The armature core of a D.C. generator is usually made of
silicon steel
cast-iron
non-ferrous material
copper
silicon steel
Satisfactory commutation of D.C. machines requires
all of the above
brushes should smoothly run in the holders
brushes should be of proper grade and size
smooth concentric commutator properly undercut
all of the above
Open circuited armature coil of a D.C. machine is
none of the above
both and
identified by the scarring of the commutator segment to which open circuited coil is connected
indicated by a spark completely around the commutator
both and
For the parallel operation of two or more D.C. compound generators we should ensure that
series fields of all generators should be either on positive side or negative side of the armature
voltage of the incoming generator should be same as that of bus bar
polarity of incoming generator should be same as that of bus bar
all the series fields should be run in parallel by means of equilizer connection
series fields of all generators should be either on positive side or negative side of the armature
If B is the flux density I the length of conductor and v the velocity of conductor then induced e.m.f. is given by
Bl2v2
Bl2v
Blv2
Blv
Blv
In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils the pole pitch will be
4
16
8
32
8
In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when
number of poles is 2
number of poles is 4
r.p.m. is less than 300
r.p.m. is more than 300
number of poles is 2
Permeance is the reciprocal of
reluctance
ampere-turns
flux density
resistance
reluctance
In D.C. generators the polarity of the interpoles
is neutral as these poles do not play part in generating e.m.f.
is the same as that of the main pole ahead
is the same as that of the immediately preceding pole
is opposite to that of the main pole ahead
is the same as that of the main pole ahead
The e.m.f. generated in a D.C. generator is directly proportional to
speed of armature
flux/pole
number of poles
all of the above
speed of armature
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