Journal of the Institution of Electrical Engineers - Part II: Power Engineering 

About: Journal of the Institution of Electrical Engineers - Part II: Power Engineering is an academic journal. The journal publishes majorly in the area(s): Stator & Electronic circuit. It has an ISSN identifier of 0367-7567. Over the lifetime, 166 publications have been published receiving 1341 citations.

The lightning discharge

Abstract: A survey of the data available indicates that lightning flashes in all thunderstorms have similar characteristics as regards the times involved and the number of strokes in a flash, and it is shown that Norinder's divergent values are due to misinter-pretation of his data. It is suggested that while the charge neutralized in a lightning flash is probably about 50% greater than has hitherto been believed, the cloud potential is only a few per cent of the accepted value, and the energy of a flash about 250 kWh, as compared with Wilson's value of about 2800 kWh. A theory is advanced bearing on the mechanism of the leader and return strokes, which enables the shape of the lightning current wave to be calculated; in addition, a form is derived for the whole current wave in a multiple flash. A synthesis made from the results of many investigations leads to a picture of the mechanism of the return stroke and to the calculation of the various field changes produced, which agree well with those observed both in shape and in amplitude. New light is thrown on the analysis of the electrostatic field change caused by a stroke. The importance of space charge is emphasized in several connections, including the neutralization of cloud charge thereby, the frequency of ?air discharges? and the peculiarity of flashes to the Empire State Building, the currents to which have been re-analysed. The effect of direct strokes to transmission lines is investigated, and it is shown that successive strokes which do not cause flashover are unlikely. The polarity of flashes to earth is shown to differ in tropical and temperate regions, and it is concluded that the polarity of strokes to phase wires cannot be deduced from that of strokes to towers. Suggestions are made as to further investigations.

The theory of the inductor alternator

Abstract: This paper describes briefly the construction of typical homopolar and heteropolar inductor alternators, and gives a theoretical basis of design which has produced satisfactory results in practice. It is shown how the ratio of alternating flux to total flux can be calculated in the normal case of rectangular rotor slots and in the special case where the rotor teeth and slots are designed to give a sinusoidal alternating flux wave. In discussing the main types of armature windings it is shown how by maintaining a certain relationship between the number of rotor slots and the number of phases, a single-phase winding may be connected to give a polyphase supply. In the derivation of the armature-reaction formula it is shown that some types of windings cause less armature reaction than others, and also that, except in the case of a true polyphase winding, an efficient damping system is necessary. Methods of predetermining the field current on open-circuit and on load are indicated; the necessity of taking precautions to avoid dangerous bearing currents in the homopolar alternator is discussed, and the paper concludes with an investigation of the losses in these alternators.

The high-voltage characteristics of earth resistances

Abstract: This paper concerns the behaviour of earth resistances under h.v. currents. The author has tried to contribute to the explanation of the phenomena causing the decrease of the earth resistance and to check the effectiveness of giving to the earth electrodes the properties of edges or points. An explanation is given for the "breakdown" of the soil, based on the results obtained from the theoretical treatment of model earths. The analysis of the experimental results obtained on model earths leads to favourable conclusions as regards the use in practice of electrodes having the properties stated above. The direct discharges on the ground surface during lightning strokes and falls of overhead h.v. line conductors are considered and the corresponding resistances and currents are estimated. The results obtained lead to the suggestion that in some cases the special earthing of h.v. line poles is not necessary, either for the protection of these lines against lightning strokes or for the operation of the line-disconnecting devices during short-circuits to earth.

Dielectric loss in thin films of insulating liquids

Abstract: This paper describes theoretical and experimental work on the dielectric loss of films of insulating liquids so thin that the motion of ions under an alternating field is limited by the boundaries of the film. Films of this thickness normally occur in porous, impregnated insulation, and lead to a dielectric loss angle which varies greatly with the applied stress. In Section (2) of the paper approximate equations are established for the dielectric loss of such a thin film, as a function of the applied stress. It is also shown that measurements on thin films afford a new method of deducing the ionic concentration, radius and mobility. In Section (3) experimental work is described upon films of an insulating liquid (trichlorbenzene) as thin as 0.03 mm. Such films show a large variation of loss angle with stress, agreeing closely with the predicted variation, except in one or two cases where the nature of the ionized impurities appeared to be abnormal. Values of ionic radius and mobility deduced from the equations of Section (2) check well with values known from electrolytic measurements. It is concluded that experiment confirms the theory put forward, except at very low stresses, where assumptions made in the theory are no longer valid. In Section (4) the equations of Section (2) are applied to an actual impregnated dielectric with non-uniform pore sizes, and it is shown that provided account is taken of the distribution of pore sizes, the theory will account satisfactorily for the variation with stress of the loss angle of condensers impregnated with liquids containing ionized impurities. Values of ionic radius and mobility deduced from these results are also of the right order of magnitude, but are less accurate than those obtained in Section (3), owing to lack of knowledge of the exact distribution of pore sizes. Detailed conclusions are given at the end of the paper.

Calibration of uniform-field spark-gaps for high-voltage measurement at power frequencies

Abstract: A calibration is given for spark-gap electrodes designed to ensure that the spark path lies in a uniform field, and it is shown that for all three sizes of electrodes investigated, covering a range of 9 to 315 kV (peak), the sparkover voltages are within 0.2% of the values given by the empirical lawV=24.22S+6.082√SkV (peak) at 20°C and atmospheric pressure of 760 mm Hg, where S is the electrode spacing in centimetres.All observations were made with vertical gaps having the lower electrode connected to earth, and comparative data were obtained for a sphere gap with electrodes 25 cm in diameter. The effects of surrounding objects and of faulty alignment of the electrodes were determined experimentally, and on the basis of these results a number of recommendations are made, giving the limits within which the spark-over voltage is defined by the above equation.