Compound Motors:

        A compound motor uses Both series and shunt field
windings. The advantage of this arrangement is that the compound
motor can be made to produce a variety of operating characteristics.
By adjusting the polarity and placement of the field windings with
respect to each other, a number of motor types can be designed. For
example, when the series and shunt fields are in series-aiding, the
motor is a Cumulative Compound motor. When the fields are 
series-opposing, the motor is a Differential Compound motor.

        Another factor in the design of a compound motor is the 
placement of the series winding. When the shunt winding is connected
directly across the armature, the motor is a Short Shunt
compound motor. When the shunt winding is connected in parallel
with the Armature and the Series Winding, the motor is a
Long Shunt compound motor. By controlling the field strengths
around the coils using cumulative/differential, or short/long shunt
methods, a compound motor can produce any characteristic that can
be produced by a pure series or shunt motor. A compound motor can
be safely operated without a load and can have the speed characteristics
of a shunt motor and the starting torque characteristics of the series 
motor.
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