Theory and calculation of alternating current phenomena . the armature coil faces the position midway betweenadjacent field-coils, as shown in Fig. 129, and thus incloses 259 260 ALTERNATING-CURRENT PHENOMENA no magnetism. The wave in this case is, in general,symmetrical. An exception to this statement may take place only in thosetypes of alternators where the magnetic reluctance of the arma-ture is different in different directions; thereby, during the syn-chronous rotation of the armature, a pulsation of the magneticflux passing through it is produced. This pulsation of the mag-netic
Theory and calculation of alternating current phenomena . the armature coil faces the position midway betweenadjacent field-coils, as shown in Fig. 129, and thus incloses 259 260 ALTERNATING-CURRENT PHENOMENA no magnetism. The wave in this case is, in general,symmetrical. An exception to this statement may take place only in thosetypes of alternators where the magnetic reluctance of the arma-ture is different in different directions; thereby, during the syn-chronous rotation of the armature, a pulsation of the magneticflux passing through it is produced. This pulsation of the mag-netic flux generates in the field-spools, and thereby makesthe field current pulsating also. Thus, we have, in this case, evenon open-circuit, no rotation through a constant magnetic field,but rotation through a pulsating field, which makes the unsymmetrical, and shifts the maximum point from itstheoretical position midway between the field-poles. In generalthis secondary reaction can be neglected, and the field assumed as Fig. 130. The relative position of the armature with respect tothe field depends upon the phase relation existing in theelectric circuit. Thus, if there is no displacement of phase be-tween current and , the current reaches its maximum atthe same moment as the or, in the position of the armatureshown in Fig. 129, midway between the field-poles. In this casethe armature current tends neither to magnetize nor demagnetizethe field, but merely distorts it; that is, demagnetizes the trail-ing pole corner, a, and magnetizes the leading pole corner, change of the total flux, and thereby of the resultant ,will take place in this case only when the magnetic densities areso near to saturation that the rise of density at the leading polecorner will be less than the decrease of density at the trailingpole corner. Since the internal self-inductive reactance of thealternator itself causes a certain lag of
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectelectriccurrentsalte
