摘要:

The paper deals with mercury-arc rectifiers, mainly of the glass-bulb type, for use with shunt-wound d.c. motors to provide variable-speed drives for industrial machinery. The method is one of growing importance, and is rapidly finding new applications as its adaptability becomes more widely appreciated.1–4The characteristics considered are of practical importance to those concerned with industrial plant driven at variable speed, and to the people on whose co-operation they depend—the rectifier and the motor manufacturers. The various control methods discussed are those which have been investigated over the last 20 years; some are now obsolete but have been includedas a matter of interest.A knowledge of rectifier and motor theory is assumed, but, to assist those less familiar with rectifier practice, the Bibliography has been made reasonably comprehensive.Attention is mainly focused on those points which are peculiar to rectifier-motor operation, and which must receive special consideration in order that the rectifier, motor and machine are used together in satisfactory and economical manner.

DOI:10.1049/pi-2.1952.0054

出版商:IEE    

年代:1952

数据来源: IET

摘要:

Two mains-fed instruments are described, each of which gives easy and precise direct-current measurement of resistance. The range of resistance covered extends in the one instrument (the megohmeter) from 10 000 ohms to 1 200 000 megohms, and in the other (the micromhometer) from 260 ohms to 330 000 megohms. In the megohmeter the value is read on a potentiometer dial which is uniformly divided in units of resistance, and in the micromhometer the value is shown directly by a galvanometer whose scale is uniformly divided in units of conductance. In neither instrument is the scale accuracy affected by changes of valves.The method, used in the micromhometer, of constraining a measuring network to conform to a pre-existing scale, and the procedure adopted for the progressive self-calibration of its many ranges, may be found suitable for other instruments.

DOI:10.1049/pi-2.1952.0058

出版商:IEE    

年代:1952

数据来源: IET

摘要:

Transformer oils usually serve well for many years, and often for the entire life of the transformer, but trouble still occurs from time to time through oxidation of the oil, which causes sludging and the formation of acids. Oxidation may be retarded by using an oxidationinhibited oil. Available types of anti-oxidant, their properties, mode of action and influence on oil properties are discussed.For the evaluation of inhibited transformer oils, new and more informative oxidation tests are required, and such tests are briefly described in the paper. A description is given of some results obtained in the laboratory, in trials with small transformers under laboratory conditions and with transformers in service. It was possible to distinguish between contamination and deterioration of oil in service, and to assess the rate of decrease of oxidation stability of the oil. Questionswhich arise from the use of inhibited oils are discussed.It is concluded that, at present, the greatest value of inhibited oils will be in distribution transformers (particularly those which have given trouble because of oil oxidation) rather than in large transformers or in switchgear. With more practical experience of the superior oxidation stability of these oils, smaller and cheaper transformers may become possible. Further development work includes attempts to improve the correlation of laboratory test methods with service performance.

DOI:10.1049/pi-2.1952.0062

出版商:IEE    

年代:1952

数据来源: IET

摘要:

The paper summarizes operating experience with transformer oils from the aspect of sludge formation and the increase of acidity with life, and it describes tests designed to study the correlation of increasing acidity found in service with predictions of performance based upon the Michie sludge test.The basis of selection of transformers and oils for these tests—which were initiated in 1943—is given, and themethod of preparing the transformers is described.Acidity values are discussed from the aspect of working conditions and transformer site. The results show a trend towards greater deterioration of oils yielding higher acidity values in the sludge test, and B.S. 148: 1933 has been revised to exclude such oils. It is concluded that, under normal operating conditions, oils complying with B.S. 148: 1951 may give satisfactory service, with the minimum of maintenance, for the whole of the expected life of the transformer.

DOI:10.1049/pi-2.1952.0063

出版商:IEE    

年代:1952

数据来源: IET

摘要:

The trip coil of a voltage-operated earth-leakage circuit-breaker is likely in practice to be paralleled by a “solid” earth by reason of contact between the frame of the protected apparatus and fortuitously earthed metal. Itis better to provide a parallel solid earth of known performance. In such a protective circuit the sensitivity of the voltage-operated trip of the circuit-breaker may be increased without fear of unwanted operation due to leakage from apparatus such as anelectric cooker, and there are advantages over the more usual method of connection without a solid earth in parallel.

DOI:10.1049/pi-2.1952.0069

出版商:IEE    

年代:1952

数据来源: IET

摘要:

The ordinary domestic consumer of electricity usually takes it for granted that if anything goes wrong with an installation or appliance, fuse will operate and thus prevent risk. There are conditions under which this will not be the case and the fact may be of some importance because of the increasing utilization of electricity per consumer and the wear and tear on the equipment. Fire outbreaks attributed to electricity and resulting in calls to the fire service are growing in number and, in the absence of a system of periodic test and inspection of domestic electrical equipment, it is the more desirable that the automatic protective devices should function when failures occur.The consumer often defeats the protective scheme by misuse, but mainly because of lack of technical appreciation of the risk incurred, and the paper is writtenin the hope that the discussion will deal with the responsibilities implicit in service, whether fire risk is likely to grow, and the extent to which it is possible, or desirable, to recommend protective measures.

DOI:10.1049/pi-2.1952.0070

出版商:IEE    

年代:1952

数据来源: IET

摘要:

Electric arc furnaces have become widely used as a means of melting quantity of material and of carrying out chemical processes requiring high temperatures. The furnace consists of a crucible containing the charge into which dip three carbon electrodes. The electric energy supplied by a 3-phase transformer, together with a limiting reactor, which is frequently connected in the transformer h.v. circuit.Over-voltages have been observed on several furnaces. In some cases these have been ascribed to switching surges, but others have remained unexplained. The author investigated an instance of this latter type on a 10-ton steel furnace. By considering the characteristics of the arc it can be shown that excess voltages can occur when one of the arcs in the furnace iseither extinguished or short-circuited by movements of the solid charge. The over-voltages derived by this means appear to explain the abnormal voltages which were measured.These abnormal voltages are uniformly distributed in the transformer and reactor windings and do not therefore call for local reinforcement of the insulation. The insulation between phases and to earth requires special consideration, and, in general, the insulation class adopted on arc-furnace transformers is higher than that used on power transformers for the same nominal voltage. If the connections in each phase are not perfectly symmetrical, the voltages generated are influenced by the phase sequence.

DOI:10.1049/pi-2.1952.0073

出版商:IEE    

年代:1952

数据来源: IET

DOI:10.1049/pi-2.1952.0074

出版商:IEE    

年代:1952

数据来源: IET

DOI:10.1049/pi-2.1952.0075

出版商:IEE    

年代:1952

数据来源: IET

DOI:10.1049/pi-2.1952.0076

出版商:IEE    

年代:1952

数据来源: IET