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

copper loss

eddy current loss

hysteresis loss

windage loss