SINGLE-PHASE COMMUTATOR MOTORS 417

at motors, all under the assumption of the same constants:

Z = 0.25 -f 3j,
Z' = 0.25 -f 2.5 j,

z0 = o.i + 0.3 y,

Z2 = 0.025 4 0.075 j,
Zi = 0.025 4'0.075 j,
£4 = 4 4 2 j,
Co = 0.3,
c4 = 0.03.

/e I gives the commutation factor of the motor as induct-
ompensated series motor (t = 0), as constant, fc = 3.82,
, the current change at leaving the brushes is 3.82 times
tin current. Such condition, under continued operation,
give destructive sparking.

ro, II shows the series repulsion motor, mth 20 per cent, of
Itage on the compensating winding, t = 0.2; and
fe III with half the voltage on the compensating winding,
>.

fe IV corresponds to.t = I, or all the voltage on the com-
ing winding, and the armature circuit closed upon itself:
on motor with secondary excitation,
re V corresponds to t = 2, or full voltage in reverse direction
sed upon the armature, double voltage on the compen-
winding.

re VI gives the minimum cornmutation factor, as derived
ying t with the speed, in the manner discussed "before.
further comparison are given, for the same motor
nts:

re VII, the plain repulsion motor, showing its good com-
on below synchronism, and poor commutation above
onism; and

re VIII, an overcompensatecl series motor, that is, eon-
jly compensated series motor, in which the compensating
g contains 20 per cent, more ampere-turns than the arma-
) giving 20 per cent, overcornpensation.
seen, overcompensation does not appreciably improve
itation at low speeds, and spoils it at higher speeds.
194 also gives the- two components of the compensating
#2, which are required to give perfect cornmutation, or.
mmutatioix current;

<; '

A
fir,
m