.m.s. electrostatic voltmeters which depend on the change of frequency of an oscillating electrode is discussed.The scope and limitations of such instruments are considered in relation to three selected types.Preliminary experimental results are given for two types.

DOI:10.1049/ji-2.1948.0175

出版商:IEE    

年代:1948

数据来源: IET