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.
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.
At which
load condition the GNA coincides with the MNA?
At no load
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 operates at no load, 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.
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.
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.
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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