Question And Answer of Testing Of DC Machine | Electrical Machine Questions
Question And Answers related to Testing if DC Machine is important for GATE examination and also in competitive exams. All the important and basic questions are covered.
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| Question And Answer of Testing Of DC Machine | Electrical Machine Questions |
Q.1
One D.C. motor drives another D.C.
motor. The second D.C. motor when
excited and driven
(a)runs as a generator
(b)does not run as a generator
(c)also runs as a motor
(d)comes to stop after sometime
Ans.
(a)runs as a generator
Q.2
Which of the following D.C. motors has
the least drop in speed between no-load
and nominal load?
(a)Series motor without commutating
poles
(b)Series motor with commutating
poles.
(c)Shunt motor with commutating
pole
(d)Compound motor without com-
mutating poles
Ans.
(c)Shunt motor with commutating
pole
Q.3
The speed of a series motor at no load
is
(a)infinity
(b)4000r.p.m.
(c)2000r.p.m.
(d)1000r.p.m.
(e)none of the above
Ans.
(a)infinity
Q.4
In a D.C. motor if the back e.m.f.is
absent
(a)motor will burn
(b)motor will not run at all
(c)motor will run at very slow speed
(d)motor will run at very high speed
Ans.
(a)motor will burn
Q.5
A series motor is started without load.
The effect is that
(a)the back e.m.f. decreases
(b)the torque increases rapidly
(c)the speed increases rapidly
(d)the current drawn increases rapidly
Ans.
(c)the speed increases rapidly
Q.6
What will happen if supply terminals
of D.C. shunt motor are interchanged?
(a)The direction of rotation will
reverse
(b)Motor will stop
(c)Motor will run at speed lower than
the normal speed in the same direc-
tion
(d) Motor will run at its normal speed
in the same direction as it was run-
ning
Ans.
(d) Motor will run at its normal speed
in the same direction as it was run-
ning
Q.7
When the electric train is moving down
a hill the D.C. motor act as
(a)D.C. series generator
(b)D.C. shunt generator
(c)D.C. shunt motor
(d)D.C. series motor
Ans.
(a)D.C. series generator
Q.8
Which of the following methods is most
economical for finding the no-load losses of a large D.C.. shunt motor?
(a)Retardation test
(b)Swinburne's test
(c)Hopkinson's test
(d)none of the above
Ans.
(b)Swinburne's test
Q.9
Which of the following statement is in-
correct ? If a starter is not used with
large D.C. motor, it will draw a starting
current which
(a)will produce very low starting
torque
(b)will produce excessive line voltage
drop
(c)will damage the commutator
(d)is many times its full-load current
Ans.
(a)will produce very low starting
torque
Q.10
The rated speed of a given D.C. shunt
motor is 900r.p.m.To run this machine
at 1000r.p.m., which of the following
speed control scheme will be used?
(a)Ward-Leonard control
(b)Armature current resistance control
(c)Field resistance control
(d)None of the above
Ans.
(c)Field resistance control
Q.11
In electric motors carbon brushes are
used to
(a)provide a path for flow of current
(b)prevent sparking during commuta-
tion
(c)prevent overheating of armature
windings
(d)brush off carbon deposits on the
commutator
Ans.
(a)provide a path for flow of current
Q.12
What is the effect produced by the
electric current in an electric motor?
(a)Heating effect only
(b)Magnetic effect only
(c)Heating as well as magnetic effect
(d)Heating as well as chemical effect
Ans.
(c)Heating as well as magnetic effect
Q.13
In a motor, energy conversion would
not have been possible but for the
(a)production of opposing back e.m.f.
Eb in the armature
(b)input energy from supply
(c)use of commutator
(d)application of Fleming's left-hand
rule
Ans.
(a)production of opposing back e.m.f.
Eb in the armature
Q.14
In a D.C. motor, unidirectional torque
is produced with the help of
(a)end plates
(b)bushes
(c)commutator
(d)both(b)and(c)
Ans.
(d)both(b)and(c)
Q.15
In a D.C. motor, the ratio Eo/Va indi-
cates
(a)running torque of the motor
(b)starting torque of the motor
(c)efficiency of the motor
(d)speed regulation of the motor
Ans.
(c)efficiency of the motor
