46 ELECTRIC DISCHARGES, WAVES AND IMPULSES.
is the field transient $ (the same as in Fig. 224) and B the arma-
ture current, decreasing from an initial value, which is m times
the final value, on the field transient.
ture current, decreasing from an initial value, which is m times
the final value, on the field transient.
Assume then that the mutual induction between field and
armature is such that 60 per cent of tho pulsation of armature
reaction appears in the field current. Forty per cent damping for
the double-frequency reaction would about correspond to tho 20
per cent damping assumed for the transient full-frequency pulsa-
tion of the polyphase machine. Tho transient field current thus
pulsates by 60 per cent around the slow field transient, as nhown
by Fig. 230; passing a maximum for every maximum of armature
armature is such that 60 per cent of tho pulsation of armature
reaction appears in the field current. Forty per cent damping for
the double-frequency reaction would about correspond to tho 20
per cent damping assumed for the transient full-frequency pulsa-
tion of the polyphase machine. Tho transient field current thus
pulsates by 60 per cent around the slow field transient, as nhown
by Fig. 230; passing a maximum for every maximum of armature
, Fig. 24.—Asymmetrical Momentary Binglo-pluwo Hhort Circuit of Allanwtor.
current, and thus maxinmm of armature* reaction, and a minimum
for every zero value of armature current, and thus armaturo reac-
tion.
tion.
Such single-phase short-circuit trannientB have occasionally boon
recorded by the oscillograph, as shown in Fig, 27. Usually, how-
ever, the circuit is closed at a point of tho wave where tho perma-
nent armature current would not bo zero, and an armature traunlent
appears, with an initial value equal, but opposite to, the initial
value of the permanent armature current. Thin IH Bhown in
Fig. 24 for the case of closing the circuit at the moment where the
recorded by the oscillograph, as shown in Fig, 27. Usually, how-
ever, the circuit is closed at a point of tho wave where tho perma-
nent armature current would not bo zero, and an armature traunlent
appears, with an initial value equal, but opposite to, the initial
value of the permanent armature current. Thin IH Bhown in
Fig. 24 for the case of closing the circuit at the moment where the