7 March 2020

DC Generator Interview Question Answer - 1


1
At what principle the DC Generator operates?


Principle of DC generator
  • The DC Generator works on the principle of the dynamically induced emf. 
  • Whenever a conductor cuts flux, dynamically induced emf in it according to the Faraday’s law of Electro – magnetic induction.


2
What are the essential conditions for the generation of emf?


The essential conditions for the generation of emf is
  • A magnetic field
  • Conductor and
  • Interaction of flux between them


3
Describe the function of commutator in the DC Generator.


Function of commutator
  • The current induced in the armature of the DC Generator is alternating. 
  •  The function of the commutator is to convert alternating current into unidirectional.


4
Describe the  function of following parts in the DC Generator  :  Pole, Pole shoes, Yoke, Field coil,  Armature core


Pole
  • The function of the pole is to carry field winding.


Pole shoes
  • The function of the pole shoes is to ( 1 ) spread flux in the air-gap ( 2 ) to support the field winding. 

Yoke
  • It provides mechanical support for the pole and whole machine.
  • It carries the flux path which is produced by poles. 

Field coil
  • The function of the field coil is to produce flux which is cut by armature. 

Armature core
  • The main function of the armature core is to provide low reluctance path of field flux.


5
Describe the function of air duct in the armature of the DC Generator?


Function of air duct
  • The function of air duct in the armature of the DC Generator is to cooling the armature.


6
Why the commutator segments are built with V – shaped grooves?


Commutator segments
  • The commutator segments are built with V – shaped grooves in order to prevent them to flying out during rotation of the armature.


7
Which type of joint is used between brush and brush - holder?


Pig – tail

8
Explain the terms : Pole pitch, Coil span, Active conductor, Full pitch coil, Short pitch coil


Pole pitch
  • The distance between two adjacent poles is called as pole pitch.

                 OR
  • The number of slots per pole is called as pole pitch.

                 OR
  • The periphery of the armature divided by the number of poles of the DC Generator is known as pole pitch.

Coil span
  • The distance between coil sides of an armature coil is called as coil span.

Active conductor
  • The length of conductor lying in the magnetic field and in which an emf is induced is called as active conductor.

Full pitch coil
  • When pole pitch is equal to coil span, it is called as full pitch coil.

Short pitch coil
  • When coil span is not equal to the pole pitch, it is called as short pitch coil.


9
How the numbers of parallel paths in the armature winding affect the voltage rating and current rating of the DC Generator?


As the numbers of parallel paths increases in the armature winding, the voltage rating of the armature winding does not affected but current rating increases.

10
Why the values of front pitch and back pitch in the armature winding have odd value?


The value of front pitch and back pitch must be odd otherwise it is difficult to place coils in the slot of the armature.

11
Which winding is also called as parallel winding? Lap winding or wave winding? Why?


Parallel winding
  • The lap winding is also called as parallel winding because there are numbers of parallel path in the armature is equal to numbers of poles.


12
Which winding is also called as series winding? Lap winding or winding? Why?


Series winding
  • The wave winding progresses in one direction round the armature in series of waves therefore it is also called as series winding.


13
Describe the function of dummy coil. Why it is used only in the wave winding?


Function of Dummy coil
  • The dummy coils are used in the wave winding when the requirement of the armature winding is not met by standard armature slots. 
  • It does not affect the electrical characteristics of the armature winding because it is not connected to the commutator segment.
  • The winding ends of the dummy coils are taped. It provides only mechanical balance to the armature winding.


14
Which winding is suitable for higher voltage rating Generator? Lap winding or Wave winding? Why?


The wave winding is suitable for higher voltage rating Generator because for the same voltage and numbers of poles, the lap winding required higher numbers of conductors than the wave winding.

15
How many numbers of parallel paths in the simplex, duplex and triplex wave winding?


Numbers of parallel paths
Simplex wave winding
  • Two parallel path

Duplex wave winding  
  • Four parallel path

Triplex wave winding   
  • Six parallel path


16
Describe the different types of DC Generators.


Types of DC Generators
  • Separately Excited DC Generator
  • DC series Generator
  • DC shunt Generator
  • DC compound Generator



17
How self excited Generator is different from separately excited Generator?


Self excited generator – Separately excited generator
  • The self excited Generators are those in which field winding is excited by the current produced by the Generator itself. 
  • The separately excited Generators are those in which field winding is excited by the separate Direct current source.


18
Why the fields winding in the DC series Generator have thick wire?


The field winding of the DC series Generator is connected in series with the armature winding so it carries full load current. Therefore the Series Generator consists of few turns having thick wire.

19
Which type of brush material have higher voltage drop?


Carbon brush

20
How many parallel paths are there in 6 – pole wave wound DC Generator?


There are always two parallel paths in the wave winding and it will be not affected by numbers of poles.




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