Question is ⇒ Slip rings are usually made of, Options are ⇒ (A) carbon or graphite, (B) brass or steel, (C) silver or gold, (D) copper or aluminium, (E) , Leave your comments or Download question paper.

Question is ⇒ Slip rings are usually made of, Options are ⇒ (A) carbon or graphite, (B) brass or steel, (C) silver or gold, (D) copper or aluminium, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	Slip rings are usually made of
A.	carbon or graphite [Wrong Answer]
B.	brass or steel [Correct Answer]
C.	silver or gold [Wrong Answer]
D.	copper or aluminium [Wrong Answer]
View Answer 11 -7 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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⇒ An important advantage of a synchronous motor over wound round induction motor is that
its power factor may be varied at will
its speed is independent of supply frequency
its speed may be controlled more easily
none of the above

⇒ When load on an over-excited or underexcited synchronous motor is increased, rate of change of its armature current as compared with that of power factor is
more
less
equal
twice

⇒ Mostly, synchronous motors are of
alternator type machines
induction type machines
salient pole type machines
smooth cylindrical type machines

⇒ In a synchronous motor, the maximum power developed depends on all of the following except
rotor excitation
maximum value of coupling angle
direction of rotation
supply voltage

⇒ Which of the following resistances can be measured by conducting insulation resistance test on a synchronous motor?
Phase to phase winding resistance
Stator winding to earthed frame
Rotor winding to earthed shaft
All of the above

⇒ The working of a synchronous motor is similar to
gear train arrangement
transmission of mechancial power by shaft
distribution transformer
turbine

⇒ The efficiency of a properly designed synchronous motor will usually fall in range
60 to 70%
75 to 80%
85 to 95%
99 to 99.5%

⇒ The maximum power developed in a synchronous motor occurs at a coupling angle of
30°
60°
90°
180°

⇒ In a synchronous motor it the back e.m.f. generated in the armature at noload is approximately equal to the applied voltage, then
the motor is said to be fully loaded
the torque generated is maximum
the excitation is said to be zero per cent
the excitation is said to be hundred per cent

⇒ When a 3-phase synchionous generator is supplying a zero power factor lagging load, the armature field affects the main field in the following way
augments it directly
directly opposes it
cross-magnetises it
none of the above

⇒ The standard full-load power factor ratings for synchronous motors are
zero or 0.8 leading
unity or 0.8 lagging
unity or 0.8 leading
unity or zero

⇒ An over-excited synchronous motor is used for
fluctuating loads
variable speed loads
low torque loads
power factor corrections

⇒ The back e.m.f. of a synchronous motor depends on
speed
load
load angle
all of the above

⇒ In a 3-phase synchronous motor, the negative phase sequence exists when the motor is
supplied with unbalanced voltage
under-loaded
over-loaded
none of the above

⇒ A synchronous motor can be started by
pony motor
D.C. compound motor
providing damper winding
any of the above

⇒ When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected
the motor stops
it runs as a reluctance motor at the same speed
it runs as a reluctance motor at a lower speed
none of the above

⇒ If the field of a synchronous motor is under-excited, the power factor will be
zero
unity
lagging
leading

⇒ A synchronous motor can be used as a synchronous capacitor when it is
under-loaded
over-loaded
under-excited
over-excited

⇒ For V-curves for a synchronous motor the graph is drawn between
field current and armature current
terminal voltage and load factor
power factor and field current
armature current and power factor

⇒ For power factor correction, synchronous motors operate at
no-load and greatly over-excited fields
no-load and under-excited fields
normal load with minimum excitation
normal load with zero excitation

⇒ Stability of a synchronous machine
decreases with increase in its excitation
increases with increase in its excitation
remains unaffected with increase in excitation
any of the above

⇒ By which of the following methods the constant speed of a synchronous motor can be changed to new fixed value ?
By changing the supply frequency
By interchanging any two phases
By changing the applied voltage
By changing the load.

⇒ Which of the following motors is nonself starting ?
D.C. series motor
synchronous motor
Squirrel cage induction motor
Wound round induction motor

⇒ A synchronous motor installed at the receiving end substation operates with such an excitation that it takes power at lagging power factor. Now if the applied voltage of the synchronous motor goes down, the power factor of the synchronous motor will
remain same
go down
improve
none of the above

⇒ If the field circuit of an unloaded salientpole synchronous motor gets suddenly open-circuited, then
it runs at a slower speed
the motor stops
it continues to run at the same speed
it runs at a very high speed

⇒ A three-phase synchronous motor will have
no slip-rings
one slip-ring
two slip-rings
three slip-rings

⇒ The duration of sudden snort-circuit test on a synchronous motor is usually about
one hour
one minute
one second
none of the above

⇒ The angle between the rotor poles and stator poles, in a synchronous motor, is known as
power factor angle
torque angle
synchronizing angle
angle of retardation

⇒ Due to which of the following reasons a synchronous motor fails to pull into synchronism after applying D.C. field current ?
High field current
Low short circuit ratio
High core losses
Low field current

⇒ The armature current of the synchronous motor
has large values for low excitation only
has large values for high excitation only
has large values for low and high excitation
any of the above