DOI:10.1049/piee.1965.0084

出版商:IEE    

年代:1965

数据来源: IET

摘要:

1.6 million homes were solely electrically heated in the United States in 1963; by 1980, the predicted number is 19 million. In most of these residences temperature is controlled by a 2-position line-voltage thermostat in each room. Suitable continuous and quasicontinuous temperature-control systems have been developed, but the price trend of the semiconductor devices they employ indicates that they will not successfully compete with line-voltage thermostats in the next decade. The 2-position line-voltage methods currently available in the United States have economic and discomfort disadvantages. Facile graphical displays of the extra heating costs caused by cycle time and droop have been derived from a basic electrical-network analogue for the electric space-heating process. Test results illustrate the cold-air currents caused by long cycle times. 2-position controlled skirting-board heaters are prone to deposit dirt on walls; this tendency increases with cycle time. The performance of a discontinuously controlled electric space-heating process is conveniently characterised by portraying the cycle time, manipulated variable and droop in a cycling-characteristic display. The current problems of 2-position line-voltage-controlled electric space heating could be remedied if two performance requirements were set. Recommended values for these are suggested; these can be met if simple design criteria are observed, as is shown using a sample thermostat constructed from standard components.

DOI:10.1049/piee.1965.0087

出版商:IEE    

年代:1965

数据来源: IET

摘要:

The use of the polarised mho distance relay for the protection of high-voltage lines has become widespread. Up to the present time, the relay has been thought to be of limited use in the protection of short lines, owing to its relatively small reach for arcing faults. However, recent practical tests have shown that the actual performance is considerably better than that predicted by theory. A new analysis is therefore developed in this paper which shows that the polarised mho relay has an offset characteristic, in the case of unbalanced faults, which encloses the origin and hence enhances the relay reach in the direction of the resistive axis. The degree of offset is a function of the source/line impedance ratio of the system to which the relay is connected. It is shown that the theory developed is in good agreement with results obtained in practice.It is shown in an Appendix that the theory also covers the cases of crosspolarised directional relays and polyphase impedance relays, both classes of relay having an offset characteristic. The paper concludes by discussing the implication of the results. It is noted that the polarised mho relay has most of the benefits of the reactance relay, while retaining the advantages of being inherently directional and insensitive to load currents and power swings. It is also noted that, by using this method of analysis, the reach for lines with series capacitance may be predicted.

DOI:10.1049/piee.1965.0088

出版商:IEE    

年代:1965

数据来源: IET

DOI:10.1049/piee.1965.0090

出版商:IEE    

年代:1965

数据来源: IET

摘要:

The action of electromagnetism can be ‘explained’ in terms of relativistic corrections to the inverse-square law of electric charges or of any convenient analogy. One of the commonest is that of the electric and magnetic circuits. What constitutes a ‘good’ magnetic circuit and a ‘good’ electric circuit in this context is generally recognised, but it is not so easy to define what one means by a good electrical machine. Yet a combination of the properties of the electric and magnetic circuits must lead to a factor which expresses in some way the ‘goodness’ of the combination. This factor can be evaluated and applied to machine theory with most interesting results. Some examples are given of the ways in which general properties of conventional machines and the performance of some rather curious machines depend on the ‘goodness’ factor.

DOI:10.1049/piee.1965.0091

出版商:IEE    

年代:1965

数据来源: IET

摘要:

The paper describes how to solve some of the problems encountered in studying the time-optimal control of a distributed-parameter system. The problems are illustrated by considering the very simple example of a system, whose behaviour is described by the one-dimensional heat-conduction or diffusion equation, in which it is desired to make the temperature zero at all points in the slab in minimum time, using a bounded control input. In order to obtain numerical results, it is necessary to represent the continuous temperature distribution by a finite number of variables. Three methods of doing this are described: the subdivision method, the Fourier-series method, and the parabolic method. Comparative numerical results are given, and the relative merits of the three methods are discussed. A recently published treatment of the finite-control-time problem is also discussed.

DOI:10.1049/piee.1965.0093

出版商:IEE    

年代:1965

数据来源: IET

摘要:

The stability criterion formulated by Nyquist1is sometimes difficult to apply. The method proved here is algebraic rather than geometric and, for a certain class of problems, leads to a simple technique readily usable in designing systems involving several parameters. The criteria discussed are embodied in three conditions.Thus it is possible to leave some design constants unspecified, and fix them in the best way to ensure stability. This implies a synthetic rather than an analytic approach to circuit design, a feature distinguishing the present method from others which rapidly become unmanageable when even a few design constants are carried.It is also shown how high-degree equations arising from the transfer function can be discussed using only the elementary theory of quadratics. The method is compared with the Routh-Hurwitz approach.

DOI:10.1049/piee.1965.0094

出版商:IEE    

年代:1965

数据来源: IET

摘要:

The use of v.l.f. alternating current as an alternative to direct current for precision resistance measurement is discussed. It is shown that this method of measurement usually enables greater bridge-circuit resolution to be obtained because of increased detector sensitivity and a reduction in the effect of thermal e.m.f.s. For typical standard resistors, the changes in resistance from the d.c. values are found to be small at the frequencies considered. The factors which determine the optimum frequency of measurement and the limits of accuracy attainable are discussed, and suggestions are made regarding possible applications of the techniques described.

DOI:10.1049/piee.1965.0095

出版商:IEE    

年代:1965

数据来源: IET

摘要:

The theory of determining the impulse response of a system by crosscorrelating the output of the system with the input is outlined. It is pointed out that pseudorandom binary input codes prove particularly convenient in facilitating interpretation of the results, and some useful properties of a class of these codes known asmsequences are enumerated.A source of error will occur in experiments using these sequences when the modulator is unable to follow the sequence exactly, and instead takes a finite time for the transition between the two binary states. The form of an error signal convenient for describing these transition delays is determined, and the cross-correlation function of the perfect sequence with this error signal is evaluated. Distinction is made between two cases, corresponding to reversible and nonreversible interstate transitions (i.e. whether or not the transition from the +1 state to the −1 state is accomplished in the same manner as that from the −1 state to the +1 state).The effect of the finite bandwidth of a perfectmsequence input on the measured response is determined by an analysis in the time domain; the results are extended to include the alteration in bandwidth due to reversible-transition errors. The method does not prove convenient for analysing the effect of bandwidth of nonreversible-transition errors to more than a first approximation of the impulse response. However, this result enables criteria to be developed to ensure that nonreversible transitions will give rise to no more serious effects on the measured response than reversible transitions.

DOI:10.1049/piee.1965.0096

出版商:IEE    

年代:1965

数据来源: IET

摘要:

The introduction explains the insulating-liquids committee structure of ERA and its relationship with insulating-oil committees of BSI in Britain and JEC and CIGRÉ internationally. The period since 1958 (the date of the last review) is surveyed, starting with changes made to BS 148 in the 1959 edition and subsequent amendments. The IEC oxidation test is discussed and compared with other national insulating-oil aging tests. A modification, reducing test duration from 8 days to 3, is described, and its correlation with the standard test considered. Mention is made of the ERA 10-year field trials on inhibited transformer oil, and particulars are given of the IEC test for electric strength of insulating oil. The possibility of an internationally agreed specification for transformer oil is discussed. The paper concludes with a brief account of research related to insulating oils, which ERA is sponsoring at three British universities.

DOI:10.1049/piee.1965.0097

出版商:IEE    

年代:1965

数据来源: IET