D.C GENERATOR

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D.C GENERATOR
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WHAT IS GENERATOR?WHAT IS THE PRINCIPLE ?

• An generator is a machine which converts
  mechanical energy into electrical energy.
• Principle of generator is the production of
  dynamically induced e.m.f according to FARADAYS
  LAWS OF ELECTROMAGNETIC INDUCTION.

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MAIN PARTS OF D.C
GENERATOR

• YOKE.
• POLE CORE AND POLE SHOE.
• FIELD COIL.
• ARMATURE CORE.
• ARMATURE WINDING.
• COMMUTATOR.
• BRUSHES AND BRUSH HOLDERS.
• BEARINGS.
• SHAFT.

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YOKE

• It provides mechanical support for the poles and
  as a protecting cover for the whole machine.
• It carries the magnetic flux produced by the
  poles.

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POLE CORE AND POLE SHOE

• The main function of pole core is to act as
  support for the field coils carries current which
  surrounds it and establish magnetic flux.
• The main function of pole shoe are it supports
  the field coil it spreads out the magnetic flux
  over a larger area.

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FIELD COILS

• Field coils are also called pole coils.
• When current is passed through these coils, they
  electromagnetise the poles which produce the
  necessary flux that is cut by revolving armature
  conductors.

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ARMATURE CORE

• Armature is the rotating part.
• It provides a path of very low reluctance to the
  flux through the armature from NORTH pole to
  SOUTH pole.
• It is cylindrical or drum shaped.

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ARMATURE WINDING OR CONDUCTORS

• Armature windings consists of conductors or
  copper wires which are placed in slots.
• It is of two types
• Open coil winding and
• Closed coil winding.
• Open coil winding is used in A.C machines.
• Closed coil winding is again divided into 2
  types.
• Ring winding and Drum winding.

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• Drum winding is again divided into two types.
• Lap winding and Wave winding.
• Lap winding is used for low voltages and high
  currents.
• Wave winding is used for high voltages and low
  currents.

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• In lap and wave winding back pitch and front
  pitch are equal to the pole pitch.
• Number of commutator segments is equal to the
  number of slots or coils.
• Pole pitch is equal to the number of conductors
  per pole.

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SIMPLEX LAP WINDING
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SIMPLEX WAVE WINDING
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COMMUTATOR

• The function of commutator is to facilitate
  collection of current from the armature
  conductor.
• It also converts the alternating current induced
  in the armature conductors into unidirectional
  current in the external load circuit.

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BRUSHES AND BRUSH HOLDERS

• The main function of brushes is to collect the
  current from commutator.
• Brushes are housed in the brush holders.
• These brush holders are used for the protection
  purpose to the brushes.
• Total number of brushes is equal to the number of
  poles.

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BEARINGS AND SHAFT

• Bearing and shaft are mainly used for smoothing
  operation because of their reliability.
• Ball bearings are frequently employed, through
  for heavy duties, roller bearing are preferable.

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ARMATURE REACTION

• Armature reaction is meant the effect of magnetic
  field set up by armature current on the
  distribution of flux under main poles of a
  generator.
• This armature reaction has two effects.
• 1.DEMAGNETISING EFFECT.
• 2.CROSS MAGNETISING EFFECT.

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DEMAGNETISING EFFECT

• It demagnetises or weakens the main flux.
• It is produced in opposite to the main field
  flux.
• It is denoted by OFd

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• This demagnetising effect is decreased by placing
  extra ampere-turns to the main field winding.
• It is essential to calculate their number, it is
  denoted by ATd.
• Demagnetising ampere turns are neutralized by
  adding extra ampere turns to the main field
  winding.

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First is the figure of demagnetising effect and
the latter is cross magnetising effect
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CROSS MAGNETISING EFFECT

• It distorts the main field flux.
• It is denoted by OFc.
• Cross magnetising effect is neutralized by
  compensating windings.