7 March 2020

DC Generator Interview Question Answer - 5


81
What are the conditions to be satisfied for production of the torque in the DC machines?


There are following conditions must be satisfied for production of torque in the DC machines:
  • The relative speed between two fields should be zero with respect to stationary observer. 
  • Numbers of stator poles is equal to the numbers of rotor poles. If the numbers of stator poles are not equal to the rotor poles, the resultant torque becomes zero.


82
What is the direction of the MNA when DC machine is loaded?


When the DC machine is loaded
  • The direction of the MNA is opposite to that of direction of the rotor rotation in the case of motor.   
  • The direction of the MNA is same as that of direction of the rotor rotation in the case of Generator.     


83
At which load condition the GNA coincides with the MNA?


At no load

84
Describe the effect on flux density distribution when the DC Generator at ( a ) No load and ( b ) Full load.


Flux density distribution
  • When the DC Generator at no load, the flux per pole remains constant. 
  • When the DC Generator at full loaded, the flux per pole increase in one half is less than the decrease in the other half of the pole due to saturation. 
  •  Therefore there is slight decrease in the flux at full load condition in the DC Generator.


85
What is the nature of the flux distribution due to ( a ) Armature flux ( b ) Field flux in the DC machine.


( a ) The armature flux distribution is triangular in nature.
( b ) The field flux distribution is trapezoidal in nature.

86
What is polarity of the poles of the 4 pole DC Generator?


Polarity of Poles
  • The polarity in the 4 - pole DC Generator is either North - North ( N – N ) or South –  South ( S – S ). 
  •  Therefore the polarity of the 4 pole DC Generator is either N – S – N – S or S – N – S – N.


87
How to identify whether the armature winding is wave wound or lap wound if the armature coils are connected to the commutator segments?


Wave winding
  • If the ends of the armature coils are connected to the commutator segments which are apart by approximately two pole pitch, it is wave winding. 
  •  If the ends of the armature coils are connected to the two consecutive commutator segments, it is called as lap winding.





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