摘要:

Experience in service and at short-circuit testing stations has demonstrated that the behaviour of circuit-breakers when breaking shortcircuit currents depends on a number of factors which have been termed conditions of severity. They include circuit power-factor, recovery voltage, earthing conditions, and current asymmetry, and are specified in certain clauses in current testing specifications.The paper deals with a further condition of severity which has been acknowledged but is not specified in specifications, namely the restriking- voltage transient and its important controlling attribute, the ate of rise of restriking voltage. The aim of the paper is to place this severity factor in its correct perspective by stating its effect on the performance of plain-break oil circuit-breakers, oil circuit-breakers fitted with arc-control devices, and air-blast circuit-breakers. Compared with the relatively small effect that rate of rise has on plainbreak and arc-control oil breakers, the importance of the effect of rate of rise on the performance of air-blast breakers is emphasized, and recommendations are made as to the utilization of this important factor in the rating, testing and selection of these breakers.A method is proposed for testing certain types of high-voltage airblast breakers whose breaking capacities are above those for which testing stations are normally equipped.

DOI:10.1049/ji-2.1944.0083

出版商:IEE    

年代:1944

数据来源: IET

摘要:

This paper reviews various problems which are met in designing highvoltage air-blast circuit-breakers, and the way in which the application resistance switching confers another degree of freedom upon the designer in meeting the many conflicting requirements.It is first of all shown that a circuit-breaker must not only break its rated breaking current but must also limit the value of surge voltage which it causes while it is opening the circuit. This can be brought about by limiting the electric strength of the breaker contact gaps.An experimental method of determining the electric strength of the nozzles under air-flow conditions is then explained, followed by discussion of the means by which resistance switching enables the designer to control the breaking capacity and the electric strength of the nozzles independently.A 132-kV breaker designed in conformity with the conclusions reached is described, and the results of a full-scale test set-up are given.The paper then gives an analysis of the validity of “unit testing” applied to multi-break breakers with resistance switching, as compared with the present two-part testing applied to oil circuit-breakers in accordance with B.S. 116, Part 2.In conclusion, proposals are made for a series of type-test duties to be applied to air-blast circuit-breakers, in order to prove compliance with their breaking-capacity ratings.

DOI:10.1049/ji-2.1944.0084

出版商:IEE    

年代:1944

数据来源: IET

摘要:

An electronic instrument is described for measuring peak voltages in the range of 2–20 kV, direct or alternating current, to an accuracy of 3%. It has a low capacitance (9 cm) and can be used in some circuits up to frequencies of 1 Mc/s or over. Its action is based on he proportionality theorem for a triode electron-optical system, in that the angle of the beam is denned by the ratio of two voltages: the anode voltage and the voltage of the modulator grid. The beam angle emains constant when both terms of this ratio are multiplied by the same factor, the modulator bias voltage being directly proportional to the voltage to be measured when the latter is applied to the anode. A high voltage is thus measured in terms of a low voltage, the instrument constituting an electron-optical potentiometer. The range of measurement can be extended as desired. The same principle can also be applied to the construction of high-voltage tubes so that they act as their own voltage-measuring instruments.

DOI:10.1049/ji-2.1944.0089

出版商:IEE    

年代:1944

数据来源: IET

摘要:

This paper has been prepared with the dual purpose of presenting to those interested, but not actively engaged, in rural electrification, a picture of the general development of electrical participation in farm processes, while at the same time offering a clearing-house of ideas for those actively engaged but whose interest is, for various reasons, localized. The main attention has been given to the less-common applications, to those which are the subject of some controversy, and to those which may appear to have a Wider field of application in the future. Emphasis has been placed on trends rather than on facts and figures.

DOI:10.1049/ji-2.1944.0092

出版商:IEE    

年代:1944

数据来源: IET

摘要:

The paper briefly reviews methods for the centralized control of switching operations on distribution networks, by injection into the distribution system of currents which differ in frequency from the main supply. The supsrimposition of ultra-audio frequencies for limited and specific purposes, such as the protection or the remote switching of a transmission line, has not, so far, been employed to any large extent in this country, and is therefore beyond the scope of the paper.Several devices employed to respond to injection currents are briefly described; and the probable applications of this method of control are outlined. Particulars of the development of remote signalling over the network of a large electricity supply undertaking are given, together with reasons for the final adoption of the method selected. Particulars of the components of the equipment are given, and the power required is analysed for two frequencies.

DOI:10.1049/ji-2.1944.0095

出版商:IEE    

年代:1944

数据来源: IET

摘要:

The effect of corona impinging on thin insulating materials, i.e. cellulose acetate and varnish cloth, is studied by exposing the material to the discharge in a plane-parallel air-gap, and determining the changes in power factor, permittivity and weight which are produced. The time elapsing before the material is electrically punctured, and the increase of acid content, are also measured. Subsidiary tests such as a comparison of the effect of direct and indirect corona, the differences arising when pure oxygen and pure nitrogen are employed separately as the discharge medium, and visual and photographic studies of the discharge and the measurements of corona onset and extinction voltages are also described. The results are discussed, and it is concluded that direct corona results in a general form of deterioration owing to the absorption and subsequent chemical action of ozone and nitrogen oxides by the material, and at the same time a highly localized or microscopic deterioration which is a consequence of electronic and/or ionic bombardment of the surface and which accounts for the ult i mate electrical breakdown. The two forms of deterioration are not related. These conclusions lead to suggestions for tests for assessment of the corona resistance of materials and rule out the possibility of any single test being in itself sufficient for this purpose.

DOI:10.1049/ji-2.1944.0100

出版商:IEE    

年代:1944

数据来源: IET