摘要:

The paper deals with some of the practical considerations that will determine the decisions on technical points taken by engineers who are responsible for the installation of motor control gear and sub-distribution switchgear, for isolating and protecting motor circuits.The functions of isolation and protection are shared by motor control gear and sub-distribution switchgear, especially when motors function in groups. Various grouping arrangements are compared.The use of 3 300 volts in motor circuits is discussed, and a reference is made to the use of 3 300-volt contactors.The increasing use of contactors emphasizes the importance of further study of the process of making and breaking circuit by means of contactors, which can be examined in more detail by a demonstration with slow-motion films.After a note on thermal overload trips, the rupturing capacity of starters is discussed with particular reference to the short-circuit values which can be fed from the transformers and supply cables usual in l.t. circuits.The rupturing capacities of rewireable and cartridge fuses are discussed, with particular reference to the time of operation of the latter on severe short-circuits.The rupturing capacity of l.t. circuit breakers is shown to involve problems akin to those which have been studied in h.t. switchgear design.Finally, the problem of the anticipation of short-circuits by leakage indication is stated in terms of practical application.

DOI:10.1049/jiee-1.1937.0123

出版商:IEE    

年代:1937

数据来源: IET

摘要:

Marine radio may conveniently be treated as a special branch of radio engineering, with its own particular problems and its own technique. No general survey of the field having been published for some time past, this paper has been prepared with a view to placing on record the state of the art obtaining in 1936.The paper has been divided into four main Sections. In the first of these is given a short summary of progress during the last 5 years, with particular reference to the nature and volume of traffic, the types of communication involved, and the growing use of direction-finding equipment by navigators.The second Section deals briefly with the types of radio equipment now customarily fitted in cargo vessels and in passenger vessels other than those which come within the “express steamer” class.In the third Section some account is given of the radio problems encountered in the “express steamer” class of vessel, and of the main equipment items selected to meet the conditions anticipated in the particular case of R.M.S. “Queen Mary.”The last Section deals with the actual radio station of R.M.S. “Queen Mary, ” as built up from the main equipment items described in the third Section, and their associated power supply and aerial systems, etc. The control-room arrangements, which handle four independent duplex circuits, are given in some detail, together with an account of the special precautions adopted to insure efficient multiplex working, quick change of wavelength, high-speed transmission and reception, and simultaneous communication on both telegraphy and telephony with both sides of the Atlantic.

DOI:10.1049/jiee-1.1937.0131

出版商:IEE    

年代:1937

数据来源: IET

摘要:

The paper presents a technical approach to the problems of safe and economical control and operation of certain power networks. The initial sections are devoted to a quantitative discussion on circuit-breaker duty and short-circuit phenomena at points of supply and at remote points on the network.Some effects of interconnected working are indicated. Means for current limitation and alternative methods of control under fault conditions are described.The design and protection of cable networks are reviewed and the characteristics of transformers briefly discussed. Finally, some comments are offered on the layout of mediumvoltage apparatus and on the problem of voltage variation at consumers' terminals.The discussion is confined to phenomena on urban networks operating at voltages not exceeding 11 kV.

DOI:10.1049/jiee-1.1937.0134

出版商:IEE    

年代:1937

数据来源: IET

摘要:

A preliminary survey is made of the difficulties involved in metering (a) active energy, wattless kVA, total kVA, and power factor, in the input circuits of mercury-arc rectifiers, owing to the presence of harmonics in current and voltage;and (b) energy output from mercury-arc rectifiers when considerable ripple exists in the current and voltage.The performance of induction-type and motor-type integrating meters is then examined experimentally on rectifier circuits, and the observed errors are quoted. Good agreement is found between the observed errors and those expected from theory and the known variation of the meter characteristics with frequency, both in the case of energy and in the case of kVA measurement. Similar tests are described on motor- and mercury-type integrating meters on the output side of rectifiers.It is concluded that a.c. power measurements can be made with satisfactory accuracy by induction- and motor-type meters. No entirely satisfactory solution is found, however, for power-factor and kVA measurement. Finally, the necessary precautions to be taken with d.c. integrating meters on the output side are dealt with.

DOI:10.1049/jiee-1.1937.0139

出版商:IEE    

年代:1937

数据来源: IET

摘要:

The paper forms a natural continuation of an earlier investigation of the electrical stability of condensers and the development of satisfactory means of obtaining compensation for temperature variation. It has been shown in a previous paper that such compensation can readily be obtained for slow temperature-changes, but that great care is necessary in matching the thermal masses of the various parts if the temperature-changes are rapid. By applying the results of this previous analysis, a condenser of reasonable size has been developed which is compensated for temperature-changes as rapid as 7 deg. C. per minute.Special design features are introduced to produce this result, the most noticeable of which are the use of springloaded steel balls in place of plain bearings and the inversion of the normal electrical connections to rotor and stator, this latter alteration being adopted to eliminate difficulties which arise with an earthed screening case.Electrical tests of the performance under varying conditions of temperature-change show that the temperature coefficient of capacitance can be adjusted to have any value between the limits + 80 and − 80 parts in a million per deg. C. and therefore that the coefficient can be so adjusted as to compensate for the inductance coefficient of the associated inductance coil. The variation of the resultant frequency coefficient of the complete circuit with change of oscillation frequency is not large, and the transient variations do not exceed 10 parts in a million per deg. C. for temperature changes at a rate of 7 deg. C. per minute.

DOI:10.1049/jiee-1.1937.0143

出版商:IEE    

年代:1937

数据来源: IET