Question is ⇒ A wide and very sensitive speed control is usually required in case of, Options are ⇒ (A) elevators, (B) steel rolling mills, (C) colliery winders, (D) all of the above, (E) , Leave your comments or Download question paper.

Question is ⇒ A wide and very sensitive speed control is usually required in case of, Options are ⇒ (A) elevators, (B) steel rolling mills, (C) colliery winders, (D) all of the above, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	A wide and very sensitive speed control is usually required in case of
A.	elevators [Wrong Answer]
B.	steel rolling mills [Wrong Answer]
C.	colliery winders [Wrong Answer]
D.	all of the above [Correct Answer]
View Answer 5 -11 Explanation:- Answer : D Discuss it below : !! OOPS Login [Click here] is required to post your answer/result Help other students, write article, leave your comments

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⇒ The hysteresis loss in a D.C. generator varies with the frequency of magrietic reversals as
1/f
f
f^1.6
f²

⇒ Which motor has the poorest speed control?
Differentially compounded motor
Cumulatively compounded motor
Shunt motor
Series motor

⇒ Which of the following loss in a D.C. generator varies significantly with the load current ?
Field copper loss
Windage loss
Armature copper loss
None of the above

⇒ For which types of D.C. motor, dynamic braking is generally used ?
Shunt motors
Series motors
Compound motors
All of the above

⇒ If t be the thickness of the laminations, then eddy current loss in a generator. will vary as
¹/_t
¹/_t²
t
t²

⇒ In Ward-Leonard control the lower limit of speed is imposed by
residual magnetism of the generator
core losses of motor
mechanical losses of motor and generator together
all of the above

⇒ The starting resistance of a D.C. motor is generally
low
around 500 ohms
1000 ohms
infinitely large

⇒ In an overloaded motor main danger arises due to
winding getting overheated
busbars getting heated
starter getting damaged
bearings getting overheated

⇒ Which of the following motors is usually used in house-hold refrigerators ?
D.C. shunt motor
D.C. series motor
Single phase induction motor (split phase start or induction run motor)
Reluctance motor

⇒ If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will
increase
decrease
remain same
become zero

⇒ Which loss in a D.C. generator varies with load ?
Copper loss
Eddy current loss
Hysteresis loss
Windage loss

⇒ Which of the following motors, on removal of load, will run at the highest speed ?
Shunt motor
Series motor
Differential compound
Cumulative compound

⇒ In case the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be
1
around 90%
anywhere between 75% and 90%
less than 50%

⇒ The armature torque of the D.C. shunt motor is proportional to
field flux only
armature current only
both (a) and (b)
none of the above

⇒ In D.C. machines fractional pitch winding is used
to improve cooling
to reduce copper losses
to increase the generated e.m.f.
to reduce the sparking

⇒ Which of the following law/rule can he used to determine the direction of rotation of D.C. motor ?
Lenz's law
Faraday's law
Coloumb's law
Fleming's left-hand rule

⇒ Which of the following tests can be conducted on all types of D.C. machines ?
Hopkinson's test
Running down test
Block rotor test
Field's test

⇒ The speed of a D.C. motor can be varied by varying
field current
applied voltage
resistance in series with armature
any of the above

⇒ For a D.C. shunt motor if the excitation is changed
torque will remain constant
torque will change but power will remain constant
torque and power both will change
torque, power and speed, all will change

⇒ During rheostatic braking the braking torque is proportional to
speed
(speed)²
(speed)^-1
(speed)^-2

⇒ Which of the following load normally needs starting torque more than the rated torque?
Blowers
Conveyors
Air compressors
Centrifugal pumps

⇒ When the speed of a D.C. motor increases
back e.m.f. increases and current drawn decreases
back e.m.f. as well as current drawn both increase
back e.m.f. as well as current drawn both decrease
back e.m.f. decreases and current drawn increases

⇒ The maximum end-play of a motor is about
10 mm
6 mm
2 mm
0.4 mm

⇒ To get the speed of D.C. motor below the normal without wastage of electrical energy ____ is used.
Ward Leonard control
rheostatic control
any of the above method
none of the above method

⇒ A direct on line starter is used for starting motors
up to 5 H.P.
up to 10 H.P.
up to 15 H.P.
up to 20 H.P.

⇒ Which D.C. motor will be preferred for cónstant speed line shafting ?
Cumulative compound motor
Differentially compound motor
Shunt motor
Series motor

⇒ D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short duration. We will select the
series motor
shunt motor
compound motor
any of the above

⇒ If the field of a D.C. shunt motor gets opened while motor is running
the speed of motor will be reduced
the armature current will reduce
the motor will attain dangerously high speed
the motor will continue to run at constant speed

⇒ The total losses in a well designed D.C. generator of 10 kW will be nearly
100 W
500 W
1000 W
1500 W

⇒ Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator ?
Providing laminations in armature core
Providing laminations in stator
Using non-magnetic material for frame
Using material of low hysteresis coefficient for armature core material