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Volume 138
Issue 1
IEE Proceedings A (Science, Measurement and Technology)
Volume 138, Issue 1, January 1991
Volume 138, Issue 1
January 1991
Electrical engineering: the backbone of society
- Author(s): David A. Jones
- Source: IEE Proceedings A (Science, Measurement and Technology), Volume 138, Issue 1, p. 1 –10
- DOI: 10.1049/ip-a-3.1991.0001
- Type: Article
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Engineering has served society throughout the history of mankind. In recent centuries there has been an acceleration of progress, and, especially since the industrial revolution, there has been an emphasis on mechanisation. Discoveries in the 18th and 19th centuries led to a knowledge of electromagnetic phenomenon; in the application of these, the profession of electrical engineering was born. At the present time, society depends on electricity and electrical engineering for almost all its activities, from leisure to business to manufacturing. The paper traces the history of the introduction of electrical equipment and devices that are now taken for granted but on which modern society heavily depends.
IEE Management & Design Division: Chairman's address. Engineering change; or is it change engineering? A personal perspective
- Author(s): D.R. Towill
- Source: IEE Proceedings A (Science, Measurement and Technology), Volume 138, Issue 1, p. 11 –21
- DOI: 10.1049/ip-a-3.1991.0002
- Type: Article
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The paper illustrates the way in which a knowledge of ‘hard’ systems can be utilised to plan and manage change in ‘soft’ systems. Many analogues may be used to ‘engineer’ change effectively, including system simplification techniques, aggregation, input/output analysis, feedforward/feedback controls, periodicity, sampling and determination of important signals in conditions of poor SNR scenarios. It is further argued that this discipline of ‘change engineering’, which is common to many walks of life, is naturally related to systems engineering concepts. Thus the graduate engineer who possesses a working knowledge of these concepts will be in demand in a wide range of professions. Thus the ‘leakage’ of good engineering graduates into commerce, line management, consultancy etc. may be a tribute to their lateral education as much as a criticism of technology orientated employers failing to offer suitable challenges and rewards.
IEE Science Education & Technology Division: Chairman's address. Magnetism: it is permanent
- Author(s): K.J. Overshott
- Source: IEE Proceedings A (Science, Measurement and Technology), Volume 138, Issue 1, p. 22 –30
- DOI: 10.1049/ip-a-3.1991.0003
- Type: Article
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Permanent magnet materials have one of the longest histories of any technological phenomenon, stretching from before 4000 BC to now. The early history of lodestones (naturally occurring magnets), their applications and their use to make artificial magnets is described. The early work of the Chinese and European magnet users culminated in the classic text ‘De magnete’ published by William Gilbert in 1600. The developments of the next two centuries were based on Gilbert's work until the development of the electromagnet enabled steels to be magnetised without recourse to a lodestone. The improvements in the magnetic properties of permanent magnets then took place gradually, by the development of steels and by optimising alloy compositions and heat treatments. In the 20th century, three major families of permanent magnet materials (metal, ceramic and rare earth) have been developed. The composition, properties and the method of manufacturing these metal (aluminium-nickel-cobalt-iron), ceramic (barium or strontium ferrite) and the three generations of the rare earth (RCo5, R2Co17 and NdFeB) magnets are described, and the possible applications of permanent magnetic materials are briefly tabulated. Finally using performance indicators that have been defined earlier, it is shown that the performance of permanent magnet materials have increased two-hundred-fold in the 20th century. The past and future of these important commercial engineering materials is permanent.
Positive DC corona and sparkover in short and long rod-plane gaps under variable humidity conditions
- Author(s): M. Boutlendj ; N.L. Allen ; H.A. Lightfoot ; R.B. Neville
- Source: IEE Proceedings A (Science, Measurement and Technology), Volume 138, Issue 1, p. 31 –36
- DOI: 10.1049/ip-a-3.1991.0004
- Type: Article
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The variations, with humidity, of the positive DC corona-current voltage characteristics and of sparkover stresses have been studied in rod-plane gaps of spacings in the range 10≤d≤150 cm. The steady component of the current in the glow regime is described by the square law equation over the whole range of gaps, requiring only adjustment of a coefficient for each combination of gap spacing and humidity employed. The rate of change of current with humidity, at any constant voltage, is the same for all gap spacings. The mean stress for sparkover is the same for gaps 50≤d≤150 cm, irrespective of rod profile, and is linear with humidity variation, but anomalous low sparkover stresses occur above 19 g/m3 in the largest gaps. In shorter gaps, the rod profile plays a larger role, and the transition from glow-controlled to streamer-controlled breakdown is demonstrated in the 20 cm gap.
