to increase the resistance of brushes

to reduce the no. of turns in the armature coil so as to reduce the no. of commutator segments

to neutralise the reactance voltage by producing a reversing e.m.f. in the short-circuited coil under commutation

all the above

to neutralise the reactance voltage to help commutation process

to neutralise the cross-magnetising effect of armature reaction

to reduce sparking at the commutator

all the above

high reliability

high efficiency

meeting higher load demands

all the above

voltage and current

current

voltage over a wide load range

voltage over a narrow load range

parallel with the field windings

series with the field windings

parallel with the load

series with the armature winding