REGULATING POLE CONVERTERS 437

and decreasing that of the outside sections of the field poles;
that is, in the latter case making the magnetic flux- distribution
at the armature periphery peaked, in the former case by making
the flux distribution flat-topped or even double-peaked.

Armature Reaction and Commutation

238. In such a split-pole converter let p equal ratio of direct
voltage to that voltage which it would have, with the same
alternating impressed voltage, at normal voltage ratio, where
p > 1 represents an overnormal, p < 1 a subnormal direct
voltage. The direct current, and thereby the direct-current
armature reaction, then is changed from the value which it

would have at normal voltage ratio, by the factor — , as the

product of direct volts and amperes must be the same as at
normal voltage ratio, being equal to the alternating power
input minus losses.

With unity power-factor, the direct-current armature reac-
tion, #, in a converter of normal voltage ratio is equal and opposite,
and thus neutralized by the alternating-current armature reac-
tion, #0, and at a change of voltage ratio from normal, by factor

p, and thus change of direct current by factor -•-• The direct-
current armature reaction thus is:

P
hence, leaves an uncompensated resultant.

As the alternating-current armature reaction at unity power-
factor is in quadrature with the magnetic flux, and the direct-
current armature reaction in line with the brushes, and with
this type of converter the brushes stand at the magnetic neutral,
that is, at right angles to the magnetic flux, the two armature
reactions are in the same direction in opposition with each other,
and thus leave the resultant, in the direction of the commutator
brushes :

The converter thus has an armature reaction proportional to
the deviation of the voltage ratio from normal.
239. If p > 1, or overnormal direct voltage, the armature