摘要:

The paper deals with magnetic locators developed in this country during the war, for locating unexploded bombs and mines. The principle of operation and methods of use are described in detail, and an account is given of certain problems encountered in the development. Their advantages and disadvantages, as compared with other types, are briefly discussed.

DOI:10.1049/ji-2.1948.0178

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The paper deals with two recent developments in the design of audio-frequency metal locators.The first is the introduction of discrimination against low-conductivity magnetic bodies for the purpose of suppressing unwanted signals. A solution is described which forms the basis of a number of these locators. The principle is to utilize the existence of a phase difference between desired and undesired signals.The need for a more radical departure from the established principles is then examined and the second development (locator No. 7) is discussed. In this locator an alternating magnetic field is set up over a large area, and local field distortions, due to metallic bodies, are observed directly by means of a balanced-coil system. In this way it is possible to attain high sensitivity and operating speed, to eliminate interference between operators, and, for war-time applications, to safeguard the user from booby-traps sensitive to an alternating field.

DOI:10.1049/ji-2.1948.0179

出版商:IEE    

年代:1948

数据来源: IET

DOI:10.1049/ji-2.1948.0182

出版商:IEE    

年代:1948

数据来源: IET

摘要:

A flash tube is a gas-filled device designed to produce a brilliant flash of light when it is used to short-circuit a charged capacitor. The discharge is characterized by a high output of radiation in the infrared and ultra-violet as well as in the visible regions.A brief historical review is followed by an outline of the general construction of modern flash tubes. Their electrical characteristics are given together with curves showing current, voltage and power against time. The effect of the tube parameters on the complete circuit characteristics are examined.Some measurements of light intensity, luminous energy and efficiency are given, and the development of the typical high-current arc spectra of xenon under flash-tube conditions is illustrated by a series of spectrograms.Circuits for the control of these tubes are described, suitable for both isolated-flash and repetition-flash applications.The concluding Sections deal with a number of recent applications and with an examination of the possibilities of the flash tube as an aid to the examination of high-speed phenomena, both photographically and visually.

DOI:10.1049/ji-2.1948.0184

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The paper is concerned with transformer economics from the viewpoint of an electricity supply undertaking. It describes a new method of approach by the device of “yearly economic efficiency.” This term is defined and its use illustrated by reference to a range of distribution transformers.A comparison formula is next deduced and applied to two transformers of the same size but having different characteristics.Finally, a supply undertaking is examined and operating conditions are tabulated. The constants necessary for the comparison or purchasing formula are obtained from the information available, and an actual purchasing formula is worked out. Economic efficiency curves for the undertaking's distribution transformers are given, and the lines on which improvements should be made are indicated.

DOI:10.1049/ji-2.1948.0188

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The paper describes measurements, at a frequency of 1 000 c/s, of the capacitance changes in air capacitors due to moisture in the atmosphere. It is shown that these changes may be considerably in excess of those due to the alterations in the permittivity of the air. Over the range of relative humidity 30–65% the total change in capacitance can be about 3 parts in 10 000 at room temperatures. The full advantage of the otherwise high stability of a precision air capacitor is lost when this effect is ignored.

DOI:10.1049/ji-2.1948.0199

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The paper describes some of the problems which arise in providing for security of supplies and economical operation on the British Grid system. Under these two headings separate consideration is given to long-term and short-term planning.Long-term planning of the system determines what generating plant and transmission equipment will be provided, and the paper indicates the extent to which actual plant/load conditions have varied from those which were planned three years previously.Short-term planning is concerned with the operation of the system as it exists and a description is given of a typical day's operation of the British Grid system. Reference is also made to the operation of the system during the 1947 fuel crisis and to other operating conditions of special interest.Probable future developments associated with load dispatching are mentioned and special attention is drawn to the financial savings which could be obtained by providing better availability on high-merit plant.

DOI:10.1049/ji-2.1948.0200

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The paper gives specific design data of two known types of pressure-recorders. They were designed for the hazardous conditions associated with the short-circuit testing of circuit breakers, and where the quantities recorded could be readily correlated with all the other physical quantities involved in such tests. Typical investigation problems and data on circuit-breaker development are given, and serve to illustrate the importance of these measuring and recording instruments.The measurement of dynamic strain by resistance-wire strain gauges is also considered, together with the technique adopted for recording dynamic strain phenomena. A typical measurement taken on a circuit-breaker mechanism is analysed.

DOI:10.1049/ji-2.1948.0204

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The transient stability limits of power systems are determined by assuming conditions to be constant over short intervals of time and using the results obtained at the end of one interval to vary the conditions at the beginning of the next interval. The analysis is tedious and it is easy to make numerical errors.If a large number of machines is involved, it is essential to use an a.c. network analyser for determining the values of power to be used for the different time intervals, but there is no reduction in the computation labour, and in practice the greater part of the time taken for a study is devoted to the latter.To reduce the computation time and the possibility of numerical errors, the “step” evaluations can be carried out semi-automatically by using the computer described. Furthermore, by reducing the time interval, greater accuracy can be obtained without an increase in overall time as compared with normal procedure.

DOI:10.1049/ji-2.1948.0208

出版商:IEE    

年代:1948

数据来源: IET

摘要:

The paper deals with vertical-shaft a.c. generators of large diameter in the speed range 50–500 r.p.m. The influence of turbine and hydraulic characteristics is first considered. This is followed by a discussion of factors which determine the generator dimensions. A brief summary of the considerations affecting rotor design leads to a detailed review of different types of rotor and pole construction and their range of application.An important feature of this type of machine is the thrust bearing and its support, which carry very heavy loads. Alternative types of bearing and bearing arrangement are therefore examined and their merits compared. Methods of bearing cooling are briefly considered.In a Section on the special arrangement of air coolers required for this class of generator, reference is made to the use of generator ventilating air for station heating. This is followed by a Section on the arrangement and operation of brakes and jacks.The stator frame, core and windings; the rotor windings; the exciters and governor generator are briefly considered, and the paper concludes with a short review of special electrical characteristics.

DOI:10.1049/ji-2.1948.0210

出版商:IEE    

年代:1948

数据来源: IET