DC Generator- Construction and Its Working

What is a DC Generator?

DC machines can be classified into two types called as DC Motor and DC Generator. A DC generator is an electrical machine which converts mechanical energy into electricity or electrical energy. When conductor slashes magnetic flux, an emf is generated, According to Faraday’s Law of Electromagnetic Induction. A DC generator can also be used as a DC motor without changing its construction. The main advantage of DC Generator is its simple construction and design.

Construction of DC Generator:

Different parts of DC Generator are:

Construction of DC Generator
  • Armature or Rotor: Rotor is a rotating part of DC generator that rotates on its axis. A rotor in a DC machine includes slotted iron laminations with slots that are stacked to shape a cylindrical armature core. The function of the lamination is to decrease the loss caused due to Eddy Current.
  • Field Coil or Stator: It is a non-moving part of DC generator, it provide magnetic fields where the coil spins. It includes two magnets with opposite polarity facing each other.
  • Yoke: It is an outer frame and it provides mechanical strength to whole assembly of motor. It is made up of cast iron or steel.
  • Pole Shoe: It enlarges region of pole, so that the flux can be spread out within the air-gap as well as extra flux can be passed through the air space toward armature. The materials used to build pole shoe is cast iron or steel.
  • Pole: It is an electromagnet and the field winding is wounded on pole and are connected either in series or in parallel with the armature winding. When the field winding is energized then the pole gives magnetic flux. The materials used for this are cast steel, cast iron.
  • Commutator: Commutator is present on Shaft of the machine, commutator works like a rectifier that changes AC voltage to DC voltage within the armature winding. It is designed with a copper segment.
  • Brushes: The brushes of a DC motor are made with graphite and carbon structure. Its function is to transfer the current from coil to load connected in the circuit of electric generator.

Working of DC Generator

The Working principle of DC Generator is that, when a current-carrying conductor is placed in a varying magnetic field, an emf is induced in the conductor, according to Faraday’s Law of Electromagnetic Induction.

Working of DC Generator

Now, according to Fleming’s right-hand rule, the direction of the induced current changes when the direction of motion of the conductor changes. For Example, Let us consider an armature rotating clockwise and a conductor at the left moving upwards. When the armature completes a half rotation, the direction of the motion of the conductor will be reversed downward. Hence, the direction of the current in every armature will be alternating. But with a split ring commutator, connections of the armature conductors get reversed when a current reversal occurs. Hence, we get unidirectional current or direct current at the terminals.

The emf equation of the DC generator is given by the equation:

Eg= PϕZN/60A

Where,

Z is the total number of armature conductor,

P is the number of poles in a generator,

A is the number of parallel lanes within the armature,

N is the rotation of armature in rpm,

E is the induced emf in any parallel lane within the armature,

Eg is the generated emf in any one of the parallel lane,

N/60 is the number of turns per second.

Also, the input power is not fully transformed into output power, which is due to losses associated with the DC Generator. There are mainly four type losses which are Hysteresis Loss, Eddy Current Loss, Iron-Core Loss, Copper Loss.

Applications of DC Generators:

Applications of DC Generator are:

  • The separately excited type DC generators are used for power and lighting purposes.
  • The series DC generator is used in arc lamps for lighting, stable current generator and booster.
  • DC generators are used to reimburse the voltage drop within Feeders.
  • DC generators are used to provide a power supply for hostels, lodges, offices, etc.