81
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What are the conditions to be
satisfied for production of the torque in the DC machines?
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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.
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82
|
What is the direction of the MNA when
DC machine is loaded?
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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.
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83
|
At which load condition the GNA
coincides with the MNA?
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At no load
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84
|
Describe the effect on flux density
distribution when the DC Generator at ( a ) No load and ( b ) Full load.
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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.
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85
|
What is the nature of the flux
distribution due to ( a ) Armature flux ( b ) Field flux in the DC machine.
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( a ) The armature flux distribution is triangular in nature.
( b ) The field flux distribution is trapezoidal in nature.
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86
|
What is polarity of the poles of the 4
pole DC Generator?
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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.
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87
|
How to identify whether the armature
winding is wave wound or lap wound if the armature coils are connected to the
commutator segments?
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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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