mcq of dc machines madhuri new
Post on 06-Jul-2018
223 Views
Preview:
TRANSCRIPT
-
8/17/2019 Mcq of Dc Machines Madhuri New
1/31
Id
Question What is the rotating part of a DC motor?
A Armature
B The field winding
C Any magnetic field
D The magnetic field developed by the field winding
Answer A
ar!s "
#nit $
Id
Question What is used to develop the magnetic field in small si%ed DC motor ?
A &inc battery
B 'ermanent magnet
C (lectromagnet
D )ption B and C both
Answer B
ar!s "
#nit $
Id
Question In DC motor tor*ue is generated by which principle?
A )hm law
B +orent% force
C The fleming,s law
D (dison,s law
Answer B
ar!s "
#nit $
Id
Question In DC series motor
A Armature winding - field winding are parallel
B Armature winding - field winding are !ept in series with source
-
8/17/2019 Mcq of Dc Machines Madhuri New
2/31
C Armature winding is !ept in series with the source
D The field winding is !ept in series with source
Answer B
ar!s "
#nit $
Id
Question In DC shunt motor
A Armature and field winding both in series with source
B Armature winding is parallel with source
C The field winding is parallel with source
D Both armature - field winding are connected in parallel with a common source
Answer D
ar!s "
#nit $
Id
Question Can you tell that where DC shunt motors are used
A Where large starting tor*ue is re*uired
B Where the load fluctuations is more
C Where the re*uired tor*ue is high
D Where the speed is re*uired to remain constant from no.load to full load.condition
Answer D
ar!s "
#nit $
Id
Question Can you tell where DC series motors are used
A Where huge starting tor*ue is re*uired - load is sub/ected to heavy fluctuations
B Where large starting tor*ue is re*uired
C Where load is sub/ected to heavy fluctuations
D Where constant speed is re*uired
Answer A
ar!s "
-
8/17/2019 Mcq of Dc Machines Madhuri New
3/31
#nit $
Id
Question Which of the following applications needs high starting tor*ue ?
A +athe
B Centrifugal pump
C +ocomotive
D Air blower
Answer C
ar!s "
#nit $
Id
Question 0elect DC motor that is preferred for cranes - hoists
A 0hunt motor
B 0eries motor
C Cumulative compound motor
D Any of those
Answer B
ar!s "
#nit $
Id
Question Two DC series motors when connected in series1 draw a current of I Amp and run at 2 rpm3
When those motors are connected in parallel and if the motors continue to draw current I1
then the speed of the motors will be
A 2
B 2 4 5
C 52
D 62
Answer A
ar!s "
#nit $
Id
Question Two DC series motors are connected in series to produce a tor*ue T3 2ow if the motors are
-
8/17/2019 Mcq of Dc Machines Madhuri New
4/31
connected in parallel1 the tor*ue produced will be
A T 4 5
B 6T
C T 4 6
D 5T
Answer B
ar!s "
#nit $
Id
Question 0elect the motor that should not be started on no load
A 0eries motor
B 0hunt motor
C Compound motor
D Brushless DC motor
Answer A
ar!s "
#nit $
Id
Question If the source voltage of a DC motor is increased1 which of the following will decrease
A 0tarting tor*ue1 operating speed1 full load current
B 0tarting tor*ue
C full load current
D operating speed
Answer A
ar!s "
#nit $
Id
Question The output power of any electrical motor is ta!en from the7
A Armature
B 8ield
C Coupling mounted on the shaft
-
8/17/2019 Mcq of Dc Machines Madhuri New
5/31
D otor frame
Answer C
ar!s "
#nit $
Id
Question If the bac! emf in a dc motor varnishes suddenly1 then the motor7
A 9un at very high speeds
B 0tart hunting
C Burn
D Come to stall
Answer C
ar!s "
#nit $
Id
