摘要:

In this paper an adaptive delta modulator (a.d.m.) is proposed which derives its companding information from the number of transitions from 0 to 1 and 1 to 0 that occur in the digital output. The companding characteristics and the s.n.r. have been analysed. The details of an experimental coder built in the laboratory are given along with the performance. At 32 kbit/s, the s.n.r. for a 800 Hz signal is >26 dB for an input variation of 30 dB. It compares well with other similar a.d.m. coders.

DOI:10.1049/piee.1979.0075

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The inherent unbalance in a 3-phase linear induction motor (l.i.m.) operating under a voltage-fed mode is accentuated by end effects at high speeds. The voltage-fed operation is analysed by identifying the slip-dependent inductance coefficients corresponding to the positive- and negative-sequence components, and taking into account the stator resistance and leakage reactances. The approach takes care of the longitudinal end effects and the skin effect in the secondary plate. The model is capable of treating the single-phase and plugging operations as special cases of interest. The theoretical and experimental characteristics of a 4-pole l.i.m. driving a rotating-disc facility under general conditions of supply unbalance are presented. Comparison of the thrust characteristics reveals that while the current-fed operation is superior for normal motor operation, the voltage-fed mode offers higher reliability as a brake.

DOI:10.1049/piee.1979.0076

出版商:IEE    

年代:1979

数据来源: IET

摘要:

A scheme for stabilising the dynamic performance of a stepping motor is described. When the motor operates unstably, the velocity varies cyclically about the synchronous speed. A signal proportional to this velocity oscillation is used to frequency modulate the command pulses, which control the switching of the motor phases. Stable operation is achieved by suitable adjustment of the phase displacement between the velocity signal and the modulating signal. The approach is derived from an analysis which provides a physical understanding of the mechanism of dynamic instability.

DOI:10.1049/piee.1979.0077

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The development of a model for predicting the dynamic response of hybrid permanent-magnet stepping motors from static flux-linkage data is described. The method involves the derivation of mathematical functions for the flux-linkage of the stator coils in terms of coil current and angular position of the rotor. A comparison of experimental and predicted responses for a typical medium-sized commercial motor is made in terms of (a) settling time against stator-circuit-resistance characteristics, (b) detailed single-step position/time waveforms and (c) pull-in rate characteristics.

DOI:10.1049/piee.1979.0078

出版商:IEE    

年代:1979

数据来源: IET

摘要:

Characteristics of a vacuum arc under an axial magnetic field have been investigated. The confinement effect of the arc between the electrodes is clearly demonstrated. By this effect, it was found that the arc is significantly stabilised, and consequently the interrupting ability of the arc increases. A demonstration of the current interruption up to 200 kA r.m.s. is shown and the design philosophy of the interruption is discussed.

DOI:10.1049/piee.1979.0079

出版商:IEE    

年代:1979

数据来源: IET

摘要:

There has been continuous development of better techniques for assessing transient instability in a power system. It has also been recognised that there is a need for additional indices of transient stability which more completely reflect all the factors that influence system stability. The bulk of the work in this area is based on deterministic models. The probabilistic nature of the basic factors which affect transient-stability performance of a power system has been demonstrated in recent papers.1,4This paper illustrates the inclusion of probabilistic considerations in transient-stability analysis of a practical power system by application to a multimachine configuration. A relatively simple multimachine system is used to demonstrate the technique of considering the probabilities associated with the type, location and clearance of faults. The approach in this paper is not restricted by the simplifying assumptions made in Reference 4. Reliability levels for different fault types and fault locations are evaluated, and the effect of variation of selected system parameters on the overall reliability of the system is investigated.

DOI:10.1049/piee.1979.0080

出版商:IEE    

年代:1979

数据来源: IET

摘要:

Automatic load following by fossil-fired generating units requires the control of the flow of air and fuel to the boiler, and of the steam flow to the turbine. Prototype load controllers designed to achieve this have been installed at coal and oil-fired power stations within the CEGB. The principle behind their design is that boiler-stored energy is made available only for system frequency regulation. This policy helps to maximise the regulation capability available to the grid system while minimising the cyclic damage inflicted on the plant. Test results and operating experience show that both coal and oil-fired units equipped with such load controllers respond successfully to both loading and frequency regulation demands. Evidence of improved coal-fired combustion efficiency has also been obtained.

DOI:10.1049/piee.1979.0081

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The selection of conductors for a modern overhead transmission or distribution system is an exercise in optimisation and balancing of conflicting requirements. Service experience and environmental considerations may often challenge established concepts for the design of future lines. The reasons for the predominance of aluminium-based conductors are outlined, and the wide available range of such conductors and the properties of each main variant are described. The influence of manufacturing processes in conductor design is set out, and the important role played by greasing is emphasised. These considerations are shown to lead to the selection of particular conductors in each of the voltage bands from 1.v. to u.h.v. Factors discussed include load density and growth, climatic environment, strength, standardisation, corrosion, external loading, corona effects and economics. The paper proceeds to describe the effects of aeolian vibration, subconductor oscillation and galloping on the choice of conductor and fittings, and on conductor bundle geometry. The rather different emphasis in choosing conductors for distribution systems is also discussed and the overriding need for standardisation stressed. The need for conductor-material specifications and acceptance testing is recognised, and the paper concludes with a brief outline of possible future trends in conductor engineering.

DOI:10.1049/piee.1979.0082

出版商:IEE    

年代:1979

数据来源: IET

摘要:

Two design methods are presented for a doubly-excited, doubly-salient, concentrated-winding type of limited-rotation double-acting rotary actuator employing natural air cooling. The first is based on specified values of current density and magnetic flux density, and the second (a development of the first) uses experimental data relating winding temperatures toI2Rlosses. A synthesis procedure is described that uses the second method for a family of actuators of different continuous torque, peak torque and aspect ratio. Curves are presented that show the variation of important design parameters with aspect ratio and scale. The use of forced convection cooling is suggested as a way of improving the performance/volume ratio of larger actuators.

DOI:10.1049/piee.1979.0085

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The polymer field has been the source of both elegant discoveries and highly useful inventions. It has responded to three main driving forces: first, the ‘push’ provided by fundamental discoveries in physics and chemistry; secondly, the ‘pull’ provided by the needs of the electrical industry; and, thirdly, the ‘feedback’ of electrical discoveries and inventions into the field of polymer chemistry. Exciting prospects in the field of biology based on the ever-increasing sophistication of polymer chemistry lie ahead of us. As new knowledge and new needs emerge, we will have ample opportunity to continue bringing electrical technology and polymer science together in ways that surely would have made Lord Kelvin proud.

DOI:10.1049/piee.1979.0086

出版商:IEE    

年代:1979

数据来源: IET