摘要:

After a brief review of the characteristics of the three principal components of the domestic thermal load, viz. electric cooking, water heating and space heating, the influence of intensive domestic electrification on the load factor of undertakings is investigated. As a result it is contended that with present methods of developing the domestic load the maximum attainable load factor of the latter eventually does not much exceed 30 per cent; that in the case of some undertakings attainment of this maximum has already been followed by deterioration: and that control of at least the water- and space-heating load, accompanied by intensified application of thermal storage, offers the only means of raising the load factor to the level necessary for sound development.A new method of centralized load control enables the demand of individual domestic installations to be limited to values that can be adjusted progressively in accordance with the system load. The share in plant capacity thus allocated to each controlled consumer can be made proportional to the amount paid as a fixed charge under a two-part tariff of conventional constitution.Finally, some recommendations as to future policy with regard to domestic electrification are put forward.

DOI:10.1049/ji-2.1941.0049

出版商:IEE    

年代:1941

数据来源: IET

摘要:

The geometric principle used in grading d.c. shunt starters is extended to the general case by the introduction of a constantp, which is shown to equal (Vb)/a, whereVis the line voltage and the flux/current relation in the relevant region is expressible as Φ =a+bI. Then ifRis the total resistance in circuit, the progression ratiokof the stepsr1,r2, etc., is the same as that ofR1,R2, etc., whereR′ =R+p. From this the grading follows as in the shunt case (for whichP= 0). The treatment is exemplified for a single motor and for the series-parallel starting of a pair of similar machines.

DOI:10.1049/ji-2.1941.0054

出版商:IEE    

年代:1941

数据来源: IET

摘要:

Fault resistance is an important factor in protection, and was not dealt with fully in the first Report Ref. F/T102. A more thorough study of this aspect of earthing has revealed very interesting results, the principal one of which is that, with a properly constructed protective multiple earthing system, the occasions when a dangerous shock may be obtained are few, and that in the majority of these cases the earth fault responsible for the liability to shock develops such a large amount of heat energy that the existence of a defective condition is likely to be revealed in some much more obvious way than by a dangerous potential on the metalwork. The maximum voltage which can occur between metalwork and earth is limited to the product of the fault current and the earth resistance, and the limiting value of the latter is 2 ohms with a P.M.E. system. Actually in the majority of cases it will be appreciably less than this. The effect of fault resistance is to reduce the current and consequently the risk of shock—at the same time, however, it may prolong the period for which the defective condition is maintained, but analysis shows that up to an appreciable value of fault resistance the energy dissipated in the fault itself is adequate either to burn it out or to draw attention to its existence, and at greater values of resistance the current is so reduced that the voltage drop across 2 ohms earth resistance is quite negligible from the shock aspect.The situation is very different from this with ordinary earthing, since there is no limitation on the earth resistance such as occurs with P.M.E. Consequently the voltage on the metalwork may have almost any value and the combined influence of the fault resistance and earth resistance may frequently be adequate to prevent the fuse blowing, and the voltage across the earth resistance may be dangerous. There are circumstances in which the fault will reveal itself by generation of heat as with P.M.E., but this does not apply generally.With earth-leakage circuit-breakers dangerous conditions tend to occur when the fault resistances are high rather than low, since at low values the trip coil is more likely to operate. If the resistance is of the order of thousands of ohms, insufficient current may flow to trip the circuit-breaker, but sufficient current may pass through the person making contact with the metalwork to constitute an unpleasant, though probably not a dangerous, shock. Low fault resistances have no influence on the operation of the earth-leakage circuit-breaker, since this may already have several hundreds of ohms in its circuit due to the impedance of the coil and the earth electrode. The non-operation of an earth-leakage circuit-breaker due to a high-resistance earth electrode does not necessarily mean that no shock can be experienced—the two facts are comparatively unrelated since the electrode may have a high resistance because it is small or in a dry place, whilst the person touching the metalwork may be in contact with soil of quite a different resistivity, or he may be standing on a conducting floor of considerable size, in which case the soil resistivity has only a small influence.Arising from the earlier Report, and further evidence which has been secured since its issue, certain alterations have been made in the recommendations. It is now proposed that distinction be no longer made between farms and ordinary installations as regards protection, and that no links for testing or other purposes be permitted in the neutral of a P.M.E. system since there is no significance in applying any test to a neutral which is earthed at possibly hundreds of places. Modifications have been made in the previous recommendations dealing with consumers' earth electrodes and the earthing of the distributor neutral, and the opportunity has been taken to make several other less important modifications.

DOI:10.1049/ji-2.1941.0055

出版商:IEE    

年代:1941

数据来源: IET

摘要:

The paper is divided into three main sections. The first of these deals with the method of manufacture and formation of the discs, and with the forward and reverse voltage/current and voltage/resistance characteristics and the effects of temperature variations, ageing and capacitance. This section includes a brief account of a theory of the operation of the rectifier.The second section describes the design of actual rectifiers for resistive or inductive loads and also a new method of design for battery-charging rectifiers, the mathematical theory of which is given in an appendix. A new method of construction is described which enables the output of a rectifier to be increased.In the final section, a description is given of some of the applications of the rectifier, including the use of oil-cooling for large outputs.

DOI:10.1049/ji-2.1941.0056

出版商:IEE    

年代:1941

数据来源: IET

摘要:

This report deals with the flashover voltage of insulators and gaps subjected to impulse voltages of different wave-shapes, with the relation between crest voltage and time to flashover at voltages above the minimum required for flashover, with breakdown while the voltage is rising rapidly, with the simultaneous application of impulse and alternating voltages, and with the proposed I.E.C. over-voltage test on insulator units.

DOI:10.1049/ji-2.1941.0058

出版商:IEE    

年代:1941

数据来源: IET

摘要:

The effects produced by the surge impedances of an overhead-line tower and of the tower-footing resistance when the tower is struck by lightning are important in that they affect the likelihood of a flashover occurring from the tower to one or more of the line conductors. This paper describes tests made at the National Physical Laboratory, primarily with a view to establishing the best methods of measurement.

DOI:10.1049/ji-2.1941.0059

出版商:IEE    

年代:1941

数据来源: IET

摘要:

Section (1) gives a survey of paper-making processes and of their power requirements.Special problems of power generation and distribution, and the protective system adopted against overload and short-circuits, are dealt with in Section(2).Drives for paper-machine auxiliaries, with a description of the “plural starter” system, are detailed in Section(3).Section(4) deals with paper-machine drives, and gives a brief description of leading types.High-accuracy speed control for paper machines is the subject of Section (5).Section (6) gives information in regard to drives for “finishing” machines, supercalenders, reeling machines and slitters.Finally, Section (7) deals with miscellaneous applications of electricity in the paper mill.

DOI:10.1049/ji-2.1941.0061

出版商:IEE    

年代:1941

数据来源: IET