Question The direction of the armature current in a dc motor is7
A The same as the generated emf
B )pposite to that of generated emf
C 2ot dependent upon the direction of the armature emf
D 2one of the above
Answer B
ar!s "
#nit $
Id
Question When a dc machine is connected to the dc supply main it will produce7
A (8 in opposition to the applied voltage
B (8 in phase with the applied voltage
C (8 decreases with time
D 2one of the above
Answer A
ar!s "
#nit $
-
8/17/2019 Mcq of Dc Machines Madhuri New
6/31
Id
Question The direction of rotation of a dc motor can be determined by7
A 8leming:s right hand rule
B 8leming:s left hand rule
C +en%:s law
D Ampere:s law
Answer B
ar!s "
#nit $
Id
Question A thic! wire is used in dc series motor field winding than that in dc shunt motor7
A To create more flu;
B To reduce the resistance
C To carry large load current
D Both
-
8/17/2019 Mcq of Dc Machines Madhuri New
7/31
B Increases
C Decreases
D Be &ero
Answer C
ar!s "
#nit $
Id
Question A DC series motor is best suited for electrical traction because7
A It develops high starting tor*ue
B It runs at very high speed
C It is cheaper in cost
D It is more rugged in construction li!e induction motor
Answer A
ar!s "
#nit $
Id
Question A DC series motor is used for overhauling load3 It can wor! stable if7
A The armature is shunted by a resistor
B The field winding is revered
C A resistor is put in series with the machine
D A divertor is put across the field
Answer A
ar!s "
#nit $
Id
Question Which of the following dc motor has ma;imum self relieving property7
A 0hunt
B 0eries
C Cumulative compound
D Differential compound
Answer B
-
8/17/2019 Mcq of Dc Machines Madhuri New
8/31
ar!s "
#nit $
Id
Question When the direction of power flow in a differential compounded motor reverses1 it will
operate as a7
A Cumulative compound generator
B Differential compound generator
C 0eries motor
D 0hunt motor
Answer A
ar!s "
#nit $Id
Question A separately e;cited dc generator is feeding dc shunt motor3 If the load tor*ue on the
motor is halved appro;imately1 then7
A Armature current of both motor and generator are halved
B Armature current of motor is halved and that of the generator is unaltered
C Armature current of generator is halved and that of the motor is unaltered
D Armature current of both motor and generator are unaltered
Answer Aar!s "
#nit $
Id
Question A flywheel is employed with a dc compound motor to reduce the pea! demand1 the
compound motor should be7
A +evel compound
B Differential compound
C Cumulative compound
D 2one of the above
Answer C
ar!s "
#nit $
-
8/17/2019 Mcq of Dc Machines Madhuri New
9/31
Id
Question The flu; lea!age coefficient in dc machine is usually7
A >3 to >3@
B "3>
C "3" to "3$
D 6 to 63
Answer C
ar!s "
#nit $
Id
Question In a separately e;cited dc generator the field is connected to7
A In series with an armature
B Across the armature
C To the e;ternal supply source
D 2one of the above
Answer C
ar!s "
#nit $
Id
Question If we increase the field of the dc generator1 its emf output7
A Increases indefinitely
B Increases till the winding burns
C Increases till the magnetic saturation ta!es place
D 8irst increases and then starts reducing
Answer C
ar!s "
#nit $
Id
Question In a dc generator the residual magnetism is of the order of7
A 63
B ">
-
8/17/2019 Mcq of Dc Machines Madhuri New
10/31
C "
D 6
Answer A
ar!s "
#nit $
Id
Question The terminal voltage of the dc shunt generator on loading7
