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Speed Control of a DC Compound Motor

A compound motor is a combination of a series and a shunt-wound motor.

Compound-wound motor (long shunt)
Compound-wound motor (long shunt)
DC Compound-wound motor (short shunt)
Compound-wound motor (short shunt)

The Speed-torque characteristics for a compound motor

DC Compound motor characteristics
Compound motor characteristics

Speed Control of a DC Compound Motor

Speed is controlled by variable resistors in the shunt field and armature circuit. The series winding may be arranged that it aids the shunt field (cumulative compound) or opposes it (differential compound).

Speed control of a DC compound motor
Speed control of a DC compound motor (long shunt type)

Cumulatively compounded motors are similar in characteristics to series motors, while differential compounded motors are similar to shunt motors as shown in the figure below:

Characteristics of cumulatively & differential DC compounded motors
Characteristics of cumulatively & differential compounded motors

Starting a DC Compound Motor

The compound motor is started with the help of a dc face-plate starter.

Applications of DC Compound Motors

Compound motors are used in applications where a wide speed range is needed but the differentially compounded types are rarely used as they tend to be unstable. The cumulatively compounded types are suitable for heavy machine tools.

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