1.
If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed willbe
A
small
B
the same as rated voltage
C
high
D
zero
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If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed willbe
small
the same as rated voltage
high
zero
The e.m.f. induced in the armature of a shunt generator is 600 V. The armatureresistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be
620 V
600 V
580 V
640 V
A 220 V D.C. generator is run at full speed without any excitation. The open circuitvoltage will be
about 50 V
220 V
zero
about 2 V
A sinusoidal voltage of 5 Hz is applied to the field of a shunt generator. The armaturevoltage wave
willbeof5xiVHz
will be of v Hz 5
will be zero
will be of 5 Hz
The open circuit voltage of a compound generator is 250 V. At full load the terminalvoltage
may be greater or less than 250 V
none of the above
will be less than 250 V
will always be 250 V
Copper brushes in D.C. machine are used
in both of the above cases
in none of the above cases
where low voltage and high currents are involved
where high voltage and small cur-rents are involved
Equilizer rings are required in case armature is
delta wound
duplex wound
wave wound
lap wound
For the parallel operation of two or more D.C. compound generators, we should ensurethat
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 thearmature(e) all conditions mentioned above should be satisfied
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
In case of a flat compounded generator
voltage remains constant irrespec¬tive of the load
speed varies in proportion to the load on the generator
voltage generated is less than the rated voltage
generated voltage is proportional to the load on the generator
In a D.C. generator the ripples in the direct e.m.f. generated are reduced by
using carbon brushes of superior quality
using equiliser rings
using conductor of annealed copper
using commutator with large number of segments
As a result of armature reaction, the reduction in the total mutual air gap flux in a D.C.generator is approximately
10 percent
5 percent
40 percent
25 percent
In a D.C. machine stray loss is the sum of
shunt field copper loss and mechanical loss
iron loss and mechanical loss
total copper loss and mechanical loss
armature copper loss and iron loss
D.C. series generator is used
voltage at the toad end of the feeder
for none of the above purpose
to supply traction load
to supply industrial load at constant voltage
The function of pole shoes in the case of D.C. machine is
to support the field coil
to discharge all the above functions
to reduce the reluctance of the magnetic path
to spread out the flux to achieve uniform flux density
The purpose of providing dummy coils in a generator is
to amplify voltage
to provide mechanical balance for the rotor
to reduce eddy current losses
to enhance flux density
When two D.C. series generators are running in parallel, an equilizer bar is used
so that two similar machines will pass approximately equal currents to the load
to reduce the combined effect of ar-mature reaction of both machines
to increase the speed and hence generated e.m.f.
to increase the series flux
When two D.C. generators are running in parallel an equilizer bar is used
to reduce the combined effect of ar-mature reaction of both the machines
so that the two identical machines will pass approximately equal currents to the load
to increase the series flux
to increase the generated e.m.f.
D.C. generators are connected to the busbars or disconnected from them only under thefloating condition
to avoid sudden loading of the primemover
to avoid mechanicaljerk to the shaft
to avoid burning of switch contacts
all above
In a D.C. generator the magnetic neutral axis coincides with the geometrical neutralaxis, when
there is no load on|he generator
the generator runs on full load
the generator runs on overload
the generator runs on designed speed
The main factor which leads to unstable parallel operation of flat and over compounded generators is
their rising voltage characteristics
unequal number of turns in their series field windings
unequal speed regulation of their primemovers
unequal series field resistances