Showing papers in "Journal of the Institution of Electrical Engineers in 1957"

Fires of electrical origin

Abstract: The incidence of electrical fires is described, and it is shown that fires due to apparatus occur at a rate of one per 104 MWh transmitted. Fires due to fixed installations do not appear to vary with time, although it is expected that these may increase during the coming years owing to the ageing of cables. There appears to be little evidence that fires are being caused by the overloading of cables. Details are given of a survey which is to start in 1957.

The electric strength of silicone liquids

Abstract: Controlled measurements of the d.c. electric strength of certain pure liquid poly-dimethyl siloxanes or silicones are reported. The liquids tested were the four lower members of the D.C. 200 series of silicone fluids having viscosities of 0.65, 1, 1.5 and 2 centistokes. The measurements were made under conditions identical with those employed for earlier experiments on pure n-paraffins which have a similar molecular structure, so that useful comparisons could be made. The use of a hydrogen-thyratron circuit to by-pass the discharge energy when breakdown occurred was found to be essential, since the discharge products, which probably included silica, were appreciably greater than for the n-paraffins.Like that of the n-paraffins, the strength of the silicones, which is of the order of 900kV/cm, was found to increase with chain length and with decreasing test-gap. The liquid of 0.65 centistokes viscosity was also tested over the temperature range −55°C to 85°C, and it was found that the strength increased with decreasing temperature, the increase being most marked at temperatures below about 20°C. This behaviour is similar to that of the n-paraffins already tested and cannot be ascribed to density changes alone.

Acoustics of large orchestral studios and concert halls

Abstract: In order to establish design criteria for orchestral studios, which should be similar in performance to good concert halls, an extensive investigation has been in progress for many years. The effects of shape on the subjective acoustic qualities of a large enclosure are here examined with reference to a large number of concert halls and music studios, and a comparison is made, in particular, between concert halls of the traditional type and those which have been built during the last few decades. The former were generally of rectangular plan with walls and ceilings overlaid with ornamentation, whereas most recent designs have fan-shaped plans, reflecting canopies and comparatively smooth surfaces. Measurements of sound levels in different parts of concert halls during orchestral concerts show that, for a given sound level in the neighbourhood of the platform, the intensity at the back of the hall is no greater in halls with fan-shaped plans and reflectors than with the traditional rectangular shape. In the former case, the gain in the intensity of the first few reflections which results from the shape of the hall is offset by a reduced reverberant sound level. The authors conclude that the modern fashion of directing the early reflections towards the back of a concert hall, although it may improve the hearing of speech, has an adverse effect on the quality of music.

Transistor circuits and applications

Abstract: Junction-transistor circuits are reviewed, and new concepts and trends in design are discussed. Improvements in transistor ratings are described, but special transistor types such as tetrodes, p-n-p-n and unipolar devices are not considered. Basic applications surveyed include low-level and power amplifiers, square-wave and sinusoidal oscillators, power convertors and regulators, waveform-shaping and computing circuits, and low-level and power-switching circuits. Numerous references are given. Transistors are capable of supplanting thermionic circuits in all except high-frequency applications (above 10 Mc/s with currently-available units). High temperatures will continue to present limitations in military applications, until silicon transistors become widely available. In more general applications, such as the entertainments field, cost is at present an important limiting consideration.

Electrical floor warming

Abstract: The development of off-peak load is of increasing importance to the electricity supply industry, and the paper gives details of experience obtained in developing off-peak electrical floor warming in the south of Scotland. Special features in the design and control of electrical floor warming are discussed, and various methods of installation are described. Particulars are given of some representative installations, including single- and two-storey buildings, multi-storey buildings, and dwelling houses. Actual operating results are quoted and analysed. A section is included on off-peak tariff design, bringing out the South of Scotland Electricity Board's approach to this problem.Some reference is made to the comparative economics of electrical floor warming and other methods of space heating. In the conclusions it is suggested that, as this method of space heating has so much to commend it, the electricity industry can confidently take further steps in its development. It is also suggested that there is scope for further research in this field.

Electricity in modern commercial horticulture

Abstract: Over the past 10 years there has been a significant change in the role of electricity in horticulture. From being largely an aid to the amateur gardener, rarely used by the commercial grower, electricity now plays a substantial part in modern commercial horticulture. Some of the earlier expectations, based chiefly on the small-scale work, have not developed as expected and hoped. In situ soil warming, for instance, has not taken its expected place in commercial horticulture, and large-scale glasshouse installations are few and far between. On the other hand, the use of soil-warming equipment to provide bottom heat for propagation in frames and propagating cases has increased substantially. Direct space heating by electricity was hardly expected to play any significant part in commercial glasshouse work, but through electrical auxiliaries alone has it been possible to develop various modern methods of large-scale automatic heating using either coal or oil. Where the circumstances and scale of requirement do justify direct electrical space heating, emphasis is placed on the need for correct design, particularly in relation to a proper basic temperature. Probably the most prominent role of electricity in commercial horticulture has been in the provision of artificial lighting for plant growing in various ways; increase of plant development and its control have both been successfully applied through the use of electric light in ways and with means which are commercially successful. The development of new wiring methods and equipment has aided the provision of safe wiring installations in horticultural premises.