摘要:

The paper is concerned with alternator voltage regulators in which a junction transistor regulates the field current of a self-excited exciter. It examines the principles upon which control circuits may be designed to ensure stability and gives experimental results on two regulating systems for a 10 kVA alternator.

DOI:10.1049/pi-a.1957.0048

出版商:IEE    

年代:1957

数据来源: IET

摘要:

An account is given of equipment and measuring techniques in use at the National Standards Laboratory, Australia, for calibrating voltage transformers. The equipment employs 3-terminal air-dielectric capacitors to form a voltage divider, the ratio and phase defect angle of which are determined by a self-contained build-up technique. Owing to the use of virtually loss-free capacitors, the phase angle of the divider is negligibly small.Two methods are described for calibrating transformers. In one, ratio balance is obtained by means of a small auxiliary variable-ratio voltage transformer, and phase balance by current injection into one of the detector bridge junctions. In the other method, ratio balance is provided by a variable 3-terminal air-capacitor in the low-voltage arm of the divider, and phase balance by voltage injection in series with that arm, a feedback amplifier providing a low-impedance injection circuit. In both methods the accuracy of measurement is approximately 2 parts in 105in ratio and 0.05′ in phase angle.The air-dielectric capacitors used in the voltage divider are tested to ensure that they have no significant voltage coefficient of capacitance or loss angle.

DOI:10.1049/pi-a.1957.0049

出版商:IEE    

年代:1957

数据来源: IET

摘要:

Regulation No. 507 in The Institution's Regulations for the Electrical Equipment of Buildings calls for a measurement of the earth-loop impedance and gives a method by which this can be done. Several instruments have been devised and are available to carry out this test, but all draw their testing current from the mains and are thus liable to serious errors. Records taken with a recording voltmeter show that in most cases there is already a voltage drop in the neutral conductor, which is varying continuously and rapidly. It is shown both theoretically and by practical tests that instruments of this character can have errors under these conditions amounting to 100% or more. Any instrument intended to carry out these tests must be such that it will give the correct value despite the presence of the continuously varying voltage drop in the neutral. An instrument is described which draws its testing current from its own hand-driven generator and is free from these errors. The Regulation also calls for a measurement of impedance, but it is suggested that in most cases the difference between impedance and resistance of an earth loop is so small that an instrument measuring resistance will be sufficient.

DOI:10.1049/pi-a.1957.0052

出版商:IEE    

年代:1957

数据来源: IET

摘要:

The paper is essentially a short critical résumé of the factors which, in general, determine the security of high-voltage a.c. overhead-line transmission systems with, in addition, a description of methods which provide a logical basis for the efficient selection of insulation levels.Transient over-voltages are the main source of danger to overhead-line insulation; they may be of internal origin, but lightning strokes are the major hazard, particularly in oversea countries where lightning is prevalent. Lightning phenomena are therefore considered; statistical data on lightning currents, stroke frequency and other variables are included. The problem of shielding by earth wires and the importance in this connection of tower footing resistance are discussed.A description of the characteristics of line insulation is given; this includes data on power-frequency and impulse tests, flashover voltages, atmospheric influences, deterioration, use of wood poles, and other related matters.The selection of insulation levels involves careful consideration of the foregoing factors with, in addition, a means of estimating line reliability or probable outage frequency. Two methods which have been developed for predicting line performance under lightning conditions are described and compared, and their application is illustrated by numerical examples.

DOI:10.1049/pi-a.1957.0057

出版商:IEE    

年代:1957

数据来源: IET

摘要:

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 situsoil 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.

DOI:10.1049/pi-a.1957.0063

出版商:IEE    

年代:1957

数据来源: IET

摘要:

Heat-pump operation in Great Britain is reviewed from the point of view of the electricity supply industry. The factors which have to be taken into consideration for possible applications are discussed, e.g. sources of low-grade heat, capacity required and special methods of utilization.British experience, including the results of laboratory investigations on heat transfer from the soil and other aspects, is described. Details of construction and operation of a practical 10 h.p. heat pump, installed to warm a laboratory building, and using the earth as its source of low-grade heat, are given. Observations of performance include load factor and maintenance and attendance.The economic aspect is dependent on the present state of development, but future improvements together with comparisons with other methods of performing the same duties are considered. The paper concludes with a discussion of the value of the heat pump as an electrical load.

DOI:10.1049/pi-a.1957.0068

出版商:IEE    

年代:1957

数据来源: IET