Theory and calculation of alternating current phenomena . ry the triple-frequency exciting current. If the primary neutral of the transformers is connected to afourth wire, in a four-wire, three-phase system or three-phasesystem with grounded neutral, and this fourth wire leads backto the generator neutral, or a neutral of a transformer in whichthe triple-frequency current can exist, that is, in which thesecondary is connected in A, the wave-shape distortion alsodisappears. 368 AL TERN A TING-C URREN T PHENOMENA It follows herefrom that in the three-phase system attentionnmst be paid to provid
Theory and calculation of alternating current phenomena . ry the triple-frequency exciting current. If the primary neutral of the transformers is connected to afourth wire, in a four-wire, three-phase system or three-phasesystem with grounded neutral, and this fourth wire leads backto the generator neutral, or a neutral of a transformer in whichthe triple-frequency current can exist, that is, in which thesecondary is connected in A, the wave-shape distortion alsodisappears. 368 AL TERN A TING-C URREN T PHENOMENA It follows herefrom that in the three-phase system attentionnmst be paid to provide a path for the third harmonic of thetransformer exciting current, either directly or inductively,otherwise a serious distortion of the wave of the trans-formers occurs. (See Theoretical Elements of ElectricalEngineering, Chapter X.) CHAPTER XXVIEFFECTS OF HIGHER HARMONICS 251. To eluculate the variation in the shape of alternatingwaves caused by various harmonics, in Figs. 185 and 186 areshown the wave-forms produced by the superposition of the. ft Fig. 185. triple and the quintuple harmonic upon the fundamental sinewave. In Fig. 185 is shown the fundamental sine wave and the com-plex waves produced by the superposition of a triple harmonicof 30 per cent, the amplitude of the fundamental, under the rela-24 369 370 AL TERN A TING-C URREN T PHENOMENA tive phase displacments of 0°, 45°, 90°, 135°, and 180°, repre-sented by the equations: sin /3 sin /3 - sin 3 j8 sin /3 - sin (3 /3 - 45°) sin /? - sin (3 /3 - 90°) sin /? - sin (3 )3 - 135°) sin 0 - sin (3 /3 - 180°).
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