1. They are broadly classified as:
ELECTRICAL MACHINES 1
Electrical Machines – except transformers are electromechanical energy converting device.
They are broadly classified as:
DC Machines AC Machines
DC Generator Transformers
DC Motor Induction Machines
Synchronous Machines

2. DIRECT CURRENT MACHINES1
Depending upon the mode of operation, a DC Machine is either called a DC Generator or DC Motor.
Cut view – DC Machine

3. DC Machines 1
When a machine converts mechanical energy into electrical energy which is DC in nature, it is called as a DC Generator.
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Whenever a machine converts electrical energy which is DC in nature, into mechanical energy, it is called a DC Motor.
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4. DC Generators:
DC Generator works on Faraday’s laws of Electro magnetic induction. According to this law, whenever a conductor cuts a magnetic flux, dynamically induced e.m.f is produced in the conductor. This e.m.f causes a current to flow when the conductor circuit is closed. The direction of induced current is given by Fleming’s right hand rule. 1

5. Thus the essential parts of a generator are:
DC Generators 1
Thus the essential parts of a generator are:
a magnetic field system (2) a system of conductors
(3) relative movement between (1) and (2)
Condition (3) can be satisfied in two different ways.
The magnetic field system can be arranged in the stationary part of the machine called the Stator, and the system of conductors in the rotating part of the machine, called the Rotor.
Alternatively, the system of conductors can be placed in the Stator and the field system in the Rotor.

6. Constructional Details – DC Machine
The various parts of a DC machine can be grouped into two categories.
Stator – Stationary part
Rotor – Rotating part
Airgap between Stator
& Rotor 1

7. Stator Parts Constructional Details – DC Machine Frame / Yoke1
Constructional Details – DC Machine
Stator Parts
Frame / Yoke
(2) Field Magnets
(3) Field or Exciting winding
(4) Interpoles
(5) Interpole winding

8. Acts as an outer protective cover for the machine1
Constructional Details – DC Machine
Stator Parts
Frame / Yoke
Acts as an outer protective cover for the machine
Serves path for the
magnetic flux
(iii) Provides mechanical
support for the poles

9. Stator Parts Constructional Details – DC Machine1
Constructional Details – DC Machine
Stator Parts
Field magnets consists of Pole core & Pole shoes.
Can be Permanent magnets or Electromagnets.
Poles are Salient in nature (ii) Welded or bolted to yoke
(iii) Even in number (iv) Forms an Hetrogeneous field system
(v) Laminated to reduce Eddy current loss
(vi) Made of Silicon steel to reduce Hysterisis loss
Portion of the core near the airgap is made wider – Pole shoe
Spreads the flux
Provides support for the field winding

10. Constructional Details – DC Machine1
Constructional Details – DC Machine
Stator Parts
Field Winding / Exciting Winding
Made of Copper Wires
When energized with DC,
electromagnetize the poles
and provide the working flux.
(iii) All windings connected in series

11. Constructional Details – DC Machine1
Stator Parts
Inter Poles / Commutator Poles
Provided in between the main poles
Fitted on to Yoke
No: of Interpoles =
No: of poles
(iv) Flux produced by the Interpoles
provide sparkless commutation

12. Constructional Details – DC Machine1
Stator Parts
Inter Pole Winding / Commutator field Winding
Windings are connected in series which are
in turn connected in series
with armature
(ii) Same electromagnetizes
the Interpoles
(iii) Made of Copper

13. Constructional Details – DC Machine1
Rotor Parts
Shaft ) Armature core & Armature winding
3) Commutator segments
4) Brush holder & Brushes

14. Constructional Details – DC Machine Rotor Parts Shaft
Provides mechanical support to the armature and to the commutator.
The rotor assembly is supported
and allowed to rotate freely by
two bearings fitted between
two end covers and the shaft.
Shaft transfers mechanical energy to and from the machine. 1

15. Constructional Details – DC Machine Rotor Parts
Armature Core with Armature winding
The purpose of armature core is to rotate the conductors in a uniform magnetic field.
Core is cylindrical in shape
Laminated to reduce Eddy current loss and made of Silicon steel to reduce
Hysterisis loss
(iii) Slots are cut in the outer
periphery of the core to
accommodate the armature conductors or winding 1

16. Constructional Details – DC Machine Rotor Parts Commutator Segments
Function of the commutator is to facilitate the collection of current from the armature conductors.
The e.m.f. generated in the armature conductors of a DC machine is an alternating e.m.f. The commutator helps in converting this alternating e.m.f.
into a direct one.
Ends of armature coil terminated to
Commutator segments
(ii) Made of Copper segments
(iii) Arranged side by side to form a ring
(iv) Insulated in between with mica 1

17. Constructional Details – DC Machine1
Rotor Parts
Brushes
The brushes collect the armature current from the commutator segments and supply it to the load (in the case of generator) or feed the current into the commutator segment (in the case of motor).
Made of graphite or carbon or a mixture of graphite and carbon or even copper and are rectangular in shape
Held in Brush holders
No: of brushes depend on the magnitude of current

18. Constructional Details – DC Machine1
Constructional Details – DC Machine
Rotor Parts
Brushes (contd.)
Usually the no: of Brushes = no: of Poles
Desirable properties for brushes:
Good Electrical Conductivity
Less coefficient of Friction

19. 1
Cut view - DC Machine