Download SNSCT Course ware: EE211 Electrical Machines

SNSCT Course ware: EE211 Electrical Machines and Drives
UNIT 2 MCQ
:: The design of mechanical parts is particularly important in case of _____ speed
machines.
~ low
~ medium
= high
~ zero
:: In ______ machines, the size of the shaft is decided by the critical speed which depends
on the deflection of the shaft.
~ small
~ medium
= large
~ any of the above
:: Commercial available medium size machines have a speed range of ______ .
~ 200 to 400 r.p.m.
~ 600 to 1000 r.p.m.
~ 1000 to 1500 r.p.m.
= 2000 to 2500 r.p.m.
:: If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be
= zero
~ small
~ the same as rated voltage
~ high
:: In D.C. shunt motors as load is reduced
~ the speed will increase abruptly
~ the speed will increase in proportion to reduction in load
= the speed will remain almost/constant
~ the speed will reduce
::The speed of a D.C. series motor is
~ proportional to the armature current
~ proportional to the square of the armature current
~ proportional to field current
= inversely proportional to the armature current
SNSCT Course ware: EE211 Electrical Machines and Drives
::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
~ 2.36%
= 4.76%
~ 6.77%
~ 8.84%
:: Which motor has the poorest speed control?
~ Differentially compounded motor
~ Cumulatively compounded motor
~ Shunt motor
= Series motor
:: For which motor the speed can be controlled from rotor side ?
~ Squirrel-cage induction motor
= Slip-ring induction motor
~ Both slip ring and squirrel cage
~ synchronous motor
:: Size of a high speed motor as compared to low speed motor for the same H.P. will be
~ bigger
= smaller
~ same
~ any of the above
:: The speed characteristics of an induction motor closely resemble the speed load characteristics
of which of the following machines
~ D.C. series motor
= D.C. shunt motor
~ universal motor
~ none of the above
:: What will happen if the relative speed between the rotating flux of stator and rotor of the
induction motor is zero ?
~ The slip of the motor will be 5%
= The rotor will not run
~ The rotor will run at very high speed
~ The torque produced will be very large
:: The rotor of an induction motor runs at
SNSCT Course ware: EE211 Electrical Machines and Drives
~ synchronous speed
= below synchronous speed
~ above synchronous speed
~zero speed
::. If a particular application needs high speed and high starting torque, then which of the
following motor will be preferred ?
= Universal motor
~ Shaded pole type motor
~ Capacitor start motor
~ Capacitor start and run motor
:: In case of high speed universal motor which of the following needs more attention ?
~ End play
~ Air gap
~ Insulation in rotor
= Balancing of rotor
:: The speed control of universal motor used for sewing machines is by
~friction
= varying the resistance
~ tapping the field
~ centrifugal mechanism
::An universal motor is also called as _____
~ Induction motor
~ Synchronous motor
= AC series motor
~ Stepper motor
::The speed of a two pole induction motor for an Indian frequency is__________
= 3000 rpm
~ 1000 rpm
~ 1500 rpm
~ 750 rpm
:: Speed control of slip ring induction motor can be easily carried by_________
= rotor resistance method
SNSCT Course ware: EE211 Electrical Machines and Drives
~ voltage control method
~ auto transformer method
~ armature control method
:: The electric motor used in portable drill is__________
= Universal motor
~ Synchronous motor
~ Stepper motor
~ Induction motor
:: Star-delta starting of motors is not possible in case of
= single phase
~ variable speed motors
~ low horse power motors
~high speed motors
:: An induction motor is identical to
~ D.C. compound motor
~ D.C. series motor
~ synchronous motor
= asynchronous motor
:: Laminations of core are generally made of
~ case iron
~ carbon
= silicon steel
~ stainless steel
:: The resistance of armature winding depends on
~ length of conductor and number of strands
~ cross-sectional area of the conductor
~ number of conductors
= length and cross section area of the conductor
:: The field coils of D.C. machine are usually made of
~ mica
SNSCT Course ware: EE211 Electrical Machines and Drives
= copper
~ cast iron
~ carbon
:: In a four-pole D.C. machine
~ all the four poles are north poles
= alternate poles are north and south
~ all the four poles are south poles
~ two north poles follow two south poles
::Which of the following component is usually fabricated out of silicon steel ?
~ Bearings
~ Shaft
= Stator core
~ insulation material
:: The frame of an induction motor is usually made of
~ silicon steel
= cast iron
~ aluminium
~ bronze
:: The shaft of an induction motor is made of
~ high speed steel
= stainless steel
~ carbon steel
~ cast iron
:: The starting torque of a squirrel-cage induction motor is
= low
~ negligible
~ same as full-load torque
~ slightly more than full-load torque
:: The electric motor used in portable drill is
~ capacitor run motor
~ hysteresis motor
= universal motor
SNSCT Course ware: EE211 Electrical Machines and Drives
~ repulsion motor
::The speed/load characteristics of a universal motor is same as that of
~ A.C. motor
~ D.C. shunt motor
= D.C. series motor
~ none of the above
::The number of slip rings on a squirrel cage induction motor is usually
~ two
~ three
~ four
= zero
:: The starting torque of a squirrel-cage induction motor is
= low
~ negligible
~ same as full-load torque
~ slightly more than full-load torque
:: In squirrel cage induction motors, the rotor slots are usually given slight skew in order to
~ reduce windage losses
~ reduce eddy currents
~ reduce accumulation of dirt and dust
= reduce magnetic hum
:: In case of D.C. machines, mechanical losses are primary function of
~ current
~ voltage
= speed
~ power
:: Iron losses in a D.C. machine are independent of variations in
~ speed
= load
~ voltage
~ speed and voltage
SNSCT Course ware: EE211 Electrical Machines and Drives
:: In D.C. machines, the cause of rapid brush wear may be
~ severe sparking and perfect contact
~ smooth commutator surface
~ imperfect contact
= sparking and imperfect contact
:: Fleming's right-hand rule regarding direction of induced e.m.f., correlates
~ magnetic flux, direction of current flow and resultant force
= magnetic flux, direction of motion and the direction of e.m.f. induced
~ magnetic field strength, induced voltage and current
~ magnetic flux, direction of force and direction of motion of conductor
::Which type of motors are used in CNC Machines
~ universal motor
= stepper motor
~ reluctance motor
~ synchronous motor