摘要:

Modern economics demand a reduction in costs and prices, and this usually means reduction in the amount of materials used. The danger is that some of the insulation materials in use have a cellulose base, which means that their ageing may be endangered if the temperature is higher than the 110°C, since, above this temperature, the cellulose materials tend to change quickly their consistency and mechanical strength.It has been generally agreed that the life expectancy of electrical machines should be seven years when continuously under rated load. General equations for change in life expectancy with temperature have been experimentally and partly deductively found and presented by Montsinger and Bussing, and experiments show that the equations are correct for continuous loads. But when the load changes the heating and cooling periods must be taken into consideration. Short-circuits or heavy overloads can be very dangerous.Equations have been developed for load changes and for straight line and exponential temperature changes, and it is shown that the cooling-off period especially can be very dangerous and take a very appreciable part of the life expectancy of the electrical equipment in question. Sample calculations on transformer and intermittent motor loads are included.

DOI:10.1049/pi-c.1960.0022

出版商:IEE    

年代:1960

数据来源: IET

摘要:

Transformation matrices relating two adequate systems of simple network co-ordinates such as node-pair voltages or link currents belong to the class of unimodular or E-matrices. The paper makes a distinction between the matrices corresponding to such voltage and current transformations, and different sets of necessary conditions are derived for each type.Since the loop- and cut-set-to-branch incidence matrices are closely related to transformation matrices, the discussion proposes new sets of necessary conditions for incidence matrices corresponding to systems of node-pair voltages or link currents. Examples are given of matrices which whilst representing a voltage transformation cannot represent a current transformation and vice versa. Another example shows an E-matrix which can represent neither a voltage nor a current transformation.

DOI:10.1049/pi-c.1960.0023

出版商:IEE    

年代:1960

数据来源: IET

摘要:

The paper introduces a method of stabilizing control systems which have backlash in their control sequence. The technique described employs an auxiliary loop to drive the motor across the backlash whenever the motor and load tend to separate. Requirements of the auxiliary loop are deduced and a phase-plane analysis is developed for a second-order position-control system with this loop operative. Analysis shows that the system with backlash is effectively linearized. It is also shown that impacts between motor and load are avoided.To establish the feasibility of the method an analogue computer study is presented. Results from the analogue show that the technique leads to considerable improvement in the step-function response. Variation of the system damping and of the ratio of inertias is also investigated. It is found that the system stabilized by the technique behaves essentially as a linear system.

DOI:10.1049/pi-c.1960.0024

出版商:IEE    

年代:1960

数据来源: IET

摘要:

In the present Part an attempt is made to determine the nature of the dissociative action which accompanies the passage of a current through a barium-strontium-oxide matrix at 1 020°K. Two identical oxide systems operating at a common temperature and passing the same quantity of electricity but at different rates might be expected to suffer the same mass of oxide dissociation. Experiment shows, however, that such is not necessarily the case and that dissociation mass is determined by rate of application of electricity rather than by the total quantity of electricity.The products of dissociation are shown to be in ionic form, and experimental arrangements are made for the separate collection of the ions in chemical form on a relatively massive scale.A working hypothesis is offered in explanation of the experimental observations.

DOI:10.1049/pi-c.1960.0025

出版商:IEE    

年代:1960

数据来源: IET

摘要:

A method of calculation, which should be adequate for strip-lines of small spacing, is proposed for the evaluation of the radiation of line-above-ground configurations. It is shown that an open-circuit is appreciably worse, from the point of view of radiation loss, than short-circuit with a right-angle corner at an intermediate level. The radiation from a matched post is slightly worse than from the short-circuit, but it should be capable of considerable improvement by the use of a terminating frame antenna. Formulae are also given for the effects of reactive posts, with applications to a simple resonator.

DOI:10.1049/pi-c.1960.0026

出版商:IEE    

年代:1960

数据来源: IET

摘要:

A quasi-static transmission-line method, as used in antenna theory, and modified to take into account effects of radiation damping, is applied to the problem of waveguide coupling through slots which may be large enough to exhibit resonance effects. It is shown that the waveguide environment significantly alters the value to be used for the slot characteristic impedance, although this quantity cannot itself be calculated by the present analysis. The method is applied in detail to the case of axially-coupled waveguides and to guides coupled, via a common broad wall, through crossed slots. It is shown that a narrow slot needs to be very near resonance to give a coupling as large as that from a circular hole of comparable dimensions.

