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
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