- 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, and is made up of both series the field coils S1 S2 and shunt field coils F1 F2 connected to the armature winding as shown in the figure below.
Both field coils provide the necessary magnetic flux, linking with the armature coil to produce torque for rotation at the desired speed. A compound wound DC motor combines the properties of shunt wound DC motor and series wound DC motors: shunt wound for efficient speed regulation and DC series motor for high starting torque.
Therefore, the compound wound DC motor offers a balance between proper speed regulation and high starting torque.
While its starting torque is not as high as a series DC motor, and its speed regulation is not as good as a shunt DC motor, a compound wound DC motor’s overall characteristics fall between these two extremes. To learn more, study our electrical MCQs.
Types of Compound Wound DC Motor
The compound wound DC motor can further be subdivided into 2 major types on the basis of its field winding connection with respect to the armature winding, and they are:
Long Shunt Compound Wound DC Motor
In case of long shunt compound wound DC motor, the shunt field winding is connected in parallel across the series combination of both the armature and series field coil, as shown in the diagram below.
Voltage and Current Equation of Long Shunt Compound Wound DC Motor
Let E and Itotal be the total supply voltage and current supplied to the input terminals of the motor. And Ia, Ise , Ish be the values of current flowing through armature resistance Ra, series winding resistance Rse and shunt winding resistance Rsh respectively.
Now we know in shunt motor, 
And in series motor 
Therefore, the current equation of a compound wound DC motor is given by
And its voltage equation is,
Short Shunt Compound Wound DC Motor
In a short shunt compound wound DC motor, the shunt field winding is parallel only to the armature winding. The series field coil handles the entire supply current before it splits into the armature and shunt field currents, as shown in the diagram below.
Voltage and Current Equation of Short Shunt Compound Wound DC Motor
Here also let, E and Itotal be the total supply voltage and current supplied to the input terminals of the motor. And Ia, Ise, Ish be the values of current flowing through armature resistance Ra, series winding resistance Rse and shunt winding resistance Rsh respectively.
But from the diagram above we can see,
Since the entire supply current flows through the series field winding.
And like in the case of a DC shunt motor,
Equation (2) and (3) gives the current equation of a short shunt compound wound DC motor.
Now for equating the voltage equation, we apply Kirchoff’s law to the circuit and get,
But since 
Thus the final voltage equation can be written as,
Apart from the above mentioned classification, a compound wound DC motor can further be sub divided into 2 types depending upon excitation or the nature of compounding. i.e.
Cumulative Compounding of DC Motor
A compound wound DC motor is said to be cumulatively compounded when the shunt field flux produced by the shunt winding assists or enhances the effect of main field flux, produced by the series winding.
Differential Compounding of DC Motor
Similarly a compound wound DC motor is said to be deferentially compounded when the flux due to the shunt field winding diminishes the effect of the main series winding. This particular trait is not really desirable, and hence does not find much of a practical application.
The net flux produced in this case is lesser than the original flux and hence does not find much of a practical application.
The compounding characteristic of the self excited DC motor is shown in the figure below.
