Chapter 10_Direct Current Motor

8/13/2019 Chapter 10_Direct Current Motor

1/28

Direct Current Motor

1. No-load speed of which of the following motor will be highest?

A. shunt motor C. cumulative compound motor

B. series motor D. differential compound motor

2. The direction of rotation of a DC series motor can be changed b

A. interchanging suppl terminals C. either of !a" and !b" above

B. interchanging field terminals D. none of the above

#. $hich of the following application re%uires high starting tor%ue?

A. &athe machine '. Centrifugal pump C. &ocomotive D. Air blower

(. )f a DC motor is to be selected for conveors* which motor would be preferred?

A. Series motor C. differentiall compound motor

'. +hunt motor D. Cumulative compound motor

,. $hich DC motor will be preferred for machine tools?

A. +eries motor C. Cumulative compound motor

B. Shunt motor D. Differential compound motor

. $hich DC motor will be preferred for constant speed line shafting?

A. Cumulative compound motor C. Shunt motor

'. Differentiall compound motor D. +eries motor

. Differentiall compound DC motors can find applications re%uiring

A. high starting tor%ue C. variable speed

B. low starting torque D. fre%uent on-off ccles

/. $hich DC motor will be preferred for elevators?

A. shunt motor C. Differential compound motor

'. series motor D. Cumulative compound motor

0. According to lemings left-hand rule* when the forefinger points in the direction of the field or flu3* the

middle finger will point in the direction of

A. current in the conductor C. resultant force on conductor

'. movement of conductor D. none of the above


2/28

14. )f the field of a DC shunt motor gets opened while motor is running

A. the speed of motor will reduce C. the motor will attain dangerously high speed

'. the armature current will reduce D. the motor will continue to run at constant speed

11. +tarters are used with DC motors because

A. these motors have high starting tor%ue

'. these motors are not self-starting

C. bac5 emf of these motors is 6ero initiall

D. to restrict armature current as there is no back emf while starting

12. )n DC shunt motors as load is reduced

A. the speed will increase abruptl

'. the speed will increase in proportion to reduction in load

C. the speed will remain almost constant

D. the speed will reduce

1#. A DC series motors is that which

A. has its field winding consisting of thick wire and less turns

'. has a poor tor%ue

C. can be started easil without load

D. has almost constant speed

1(. or starting a DC motor a starter is re%uired because

A. it limits the speed of the motor

B. it limits the starting current to a safe value

C. it starts the motor

D. none of the above

1,. The tpe of DC motor used for shears and punches is

A. shunt motor C. differential compound DC motor

'. series motor D. cumulative compound DC motor

1. )f a DC motor is connected across the AC suppl it will

A. run at normal speed


3/28

'. not runs

C. run at lower speed

D. burn due to heat produced in the field winding by eddy current

1. To get the speed of DC motor below the normal without wastage of electrical energ 777 is used.

A. ard !eonard control C. an of the above method

'. rheostatic control D. none of the above method

1/. $hen two DC series motors are connected in parallel* the resultant speed is

A. more than the normal speed C. normal speed

'. less than the normal speed D. 6ero

10. The speed of a DC shunt motor more than full-load speed can be obtained b

A. decreasing the field current C. decreasing the armature current

'. increasing the field current D. increasing the armature current

24. )n a DC shunt motor* speed is

A. independent of armature current

'. directl proportional to the armature current

C. proportional to the s%uare of the current

D. inversel proportional to the armature current

21. A direct on line starter is used for starting motors

A. up to " #.$. '. up to 14 8.9. C. up to 1, 8.9. D. up to 24 8.9.

22. )f a speed of a DC shunt motor is increased the bac5 emf of the motor will

A. decrease B. increase C. remain same D. become 6ero

2#. $hat will happen if the bac5 emf of a DC motor vanishes suddenl?

A. the motor will stop C. the armature may burn

'. the motor will continue to run D. the motor will run nois

2(. )n case of DC shunt motors the speed is dependent on bac5 of emf onl because

A. bac5 emf is e%ual to armature drop C. flu3 is proportional to armature current

'. armature drop is negligible D. flu% is practically constant in DC shunt motor

2,. )n a DC shunt motor* under condition of ma3imum power* the current in the armature will be


4/28

A. almost negligible C. less than full-load current

'. rated full-load current D. more than full&load current

2. $hich DC motor will have least percentage increase of input current* for the same percentage

increase in the tor%ue

A. shunt motor C. cumulative compound motor

B. series motor D. separatel e3cited motor

2. These da DC motors are widel used in

A. pumping sets '. air compressor C. electron traction D. machine shops

2/. ' loo5ing at which part of the motor* it can be easil confirmed that a particular motor is DC motor?

A. rame '. +haft C. Commutator D. +tator

20. )n which of the following applications DC series motor is invariabl used?

