The field winding is driven in series with the armature winding and the field strength will vary with changes in the armature current. If your speed is reduced by a load, the series engine will develop more torque. Its starting torque is higher than those of other types of direct current electric motors.
The field winding is driven in parallel with that of the armature and the field strength is considered independent of the armature current. Shunt-type motor speed only depends on changes in load and starting torque is lower than other types of DC motors T2535173S.
It is used in cases where it is desired to have a constant speed for a variable load, being possible to start the engine with a very light load or without load. This type of motor is widely used in speed control system in the independent excitation configuration, thus, the field winding is driven in series with the armature and another in parallel.