Question is ⇒ If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking, Options are ⇒ (A) regenerative, (B) plugging, (C) dynamic braking, (D) none of the above, (E) any of the above, Leave your comments or Download question paper.

Question is ⇒ If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking, Options are ⇒ (A) regenerative, (B) plugging, (C) dynamic braking, (D) none of the above, (E) any of the above, Leave your comments or Download question paper. Previous question Next question


Q1.	If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking
A.	regenerative [Wrong Answer]
B.	plugging [Correct Answer]
C.	dynamic braking [Wrong Answer]
D.	none of the above [Wrong Answer]
E.	any of the above [Wrong Answer]
View Answer 9 -3 Explanation:- Answer : B 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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⇒ VVhat is the effect produced by the electric current in an electric motor ?
Heating effect only
Magnetic effect only
Heating as well as magnetic effect
Heating as well as chemical effect

⇒ In a D.C. generator all of the following could be the effects of iron losses except
Loss of efficiency
Excessive heating of core
Increase in terminal voltage
Rise in temperature of ventilating air

⇒ In a differentially compounded D.C. motor, if shunt field suddenly opens
the motor will first stop and then run in opposite direction as series motor
the motor will work as series motor and run at slow speed in the same direction
the motor will work as series motor and run at high speed in the same direction
the motor will not work and come to stop

⇒ The losses occurring in a D.C. generator are given below. Which loss is likely to have highest proportion at rated load of the generator ?
hysteresis loss
field copper loss
armature copper loss
eddy current loss

⇒ Following motor is used where high starting torque and wide speed range control is required.
Single phase capacitor start
Induction motor
Synchronous motor
D.C. motor

⇒ If B_max is the maximum flux density, then eddy cu rrent loss will vary as
B_max
(B_max)²
(B_max)^1.2
(B_max)^2.4

⇒ The hysteresis loss in a D.C. machine least depends on
Frequency of magnetic reversals
Maximum value of flux density
Volume and grade of iron
Rate of flow of ventilating air

⇒ According to Fleming's left hand rule, when the forefinger points in the direction of the field or flux, the middle finger will point in the direction of
current, in the conductor
movement of conductor
resultant force on conductor
none of the above

⇒ 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

⇒ Torque developed by a D.C. motor depends upon
active length of the conductor
current flow through the conductors
number of conductors
radius of armature

⇒ Which of the following method of speed control, of D.C. machine will offer minimum efficiency ?
Voltage control method
Field control method
Armature control method
All above methods

⇒ Which D.C. motor has got maximum self loading property?
Series motor
Shunt motor
Cumulatively compounded motor
Differentially compotinded motor

⇒ Which D.C. motor will be suitable alongwith flywheel for intermittent light and heavy loads?
Series motor
Shunt motor
Cumulatively compounded motor
Differentially compounded motor

⇒ What will happen if supply terminals of D.C. shunt motor are interchanged ?
The direction of rotation will reverse
Motor will stop
Motor will run at speed lower than the normal speed in the same direction
Motor will run at its normal speed in the same direction as it was running

⇒ When the electric train is moving down a hill the D.C. motor act as
D.C. series generator
D.C. shunt generator
D.C. shunt motor
D.C. 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

⇒ In regenerative braking
motor energy is dissipai.ed as heat
motor energy is dissipated in armature heating
motor energy is dissipated in windage losses
motor is rnade to run as a generator

⇒ In D.C. machines the residual magnetism is of the order of
2 to 3 per cent
10 to 15 per cent -
20 to 25 per cent
50 to 75 per cent

⇒ D.C. series motors are used
where load is constant
where load changes frequently
where constant operating speed is needed
in none of the above situations.

⇒ If the no-voltage release of a D.C. motor starter fails to work on resumption of supply after a break, the motor will
not start automatically
start automatically without trouble
get damaged
develop very low torque

⇒ A face plate starter is employed for starting
induction motor
universal motor
synchronous motor
d.c. series motor

⇒ Ward-Leonard system of speed control is not recommended for
very low speeds
frequent motor reversals
wide speed range
constant speed operation

⇒ Which losses can be determined by performing the retardation test ?
Friction losses
Eddy current losses
Stray losses
Copper losses

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

⇒ 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

⇒ Three point starter can be used for
series motor only
shunt motor only
compound motor only
both shunt and compound motor

⇒ Hopkinson's test on D.C. machines is conducted at
no-load
part load
full-load
overload

⇒ Which of the following can be used to control the speed of a D.C. motor ?
Thermistor
Thyristor
Thyratron
Transistor

⇒ 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