A. starter for a car C. an motor

'. drive for a water pump D. motor operation in AC or DC

#4. )n DC machine fractional pitch winding is used

A. to improved cooling C. to increase the generated emf

'. to reduce copper losses D. to reduce sparking

#1. A three point starter is considered suitable for

A. shunt motors C. shunt* compound and series motor

B. shunt as well as compound motors D. all DC motor

#2. +mall DC motors up to , 8.9. usuall have

A. ' poles '. ( poles C. poles D. / poles

##. )n case the conditions for ma3imum power for a DC motor are established* the efficienc of the motor

will be

A. 144: C. anwhere between ,: and 04:

'. around 04: D. less than "()

#(. A shearing machine has cclic load consisting of intermittent light and heav loads. $hich of the

following DC motor will be suitable for this purpose?

A. series motor C. cumulative compound motor

'. shunt motor D. differential compound motor


5/28

#,. The ratio of starting tor%ue to full-load tor%ue is least in case of

A. series motor B. shunt motor C. compound motor D. none of the above

#. )n DC motor which of the following can sustain the ma3imum temperature rise?

A. +lip rings '. Commutator C. *ield winding D. Armature winding

#. $hich of the law;rule can be used to determine the direction of rotation DC motor?

A. &en6s law '. aradas law C. Coulombs law D. *leming+s left&hand rule

#/. $hich of the following load normall needs starting tor%ue more than the rated tor%ue?

A. blowers B. conveyors C. air compressor D. centrifugal pumps

#0. The starting resistance of a DC series motor is generall

A. low '. around ,44< C. 1444< D. infinitel large

(4. The speed of a DC series motor is

A. proportional to the armature current

'. proportional to the s%uare of the armature current

C. proportional to field current

D. inversely proportional to the armature current

(1. )n a DC series motor* if the armature current is reduced b ,4:* the tor%ue of the motor will be e%ual

to

A. 144: of the previous value D. 14: of the previous value

'. ,4: of the previous value =. none of the above

C. '") of the previous value

(2. The current drawn b the armature of DC motor is directl proportional to

A. the torque required C. the voltage across the terminals

'. the speed of the motor D. none of the above

(#. The power mentioned on the name plate of an electric motor indicates

A. the power drawn in 5$ C. the gross power

'. the power drawn in 5>A D. the output power available at the shaft

((. )n $ard &eonard method of speed control of a DC motor* change in speed of motor is obtained b the

A. change in armature voltage of DC motor


6/28

'. change in the field e3citation of the DC motor

C. change in armature current of DC motor

D. change in suppl voltage

(,. $hich DC motor has got ma3imum self loading propert?

A. series motor C. cumulativel compounded motor

'. shunt motor D. differentially compounded motor

(. $hich DC motor will be suitable along with flwheel for intermittent light and heav loads?

A. +eries motor C. cumulatively compounded motor

'. +hunt motor D. Differentiall compounded motor

(. )f a DC shunt motor is wor5ing at no load and if shunt field circuit suddenl opens

A. nothing will happen to the motor

'. this will ma5e armature to ta5e heav current* possibl burning it

C. this will result in e%cessive speed, possibly destroying armature due to e%cessive

centrifugal stresses

D. motor will run at ver slow speed

(/. DC series motor are used

A. where load is constant C. where constant operating speed is needed

'. where load changes fre%uentl D. in none of the above situations

(0. or the same 8.9. rating and full load speed* following motor has poor starting tor%ue

A. shunt C. differentially compounded

'. series D. cumulativel compounded

,4. )n case of conductivel compensated DC series motors* the compensating winding is provided

A. as separatel wound unit C. in series with armature winding

'. in parallel with armature winding D. in parallel with field winding

,1. +par5ing at the commutator of a DC motor ma result in

A. damage to commutator segments C. increased power consumption

'. damage to commutator insulation D. all of above

,2. $hich of the following motor is preferred for operation in highl e3plosive atmosphere?


7/28

A. +eries motor '. +hunt motor C. Air motor D. batter operated motor

,#. )f the suppl voltage for a DC motor is preferred for the following will decrease?

A. +tarting tor%ue '. perating speed C. *ull&load current D. All of the above

,(. $hen the speed of a DC motor increases

A. back emf increases and current drawn decreases

'. bac5 emf as well as current drawn both increase

C. bac5 emf as well as current drawn both decrease

D. bac5 emf decreases and current drawn increases

,,. As compared to an induction motor* the air gap in a DC motor is

A. less than ,4: C. same

'. between ,4: and 04: D. more

,. ield winding of a DC series motor is usuall provided with thic5 wire

A. to provide large flu3 C. as it carries large load current

'. to reduce the use of insulating materials D. in order to reduce edd current

,. $hich one of the following is not the function of pole shoes in a DC machine?

