Mcq of Dc Machines Madhuri New

8/17/2019 Mcq of Dc Machines Madhuri New

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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

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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

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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

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Question In DC series motor

A Armature winding - field winding are parallel

B Armature winding - field winding are !ept in series with source


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C Armature winding is !ept in series with the source

D The field winding is !ept in series with source

Answer B

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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

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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

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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

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Question Which of the following applications needs high starting tor*ue ?

A +athe

B Centrifugal pump

C +ocomotive

D Air blower

Answer C

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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

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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

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Question Two DC series motors are connected in series to produce a tor*ue T3 2ow if the motors are


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connected in parallel1 the tor*ue produced will be

A T 4 5

B 6T

C T 4 6

D 5T

Answer B

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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

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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

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Question The output power of any electrical motor is ta!en from the7

A Armature

B 8ield

C Coupling mounted on the shaft


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D otor frame

Answer C

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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

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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

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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

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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

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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


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B Increases

C Decreases

D Be &ero

Answer C

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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

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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

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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


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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

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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 "

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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

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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

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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

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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

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Question In a dc generator the residual magnetism is of the order of7

A 63

B ">


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C "

D 6

Answer A

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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

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Question 8or parallel operation1 the dc shunt generator normally preferred are7

A 0hunt generator

B 0eries generator

C #nder compound generator

D Both


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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

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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

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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

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Question The output indicated on the name plate of any motor is always the7

A ross power


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B 'ower drawn in volt amperes

C 'ower drawn in watts

D )utput power at the shaft

Answer D

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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

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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

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Question In a d3c3 motor1 unidirectional tor*ue is produced with the help of

A brushes

B commutator

C end.plates

D both


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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

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Question The normal value of the armature resistance of a d3c3 motor is

A >3>>

B >3

C ">

D ">>

Answer B

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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

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Question The mechanical power developed by the armature of a d3c3 motor is e*ual to


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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

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Question The induced e3m3f3 in the armature conductors of a d3c3 motor is

A sinusoidal

B trape%oidal

C rectangular

D alternating

Answer A

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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

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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


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Answer D

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Question The ma;imum tor*ue of d3c3 motors is limited by

A commutation

B heating

C speed

D armature current

Answer A

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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

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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


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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

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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

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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

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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>>


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B ">

C 6>

D "6@

Answer A

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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

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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

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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


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Answer C

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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

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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

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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


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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

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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

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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

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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


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D parabola upto full.load and a straight line at overloads3

Answer D

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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 "

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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

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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

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Question A series motor is best suited for driving

A lathes

B cranes and hoists

C shears and punches

D machine tools

Answer B

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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

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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

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Question A shunt d3c3 motor wor!s on a3c3 mains


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A unsatisfactorily

B satisfactorily

C not at all

D none of the above

Answer A

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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

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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

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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


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D tapped.field control

Answer

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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 "

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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

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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

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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

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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

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Question 0tatement "3 A direct.on.line


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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

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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

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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

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Question 2eglecting all losses1 how is the developed tor*ue


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C T6 ∝ '$

D T is independent of '

Answer B

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Question The principal of dynamically induced e3m3f3 is utili%ed in

A Transformer

B Cho!e

C enerator

D Thermocouple

Answer C

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Question Which of the following is not a part of dc machine

A Armature

B Commutator

C 8ield winding

D Damping winding

Answer D

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Question 8ield coils of a dc generator are usually made of

A ica

B Copper

C Cast iron

D Carbon

Answer B

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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

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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

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Question The function


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B 9educe the armature reaction

C 9educe iron weight

D Dissipate more heat

Answer A

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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

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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

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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


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Question 8or a 5.pole machine having wave winding is impossible with HHH3 Armature

conductors

A $>

B $6

C $5

D $@

Answer B

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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

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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

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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

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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

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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

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Question An @.pole1 dc generator has a simple; wave wound armature containing $6 coils of .turns


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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

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Mcq of Dc Machines Madhuri New