摘要:

Some properties of the electric vector potential, appearing in problems dealing with eddy currents induced in nonmagnetic metallic solids by the external magnetic field, are considered- The boundary condition for the electric vector potential at the boundary surface of the solid is established. The magnetic field produced by the eddy currents flowing in the solid is examined. An interpretation of the electric vector potential is given. An iterative process for solution of the boundary-value problem for the electric vector potential is presented. The results obtained for transients are adapted to time-harmonic fields.

DOI:10.1049/ip-a-1.1985.0082

出版商:IEE    

年代:1985

数据来源: IET

摘要:

In order to determine the stremes in high voltage DC cable accessering containing a combination of Voltalit (a proprietary epoxy Insulation), SF4and paper/oil inxulation, a knowledge of the surface and bulk conductivily of the Voltalit is required. It ii also necessary to determine the coefficient govering the dependence of both conductivities with temperature and stress, and the variation of conductivities with time after the application of a itep function of direct voltage. Although the bulk conductity of Voltalit has been determined previously, the surface conductlvity In an environment of SF6it not available. The time dependence of both bulk and surface conductvities after the application of a direct voltage are also unknown. Measurements are made over the range of stress and temprature expected in cable accessories, and equations relating both bulk and surface conductivities with stress and temperature determined. The variation of conductiviiy with time after the application of a step voltage is also presented

DOI:10.1049/ip-a-1.1985.0083

出版商:IEE    

年代:1985

数据来源: IET

摘要:

Imaging of 2-dimenslonal distributions of electric conductivity, from voltages measured on perlpheries of the distributions, is studied. It is understood that low-frequency electric currents are injected into the distributions. Optimum placement of electrodes, for maximising the value and sensitivity of voltage measurements, is studied theoretically and experimentally. The imaging theory developed suggests that arbitrary conductivity distributions cannot be unambiguosly reconstructed. Pieccwisc-constant distributions can be imaged successfully, however. Specimen images reconstructed from laboratory measurements, are presented of circularly symmetric conductivity distributions and of piecewise-constant disuibutions.

DOI:10.1049/ip-a-1.1985.0084

出版商:IEE    

年代:1985

数据来源: IET

摘要:

An example of how a general management goes about the formulation of long-term policy and investment programmes, where rapidly changing technology is linked to rapidly changing needs in the market place, in a newly competitive environment, in a time frame extending over the next 15 years. British Telecom is in the middle of an investment programme that will transform analogue network into a digital system. The initial objective was to reduce operating costs, but market demands for new services require additional and substantial investment decisions, with the total running at the rate of £1 billion per year for atleast the next five years. The present ‘layered’ network has been built up by adding services. As the ‘product life cycles’ of the several technologies reach out into the future, new possibilities emerge such as mobile radio where the cellular network can be divided down to accomodate millions of subscribers and, in the longer term, the realisation of an all digital main network serving the business environment, with local intelligence in each subscriber's PABX. As an example of the pace of technology, a 15000 line exchange as now manufactured is based on the technology of about six years ago, and occupies 15 racks. With currently developed technologies, this can be reduced to 3 racks. Extrapolating to techniques of high-density wafer integration, by 1995 only two circuit boards will be required, a small fraction of one rack. The market needs are changing, and a wide adoption of electronic funds transfer by retailers will generate a heavy demand for short duration calls, increasing the processing load. The area of limited improvement is the production of software, where costs are being reduced by a factor of only two per decade.

DOI:10.1049/ip-a-1.1985.0086

出版商:IEE    

年代:1985

数据来源: IET

摘要:

A summary of the discussion meeting includes the introductory talks by representatives of BP, a major clearing bank and a venture capitalist. ‘Technical reviews and appraisals’ is a methodology introduced by the Engineering Council They provide directors and managers with a clearer view of their company's performance, both for the improvement of operational effectiveness, and for development to meet the needs of the future. In addition to providing the company with a regular appraisal and guide towards the future, the reviews are also of considerable importance to investors, including the banks, financial institutions and shareholders. Increasingly in the future these investors will not only be interested in the historic performance of the company in financial terms, but will be seeking a better understanding of the underlying technical health of the enterprise. Technical reviews will assist in this comprehension.

DOI:10.1049/ip-a-1.1985.0087

出版商:IEE    

年代:1985

数据来源: IET