A Increases slightly
B Decreases sharply
C Decreases slightly
D Increases sharply
Answer C
ar!s "
#nit $
Id
Question 8or parallel operation1 the dc shunt generator normally preferred are7
A 0hunt generator
B 0eries generator
C #nder compound generator
D Both
-
8/17/2019 Mcq of Dc Machines Madhuri New
11/31
#nit $
Id
Question 8lashing of field of dc generator means7
A 2eutrali%ation of residual magnetism
B Creation of the residual magnetism by a dc source
C Increasing the flu; density by providing e;tra ampere.turns in the field
D 2one of the above
Answer B
ar!s "
#nit $
Id
Question In an arc welding in order to obtain steady arc one should use7
A DC series generator
B DC shunt generator
C DC differential compound generator
D DC cumulative compound generator
Answer C
ar!s "
#nit $
Id
Question With the increase in the speed of a dc motor7
A Both bac! emf as well as line current increases
B Both bac! emf and line current falls
C Bac! emf increases but the line current falls
D Bac! emf falls and line current increases
Answer C
ar!s "
#nit $
Id
Question The output indicated on the name plate of any motor is always the7
A ross power
-
8/17/2019 Mcq of Dc Machines Madhuri New
12/31
B 'ower drawn in volt amperes
C 'ower drawn in watts
D )utput power at the shaft
Answer D
ar!s "
#nit $
Id
Question In a dc compound motor field regulator is provided to7
A Control the flu;
B +imit the ampere current
C Demagneti%e the field partially
D 2one of the above
Answer A
ar!s "
#nit $
Id
Question The direction of rotation of dc shunt motor can be reversed by interchanging7
A The supply terminals
B The field terminals
C The armature terminals only
D (ither field or armature terminals
Answer D
ar!s "
#nit $
Id
Question In a d3c3 motor1 unidirectional tor*ue is produced with the help of
A brushes
B commutator
C end.plates
D both
-
8/17/2019 Mcq of Dc Machines Madhuri New
13/31
ar!s "
#nit $
Id
Question The counter e3m3f3 of a d3c3 motor
A often e;ceeds the supply voltage
B aids the applied voltage
C helps in energy conversion
D regulates its armature voltage
Answer C
ar!s "
#nit $
Id
Question The normal value of the armature resistance of a d3c3 motor is
A >3>>
B >3
C ">
D ">>
Answer B
ar!s "
#nit $
Id
Question The (b4E ratio of a d3c3 motor is an indication of its
A efficiency
B speed regulation
C starting tor*ue
D 9unning Tor*ue
Answer A
ar!s "
#nit $
Id
Question The mechanical power developed by the armature of a d3c3 motor is e*ual to
-
8/17/2019 Mcq of Dc Machines Madhuri New
14/31
A armature current multiplied by bac! e3m3f3
B power input minus losses
C power output multiplied by efficiency
D power output plus iron losses
Answer A
ar!s "
#nit $
Id
Question The induced e3m3f3 in the armature conductors of a d3c3 motor is
A sinusoidal
B trape%oidal
C rectangular
D alternating
Answer A
ar!s "
#nit $
Id
Question A d3c3 motor can be loo!ed upon as d3c3 generator with the power flow
A reduced
B reversed
C increased
D modified
Answer B
ar!s "
#nit $
Id
Question In a d3c3 motor1 the mechanical output power actually comes from
A field system
B air.gap flu;
C bac! e3m3f3
D electrical input power
-
8/17/2019 Mcq of Dc Machines Madhuri New
15/31
Answer D
ar!s "
#nit $
Id
Question The ma;imum tor*ue of d3c3 motors is limited by
A commutation
B heating
C speed
D armature current
Answer A
ar!s "
#nit $
Id
Question Which of the following *uantity maintains the same direction whether a d3c3 machine runs
as a generator or as a motor ?
A induced e3m3f3
B armature current
C field current
D supply current
Answer A
ar!s "
#nit $
Id
Question #nder constant load conditions1 the speed of a d3c3 motor is affected by
A field flu;
B armature current
C bac! e3m3f3
D both
-
8/17/2019 Mcq of Dc Machines Madhuri New
16/31
Question It is possible to increase the field flu; and1 at the same time1 increase the speed of a d3c3
motor provided its 3333333333 is held constant3
A applied voltage
B tor*ue
C Armature circuit resistance
D armature current
Answer D
ar!s "
#nit $
Id
Question The current drawn by a "6> . E d3c3 motor of armature resistance >3 F and bac! e3m3f3 "">
E is 3333333333 ampere3
A 6>
B 65>
C 66>
D
Answer A
ar!s 6
#nit $
IdQuestion The shaft tor*ue of a d3c3 motor is less than its armature tor*ue because of 3333333333 losses3
A copper
B mechanical
C iron
D rotational
Answer D
ar!s "
#nit $
Id
Question A d3c3 motor develops a tor*ue of 6>> 2.m at 6 rps3 At 6> rps it will develop a tor*ueof3333333333 2.m3
A 6>>
-
8/17/2019 Mcq of Dc Machines Madhuri New
17/31
B ">
C 6>
D "6@
Answer A
ar!s 6
#nit $
Id
Question 2eglecting saturation1 if current ta!en by a series motor is increased from "> A to "6 A1 the
percentage increase in its tor*ue is 33333333 percent
A 6>
B 55
C $>3D "3
Answer B
ar!s 6
#nit $
Id
Question If load on a d3c3 shunt motor is increased1 its speed is decreased due primarily to
A increase in its flu;
B decrease in bac! e3m3f3
C increase in armature current
D increase in brush drop
Answer B
ar!s "
#nit $
Id
Question If the load current and flu; of a d3c3 motor are held constant and voltage applied across itsarmature is increased by "> per cent1 its speed will
A decrease by about "> per cent
B remain unchanged
C increase by about "> per cent
D increase by 6> per cent3
-
8/17/2019 Mcq of Dc Machines Madhuri New
18/31
Answer C
ar!s "
#nit $
Id
Question If the pole flu; of a d3c3 motor approaches %ero1 its speed will
A approach %ero
B approach infinity
C no change due to corresponding change in bac! e3m3f3
D approach a stable value somewhere between %ero and infinity3
Answer B
ar!s "
#nit $
Id
Question If the field circuit of a loaded shunt motor is suddenly opened
A it would race to almost infinite speed
B it would draw abnormally high armature current
C circuit brea!er or fuse will open the circuit before too much damage is done to the motor
D tor*ue developed by the motor would be reduced to %ero3
Answer C
ar!s "
#nit $
Id
Question A d3c3 shunt motor is found suitable to drive fans because they re*uire
A small tor*ue at start up
B large tor*ue at high speeds
C practically constant voltage
D both
-
8/17/2019 Mcq of Dc Machines Madhuri New
19/31
Question Which of the following load would be best driven by a d3c3 compound motor ?
A reciprocating pump
B centrifugal pump
C electric locomotive
D fan
Answer A
ar!s "
#nit $
Id
Question As the load is increased1 the speed of a d3c3 shunt motor
A increases proportionately
B remains constant
C increases slightly
D reduces slightly
Answer D
ar!s "
#nit $
Id
Question Between no.load and full.load1 3333333333 motor develops the least tor*ue
A series
B shunt
C cumulative compound
D differential compound
Answer A
ar!s "
#nit $
Id
Question The Ta4Ia graph of a d3c3 series motor is a
A parabola from no.load to overload
