Below we have the schematic diagrams and equivalent circuit diagrams of two types of compound DC motor. In compound DC motors, a combination of shunt and series fields is used to combine characteristics of shunt and series DC motors.
In long-shunt compound DC motors, the series filed is placed between the shunt field and armature (shunt field farther than series field from armature).
In short-shunt compound DC motors, the shunt field is between the series field and armature (shunt field closer than series field to armature).
Depending on the direction of fluxes produced by the series and shunt field windings, the series and shunt fields can assist each other (cumulative compound) or oppose each other (differential compound).
Speed-Torque Characteristic
Due to the combined effects of a shunt field and a series field, the speed-torque characteristic of a cumulatively-compounded DC motor will fall between those of shunt and series motors:
