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# Electrical

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## Content

1) In generators, what principle is used to convert mechanical motion to electrical energy? a) Atomi omic rea react ctiion b) Elect ectrica ricall att attract ractio ion n c) Magnet Magnetic ic repuls repulsion ion d) Magnet Magnetic ic induct induction ion 2) When you use the let!hand rule or generators, what is indicated by the middle inger? a) "irection o lu# b) "irection o motion c) "ire "irect ctio ion n o curr curren entt lo low w d) "ire "irect ctio ion n o o the the mag magne neti tic c ie ield ld \$) %he output voltage o an elementary generator is coupled rom the armature to the brushes by what devices? a) &lip rings b) Interpoles c) %erminals d) 'igtails () An elementary elementary generator consists o a single single coil rotating in a magnetic ield ield Why is *+ voltage induced in the coil as it passes through the neutral plane? a)lu# lines are too dense b) lu# lines are not being cut c) lu# lines are not present d) lu# lines are being cut in the wrong direction -) What components components cause.s) a generator to to produce a dc voltage instead instead o an ac voltage at its output? a) %he brushes b) %he armature c) %he slip rings d) %he commutator   /) When two ad0acent segments o the the commutator on a single!loop dc generator come in contact with with the brush at the same time, which o the ollowing conditions will occur? a) %he output voltage will be ero b) %he output voltage will be ma#imum negative c) %he output voltage will be ma#imum positive ) In an elementary, elementary, single!coil, single!coil, dc generator with one pair o poles, what what is the ma#imum number o pulsations pulsations produced in one revolution? a) +ne b) %wo c) %hree d) our   3) I an elementary elementary dc generator has a two coil armature armature and our ield ield poles, what is the total number number o segments re4uired in the commutator? a) 3 b )2 c) 1/ d) ( 5) 6ow can you vary the strength o the magnetic ield in a dc gene rator? a) 7y varying the armature current b) 7y varying the speed o armature rotation c) 7y varying the voltage applied to the electromagnetic ield coils d) 7y varying the polarity o the ield poles 18) 9nder which o the ollowing conditions does spar:ing occur between the brushes and the commutator? a) Whe When operating under der normal condi nditions b) Whe When there is impro proper per commutation c)Whe When there is is an an e# e#cessive lo load cu current d) Wh When commutation is is in in th the ne neutral pl plane 11) 11) "istortion o the main ield by interaction with the armature ield deines what term? a) ;ommutation b) Mutual reaction c) Armature reaction

d) Mutual induction

12) "istortion o the main main ield by interaction with with the armature ield can be compensated or by the use o  a) slip rings c) interpoles c) a commutator d) special brushes 1\$) Motor reaction in a dc generator is a physical orce caused by the magnetic interaction between the armature armature and and the ield What eect, i any, does this orce orce have on the operation o the generator?

1

a) It tends tends to oppo oppose se the the rot rotat atio ion n o o the the arma armatu ture re c) It causes the generator to vibrate

b) It tends tends to aid aid the the rota rotati tion on o the the arm armat atur ure e d) *one

1() In dc generators, copper losses are caused by which o the ollowing actors? a) <eluctance in the ield poles b) <esistance in the armature winding c) <eactance in the armature and ield windings d) All o the above 1-) Eddy currents in armature cores are :ept low by which o the ollowing actions? a) 9sin 9sing g pow powde dere red d iro iron n as as a cor core e mat mater eria iall b) =imi =imiti ting ng arm armat atur ure e cur curre rent nt c) Insulating the core d) =aminating the iron in the core 1/) What ma:es the drum!type armature more eicient than the >ramme!ring armature? a) %he drum!type armature has more windings than the >ramme!ring armature b) %he drum!type armature can be rotated aster than the >ramme!ring armature c) %he drum!type armature coils are ully e#posed to the magnetic ield, while the the >ramme!ring >ramme!ring armature coils are only partially partially e#posed to the magnetic ield ield d) %he drum!type armature has a laminated core, while the >rammering armature has a solid core 1) Which o the ollowing is *+% a ma0or classiication o dc generators? a) ;omp ;ompoun ound! d!wo woun und d b) &eri &eries es!w !wou ound nd c) &hunt!wound d) =ap!wound 13) What characteristic o series!wound generators ma:es them unsuitable or most applications? a) %hey re4uire e#ternal ield e#citation b) %he output voltage varies as the speed varies c) %hey are not capable o supplying heavy loads d) %he output voltage varies as the load 15) When two or more generators are used to supply a common load, what term is applied to this method o    operation? a) &eries b) ;ompound c) &plit!load d) 'arallel 28) When you u se the right!hand rule or motors, what 4uantity is indicated by the e#tended oreinger? a) "ire "irect ctio ion n o o llu# nort north h to to sou south th b) "ire "irect ctio ion n o o lu# lu# sout south h to to nor north th c) "irection o current d) "irection o motion 21) What determines the direction o rotation o a dc motor? a) %he type o o armature b) %he method o e#citation c) %he number o armature coils d) %he polarity o armature current and direction o magnetic lu# 22) Which, i any, o the ollowing situations is a ma0or electrical dierence between a dc motor and a dc generator? a) %he armatures are dierent b) %he shunt connections are d ierent c) %he dc generator re4uires a commutator, the the dc motor does not d) *one o the above 2\$) In a dc motor, what causes counter em? a) Im Improper com comm mutation b) Armature re reaction c) >enerator action d) E#cessive speed

2() In a dc motor, how, i at all, does counter em aect speed? a) It causes the speed to increase b) It causes the speed to decrease c) It caus causes es rapi rapid d lu luct ctua uati tion ons s o o the the spee speed d d) It does does not not ae aect ct spee speed d

2

2-) What is the load on a dc motor? a) %he ield current b) %he armature current c) %he mechan mechanica icall devi device ce the the motor motor moves moves d) %he total total curren currentt draw drawn n rom rom the source source 2/) When a series dc motor is operated without a load, which o the ollowing conditions occurs? a) %he %he arm armat atur ure e draw draws s e#ce e#cess ssiv ive e curr curren entt b) %he %he vol volta tage ge re4 re4ui uire reme ment nt incr increa ease ses s c) %he armature will not turn d) %he armature speeds out o control 2) A dc series motor is best suited or which o the ollowing applications? a) &teady load, low tor4ue b) ariable load, low tor4ue c) &teady load, high tor4ue d) ariable load, high tor4ue 23) What is the main advantage o a shunt motor over a series motor? a) A shunt motor develops higher tor4ue at lower speeds than a series motor  b) A shunt motor can be operated at higher speeds than a series motor  c) A shunt motor draws less current rom the source than a series motor  d) A shunt motor maintains a more constant speed under varying load conditions than a series motor  25) 6ow can the direction o rotation be changed in a dc motor? a) +nly by reversing the ield connections b) +nly by reversing the armature connections c) 7y reversing both the armature connections and the ield connections d) (7y reversing either the armature connections or the ield connections \$8) When the voltage applied to the armature o a dc shunt motor is decreased, what happens to the motor speed? a) It becomes uncontrollable b) It decreases c) It increases d) %he motor stops \$1) In a dc motor, the neutral plane shits in what direction as the result o armature reaction? a) ;loc:wise b) ;ountercloc:wise c) In the direction o rotation d) +pposite the direction o rotation \$2) Magnetic induction in an a lternator is a result o relative motion between what two elements? a )%he rotor and the armature b) %he armature and the ield c )%he ield and the stator d) %he rotor and the ield \$\$) oltage is induced in what part o an alternator? a) %he commutator b) %he brushes

c) %he armature

\$() Alternators Alternators are rated using which o the ollowing terms? a )olts b) Watts c)Amperes \$-) Which o the ollowing motors [email protected] types o ac motor? a) &eries b) &ynchronous c) Induction

d) %he ield

d) olt!amperes

d) All o the above

\$/) Which o the ollowing types o motors is widely used to power small appliances? a) 9niversal b) &ynchronous c) 'olyphase d) ;ompound \$) What type o ac motor is most widely used? a) &eries b) 9niversal c) &ynchronous

d) &ingle!phase induction

\$3) What type o ac motor uses a combination o inductance and capacitance to apply out!o!phase currents to the start windings? a) %hree!phase b) &eries c) &ynchronous d) &plit!phase induction

3

\$5) %he speed o the motor can be varied by  a) ;hanging supply re4uency b) ;hanging no o poles d) ) 9sing multi speed windings d) All the above (8) %he type o single!phase induction motor having the highest power actor at ull load is a) shad shaded ed pole pole type type .b) .b) spli split! t!ph phas ase e type type .c) capacitor!start type .d) capacitor!run type

(1

;alcul ;alculate ate the the percen percentag tage e o regul regulati ation on o gener generato atorr with with a no load load voltag voltage e o (/2 volt volt and and ull ull load load volt volt ((8  a 1-8B b 18-B c -B d 5-B

(2

At what what poin pointt shoul should d brush brush contac contactt chang change e rom rom one one comm commuta utator tor segmen segmentt to the ne#t ne#t a a ull positive voltage b at ull negative voltage c at M*A d at >*A

(\$

;opper loss osses incr ncrease asC a voltage increases c s4uare o current

(( ((

b d

%otal tal num numbe berr o o com commu muta tato torr seg segme ment nt is e4ua e4uall toC toC a e4ual the number o ield coil b c e4ual the twice o armature loop d

current increases s4uare o the resistance

e4ual the number o armature turn e4uals the twice o armature conductor

(-

In motor motor moves moves in in same same direct direction ion as the rotat rotatin ing g stato statorr iel ield d due due toC toC a laming let hand rule b right hand rule c grip rule d len law