A. to reduce eddy current loss C. to spread out flu3 for better uniformit

'. to support the field coils D. to reduce the reluctance of the magnetic path

,/. The mechanical power developed b a shunt motor will be ma3imum when the ratio of bac5 emf to

applied voltage is

A. (.4 '. 2.4 C. 1.4 D. (."

,0. The condition for ma3imum power in case of DC motor is

A. bac5 emf @ 2 3 suppl voltage C. suppl voltage @ 3 bac5 emf

B. back emf - % supply voltage D. suppl voltage @ bac5 emf

4. or which of the following applications a DC motor id preferred over an AC motor?

A. &ow speed operation C. ariable speed operation

'. 8igh speed operation D. i3ed speed operation


8/28

1. )n DC machines the residual magnetism is of the order of

A. ' to / per cent '. 14 to 1, per cent C. 24 to 2, per cent D. ,4 to , per cent

62.)f be the tor%ue and the armature current for a DC motor* which of the following relation is valid

before saturation?

A. '. C. D.

#. $hich DC motor is generall preferred for cranes and hoists?

A. Series motor C. Cumulativel compounded motor


(. Three point starter can be used for

A. series motor onl C. compound motor onl

'. shunt motor onl D. both shunt and compound motor

,. +par5ing is discouraged in a DC motor because

A. it increases the input power consumption C. both !a" and !b"

B. commutator gets damaged D. none of the above

. +peed control b $ard &eonard method gives uniform speed variation

A. in one direction C. below normal speed onl

B. in both directions D. above normal speed onl

. lwheel is used in with DC compound motor to reduce the pea5 demand b the motor* compound

motor will have to be

A. level compounded C. cumulatively compounded

'. under compounded D. differentiall compounded

/. ollowing motor is used where high starting tor%ue and wide speed range control is re%uired.

A. +ingle phase capacitor start D. DC motor

'. )nduction motor =. None of the above

C. +nchronous motor

0. )n a differentiall compounded DC motor* if shunt field suddenl opens

A. the motor will first stop and then run in opposite direction as series motor


9/28

'. the motor will wor5 as series motor and run at slow speed in the same direction

C. the motor will wor5 as series motor and run at high speed in the same direction

D. the motor will not wor5 and come to stop

4. $hich of the following motor has the poorest speed regulation?

A. shunt motor C. differential compound motor

B. series motor D. cumulative compound motor

1. 'uses* trains trolles* hoists* cranes re%uire high starting tor%ue and therefore ma5e use of

A. DC series motor C. induction motor

'. DC shunt motor D. all of the above

2. As the load is increased the speed of DC shunt motor will

A. reduce slightly C. increase proportionatel

'. increase slightl D. remain unchanged

#. The armature tor%ue of the DC shunt motor is proportional to

A. field flu3 onl C. both !a" and !b"

B. armature current only D. none of the above

(. $hich of the following method of speed control of DC machine will offer minimum efficienc?

A. voltage control method C. armature control method

'. field control method D. all above methods

,. suall wide and sensitive speed is desired in case of

A. centrifugal pumps C. steel rolling mills

'. elevators D. colliery winders

. The speed of a motor falls from 1144 rpm at no-load to 14,4 rpm at rated load. The speed regulation

of the motor is

A. 2.#: B. 0.12) C. .: D. /./(:

. The armature voltage control of DC motor provides

A. constant torque drive C. constant current drive

'. constant voltage drive D. none of the above

/. The speed regulation of a DC motor is


10/28

A. C.

'. D.

0. As there is no bac5 emf at the instant of starting a DC motor* in order to prevent a heav current from

flowing though the armature circuit

A. a resistance is connected in series with armature

'. a resistance is connected parallel to the armature

C. armature is temporaril open circuited

D. a high value resistor is connected across the field winding

/4. The speed of a DC shunt motor can be increased b

A. increasing the resistance in armature circuit

B. increasing the resistance in field circuit

C. reducing the resistance in the field circuit

D. reducing the resistance in the armature circuit

81.)f be the armature current* then speed of a DC shunt motor is

A. independent of C. varies as

'. proportional to D. varies as

/2. )n case the bac5 emf and the speed of a DC motor are doubled* the tor%ue developed b the motor

will

A. remain unchanged C. increase four folds

'. reduce to one-fourth value D. be doubled

/#. At the instant of starting when a DC motor is put on suppl* it behaves li5e

A. a highl resistive circuit C. a capacitive circuit

B. a low resistance circuit D. none of the above

/(. The speed of a DC motor can be varies b varing

A. field current C. resistance in series with armature


11/28

'. applied voltage D. any of the above

/,. $hich one of the following is not necessaril the advantage of DC motors over AC motors?

A. low cost '. wide speed range C. stabilit D. high starting tor%ue

/. oe a Dc shunt motor if the e3citation is changed

A. tor%ue will remain constant

B. torque will change but power will remain constant

C. tor%ue and power both will change

D. tor%ue* power and speed all will change

/. $hich motor has the poorest speed control?

A. differentiall compounded motor C. shunt motor

'. cumulativel compounded motor D. Series motor

//. The plugging gives the

A. 6ero tor%ue bra5ing C. highest torque braking

'. smallest tor%ue bra5ing D. none of the above

/0. The armature voltage control of DC motor provides

A. constant voltage drive C. constant torque drive

'. constant current drive D. none of the above

04. )f a Dc motor designed for (4BC ambient temperature is to be used for ,4BC ambient temperature*

then the motor

A. of lower 8.9. should be selected

'. of higher 8.9. should be selected

C. can be used for ,4BC ambient temperature also

D. is to be derated by a factor recommended by manufacturer and select the ne%t higher #.$.

motor

01. )f the terminals of armature of DC motor are interchanged* this action will offer following 5ind of

bra5ing

A. regenerative C. dnamic bra5ing =. an of the above

B. plugging D. none of the above

02. $hich of the following motors one will choose to drive the rotar compressor?


12/28

A. DC shunt motor '. DC series motor C. universal motor D. Synchronous motor

0#. )f a speed of a DC shunt motor is increased* the bac5 emf of the motor will

A. increase '. decrease C. remain same D. become 6ero

0(. $h are the DC motors preferred for traction applications?

A. tor%ue and speed are inversel proportional to armature current

'. tor%ue is proportional to armature current

C. tor%ue is proportional to s%uare root of armature current

D. the speed is inversely proportional to the torque and the torque is proportional to square of

armature current

0,. $hich of the following motors have almost constant speed over their full load range?

A. AC series motors C. &ow resistance s%uirrel cage motors

'. DC series motors 3. Both 4c5 and 4d5

C. DC shunt motors

0. $hich of the following motors is usuall used in house-hold refrigerators?

A. DC shunt motor D. eluctance motor

'. DC series motor =. +nchronous motor

C. Single phase induction motor 4split phase start or induction run motor5

0. $hich of the following motors is most suitable for signaling devices and man 5inds of timers?

A. DC shunt motor C. )nductance motor

'. DC series motor D. 6eluctance motor

0/. $hich motor should not be started on no-load?

A. series motor C. cumulativel compounded motor

'. shunt motor D. differentiall compounded motor

00. $ard-&eonard control is basicall a

A. voltage control method C. field control method

'. field diverter method D. armature resistance control method

144. or constant tor%ue drive speed which speed control method is preferred?

A. ield control C. +hunt armature control


13/28

B. Armature voltage control D. echanical loading sstem

141. )n $ard-&eonard control the lower limit of speed is imposed b

A. residual magnetism of the generator C. mechanical losses of motor and generator together

'. core losses of motor D. all of the above

142. The main disadvantage of the $ard-&eonard control method is

A. high initial cost C. low efficienc at light loads

'. high maintenance cost D. all of the above

14#. $hich of the following can be used to control the speed of a DC motor?

A. Thermistor B. 7hyristor C. Thratron D. Transistor

14(. The losses occurring in DC generator are given below. $hich loss is li5el to have the least

proportion?

A. magnetic losses C. mechanical losses

'. armature copper losses D. field copper losses

14,. The hsteresis loss in a DC machine least depends on

A. fre%uenc of magnetic reversals C. >olume and grade of iron

'. ma3imum value of flu3 densit D. 6ate of flow of ventilating air

14. )n a DC generator all of the following could be the effects of iron losses e3cept

A. &oss of efficienc C. 8ncrease in the terminal voltage

'. =3cessive heating of core D. ise in temperature of ventilating air

14. The losses occurring in a DC generator are given below. $hich loss is li5el to have highest

proportion at rated load of generator?

A. hsteresis loss C. armature copper loss

'. field copper loss D. edd current loss

14/. )f Et be the thic5ness of the laminations* then edd current loss in generator will var as

A. '. C. D.

140. $hich of the following loss in a DC generator varies significantl with the load current?

A. field copper loss C. armature copper loss

'. windage loss D. none of the above


14/28

110. )f is the ma3imum flu3 densit* then edd current loss will var as

A. '. C. D.

111. The hsteresis loss in a DC generator varies with the fre%uenc of magnetic reversals as

A. B. C. D.

112. $hich of the following method of bra5ing is used in rolling mills?

A. dnamic bra5ing C. regenerative

B. plugging D. mechanical bra5es

11#. egenerative method of bra5ing based on that

A. bac5 emf is less than the applied voltage C. back emf of rotor is more than the applied voltage

'. bac5 emf is e%ual to the applied voltage D. none of the above

11(. The retardation test is applicable to shunt motors and generators and is used to find

A. the copper losses C. the friction losses

B. the stray losses D. the edd current losses

11,. our point starter in the DC motor is used

A. to decrease the field current

'. to increase the field current

C. not to effect the current passing through 9#old on+ coil even if any change in the field

current takes place

D. all of the above

=. none of the above

11. $hich of the following motors is used in the locomotives motors drives?

A. DC series motor C. +nchronous motor

'. AC series motor D. )nduction motor

11. )n ha6ardous area of gass mines* material transportation is done b vehicles powered b

A. AC mains '. DC mains C. )C engines D. batteries

11/. Compensating winding in a DC machine is placed


15/28

A. on yoke in the pole faces C. on armature

'. on o5e in the interpolar gap D. none of the above

110. DC series machine has field consisting of

A. man numbers of turns of thic5 wire C. few numbers of turns of thick wire

'. man numbers of turns of thin wire D. few numbers of turns of thin wire

124. Tor%ue developed b a DC motor depends upon

A. magnetic field D. number of conductors

'. active length of the conductor =. radius of armature

C. current flow through the conductors *. all above factors

121. DC shunt motors are used for driving

A. trains '. cranes C. hoists D. machine tools

122. )n a manual shunt motor starter

A. over load relay is connected in series and no volt relay in parallel with the load

'. over load rela is connected in parallel and no volt rela in series with the load

C. over load rela and no volt rela are both connected in series with the load

D. over load rela and no volt rela are both connected in parallel with load

12#. $hich of the following steps is li5el to result in reduction of hsteresis loss in a DC generator?

A. providing laminations in armature core

'. providing laminations in stator

C. using non-magnetic material for frame

D. using material of low hysteresis coefficient for armature core material

12(. $hich loss in a DC generator varies with load?

A. copper loss '. edd current loss C. hsteresis loss D. windage loss

12,. $hich loss in a DC generator does not var with load as well as flu3 densit?

A. copper loss '. edd current loss C. hsteresis loss D. windage loss

12. $hich of the following loss in a DC generator is dissipated in the form of heat?

A. mechanical loss C. copper loss

'. core loss D. all of the above


16/28

12. $hich of the following losses are significantl reduced b laminating the core of a DC generator?

A. hsteresis losses C. copper losses

B. 3ddy current losses D. windage losses

12/. The total losses in a well designed DC generator of 14 5$ will be nearl

A. 144 $ B. "(( C. 1444 $ D. 1,44 $

120. The condition for ma3imum efficienc for a DC generators is

A. edd current losses @ stra losses C. copper losses @ 4

'. hsteresis losses @ edd current losses D. variable losses - constant losses

1#4. DC generators are normall designed for ma3imum efficienc around

A. full&load '. rated rpm C. rated voltage D. all of the above

1#1. )n a DC generator* the iron losses mainl ta5e place in

A. o5e '. commutator C. armature conductor D. armature rotor

1#2. DC generators are installed near the load centers to reduce

A. iron losses B. line losses C. spar5ing D. corona losses

1##. The purpose of retardation test on DC shunt machines is to find out

A. stray losses C. field copper losses

'. edd current losses D. windage losses

1#(. $hich of the following tests will be suitable for testing two similar DC series motors of large

capacit?

A. +winburnes test C. *ield test

'. 8op5insons test D. 'ra5e test

1#,. 8op5insons test on DC machines is conducted at

A. no-load '. part load C. full&load D. overload

1#. During rheostat bra5ing of DC series motors

A. motor is run as a generator C. motor is run at reduced speed

'. motor is reversed in direction

1#. or which tpe of DC motor* dnamic bar5ing is generall used?

A. shunt motors '. series motors C. compound motors D. all of the above


17/28

1#/. During rheostatic bra5ing the bra5ing tor%ue is proportional to

A. speed '. C. D.

1#0. $hich method of bra5ing is generall used in elevators?

A. plugging '. renegerative bra5ing C. rheostatic bra5ing D. none of the above

1(4. )n variable speed motor

A. a stronger commutating field is needed at low speed than at high speed

B. a weaker commutating field is needed at low speed than at high speed

C. same commutating field is needed at low speed than high at high speed

D. none of the above is correct

1(1. $hen the armature of a DC motor rotates* emf induced is

A. self-induced emf C. back emf

'. mutuall induced emf D. none of the above

1(2. $here DC motor of 8.9. 12 or more re%uires fre%uent starting* stopping* reversing and speed

control

A. drum type controller is used C. four point starter is used

'. three point starter is used D. all above can be used

1(#. )f DC shunt motor is wor5ing at full load and if shunt field circuit suddenl opens

A. this will make armature to take heavy current, possibly burning it

'. this will result in e3cessive speed* possibl destroing armature due to e3cessive centrifugal

stresses

C. nothing will happen to motor

D. motor will come to stop

1((. DC motor is to drive a load which has certain minimum value for most of the time and some pea5

value for short duration. $e will select the

A. series motor '. shunt motor C. compound motor D. an of the above

1(,. Dc motor is to a drive a load which is almost nil for certain part of the load ccle and pea5 value

for short duration. $e will select this

A. series motor '. shunt motor C. compound motor D. an of the above

1(. $hich DC motor has got ma3imum self relieving propert?