DOI:10.1049/pi-c.1960.0027

出版商:IEE    

年代:1960

数据来源: IET

摘要:

A method is given for the design of a class of wide-angle reflectors in which the aberrations are reduced by coating the reflector surface with a dielectric. At microwave frequencies this dielectric may take the form of an array of metal plates or waveguides and the constraint imposed by this form greatly simplifies the analysis. The path of the feed point is chosen so that only selected rays from it are equally phased. It is then found that both of the reflector's profiles and the path of the feed point can be described by a single parameter. The residual aberrations of several cylindrical systems, including the corrected parabola and circle, are analysed to find a reflector for which the scanning arc is the circle with centre at the vertex of the reflector. A refocusing procedure, which is found to be necessary, produces this scanning arc. Experimental results in agreement with the theory are given.It is shown that the design principle can be used to programme a step-wise procedure for the design of corrected surfaces using nonconstrained natural dielectric coatings.

DOI:10.1049/pi-c.1960.0028

出版商:IEE    

年代:1960

数据来源: IET

摘要:

The paper discusses a technique for improving the response of a saturating servo mechanism subjected to random signals. It is shown that a non-linear error detector gives a considerable reduction in error magnitude for a large range of input signals. It is possible to design the additional non-linearity to optimize the performance of the system for all input magnitudes. This form of non-linearity has previously been shown to effect improvement in the response of such systems to step-function and sinusoidal inputs.Experimental work verifies the predicted results for a particular system, and shows that considerable latitude is permitted for the characteristic of the additional non-linearity.

DOI:10.1049/pi-c.1960.0029

出版商:IEE    

年代:1960

数据来源: IET

摘要:

In most waveguides of practical interest the wave impedance in the direction of propagation of the wave is positive and its magnitude does not vary with position. It is shown that, in general, a guiding structure supporting a hybrid mode, i.e. a mode having axial components of both the electric and magnetic fields, can present a negative wave impedance. The case of the EH11mode on a dielectric rod is then considered, and it is shown that for this mode the wave impedance is negative over part of the transverse plane and hence leads to regions of negative power flow if the usual interpretation of the Poynting vector is employed. The total power flow, however, is still positive, since the negative power density and the negative wave impedance occur only in a restricted part of the cross-section.The orthogonality of the fields is also discussed, and it is shown that for hybrid modes the transverse electric and magnetic fields are not at right angles to each other.

DOI:10.1049/pi-c.1960.0030

出版商:IEE    

年代:1960

数据来源: IET

摘要:

The radiation from the open-circuited end of an externally dielectriccoated metallic waveguide can be controlled by varying the size of the guide, the thickness and/or the dielectric constant of the coating. A new type of aerial designed around this principle is given the name ‘surface-wave aerial’ and radiation-pattern measurements are used to confirm the theory underlying this type of radiator.According to its mode of operation it belongs to the category of end-fire aerials, which are briefly reviewed to show that surface-wave aerials occupy a place in their own right amongst the many possible arrangements that utilize the end-fire effect to produce a directional radiation pattern.The theory of the surface-wave aerial is developed in detail, a necessary preliminary step being a full theoretical analysis of the properties of the first-order cylindrical surface wave. It is shown that a dielectric-coated cylinder which is approximately a wavelength in circumference can act as a waveguide for higher-order surface waves, of which the first order is an example.The ‘characteristic equation’ is determined for the general case from which the cut-off frequency, propagation coefficient and conditions under which propagation can take place are derived in turn.Two specific cases are evaluated numerically and the results are used to calculate the polar diagrams of surface-wave aerials operating at 9Gc/s.The wavelength constant as well as the continuous radiation loss of a surface waveguide for which λg/λ0≃1 are measured directly and the results obtained are used to account for the radiation pattern of very long aerials. In conclusion, an outline of future work is given.

DOI:10.1049/pi-c.1960.0031

出版商:IEE    

年代:1960

数据来源: IET