Study of the electric fields required for streamer propagation in humid air
- Author(s): N.L. Allen and M. Boutlendj
- Source: IEE Proceedings A (Science, Measurement and Technology), Volume 138, Issue 1, p. 37 –43
- DOI: 10.1049/ip-a-3.1991.0005
- Type: Article
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The electric field required to sustain streamer propagation is important to the interpretation of breakdown in nonuniform field geometries. Basic measurements of the minimum field for propagation have been carried out in uniform fields. These have shown that above a ‘threshold’ value of field, there is an increasing probability of propagation up to a ‘stability’ field at which propagation always occurs. Comparison is made (a) with earlier work in both uniform and nonuniform fields, (b) with a survey of the mean stresses required for breakdown under lightning impulse and steady voltages. This leads to the conclusions that the stability field is a better parameter to use than the threshold field in making comparisons with lightning impulse breakdown and that the threshold field corresponds more closely with the stress required for steady voltage breakdown. Humidity effects are discussed.
Time domain model for the ferromagnetic core, including the effects of hysteresis and eddy currents
- Author(s): S.R. Naidu
- Source: IEE Proceedings A (Science, Measurement and Technology), Volume 138, Issue 1, p. 44 –50
- DOI: 10.1049/ip-a-3.1991.0006
- Type: Article
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A time domain model for the ferromagnetic core is presented. The model includes the effects of hysteresis and eddy currents. Simulation of the nonlinear B-H trajectories is based on Preisach's theory, and it requires only the limiting hysteresis loop as input data. The model has been checked against measurements of the inrush currents obtained for a small transformer. There is satisfactory agreement between the calculated and measured current transients.
Dependence of electrical tree inception and growth on mechanical properties
- Author(s): D.W. Auckland and B.R. Varlow
- Source: IEE Proceedings A (Science, Measurement and Technology), Volume 138, Issue 1, p. 51 –54
- DOI: 10.1049/ip-a-3.1991.0007
- Type: Article
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The mechanical properties of an unsaturated polyester resin have been varied by the addition of a plasticising polyester resin. Specifically, the tensile strength, modulus of elasticity and fracture toughness have been determined over a range of plasticisation. The initiation and growth of electrical trees in a needle-plane geometry in this range of materials have been investigated. Two conflicting criteria determine the initiation and growth: the presence of internal mechanical strain, and the intrinsic mechanical properties of the material. The initial internal mechanical strain, resulting from the manufacturing process, greatly enhances tree inception and propagation. This effect is dominant and masks the intrinsic dependence of tree initiation and growth on mechanical properties. In strain-free samples, however, the reduction in inception time and the increase in growth rate resulting from the plasticisation of the material, and the ensuing changes in mechanical properties, are clearly shown.
Electromagnetic energy changes due to charges moving through constant, or zero, magnetic field
- Author(s): C.J. Carpenter
- Source: IEE Proceedings A (Science, Measurement and Technology), Volume 138, Issue 1, p. 55 –70
- DOI: 10.1049/ip-a-3.1991.0008
- Type: Article
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The paper examines the interaction between a charge q moving at constant velocity through a region in which the magnetic flux density may be zero, but the A vector is not. The simplest example of the source of A is a closed toroid carrying constant current. The motion of q induces an EMF in the toroid, causing an exchange of energy with the current source, although the toroid produces no external magnetic flux or induced electric field. It is shown that the apparent anomaly of a transfer of energy without a force on q is resolved by the changes of internal energy and by the definition of what is meant by the term ‘force’. The interaction depends on the vector A, and illustrates the consequences of a change of electrokinetic momentum, a concept, due to Maxwell, whose practical application has been explored in previous papers. Its predictions are, necessarily, consistent with those of field theory, but assigning the momentum and stored energy to the charges, instead of the field, clarifies the operating principle, defines the parameters in terms of inductance, and provides an equivalent circuit, as in other electrical machines, whereas the alternative field concept of flux linkage is difficult to apply to a charge q moving through no flux. The Aharonov-Bohm effect, which is commonly stated to be inconsistent with classical electromagnetism, provides an example of the momentum change in terms of the quantum-mechanical phase change due to the vector A.