18/28

A. Series motor C. Cumulativel compounded motor


1(. >oltage e%uation for DC motor is

A. B. C. D.

1(/. A 2#4 > DC shunt motor ta5es #2 A at full load. The bac5 emf on full load* if the resistance of

motor armature and shunt field windings are 4.2 < and 11, < respectivel* will be

A. 214 > '. 21, > C. 224 > D. ''0

1(0. )n the DC motor the iron losses occur in

A. the field B. the armature C. the brushes D. the commutator

1,4. The speed of a DC shunt motor is re%uired to be more than full load speed. This is possible b

A. reducing the field current D. increasing the e3citation current

'. decreasing the armature current =. none of the above method

C. increasing the armature current.

1,1. ne DC motor drives another DC motor. The second DC motor when e3cited and driven

A. run as a generator C. also runs as a motor

'. does not run as a generator D. comes to stop after sometimes

1,2. $hich of the following DC motors has the least drop in between no-load and nominal load?

A. series motor without commutating poles C. shunt motor with commutating pole

'. series motor with commutating poles D. compound motor without commutating poles

1,#. The speed of a series motor at no load is

A. infinity C. 2444 rpm =. none of the above

'. (444 rpm D. 1444 rpm

1,(. )n a DC motor if the bac5 emf is absent

A. motor will burn C. motor will run at ver slow speed

'. motor will not run at all D. motor will run at ver high speed

1,,. A series motor is started without load. The effect is that

A. the bac5 emf decreases C. the speed increases rapidly

'. the tor%ue increases rapidl D. the current drawn increases rapidl


19/28

1,. $hat will happen if suppl terminals of DC shunt motor are interchanged?

A. the direction of rotation will reverse

'. motor will stop

C. motor will run at speed lower than the normal speed in the same direction

D. motor will run at its normal speed in the same direction as it was running

1,. $hen the electric train is moving down a hill the DC motor act as

A. DC series generator C. DC shunt motor

'. DC shunt generator D. DC series motor

1,/. $hich of the following methods is most economical for finding the no-load losses of a large DC

shunt motor?

A. etardations test C. 8op5insons test

B. Swinburne+s test D. none of the above

1,0. $hich of the following statement is incorrect? )f a starter is not used with large DC motor* it will

draw a starting current which

A. will produce very low starting torque C. will damage the commutator

'. will produce e3cessive line voltage drop D. is man times its full-load current

14. The rated speed of a given DC shunt motor is 044 rpm. To run this machine at 1444 rpm* which

of the following speed control scheme will be used?

A. $ard-&eonard control C. *ield resistance control

'. Armature current resistance control D. None of the above

11. )n electric motors carbon brushes are used to

A. provide a path for flow of current C. prevent overheating of armature

'. prevent spar5ing during commutation D. brush off carbon deposits on the commutator

12. $hat is the effect produced b the electric current in an electric motor?

A. heating effect onl C. heating as well as magnetic effect

'. magnetic effect onl D. heating as well as chemical effect

1#. )n a motor* energ conversion would not have been possible but for the

A. production of opposing back emf in the armature

'. input energ from suppl


20/28

C. use of commutator

D. application of lemings left-hand rule

1(. )n a DC motor* unidirectional tor%ue is produced with the help of

A. end plates '. bushes C. commutator D. both 4b5 and 4c5

165. )n a DC motor* the ratio indicates

A. running tor%ue of the motor C. efficiency of the motor

'. starting tor%ue of the motor D. speed regulation of the motor

1. The speed of a DC motor* under constant load conditions* is affected b

A. bac5 emf B. field flu% C. armature current D. none of the above

1. A DC shunt motor is rotating in cloc5wise direction as viewed from one end. The polarit of

connection of the armature and field winding are reversed simultaneousl. The motor will

A. rotate in clockwise direction C. will not rotate at all

'. rotate in anti-cloc5wise direction D. gain e3cessivel high speed

1/. )f the field current of a loaded shunt motor is suddenl opened

A. tor%ue developed b the motor would be reduced to 6ero

'. it would race to almost infinite speed

C. it would draw normall high armature current

D. the fuse or circuit breaker will open the circuit before too much damage is done to the

motor

10. A series motor is best suited for driving

A. machine tools B. cranes and hoists C. shear and punches D. none of the above

14. $hich of the following motor has high starting tor%ue?

A. +nchronous motor C. DC series motor

'. AC series motor D. )nductor motor

11. $hile starting a differential compound motor* it is best to short the series field in order to avoid

A. e3cessive starting period C. tripping of the circuit brea5er

B. motor starting in wrong direction D. large in rush of current

12. )n a DC motor constant tor%ue is produced due to


21/28

A. rotor laminations C. pole shoes

'. end F plates D. commutator

1#. The operation of electric generators and motors depend on the interaction between magnetic field

and

A. copper conductor C. electric current

'. electric field D. commutator

1(. The simplest form for a motor controller is

A. rela B. toggle switch C. drum switch D. magnetic switch

1,. All motors* basicall* operate on the principle of either repulsion or

A. induction '. semi-conduction C. capacitance D. electro-magnetism

1. The ma3imum end-pla of a motor is about

A. 14 mm '. mm C. 2 mm D. (.0 mm

1. A face starter is emploed for starting

A. induction motor '. universal motor C. snchronous motor D. DC series motor

1/. )f the no-voltage release of a DC motor starter fails to wor5 on resumption of suppl after a brea5*

the motor will

A. not start automaticall C. get damaged

'. start automaticall without trouble D. develop ver low tor%ue

10. A DC series motor* as compared to shunt and compound motors* has the highest tor%ue at the

start because of its comparativel

A. stronger series field C. large armature current

'. lower armature resistance D. fewer series turns

1/4. $hich of the following motors* on removal of load* will run at the highest speed?

