Question is ⇒ In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be, Options are ⇒ (A) 3000 r.p.m., (B) 1500 r.p.m., (C) 750 r.p.m., (D) none of the above, (E) , Leave your comments or Download question paper.

Question is ⇒ In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be, Options are ⇒ (A) 3000 r.p.m., (B) 1500 r.p.m., (C) 750 r.p.m., (D) none of the above, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be
A.	3000 r.p.m. [Wrong Answer]
B.	1500 r.p.m. [Correct Answer]
C.	750 r.p.m. [Wrong Answer]
D.	none of the above [Wrong Answer]
View Answer 5 -4 Explanation:- Answer : B Discuss it below : Rakesh Juyal Said on 2020-10-14 18:36:57 12050/4 !! OOPS Login [Click here] is required to post your answer/result* Help other students, write article, leave your comments

Previous question Next question

Also Read Similar Questions Below :

⇒ 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

⇒ A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because
synchronous motor has no slip
stator supply is not required to produce magnetic field
mechanical load on the rotor remains constant
synchronous motor has large airgap

⇒ 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

⇒ Slip rings are usually made of
carbon or graphite
brass or steel
silver or gold
copper or aluminium

⇒ A synchronous motor connected to infinite bus-bars has at constant full load, 100% excitation and unity power factor. On changing the excitation only, the armature current will have
no change of power factor
lagging power factor with over-excitation
leading power factor with underexcitiltion
leading power factor vvith over-excitation

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

⇒ 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 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 will depend on
the rotor excitation only
the supply voltage only
the rotor excitation and supply voltage both
the rotor excitation, supply voltage and maximum value of coupling angle (90°)

⇒ In case one phase of a three-phase synchronous motor is short-circuited the motor will
not start
run at 2/3 of synchronous speed
run with excessive vibrations
take less than the rated load

⇒ 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

⇒ 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

⇒ The speed of a synchronous motor
increases as the load increases
decreases as the load decreases
always remains constant
none of the above

⇒ The construction of a synchronous motor resembles
a series motor
an induction motor
an alternator
a rotary converter

⇒ VVhen the voltage applied to a synchronous motor is increased, which of the following will reduce ?
Stator flux
Pull in torque
Both (a) and (b)
None of the above

⇒ If excitation of a synchronous motor running with a constant load is decreased from its normal value, ignoring effects of armature reaction, it leads to
increase in both armature current and power factor angle
increase in back e.m.f. but decrease in armature current
increase in both armature current and power factor which is lagging
increase in torque angle but decrease in back e.m.f.

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

⇒ The effect of increasing the load on a synchronous motor running with normal excitation is to
decrease both arrnature current and power factor
decrease armature current but increase power factor
increase armature current but decrease power factor
increase both its armature current and power factor

⇒ The shaft of synchronous motor is made of
mild steel
chrome steel
alnico
stainless steel

⇒ Synchronous motors are generally not self-starting because
the direction of rotation is not fixed
the direction of instantaneous torque reverses after half cycle
startes cannot be used on these machines
starting winding is not provided on the machines

⇒ If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then
the stator current will be zero
the stator current will be very small
the stator current will be very high
the back e.m.f. will be more than the supply voltage

⇒ The mechanical displacement of the rotor with respect to the stator, in polyphase multipolar synchronous motor running at full load, is of the order of
zero degree
two degrees
five degrees
ten degrees

⇒ Which of the following motors will be used in electric clocks ?
D.C. shunt motor
D.C. series motor
A.C. induction motor
A.C. synchronous motor

⇒ A synchronous motor can develop synchronous torque
when under loaded
while over-excited
only at synchronous speed
below or above synchronous speed

⇒ The oscillations in a synchronous motor can be damped out by
maintaining constant excitation
running the motor on leading power factors
providing damper bars in the rotor pole faces
oscillations cannot be damped

⇒ The operating speed of a synchtunous motor can be changed to new fixed value by
changing the load
changing the supply voltage
changing frequency
using brakes

⇒ In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be
3000 r.p.m.
1500 r.p.m.
750 r.p.m.
none of the above

⇒ A synchronous machine with large air gap has
a higher value of stability limit
a small value of inherent regulation
a higher synchronizing power which makes the Machine less sensitive to load variations
all of the above

⇒ The maximum speed variation in a 3- phase synchronous motor is
10 per cent
6 per cent
4 per cent
2 per cent

⇒ A synchronous motor will always stop when
supply voltage fluctuates
load in motor varies
excitation winding gets disconnected
supply voltage frequency changes