107 practice sets · Page 5 of 6
In a D.C. generator
external resistance = internal char-acteristic - armature reaction
internal characteristic = magnetisation characteristic - ohmic drop
external characteristic = magnetisation characteristic - ohmic drop - armature reaction
magnetisation characteristic = external characteristic
The series field of a short-shunt D.C. generator is excited by
external current
armature current
shunt current
load current
The e.m.f. generated by a shunt wound D.C. generator is E. Now while pole flux remainsconstant, if the speed of the generator is doubled, the e.m.f. generated will be
E/2
2E
slightly less than E
E
Which of the following components of a D.C, generator plays vital role for providingdirect current of a D.C. generator ?
Dummy coils
Commutator
Eye bolt
Equilizer rings
In lap winding, the number of brushes is always
double the number of poles
same as the number of poles
half the number of poles
two
While applying Flemings right-hand rule to And the direction of induced e.m.f., the thumb points towards
direction of induced e.m.f.
direction of flux
direction of motion of the conductor if forefinger points in the direction of generatede.m.f.
direction of motion of conductor, if forefinger points along the lines of flux
If brushes of a D.C. generator are moved in order to bring these brushes in magneticneutral axis, there will be
demagnetisation only
cross magnetisation as well as magnetisation
crossmagnetisation as well as demagnetising
cross magnetisation only
Armature reaction in a generator results in
demagnetisation of leading pole tip and magnetisation of trailing pole tip
demagnetisation of trailing pole tip and magnetisation of leading pole tip
damagnetising the centre of all poles
magnetising the centre of all poles
With a D.C. generator which of the following regulation is preferred ?
100% regulation
infinite regulation
50% regulation
1% regulation
In case of D.C. machines, mechanical losses are primary function of
current
voltage
speed
none of above
A cumulatively compounded long shunt generator when operating as a motor would be
cumulatively compounded long shunt
differentially compounded long shunt
cumulatively compounded short shunt
differentially compounded short shunt
Armature reaction of an unsaturated D.C. machine is
crossmagnetising
demagnetising
magnetising
none of above
The commutator segments are connected to the armature conductors by means of
copper lugs
resistance wires
insulation pads
brazing
In a commutator
copper is harder than mica
mica and copper are equally hard
mica is harder than copper
none of the above
Which of the following statement about D.C. generators is false ?
Compensating winding in a D.C. machine helps in commutation
In a D. C. generator interpoles winding is connected in series with the armaturewinding
Back pitch and front pitch are both odd and approximately equal to the pole pitch
Equilizing bus bars are used with parallel running of D.C. shunt generators
Which of the following could be lamina-proximately the thickness of laminations of a D.C. machine ?
0.005 mm
0.05 mm
0.5 m
5 m
In D.C. generators, current to the external circuit from armature is given through
commutator
solid connection
slip rings
none of above
Laminations of core are generally made of
case iron
carbon
silicon steel
stainless steel
Brushes of D.C. machines are made of
carbon
soft copper
hard copper
all of above
In a D.C. generator the critical resistance refers to the resistance of
brushes
field
armature
load