A. shunt motor C. differential compound

B. series motor D. cumulative compound

1/1. The mechanical power developed b a DC motor is e%ual to

A. power input G losses C. power output 3 losses

'. back emf % armature current D. power output 3 efficienc

1/2. $hich of the following statement is correct* in case of a DC series motor?


22/28

A. it should be directly connected to the load

'. it ma run awa if its field becomes open

C. it is a constant speed motor

D. it cannot be used where high starting tor%ue is re%uired

1/#. The variable resistor shunting the field of a DC series motor is called a

A. armature divertor C. field divertor

'. voltage regulator D. potential divider

1/(. 'etween ields test and 8op5insons test the main common thing is that both

A. use negligible power C. need two similar mechanically coupled motors

'. are regenerative tests D. need two electricall coupled series motors

1/,. The use of armature divertor in the rheostatic method of speed control for a DC shunt motor

ma5es the method

A. less e3pensive C. suitable for rapidly changing loads

'. less wasteful D. unsuitable for changing loads

1/. The series parallel sstem of speed control series motors widel used in traction wor5 gives a

speed range of about

A. 1H14 '. 1H/ C. 1H D. :;0

1/. )f a conditions for ma3imum power for a DC motor are established* the efficienc of the motor will

be

A. less than "() '. 4 to 4: C. /4 to 04: D. 144:

1//. )n which of the following tests onl one motor is re%uired?

A. Brake test '. 8op5insons test C. ields test D. +winburnes test

1/0. in ields test for series motors one motor drives the other machine as

A. cumulative compound generator C. separately e%cited generator

'. differential compound generator D. series generator

104. A motor for punching machine is usuall subIected to

A. no load '. continuous part load C. continuous full load D. intermittent load

101. $hich of the following is not necessaril the advantage of DC motor over AC motors?

A. better speed control C. high starting tor%ue


23/28

B. low cost D. wide speed range

102. The armature shaft of a DC motor must be able to withstand

A. an unbalance magnetic pull on the armature core

'. twisting strains due to transmission of tor%ue

C. bending moment due to the weight of the armature and commutator

D. all of the above

10#. $hich of the following loss of DC motor decreases with increase in load?

A. riction and windage loss C. 'rush contact loss

'. Core loss D. none of the above

10(. )n an overload motor main danger arises due to

A. winding getting overheated C. starter getting damaged

'. bus bars getting heated D. bearings getting overheated

10,. A wide and ver sensitive speed control is usuall re%uired in case of

A. elevators C. collier winders

'. steel rolling mills D. all of the above

10. or which application a DC motor is preferred over an AC motor?

A. high speed operation C. fi3ed speed operation

'. low speed operation D. variable speed operation

10. egenerative bra5ing on DC shunt motors is used when

A. the load has overhauling characteristics

'. the load is variable

C. the load also acts as a bra5ing force

D. the load is constantl decreasing

10/. $hich motor should be used for centrifugal pumps?

A. series motor B. shunt motor C. either of the above D. none of the above

100. $hich of the following methods is most effective in finding out the no load losses in a large DC

shunt motor?

A. ields test C. 'loc5 rotor test =. 8op5insons test


24/28

'. $ard-&eonard test D. Swinburne+s test

244. A DC motor can be easil identified b

A. winding B. commutator C. si6e of conductor D. o5e

241. The function of a field regulator for compound motors is to

A. control the flu% C. demagneti6e the field partiall

'. limit the armature current D. none of the above

242. The main disadvantage of 8op5insons test for finding efficienc of the shunt DC motors is that it

A. needs one motor and one generator C. re%uires full load power

B. requires two identical shunt machines D. ignores an change in iron loss

24#. $hich losses can be determined b performing the retardation test?

A. friction losses '. edd current losses C. stray losses D. copper losses

24(. The generated emf and the current are in the opposite direction in case of

A. DC generators B. DC motors C. both !a" and !b" D. none of the above

24,. +peed control of a cumulativel compounded DC motor can be effected through change of

A. field resistance C. armature voltage

'. armature resistance D. any of the above

24. $ard-&eonard sstem of speed control is not recommended for

A. ver low speeds C. wide speed range

'. fre%uent motor reversals D. constant speed range

24. $hich of the following can be used for controlling the speed of a DC motor?

