摘要:

Owing to the combination of high current density and low forward voltage drop in the rectifying junction of a semi-conductor rectifier, the physical size and thermal capacity for a given rating are low, so that the current on overload can be much greater than for other types of rectifier. Consequently, the junction-temperature rise on overload is extremely rapid, and in some cases considerable temperature fluctuations occur at mains frequency. It is therefore necessary to be able to monitor the junction temperature dynamically (i.e. under working conditions at mains frequency) and to observe the rise of temperature with time. A further necessity for dynamic testing occurs since the measurement of the forward characteristic at high current by d.c. methods can result in excessive heating and possible failure. In the apparatus to be described the separation of forward and reverse half-cycles is secured by means of a synchronous commutator, permitting independent measurement of forward and reverse current and voltage at mains frequency, and hence continuous indication of junction temperature. Operation of the rectifier at full rating without expenditure of the full power necessary to accomplish this by direct methods is also possible. This is particularly useful in life testing large numbers of semi-conductor rectifiers. Limited experience indicates that this method of testing provides operating conditions which are in all ways identical to those which a device experiences under fullload conditions

DOI:10.1049/pi-c.1959.0003

出版商:IEE    

年代:1959

数据来源: IET

摘要:

When a waveguide supporting a given mode is bent at some point along its length, there is generally a problem in providing for the continuity of the same undisturbed field pattern throughout. The hollow metal rectangular waveguide transmitting the dominant H01mode and bent in the E-plane is an exception to this, but for the most part mode conversion occurs at the bend, which can have serious consequences in multi-mode tubular waveguides or in surface waveguides. To minimize this difficulty in the circular Hoi waveguide, a proposal was made previously to use an inhomogeneous dielectric in association with the waveguide as a means of accelerating the wave pattern on the outside of the bend and retarding it on the inside, so as to approach much more closely the ideal conditions. In the present paper this idea has been extended to other forms of waveguide, and dielectrics which might find application in this way are briefly discussed.

DOI:10.1049/pi-c.1959.0004

出版商:IEE    

年代:1959

数据来源: IET

摘要:

Polynomials associated with network functions are investigated by simple topological methods.The main result is contained in Theorem 1, which states that the determinant of the nodal admittance matrixPof a connectedRLCnetwork without transformers is of the form:detP=[Polynomial in λ containing a constant term and of degree (2N+2−SC−SCR−SL−SLR)]/λN+1−SL−SLR.Here, λ is the complex frequency variable,Nis the number of nodes in the network andSC,SCR,SLandSLRare the connectivities of those sub-networks of the given network formed, respectively, of the capacitors only, the capacitors and resistors only, the inductors only and the inductors and resistors only.This result is based upon an expression for detPas the sum of tree-products, which are defined.A dual result is obtained for the determinant of the loop-impedance matrix, and the extension to other network functions is indicated, the driving-point admittance function being taken as an example.

DOI:10.1049/pi-c.1959.0005

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The paper describes some measurements of time-decrease of permeability on three types of samples stamped out from 4%-silicon hot-rolled transformer steel. The first samples contained severe mechanical stresses. Secondly, samples annealed at 800°C were used, and the maximum time of permeability decrease of about 24 hours was reduced after annealing to about 8 hours.Finally samples annealed at 1250°C in hydrogen atmosphere were measured and the results showed that the time-decrease phenomenon as practically eliminated according to the theory of Snoek.

DOI:10.1049/pi-c.1959.0006

出版商:IEE    

年代:1959

数据来源: IET

摘要:

A method is described for statistically analysing the relationship between weather and electricity demand for applications to practical load estimating by electricity supply engineers. The characteristics of the specific meteorological elements to which the demand has been found to respond are discussed, particularly those affecting heating and lighting demands. The thermal-lag factor appropriate to the delay in consumer response to temperature changes and the influence of the cooling power of the wind on heating load are examined. In order to assess the lighting load, observations of the atmospheric transmission of light are used to derive a method for reducing cloud and visibility forecasts to their daylight illumination equivalents.

DOI:10.1049/pi-c.1959.0007

出版商:IEE    

年代:1959

数据来源: IET

摘要:

A brief description of the standard inductors at the National Physical Laboratory is given. The principal characteristics of self- and mutual inductors are then considered in relation to their measurement. The methods of inductance measurement at the N.P.L. are described; these include the calibration of mutual and self-inductors, the measurement of their variation with frequency, the a.c. resistance of inductors, and the components of self-capacitance. Emphasis is given to the precautions necessary to ensure precision.

DOI:10.1049/pi-c.1959.0008

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The first part of the paper is concerned with the choice of the optimum filter for the extrapolation or interpolation of a signal which is contaminated by noise. The problem has been completely solved by Wiener in his book on the subject. The method used here for solving the integral equations is different and leads to the solution for the lagging case without having to approximate ε−pτby the ratio of polynomials inp. Laplace transformations are used and lead directly to the solution. The second part of the paper deals with the solution of the optimum filter when the error is minimized at a particular time after switching on, the averaging being taken over an ensemble. Examples of each problem are given.

DOI:10.1049/pi-c.1959.0009

出版商:IEE    

年代:1959

数据来源: IET

摘要:

In this Part, the conductivity of the oxide-cathode matrix in an S-type valve in the presence of a magnetic field is examined, and it is shown that the matrix exhibits a powerful magnetic-resistance effect. However, the effect occurs only when the electron transfer is by free flight through the hollow pores of the matrix and when the magnetic field is in a transverse direction, and the solid-particle phase of the conduction mechanism shows no measurable magneto-resistance effect.

DOI:10.1049/pi-c.1959.0010

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The paper presents a comparison of Millington's method and the equivalent numerical distance method with theory. It is shown that Millington's method may be used in most practical problems of groundwave propagation. For overland paths the errors of this method are very small; for land-sea paths they may be larger, up to about 2.7 dB for 2-section paths, up to about 5.5 dB for 3-section paths, and up to about 2.5 dB for each land-sea boundary for very long paths. In most cases the equivalent numerical distance method shows considerable errors. This method may be used for paths representing small numerical distances, especially for overland paths. It may also be applied to longer paths when the differences between the electrical parameters of the sections are insignificant.

DOI:10.1049/pi-c.1959.0011

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The papers unearthed dealt mainly with problems connected with the flow of electromagnetic energy, and showed that Heaviside had extended Maxwell's theory so that gravitation could be fitted in with electromagnetism.It was also found that Heaviside had evolved a rigorous justification for his ‘operation’ of extracting the square root of the process of partial differentiation; for he had discovered the conditions under which his differential time operatorplost its original significance and became the transform parameter of an infinite integral of the Stieltjes type which obeys all the laws of algebra and analysis.

DOI:10.1049/pi-c.1959.0012

出版商:IEE    

年代:1959

数据来源: IET