Principle and Construction of DC Generator

Most of the Machines in use are A.C machines. The DC machines are mainly used in industries. The principle advantage of DC machines mainly DC motor is fine control of speed.

DC generator converts mechanical energy into electrical energy


The Principle of generator is based on Faraday’s Law of electromagnetic induction which states that when every flux is cut by conductor emf is induced in the conductor. The direction of induced emf is given by Fleming's right hand rule.



The various parts of generator are

1 Field System              

2. Armature            

3. Commutator

4. Brushes

Components of DC Generator, Parts of DC generator

Read Also Introduction to Electrical Power System

1. Field System

It produces uniform magnetic field within which armature rotates. The Parts of field system are Yoke, Pole Shoe, Pole Core, Magnetising coils. Yoke is made of cast iron in small rating machines and cast steel in large rating machines.  It serves double purpose

(i)                           it provides mechanical support for the poles and acts as the protective cover for the whole machine.

(ii)                        It provides path to magnetic flux produced by the poles.

 It is solid. Yoke also supports field poles, interpoles (Commutating Poles), Compensating windings and also provide return path to magnetic flux created by field windings Pole Core is used to carry field coils. Pole core may be laminated or Solid. Pole Shoe acts as a support for field coils and spreads flux uniformly over the armature periphery. Pole Shoe are always laminated to reduce eddy current losses. Field coils carry DC exciting current. The mmf developed by the filed coils produce a magnetic flux that passes through The poles pieces, air gap, armature and yoke

Laminate Pole, Solid Pole, Laminations

Read Also Electric Circuit | Terms Related to Electric Circuit | What is Electric Circuit

2. Armature


Armature is the rotating part of machine. Armature is made of silicon steel. It is made of laminations. It has slots on outer periphery. The laminations are coated with thin Film of insulation. The purpose of Laminating the armature is to reduce eddy current losses. The slots of armature contains armature winding. The main function of armature is to rotate the Armature conductors in the uniform magnetic field. In addition to this it provides low reluctance path to magnetic flux.

Armature, Slots, Lamination

3. Commutator

It is also called mechanical rectifiers. They convert alternating induced voltage in armature winding into D.C voltage. They are made of copper segments insulated from each other by mica sheets. It also provides electrical connection between the rotating armature coils and stationary external load. The number of commutator segments are equal to number of armature coils


 Read Also Why Transformer is not Connected to DC

4. Brushes

Brushes are rectangular in shape and are made of copper/graphite/carbon. The function of brushes is to collect the current from commutator and supply to external Load. Allowed current density in case of carbon brushes are 5 A/cmand in case of copper brushes is 23 A/cm2. the number of brushes is equal to number of poles


 Read Also 

02.Principle and Construction of DC generator  

03.Electric Circuit | Terms Related to Electric Circuit | What is Electric Circuit

04.Electric Charge | Electric Current | Voltage

05.Series and Parallel Combination of Resistances


07.Electrical Thumb Rules

08.Kirchhoff’s Laws

09.Where does the reactive power Go?

10.Why Transformer is not Connected to DC





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