B straight line throughout
C parabola throughout
-
8/17/2019 Mcq of Dc Machines Madhuri New
20/31
D parabola upto full.load and a straight line at overloads3
Answer D
ar!s "
#nit $
Id
Question As compared to shunt and compound motors1 series motor has the highest tor*ue because
of its comparatively 3333333333 at the start3
A lower armature resistance
B stronger series field
C fewer series turns
D larger armature current
Answer Bar!s "
#nit $
Id
Question #nli!e a shunt motor1 it is difficult for a series motor to stall under heavy loading because
A it develops high overload tor*ue
B its flu; remains constant
C it slows down considerably
D its bac! e3m3f3 is reduced to almost %ero3
Answer A
ar!s "
#nit $
Id
Question When load is removed1 3333333333 motor will run at the highest speed3
A shunt
B cumulative.compound
C differential compound
D series
Answer D
ar!s "
-
8/17/2019 Mcq of Dc Machines Madhuri New
21/31
#nit $
Id
Question A series motor is best suited for driving
A lathes
B cranes and hoists
C shears and punches
D machine tools
Answer B
ar!s "
#nit $
Id
Question A 66> E shunt motor develops a tor*ue of 5 2.m at armature current of "> A3 The tor*ue produced when the armature current is 6> A1 is
A 5 2.m
B @" 2.m
C ">@ 2.m
D 2one of the above
Answer C
ar!s 6#nit $
Id
Question The d3c3 series motor should never be switched on at no load because
A the field current is %ero
B The machine does not pic! up
C The speed becomes dangerously high
D It will ta!e too long to accelerate3
Answer C
ar!s "
#nit $
Id
Question A shunt d3c3 motor wor!s on a3c3 mains
-
8/17/2019 Mcq of Dc Machines Madhuri New
22/31
A unsatisfactorily
B satisfactorily
C not at all
D none of the above
Answer A
ar!s "
#nit $
Id
Question A 6>> E1 "> A motor could be rewound for ">> E1 6> A by using 3333333333 as many turns per
coil of wire1 having 3333333333 the cross.sectional area3
A twice1 half
B thrice1 one thirdC half1 twice
D four times1 one.fourth
Answer C
ar!s 6
#nit $
Id
Question The speed of a d3c3 motor can be controlled by varyingA its flu; per pole
B resistance of armature circuit
C applied voltage
D all of the above
Answer D
ar!s "
#nit $
Id
Question The most efficient method of increasing the speed of a $3G !W d3c3 shunt motor would be
the 33333333333method3
A armature control
B flu; control
C Ward.+eonard
-
8/17/2019 Mcq of Dc Machines Madhuri New
23/31
D tapped.field control
Answer
ar!s "
#nit $
Id
Question In the rheostatic method of speed control for a d3c3 shunt motor1 use of armature divertor
ma!es the method
A less wasteful
B less e;pensive
C unsuitable for changing loads
D suitable for rapidly changing loads
Answer Dar!s "
#nit $
Id
Question The chief advantage of Ward.+eonard system of d3c3 motor speed control is that it
A can be used even for small motors
B has high overall efficiency at all speeds
C gives smooth1 sensitive and wide speed control
D uses a flywheel to reduce fluctuations in power demand
Answer C
ar!s "
#nit $
Id
Question The flu; control method using paralleling of field coils when applied to a 5.pole series d3c3motor can give 33333333333 speeds3
A 6
B $
C 5
D
Answer B
ar!s "
-
8/17/2019 Mcq of Dc Machines Madhuri New
24/31
#nit $
Id
Question The series.parallel system of speed control of series motors widely used in traction wor!
gives a speed range of about
A " 7 6
B " 7 $
C " 7 5
D " 7
Answer C
ar!s "
#nit $
IdQuestion In practice1 regenerative bra!ing is used when
A *uic! motor reversal is desired
B load has overhauling characteristics
C controlling elevators1 rolling mills and printing presses etc3
D other methods can not be used3
Answer B
ar!s "
#nit $
Id
Question 0tatement "3 A direct.on.line
-
8/17/2019 Mcq of Dc Machines Madhuri New
25/31
A 0upply voltage
B 0*uare of the supply voltage
C 0*uare of the flu; density
D 0*uare of the armature speed
Answer D
ar!s "
#nit $
Id
Question Which of the following are the variable losses in a rotating machine
A Core loss and mechanical loss
B Core loss and stray load loss
C Copper loss and core loss
D Copper loss and stray load loss
Answer D
ar!s "
#nit $
Id
Question enerally the 2o +oad +osses of an electrical machine is represented in its e*uivalent
circuit by a
A 'arallel resistance with a low value
B 0eries resistance with a low value
C 'arallel resistance with a high value
D 0eries resistance with a high value
Answer C
ar!s "
#nit $
Id
Question 2eglecting all losses1 how is the developed tor*ue
-
8/17/2019 Mcq of Dc Machines Madhuri New
26/31
C T6 ∝ '$
D T is independent of '
Answer B
ar!s "
#nit $
Id
Question The principal of dynamically induced e3m3f3 is utili%ed in
A Transformer
B Cho!e
C enerator
D Thermocouple
Answer C
ar!s "
#nit $
Id
Question Which of the following is not a part of dc machine
A Armature
B Commutator
C 8ield winding
D Damping winding
Answer D
ar!s "
#nit $
Id
Question 8ield coils of a dc generator are usually made of
A ica
B Copper
C Cast iron
D Carbon
Answer B
ar!s "
-
8/17/2019 Mcq of Dc Machines Madhuri New
27/31
#nit $
Id
Question +aminated yo!e in dc motor can reduce
A 0peed regulation
B Iron loss
C Temperature rise
D 0par!ing on load
Answer B
ar!s "
#nit $
Id
Question 'ole shoe of a dc machine is laminated for the purpose of
A Decreasing hysteresis loss
B Decreasing (ddy current loss
C Decreasing both hysteresis and (ddy current loss
D anufacturing ease
Answer B
ar!s "
#nit $
Id
Question The function
-
8/17/2019 Mcq of Dc Machines Madhuri New
28/31
B 9educe the armature reaction
C 9educe iron weight
D Dissipate more heat
Answer A
ar!s "
#nit $
Id
Question The ventilating ducts in most of the dc machines are
A 9adial
B +ongitudinal
C 9adial as well as +ongitudinal
D 2one of the above
Answer C
ar!s "
#nit $
Id
Question The armature of the dc machine is made of
A Conducting material
B Insulating material
C 2on ferrous material
D 0ilicon steel
Answer D
ar!s "
#nit $
Id
Question A 5 pole generator with " coils has a two layer lap winding3 The pole pitch is
A $6
B "
C @
D 5
Answer C
-
8/17/2019 Mcq of Dc Machines Madhuri New
29/31
ar!s 6
#nit $
Id
Question 8or a 5.pole machine having wave winding is impossible with HHH3 Armature
conductors
A $>
B $6
C $5
D $@
Answer B
ar!s 6
#nit $Id
Question In a lap winding1 the number of brushes is always HHH the number of poles
A Double
B 0ame as
C alf
D 2one of the above
Answer B
ar!s "
#nit $
Id
QuestionA 'J'ole lap wound dc machine had an armature current Ia3 The conductor current in thearmature winding is
AIa
BIa4 '
C' 3 Ia
D 2one of the above
Answer B
ar!s "
-
8/17/2019 Mcq of Dc Machines Madhuri New
30/31
#nit $
Id
Question A lap wound dc machine has 5>> conductors and @ poles3 The voltage induced per
conductor is 6 volt3 The machine generates a voltage of
A ">> volt
B 6>> volt
C 5>> volt
D @>> volt
Answer A
ar!s 6
#nit $
IdQuestion The dummy coils in a dc machines are useful to
A Increase the efficiency
B Improve the commutation
C 9educe the cost of the machine
D aintain the mechanical balance of armature
Answer D
ar!s "
#nit $
Id
Question A armature resistance of a pole lap wound dc machine is >3> ohm3 If the armature is
rewound as a wave winding1 What is armature resistance?
A >35 ohms
B >3$> ohms
C >3" ohms
D >3"> ohms
Answer A
ar!s 6
#nit $
Id
Question An @.pole1 dc generator has a simple; wave wound armature containing $6 coils of .turns
-
8/17/2019 Mcq of Dc Machines Madhuri New
31/31
each3 Its flu; per pole is >3> Wb3 The machine is running at 6> rpm3 The induced
armature voltage is
A volt
B "6 volt
C $@5 volt
D G@ volt
Answer C
ar!s 6
#nit $
top related