Investigation of ablation-dominated AC nozzle arcs
- Author(s): M.T.C. Fang and W.H. Bu
- Source: IEE Proceedings A (Science, Measurement and Technology), Volume 138, Issue 1, p. 71 –77
- DOI: 10.1049/ip-a-3.1991.0009
- Type: Article
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The behaviour of ablation-dominated AC arcs in supersonic nozzle has been analysed. For a given gas and nozzle material, the dynamic behaviour of arcs burning in affinely related nozzles is fully determined by three non-dimensional coefficients: the nozzle coefficient N; the ablation coefficient Ab; and the non-dimensional frequency Ω. For circuit-breaker operations, the values of these three non-dimensional parameters are such that flow reversal (i.e. from the nozzle to the upstream tank), caused by inner nozzle wall ablation, cannot be avoided. When this happens, the arc and flow conditions at current-zero are dependent on N (i.e. peak current for a fixed stagnation pressure). The temperature of the gas in the external flow can be much higher than that in the upstream tank. The peak current therefore has a direct influence on the thermal and dielectric recovery processes inside the nozzle. Arc modelling cannot in general be divided into a quasi-steady-state (hence DC) phase and a current-zero period.
Function representation of lightning impulses produced by a testing circuit with continuity of voltages and currents at a tested object
- Author(s): R. Sobocki
- Source: IEE Proceedings A (Science, Measurement and Technology), Volume 138, Issue 1, p. 78 –82
- DOI: 10.1049/ip-a-3.1991.0010
- Type: Article
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Mathematical formula describing full and chopped lightning impulses occurring when a tested device is represented by a complex impedance, and for nonzero initial conditions at a chopping moment, have been derived. The derived method of parameter calculation of the formula fitting chopping of the impulse is presented. Interpolation formulas for computation of the full impulse formula coefficients are proposed. An application example of the method is also given.
The chemistry of electric fuse arcing
- Author(s): D.R. Barrow ; A.F. Howe ; N. Cook
- Source: IEE Proceedings A (Science, Measurement and Technology), Volume 138, Issue 1, p. 83 –88
- DOI: 10.1049/ip-a-3.1991.0011
- Type: Article
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Manufacturers of high-breaking-capacity fuselinks seek more accurate models of fuse behaviour during the arc period of operation. These models will only be produced if the understanding of fuse arc phenomena is improved. Arcing produces elevated temperature and pressure within the plasma and hence a chemically active environment. Experiments were done on very fast acting fuses with silver elements to ascertain the significance of the chemical reactivity. The tests included calorimetry, ‘wet’ analysis of fuse fulgurite, electron spectroscopy for chemical analysis, and determination of gas produced. The conclusions were that no chemical change takes place during fuse arcing. Current limitation must arise, therefore, from physical processes.
Insulator flashover in SF6 under impulse voltage conditions
- Author(s): I. Al-Bawy and O. Farish
- Source: IEE Proceedings A (Science, Measurement and Technology), Volume 138, Issue 1, p. 89 –97
- DOI: 10.1049/ip-a-3.1991.0012
- Type: Article
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The paper describes a study of the impulse-flashover characteristics of insulating spacers in an SF6-gas environment. Measurements have been made using 0.15/20 μs and 0.15/1500 μ/s waveforms for:(a) plain cylindrical spacers(b) spacers with a defect at the insulator/gas/electrode triple junction(c) spacers with metal inserts which shift the maximum field to the midgap region.It has been shown that, when the spacer is discharged between pulses, the effect of the triple-junction defect is independent of the polarity of the adjacent electrode, whereas, when charges are allowed to accumulate during the tests, there is a further large reduction in strength only for the case of a defect at the cathode. This has been explained on the basis of the dependence of the surface charge accumulation on the rate of production of initiatory electrons. Metal inserts have been found to provide effective shielding of the triple junction, provided that the midgap field remains below the inception level. However, unlike the case of the triple-junction defect where the region of enhanced field is highly localised, the inserts increase the field over a wide area so that the conditions for discharge propagation are satisfied at the inception level. This has been confirmed by comparison of the breakdown data with calculated values of discharge inception voltage.
Measurement of thermal transients in a thermal print head used for dye diffusion colour printing
- Author(s): P.W. Webb and R.A. Hann
- Source: IEE Proceedings A (Science, Measurement and Technology), Volume 138, Issue 1, p. 98 –100
- DOI: 10.1049/ip-a-3.1991.0013
- Type: Article
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An examination of a thermal print head used for dye diffusion thermal transfer printing (D2T2) is presented and the results related to the various problems that can arise when this printing technique is used. Transient measurements are described that show how the temperature distribution over the surface of the thermal print head changes with time. Irregularities in these thermal distributions can give rise to imperfections in the colour printing process.
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