A. Thermistor '. Transistor C. Thratron D. 7hyristor

24/. 8op5insons test is conducted at

A. no load '. part load C. low load D. full load

240. $hich of the following tests can be conducted on all tpes of DC machines?

A. 8op5insons test C. 'loc5 rotor test 3. Brake test

'. unning down test D. ields test

214. )n case of a shunt motor if the suppl voltage is increased b 14:* which of the following will

decrease?


25/28

A. full load current '. full load speed C. starting tor%ue D. none of the above

211. $hich of the following* in a DC motor* can sustain the ma3imum temperature rise?

A. Commutator '. Armature windings C. +lip rings D. *ield windings

212. +peed control varing the armature circuit resistance* in a DC motor* provides a

A. constant torque drive C. constant power drive

'. variable tor%ue drive D. variable power drive

21#. +peed control b the variation of flu3* in a DC shunt motor* will give

A. constant tor%ue drive C. constant power drive

'. variable tor%ue drive D. variable power drive

21(. $hich of the following tests can be used to determine no-load losses in a DC shunt motor?

A. unning down test C. ield test

B. Swinburne+s test D. 'ra5e test

21,. )n regenerative bra5ing

A. motor energ is dissipated as heat C. motor energ is dissipated in windage losses

'. motor energ is dissipated in armature D. motor is made to run as a generator

21. egenerative bra5ing on shunt motors is used when

A. the load is variable C. the load acts as a braking force

'. the load is constantl decreasing D. the load has overhauling characteristics

21. $hich of the following methods gives the greatest brea5ing tor%ue?

A. egenerative bra5ing C. heostatic bra5ing

B. $lugging D. None of the above

21/. A bra5e test on DC motors is usuall restricted to

A. small horse power motors C. high speed motors

'. variable speed motors D. open frame tpe motor

210. The electric motor is a machine which converts mechanical energ into electrical energ.

Answer;


26/28

224. The bod of DC mill motors is made in two halves bolted together for eas access to the field

windings and intel Er poles. Answer; >3S

221. A DC motor wor5s on the principle that when a current carring conductor is placed in a magnetic

field* it e3periences a force whose direction is given b lemings right-hand rule. Answer; >3S

222. )n a DC motor the bac5 of counter emf acts in opposition to the current in the machine.

Answer; >3S

223. >oltage e%uation of a motor is given b . Answer; 3S

225. Condition for ma3imum power developed in armature of a DC motor is . Answer; 3S

2#. Three point starters are not completel satisfactor when used with motors whose speed must be

controlled b inserting resistance in the shunt field circuit. Answer; >3S

2#. $hen a mechanical load is put on a motor* the electrical power input to motor automaticall

changes to match it !load". Answer; >3S


27/28

2#/. The speed of a DC motor can be changed b field control method onl. Answer; 3S

2(1. )n a series motor* variations of flu3 can be brought about b armature divertor onl.

Answer; 3S

2(#. heostatic control method is a common method of speed control of series motors. Answer; >3S

2((. heostat control method is used when speeds above the no-load speed is re%uired. Answer; 3S

2(. $hen the speed is controlled b regulating the motor terminal voltage while maintaining constant

field current* it is called voltage control. Answer; >3S

2(. $ard-&eonard method of speed control not onl gives a wide range of operating speeds* but

reduces to the ver minimum the wastage of energ that ma ta5e place at starting and stopping.

Answer; >3S

2(/. =lectro-mechanical or friction bra5es are operated b electro-magnets or electric-operated

thrusters. Answer; >3S

2(0. )n rheostatic bra5ing the connection to the armature terminals are reversed so that the motor

tends to run in the opposite direction. Anwer; 3S

252.. Answer; 3S

2,(. Armature copper loss is about #4 to (4: of total full-load losses. Answer; >3S

2,,. The voltage drop at the brush is almost 777 of armature current. Answer; independent

2,. ield copper loss constitutes about ,4: of total full-load losses. Answer; 3S

2,/. or good generators the value of overall or commercial efficienc ma be as high as 0,:.


28/28

Answer; >3S

2,0. A direct on line starter is used for starting motors up to , 8.9. Answer; >3S

24. =fficienc will be ma3imum when variable losses are e%ual to constant losses. Answer; >3S

21. 'ra5e test is a tpical e3ample of an indirect test. Answer; 3S

2#. An indirect method of testing consists in measuring the losses and then calculating the efficienc.

Answer; >3S

2(. 777 test is regenerative test for determining efficienc of DC machines. Answer; #opkinson+s

2,. )n +winburnes test the losses are measured separatel and efficienc at an designed load is

pre-determined. Answer; >3S

2. 8op5insons test is uneconomical. Answer; 3S

2/. ields test is applicable to two dissimilar series motors. Answer; 3S

24. $hen the speed of the motor is controlled b regulating the motor terminal voltage while

maintaining constant 7777 current* it is called voltage control. Answer; field

Chapter 10_Direct Current Motor

Documents