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DC Machines And Its Types

A machine that converts DC electrical power into mechanical power are known as an electrical DC motors. Its operation is based on the principle that when a current carrying conductor is placed in a magnetic field, the conductor experiences a mechanical force. The direction of this force is given by Fleming’s left hand rule and its magnitude is given by:

F = B×I×l  Newton

Basically, there is no constructional difference between an electrical DC motors and DC generators. The same machine can be run as a DC generator or DC motor.

Types Of DC Machines

DC machines (Motor or Generator) on the basis excitation are classified in to four types.

Separately Excited DC Machine

Shunt Wound DC Machine

Series Wound DC Machine

Compound Wound DC Machine

Separately Excited DC Machine

Like different DC motors, these motors even have both stator coil and rotor. Stator coil refers to the static part of motor that consists of the field windings and the rotor is that the moving coil that contains armature windings or coils. Separately excited DC motor has field coils almost like that of shunt wound DC motor. The name suggests the construction of this type of motor. Usually, in other DC motors, the field coils and the armature coils each are energized from one supply. The field of them does not need any separate excitation however, in separately excited DC motor, separate supply Provided for excitation of each field winding and armature coil.

Separately Excited DC Motor

Here, the field coil is energized from a separate DC voltage supply and the armature coil is additionally energized from another supply. Armature voltage supply could also be variable however, independent constant DC voltage is employed for energizing the field coil. So, those coils are electrically isolated from one another, and this connection is the specialty of this sort of DC motor.

Shunt Wound DC Machine

A machine within which field coils are connected in parallel with the armature is called a shunt machine. Shunt field winding receives the complete output voltage just in case of generator and supply voltage in case of motor, thus it’s usually provided with fine wire having large number of turns and carries a small field current.

shunt generator
Shunt Wound DC Generator

The only difference between DC shunt motor and DC shunt generator is the direction of current otherwise they had the same construction.

Series Wound DC Machine

A DC machine within which field windings are connected in series with the armature is termed series wound DC machine. In this case field winding carries the armature current and armature current is high therefore field winding is made of thick wire with small number of turns. Figure given below shows the connection diagram for DC series generator and DC series motor. Direction of current are totally opposite in generator and motor otherwise they have same construction.

series generator
Series Wound DC Generator

Compound Wound DC Machine

A DC machine having each shunt and series field windings are known as compound DC machines. Shunt winding has larger number of turns of thin wire and series Winding has few turns of thick wire. Compound machine could also be connected in two ways. If shunt field is connected in parallel with the armature only, then its known as short shunt compound DC machine. Figure given below shows the connection diagram for DC short-shunt compound generator and DC short-shunt compound motor. Direction of current are totally different in generator and motor otherwise they have same construction.

short shunt
Short Shunt DC Machine
long shunt
Long Shunt DC Machine

Besides this, if magnetic flux created by series field winding assist or aids the flux produced by shunt field winding , the machine is called cumulatively compounded DC machine.
If the flux due to series field winding opposes the flux due to shunt field winding, then machine is said to be deferentially compounded DC machine.

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