Electrical Machines - II Mid - II, April - 2012

1.Irrespective of the supply frequency the torque developed by SCIM is same whenever __________ is same
  • supply voltage
  • external load
  • rotor resistance
  • slip speed
Answer: D
2.The effect of increasing the length of air gap in an induction motor will be to increase the
  • power factor
  • speed
  • magnetizing current
  • air gap flux
Answer: C
3.The efficiency and p.f of a SCIM increases in proportional to its
  • speed
  • mechanical load
  • voltage
  • rotor torque
Answer: B
4.Pull out torque of a SCIM occurs at that value of slip where the rotor power factor equals
  • unity
  • 0.707
  • 0.866
  • 0.5
Answer: B
5.In circle diagram for a 3 phase I.M the diameter of circle is determined by
  • rotor current
  • exciting current
  • stator current
  • none
Answer: C
6.The no. of stator poles produced in the rotating magnetic field of a 3 phase I.M having 3 slots per pole per phase is
  • 3
  • 4
  • 5
  • 6
Answer: D
7.The wrong statement is A Schrage motor is capable of behaving as an
  • inverted induction motor
  • slip ring induction motor
  • shunt motor
  • series motor
Answer: D
8.The synchronous slip of a linear I.M does not depend on
  • width of pole pitch
  • no. of poles
  • supply frequency
  • all above
Answer: B
9.In case of 3 phase I.M having synchronous speed of 1500 r.p.m and running with s=0.04 revolvingspeed of stator flux in space is ____________ r.p.m.
  • 1500
  • 1000
  • 500
  • 800
Answer: A
10.The fractional slip of an induction motor is the ratio of
  • rotor Cu loss/rotor input
  • stator Cu loss/stator input
  • rotor Cu loss/rotor output
  • rotor Cu loss/stator input
Answer: A
11.When load is placed on 3 phase I.M its rotor torque------------.
Answer: increaes
12.A 6 pole 50Hz 3 phase I.M has full load speed of 950 r.p.m, at half load its speed would be---------
Answer: 975
13.In case of 3 phase I.M having synchronous speed of 1500 r.p.m and running with s=0.04 rotor speed is --------- r.p.m.
Answer: 1440
14.In case of 3 phase I.M having synchronous speed of 1500 r.p.m and running with s=0.04speed of rotor flux relative to rotor is ---------r.p.m.
Answer: 60
15.The no. of stator poles produced in the rotating magnetic field of a 3 phase I.M having 3 slots per pole per phase is -------------.
Answer: 6
16.The term given by the difference of synchronous speed and actual speed is called-------------
Answer: slip speed
17.A slip ring I.M runs at 290 r.p.m at full load when connected to 50 Hz supply, determine the slip------------
Answer: 3.33%
18.A slip ring I.M run at 290 r.p.m at full load when connected to 50 Hz supply determine the poles------------
Answer: 20
19.When I.M runs at a speed greater than synchronous speed is-----------------.
Answer: inuction generator
20.Stopping a motor by instantaneously by reversing its terminals till it stop is called -------------------
Answer: plugging