- Compound Wound DC Motor Definition: A compound wound DC motor (also known as a DC compound motor) is defined as a self-excited motor using both series and shunt field coils to combine the benefits of high starting torque and good speed regulation.
- Types of Compound Wound DC Motors: These motors are categorized into long shunt and short shunt types, based on how the field windings are connected with the armature winding.
- Voltage and Current Equations: The voltage and current equations for compound wound DC motors can be derived using Kirchhoff’s laws, tailored to each motor type’s configuration.
- Cumulative Compounding: In cumulatively compounded motors, the shunt field flux supports the main field flux, enhancing the motor’s performance.
- Differential Compounding: Differentially compounded motors have shunt field flux that opposes the main field flux, reducing overall flux and making these motors less practical for most applications.
A compound wound DC motor (also known as a DC compound motor) is a type of self-excited motor. It has series field coils S1 S2 and shunt field coils F1 F2 on the armature winding, as in the figure below.
Both field coils supply magnetic flux that links the armature and produces torque. A compound wound DC motor sits between a shunt wound DC motor and a series wound DC motors. The shunt path helps hold speed. The series path, as on a DC series motor, raises starting torque.
That mix of speed holding and starting torque is the reason for using a compound wound DC motor.
Starting torque is lower than a series DC motor, and speed holding is weaker than a shunt DC motor. Cumulative compounding still sits between those two curves. More questions are in the electrical MCQs.
Types of Compound Wound DC Motor
A compound wound DC motor is classed as long-shunt or short-shunt by how the shunt field sits relative to the armature winding:
Long Shunt Compound Wound DC Motor
In a long-shunt compound wound DC motor, the shunt field is in parallel with the armature and series field together, as below.
Voltage and Current Equation of Long Shunt Compound Wound DC Motor
Let E and Itotal be supply voltage and current at the motor terminals. Let Ia, Ise , Ish be the currents in armature resistance Ra, series resistance Rse and shunt resistance Rsh.
In a shunt motor, 
And in series motor 
For the long-shunt compound wound DC motor the current equation is
and the voltage equation is
Short Shunt Compound Wound DC Motor
In a short-shunt compound wound DC motor the shunt field is in parallel with the armature winding only. Line current still flows through the series field before it splits to the armature and shunt, as below.
Voltage and Current Equation of Short Shunt Compound Wound DC Motor
Again let E and Itotal be supply voltage and current at the terminals, and Ia, Ise, Ish the currents in Ra, Rse and Rsh.
From the diagram,
because the series field carries the full supply current.
As in a DC shunt motor,
Equations (2) and (3) are the short-shunt current relations.
Applying Kirchoff’s law around the circuit gives
But since 
so the voltage equation is
Compounding is also cumulative or differential, by the direction of the two field fluxes.
Cumulative Compounding of DC Motor
The motor is cumulatively compounded when shunt-field flux adds to the series-field flux.
Differential Compounding of DC Motor
A compound wound DC motor is differentially compounded when shunt-field flux opposes the series field. Net flux then falls as load current rises, so speed can increase with load and the connection is rarely used.
Net flux is then lower than the series flux alone.
The compounding curves of the self-excited DC motor are shown below.
