Contents
Explain The Construction of DC Generator
DC generator is Electrical machine which 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.
Parts of DC Generator
The various parts DC Generator are
- Field System
- Armature
- Commutator
- Brushes
Field System
It produces uniform magnetic field within which armature rotates. The Parts of field system are Yoke, Pole Shoe, Pole Core, Magnetizing coils.
Yoke is made of cast iron in small rating machines and cast steel in large rating machines. It is solid and serves double purpose.
- It provides mechanical support for the poles and acts as the protective cover for the whole machine.
- It provides path to magnetic flux produced by the poles.
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.
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.
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.
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/cm2 and in case of copper brushes is 23 A/cm2. The number of brushes is equal to number of poles.
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