Question is ⇒ Four point starter in the D.C. motor is used, Options are ⇒ (A) to decrease the field current, (B) to increase the field current, (C) not to effect the current passing through Hold on coil even if any change M the field current takes place, (D) all of the above, (E) none of the above, Leave your comments or Download question paper.

Question is ⇒ Four point starter in the D.C. motor is used, Options are ⇒ (A) to decrease the field current, (B) to increase the field current, (C) not to effect the current passing through Hold on coil even if any change M the field current takes place, (D) all of the above, (E) none of the above, Leave your comments or Download question paper. Previous question Next question


Q1.	Four point starter in the D.C. motor is used
A.	to decrease the field current [Wrong Answer]
B.	to increase the field current [Wrong Answer]
C.	not to effect the current passing through Hold on coil even if any change M the field current takes place [Correct Answer]
D.	all of the above [Wrong Answer]
E.	none of the above [Wrong Answer]
View Answer 7 -3 Explanation:- Answer : C 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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⇒ Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed control
drum type controller is used
three point starter is used
four point starter is used
all above can be used

⇒ If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens
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
nothing will happen to motor
motor will come to stop

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

⇒ In D.C. motor which of the following can sustain the maximum temperature rise?
Slip rings
Commutator
Field winding
Armature winding

⇒ In a manual shunt motor starter
over load relay is connected in series and no volt relay in parallel with the load
over load relay is connected in parallel and no volt relay in series with the load
over load relay and no volt relay are both connected in series with the load
over load relay and no volt relay are both connected in parallel with the load

⇒ The armature voltage control of D.C. motor provides
constant torque drive
constant voltage drive
constant current drive
none of the above

⇒ 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

⇒ In the D.C. motor the iron losses occur in
the field
the armature
the brushes
the commutator

⇒ 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

⇒ Ward-Leonard control is basically a
voltage control method
field divertor method
field control method
armature resistance control method

⇒ In Ward Leonard method of speed control of a D.C. motor, change in speed of motor is obtained by the
change in armature voltage of D.C. motor
change in the field excitation of the D.C. motor
change in armature current of D.C. motor
change in supply voltage

⇒ Which of the following statement is incorrect ? If a starter is not used with large D.C. motor, it will draw a starting current which
will produce very low starting torque
will produce excessive line voltage drop
will damage the cOmmutator
is many times its full-load current

⇒ The mechanical power developed by a D.C. motor is equal to
power input + losses
back e.m.f. X armature current
power output X losses
power output X efficiency

⇒ 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

⇒ Hopkinson's test is conducted at
no load
part load
low load
full load

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

⇒ 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

⇒ 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

⇒ 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

⇒ Which of the following motor has the poorest speed regulation ?
Shunt motor
Series motor
Differential compound motor
Cumulative compound motor

⇒ A D.C. series motor is that which
has its field winding consisting of thick wire and less turns
has a poor torque
can be started easily without load
has almost constant speed

⇒ 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 is generally preferred for cranes and hoists ?
Series motor
Shunt motor
Cumulatively compounded motor
Differentially compounded motor

⇒ 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

⇒ 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 armature voltage control of D.C. motor provides
constant voltage drive
constant current drive
constant torque drive
none of the above

⇒ In a D.C. motor constant torque is produced due to
rotor laminations
end-plates
pole shoes
commutator

⇒ 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 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