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Home⇒ Engineering⇒
Polyphase induction motors
1-Dont try to cram or spend more time here just read it fast and cover syllabus then practice MCQ's cheptor of same topic to check your progress. . |
2-Wrong options are also given but dont concentrate there, Right answer is in bold format. |
Q21 ⇒ If the rotor circuit of a squirrel cage
induction motor is open, the rotor will not run [other wrong options] [Discuss in forum] run at very high speed run at very low speed make noise |
Q22 ⇒ The rotor of an induction motor cannot
run with synchronous speed because rotor torque would then become zero [other wrong options] [Discuss in forum] Lenz's law would be violated induction motor would then become synchronous motor air friction prevents it to do so |
Q23 ⇒ The primary winding of a Schrage
motor is located in lower part of rotor [other wrong options] [Discuss in forum] in stator in upper part of rotor partly in stator and partly in rotor |
Q24 ⇒ In case of a 3-phase wound-rotor induction
motor, an increase in rotor resistance
affects the motor performance in
the following way starting current decreases [other wrong options] [Discuss in forum] the motor efficiency decreases the motor efficiency increases starting current increases the maximum torque is reduced |
Q25 ⇒ Slip rings for induction motors are
made of phosphor bronze [other wrong options] [Discuss in forum] aluminium carbon cobalt steel |
Q26 ⇒ A wound rotor induction motor is
usually not selected when cost is the main consideration [other wrong options] [Discuss in forum] variable speed operation is desired high starting torque is the main consideration external voltage is to be fed into rotor |
Q27 ⇒ The stator frame in an induction motor
is used as a return path for the flux [other wrong options] [Discuss in forum] to protect the whole machine to ventilate the armature to hold the armature stampings/ stator |
Q28 ⇒ What is the function of putting resistance
in parallel to one phase of 3-phase
induction motor ? To achieve a smooth' starting [other wrong options] [Discuss in forum] To attain a higher starting torque To reduce the starting current to a very low value To attain a higher maximum torque |
Q29 ⇒ For a 50 H.P. motor, which type of rotor
will be preferred ? Wound rotor [other wrong options] [Discuss in forum] Die cast aluminium rotor Squirrel cage rotor using round copper bars Squirrel cage rotor using rectangular copper bars |
Q30 ⇒ The overheating of an induction motor
may be due to any of the above [other wrong options] [Discuss in forum] overloading loss of ventilation low supply voltage |
Q31 ⇒ The two important parts of a 3-phase
induction motor are rotor and stator [other wrong options] [Discuss in forum] rotor and armature slip ring and brushes stator and field |
Q32 ⇒ In Ns is the synchronous speed and s
the slip, then actual running speed of
an induction motor will be (1 - s)Ns [other wrong options] [Discuss in forum] Ns s.Ns (Ns - 1) |
Q33 ⇒ The good power factor of an induction
motor can be achieved if the average
flux density in the air gap is small [other wrong options] [Discuss in forum] absent large infinity |
Q34 ⇒ Stepless speed control of induction motor
is possible by which of the following
methods ? Changing the number of poles [other wrong options] [Discuss in forum] e.m.f. injection in rotor circuit Cascade operation None of the above |
Q35 ⇒ DOL starting of induction motors is
usually restricted to low horsepower motors [other wrong options] [Discuss in forum] variable speed motors high horsepower motors high speed motors |
Q36 ⇒ A 3-phase induction motor delta connected
is carrying too heavy load and
one of its fuses blows out. Then the
motor will stop and carry heavy current causing permanent damage to its winding [other wrong options] [Discuss in forum] will continue running burning its
one phase will continue running burning its two phase will continue running without any harm to the winding |
Q37 ⇒ A pump induction motor is switched on
to a supply 30% lower than its rated
voltage. The pump runs. What will
eventually happen ? It will get heated and subsequently get damaged [other wrong options] [Discuss in forum] stall after sometime stall immediately continue to run at lower speed without damage |
Q38 ⇒ In a three-phase induction motor power factor at starting is low as compared to that while running [other wrong options] [Discuss in forum] power factor at starting is high as
compared to that while running power factor at starting in the same as that while running |
Q39 ⇒ The torque of a rotor in an induction
motor under rurming condition is maximum at the value of the slip which makes rotor reactance per phase eclual to the resistance per phase [other wrong options] [Discuss in forum] at the unit value of slip at the zero value of slip at the value of the slip which makes the rotor reactance half of the rotor resistance |
Q40 ⇒ In an induction motor s = Ns - N/Ns [other wrong options] [Discuss in forum] s = N - Ns/N s = Ns - N/N s = N - Ns/Ns |
Or |