摘要:

The principle of thyristor-assisted commutation was easily demonstrated on small laboratory-type machines, but the commercial significance of the concept could only be investigated by constructing a machine of a size where commutation would normally be a problem. A 300 kW, 3000 rev/min version was built and the performance of this prototype is described. In particular, it is explained how the problematic sliding-contact performance of this type of machine was satisfactorily achieved using (eventually) only commutators and brushgear of conventional construction. Companion papers describe the commutating-time calculations and the terminal characteristics of the machine.

DOI:10.1049/piee.1976.0012

出版商:IEE    

年代:1976

数据来源: IET

摘要:

A calculation of the commutating time for machines using thyristor-assisted commutation is as important to these machines as the calculation of current-reversal curves for conventional d.c. machines. New factors enter into the determination of the inductance of a commutating coil, particularly an inductance component attributable to a main-pole-axis flux change. Different procedures also apply to the calculation of armaturereaction m.m.f. and interpole-induced voltage. A logical design procedure is described and applied to a typical machine. The development and the terminal characteristics of such a machine are described in companion papers.

DOI:10.1049/piee.1976.0013

出版商:IEE    

年代:1976

数据来源: IET

摘要:

Machines with thyristor-assisted commutation(t.a.c.) have some unusual output characteristics. The small number of commutator sections and the consequently wide interpoles cause voltage and torque pulsations of appreciable amplitude, although the current ripple is usually small. A change in the commutating time with current causes an effective brush swing, resulting in an interpole-generated component of the armature voltage that is current dependent, and also changing the main-pole flux. This current-dependent brush-swing is very advantageous in lapwound machines, as it automatically acts to compensate unbalance of the generated voltages to an extent that makes equalising connections unnecessary. The development of a t.a.c. machine and the commutating-time calculations are described in companion papers.

DOI:10.1049/piee.1976.0014

出版商:IEE    

年代:1976

数据来源: IET

摘要:

Linear induction motors (l.i.ms) have many possible applications, ranging from low-speed cranes to high-speed ground-vehicle propulsion. However, in average and high-speed l.i.ms, the end effects cause considerable deterioration in the performance in low-slip regions. The paper introduces the concept of realistic goodness factorGR, which takes into account by appropriate coefficients the airgap leakage, secondary sheet skin effect and transverse edge effects. Approximations involved in obtainingGRare discussed and essentially a one-dimensional analysis is used. It is shown that the end-effect influence can be expressed as a function ofGR, slip and the number of poles. An optimum goodness-factor criterionGoto aid an optimum l.i.m. design is proposed. It is demonstrated thatGocan be achieved in practice, and leads to a good-performance, low-weight l.i.m. Numerical results based on a full-size existing l.i.m. test vehicle are given.

DOI:10.1049/piee.1976.0015

出版商:IEE    

年代:1976

数据来源: IET

摘要:

The paper reviews the needs of the blind community for printed material, and surveys current developments in the applications of automation to increase the availability of Braille. The problems of automatic translation of English text to Braille are considered. Some possible systems for giving a greatly improved access to Braille are surveyed, and an automated system for map and diagram production is reviewed. The future provision of information services for the blind, using special systems or existing systems with special terminals, is discussed. The technical problems are not trivial, but collaborative ventures, with international cooperation, could offer solutions in a relatively short time scale.

DOI:10.1049/piee.1976.0017

出版商:IEE    

年代:1976

数据来源: IET

摘要:

The sequential return difference method is applied to the design of a digital controller for a multivariable digital system. Although the open loop system is unstable, it is shown that a controller which provides good transient behaviour and low interaction may be designed by the appropriate sequence of single-loop, digital, root-locus designs.

DOI:10.1049/piee.1976.0018

出版商:IEE    

年代:1976

数据来源: IET

摘要:

The paper deals briefly with the history of engineering and its recognition as a profession. The growth of professional institutions is traced and their contribution to the education, training and qualification of engineers is explained, with reference to the Council of Engineering Institutions. After a review of the present situation, the roles of professional chartered and technician engineers are considered, with special emphasis on trends and possibilities in the development of engineering, especially electrical engineering, in the final decade of the 20th century. A significant problem is likely to be a decline in the output of engineering graduates; some reasons for this and some possible solutions are suggested in the paper.

DOI:10.1049/piee.1976.0019

出版商:IEE    

年代:1976

数据来源: IET

摘要:

Steady-state ionisation currents under uniform field conditions have been measured in SF6over the range 110 ≤E/p≤1000V cm−1torr−1with gas pressures varying from 1 to 10 torr, at 20°C. Sparking potentialsVswere also measured for a range 1≤pd≤20 torr-cm. Townsend's primary ionisation (α/p) and electron-attachment (η/p) coefficients were found to depend onE/ponly. The values of secondary-ionisation coefficient (γ) were also determined over the range 140≤E/p≤600 V cm−1torr−1. Measurements ofVsof SF6have shown that the deviations from Paschen's law rise up to ±3.5% at values ofpdnear the Paschen minimum.

DOI:10.1049/piee.1976.0020

出版商:IEE    

年代:1976

数据来源: IET