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SINGLE-ENERGY TRANSIENTS, 37

apparatus, however, these momentary starting currents usually
are far more limited than in transformers, by the higher stray field
(self-inductive reactance), etc., of the apparatus, resulting from

the air gap in the magnetic circuit.

19. As instance of the use of the single-energy transient in
engineering calculations may bo considered the investigation of
the momentary short-circuit phenomena of synchronous alter-
nators. In alternators, especially high-speed high-power ma-
chines as turboalternators, the momentary short-circuit current
may be many times greater than the final or permanent short-
circuit current, and this excess current usually decreases fairly
slowly, lasting for many cycles. At the same time, a big cur-
rent rush occurs in the field. This excess field current shows
curious pulsations, of single and of double frequency, and in
the beginning the armature currents also show unsymmetrical
shapes. Some oscillograms of three-phase, quarter-phase, and
single-phase short circuits of turboaltornators are shown in Figs.
25 to 28.

By considering the transients of energy storage, these rather
complex-appearing phenomena can be easily understood, and pre-
determined from the constants of the machine with reasonable
exactness.

In an alternator, the voltage under load is affected by armature
reaction and armature self-induction. Under permanent condi-
tion, both usually act] in the same way, reducing the voltage at
noninduetive and still much more at inductive load, and increasing
it at antiiuduetive load; and both are usually combined in one
quantity, the synchronous reactance XQ. In the transients result-
ing from circuit changes, as short circuits, the self-inductive
armature reactance and the magnetic armature reaction act very
differently:* the former is instantaneous in its effect, while the
latter requires time. The self-inductive armature reactance #i con-
sumes a voltage x\i by the magnetic flux surrounding the armature
conductors, which results from the m.ra.f. of the armature cur-
rent, and therefore requires a component of the magnetic-field flux
for its production. AH the armature magnetic flux and the current
which produces it must be simultaneous (the former being an
integral part of the phenomenon of current flow, as seen in Lecture
II), it thus follows that the armature reactance appears together
* Bo ttlwo in their effect on synchronous operation, in hunting, etc.



	SINGLE-ENERGY TRANSIENTS, 37 apparatus, however, these momentary starting currents usually are far more limited than in transformers, by the higher stray field (self-inductive reactance), etc., of the apparatus, resulting from the air gap in the magnetic circuit. 19. As instance of the use of the single-energy transient in engineering calculations may bo considered the investigation of the momentary short-circuit phenomena of synchronous alter- nators. In alternators, especially high-speed high-power ma- chines as turboalternators, the momentary short-circuit current may be many times greater than the final or permanent short- circuit current, and this excess current usually decreases fairly slowly, lasting for many cycles. At the same time, a big cur- rent rush occurs in the field. This excess field current shows curious pulsations, of single and of double frequency, and in the beginning the armature currents also show unsymmetrical shapes. Some oscillograms of three-phase, quarter-phase, and single-phase short circuits of turboaltornators are shown in Figs. 25 to 28. By considering the transients of energy storage, these rather complex-appearing phenomena can be easily understood, and pre- determined from the constants of the machine with reasonable exactness. In an alternator, the voltage under load is affected by armature reaction and armature self-induction. Under permanent condi- tion, both usually act] in the same way, reducing the voltage at noninduetive and still much more at inductive load, and increasing it at antiiuduetive load; and both are usually combined in one quantity, the synchronous reactance XQ. In the transients result- ing from circuit changes, as short circuits, the self-inductive armature reactance and the magnetic armature reaction act very differently:* the former is instantaneous in its effect, while the latter requires time. The self-inductive armature reactance #i con- sumes a voltage x\i by the magnetic flux surrounding the armature conductors, which results from the m.ra.f. of the armature cur- rent, and therefore requires a component of the magnetic-field flux for its production. AH the armature magnetic flux and the current which produces it must be simultaneous (the former being an integral part of the phenomenon of current flow, as seen in Lecture II), it thus follows that the armature reactance appears together * Bo ttlwo in their effect on synchronous operation, in hunting, etc.