Compound Wound DC Motor or DC Compound Motor
A compound wound DC motor or rather a DC compound motor falls under the category of self excited motors, 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 the field coils provide for the required amount of magnetic flux, that links with the armature coil and brings about the torque necessary to facilitate rotation at desired speed.
As we can understand, a compound wound DC motor is basically formed by the amalgamation of a shunt wound DC motor and series wound DC motor to achieve the better off properties of both these types. Like a shunt wound DC motor is bestowed with an extremely efficient speed regulation characteristic, whereas the DC series motor has high starting torque.
So the compound wound DC motor reaches a compromise in terms of both this features and has a good combination of proper speed regulation and high starting toque. Though its staring torque is not as high as in case of DC motor, nor is its speed regulation as good as a shunt DC motor. Overall characteristics of DC shunt motor falls somewhere in between these 2 extreme limits.
Types of Compound Wound DC MotorThe 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:
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Long Shunt Compound Wound DC MotorIn 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 MotorLet 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,