Question is ⇒ During rheostat braking of D.C. series motors, Options are ⇒ (A) motor is run as a generator, (B) motor is reversed in direction, (C) motor is run at reduced speed, (D) , (E) , Leave your comments or Download question paper.

Question is ⇒ During rheostat braking of D.C. series motors, Options are ⇒ (A) motor is run as a generator, (B) motor is reversed in direction, (C) motor is run at reduced speed, (D) , (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	During rheostat braking of D.C. series motors
A.	motor is run as a generator [Correct Answer]
B.	motor is reversed in direction [Wrong Answer]
C.	motor is run at reduced speed [Wrong Answer]
View Answer 3 -1 Explanation:- Answer : A 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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⇒ Which of the following losses are significantly reduced by laminating the core of a D.C. generator ?
Hysteresis losses
Eddy current losses
Copper losses
Windage losses

⇒ The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is
4.0
2.0
1.0
0.5

⇒ The speed of a D.C. series motor is
proportional to the armature current
proportional to the square of the armature current
proportional to field current
inversely proportional to the armature current

⇒ Regenerative method of braking is based on that
back e.m.f. is less than the applied voltage
back e.m.f. is equal to the applied voltage
back e.m.f. of rotor is more than the applied voltage
none of the above

⇒ Small D.C. motors up to 5 H.P. usually have
2 poles
4 poles
6 poles
8 poles

⇒ The main disadvantage of Hopkinson's test for finding efficiency of the shunt D.C. motors is that it
needs one motor and one generator
requires two identical shunt machines
requires full-load power
ignores any change in iron loss

⇒ One D.C. motor drives another D.C. motor. The second D.C. motor when excited and driven
runs as a generator
does not run as a generator
also runs as a motor
comes to stop after sometime

⇒ 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

⇒ If the supply voltage for a D.C. motor is increased, which of the following will decrease ?
Starting torque
Operating speed
Full-load current
All of the above

⇒ Which one of the following is not necessarily the advantage of D.C. motors over A.C. motors ?
Low cost
Wide speed range
Stability
High starting torque

⇒ 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

⇒ Which D.C. motor will be preferred for machine tools ?
Series motor
Shunt motor
Cumulative compound motor
Differential compound motor

⇒ A D.C. shunt motor is rotating in clockwise direction as viewed from one end. The polarity of connection of the armature and field winding are reversed simultaneously. The motor will
rotate in clockwise direction
rotate in anti-clockwise direction
will not rotate at all
gain excessively high speed

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

⇒ When the armature of a D.C. motor rotates, e.m.f. induced is
self-induced e.m.f.
mutually induced e.m.f.
back e.m.f.
none of the above

⇒ 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

⇒ The simplest form of a motor controller is
relay
toggle switch
drum switch
magnetic switch

⇒ If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens
nothing will happen to the motor
this will make armature to take heavy current, possibly burning it
this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
motor will run at very slow speed

⇒ The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load. The speed regulation of the motor is
0.0236
0.0476
0.0677
0.0884

⇒ The power mentioned on the name plate of an electric motor indicates
the power drawn in kW
the power drawn in kVA
the gross power
the output power available at the shaft

⇒ What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?
The motor will stop
The motor will continue to run
The armature may burn
The motor will run noisy

⇒ The speed of a series motor at no load is
infinity
4000 r.p.m.
2000 r.p.m.
1000 r.p.m.

⇒ A D.C. motor can be easily identified by
winding
commutator
size of conductor
yoke

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

⇒ Which of the following methods gives the greatest breaking torque ?
Regenerative braking
Plugging
Rheostatic braking
None of the above.

⇒ A brake test on D.C. motors is usually restricted to
small horse power motors
variable speed motors
high speed motors
open frame type motors.

⇒ The series parallel system of speed control of D.C. series motors widely used in traction work gives a speed range of about
1 : 10
1 : 8
1 : 6
1 : 4

⇒ Speed control by Ward Leonard method gives uniform speed variation
in one direction
in both directions
below normal speed only
above normal speed only

⇒ Regenerative braking on shunt motors is used when
the load is variable
the load is constantly decreasing
the load acts as a braking force
the load has overhauling characteristics.

⇒ A series motor is' best suited for driving
machine tools
cranes and hoists
shear and punches
none of the above