Theory and calculation of alternating current phenomena . can exist onlyin a circuit with external negative reactance, as capacity, etc. ALTERNATING-CURRENT GENERATOR 2G1 If the armature current lags, it reaches the maximum laterthan the ; that is, in a position where the armature-coilpartly faces the field-pole which it approaches, as shown in dia-gram in Fig. 130. Since the armature current is in opposite direc-tion to the current in the following field-pole (in a generator), thearmature in this case will tend to demagnetize the field. If, however, the armature current leads—that is, r
Theory and calculation of alternating current phenomena . can exist onlyin a circuit with external negative reactance, as capacity, etc. ALTERNATING-CURRENT GENERATOR 2G1 If the armature current lags, it reaches the maximum laterthan the ; that is, in a position where the armature-coilpartly faces the field-pole which it approaches, as shown in dia-gram in Fig. 130. Since the armature current is in opposite direc-tion to the current in the following field-pole (in a generator), thearmature in this case will tend to demagnetize the field. If, however, the armature current leads—that is, reaches itsmaximum while the armature-coil still partly faces the field-polewhich it leaves, as shown in diagram, Fig. 131—it tends tomagnetize this field-pole, since the armature current is in thesame direction as the exciting current of the preceding fieldspools. Thus, with a leading current, the armature reaction of thealternator strengthens the field, and thereby, at constant fieldexcitation, increases the voltage; with lagging current it weakens. Fig. 131. the field, and thereby decreases the voltage in a generator. Ob-viously, the opposite holds for a synchronous motor, in which thearmature current is in the opposite direction; and thus a laggingcurrent tends to magnetize, a leading current to demagnetize,the field. 186. The generated in the armature by the resultantmagnetic flux, produced by the resultant of the field andof the armature, is not the terminal voltage of the machine; theterminal voltage is the resultant of this generated and of self-inductive reactance and the representing thepower loss by resistance in the alternator armature. That is,in other words, the armature current not only opposes or assiststhe field in creating the resultant magnetic flux, but sendsa second magnetic flux in a local circuit through the armature,which flux does not pass through the field-spools, and is calledthe magnetic flux of armatur
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