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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