(/ (/

In cap capacit acitor or star startt in induct ductiion motor  otor  a star starti ting ng win windi ding ng is is con conne nect cted ed in in par paralle allell wit with h main main windi inding ng b star starti ting ng wind windin ing g is is con conne nect cted ed in in seri series es with with main main windi inding ng c star starti ting ng wind windin ing g is is con conne nect cted ed in paral paralle lell wit with h au# au#il ilia iary ry wind windin ing g d au#il au#iliar iary y windi winding ng is is conne connecte cted d in parall parallel el with with main main windi winding ng and and is is place placed d physic physicall ally y at right right angle angle

(

In capacitor start IM a in cap capa acitor ci circuit uit cu current le leads 58o by voltage b in cap capa acitor ci circuit uit vo voltage le leads 58o by current c in capa capaci cito torr cir circu cuit it curr curren entt lea leads ds the the lin line e vol volta tage ge by (-o d in capa capaci cito torr cir circu cuit it curr curren entt lag lags s the the line line volt voltag age e by by ((-o

(3

In capacitor start IM a capa capaci cito torr is is con conne nect ctin ing g b capa capaci cito torr is is con conne nect ctin ing g c capa capaci cito torr is is con conne nect ctin ing g d capa capaci cito torr is is con conne nect ctin ing g

(5 (5

-8

in seri series es with ith mai main n ie ielld win windi ding ng in in par paral alle lell wit with h star starti ting ng win windi ding ng in in ser serie ies s wit with h sta start rtin ing g win windi ding ng in in ser serie ies s wit with h rot rotor or windi inding ng

&ync &ynchr hron onou ous s mot motor or has has the the disa disadv dvan anta tage ge o re4u re4uir irin ing g a ac e#citer voltage or stator b c ac e#citer voltage or rotor

dc e#citer voltage or stator

lashing th the iield me means a mome moment ntar aril ily y pass passin ing g curr curren entt thro throug ugh h iel ield d coil coils s in sam same e way way as nor norma mall lly y low lows s b pass passin ing g curr curren entt thro throug ugh h iel ield d coil coils s in opp oppos osit ite e way way as norm normal ally ly lo low w or or long long per perio iods ds

4

c d -1 -1

mome moment ntar aril ily y pass passin ing g curr curren entt thr throu ough gh ie ield ld coil coils s in oppo opposi site te way way as as norm normal ally ly either a or d

Adva Advant ntag age e o o bru brush shle less ss alte altern rnat ator or over over ac ac gener generat ator  or  a low maintenance cost b c better perormance at high altitude d

brushes D slip ring are eliminated all

-2 -2

Esse Essent ntia iall part part o brus brushl hles ess s gene genera rato tor  r  a main generato ator, e#citer generator  ator  b mai main gen gener erat ator or,, perm ermanen anentt mag ag >ener enerat ator  or  c e#ci e#citter gene generrator tor, per perma mane nent nt mag ag >en >ener erat ator  or  d main main gene genera rato torr, perm perman anent ent mag mag >ene >enera rato torr, e#ci e#cite terr gene genera rato tor  r

-\$ -\$

&had &haded ed ring ring is pres presen entt on on pol pole e o o sha shade ded d pol pole e mot motor  or  a trailing edge o pole b leading edge o pole

c

center o pole

-(

&lip is the a di dier eren ence ce betw between een actu actual al roto rotorr spe speed ed and and syn synch chro rono nous us spee speed d in in dc dc mot motor ors s b di dier eren ence ce bet betwe ween en act actua uall rot rotor or spe speed ed and and syn synch chro rono nous us spe speed ed in in ac ac moto motors rs c di dier eren ence ce bet betwe ween en act actua uall roto rotorr spee speed d and and sync synchr hron onou ous s spee speed d in ind induc ucti tion on mot motor  or  d all

-- --

In ele eleme ment ntar ary y dc dc gen gener erat ator or,, ii numb number er o o coil coil is is incr increa ease sed d a induced em em wi will in increase b numb number er o ripp ripple le re4 re4ue uenc ncy y wil willl inc incre reas ase, e, resu result ltin ing g in in ste stead ady y dc dc c ripple will decrease d both c and d

-/ -/

>ene >enera rato torr cont contro roll unit unit is capa capabl ble e o o per peror ormi ming ng a volt voltag age e regu regula lati tion on,, over over vol volt t 'ro 'rote tect ctio ion, n, rev rever erse se pol polar arit ity y prot protec ecti tion on b revers reverse e curre current nt and dier dierent ential ial voltag voltage e prote protecti ction on over over volt volt and under under volt volt protec protectio tion n c anti anti cycle cycle protec protectio tion, n, genera generator tor line line contac contactor tor contro controll lash lash and start start relay relay contro controll d all

- -

"ire "irect ctio ion n o rot rotat atio ion n o gen gener erat ator or whe when n view viewed ed rom rom the the driv drive e end a cloc:wise b anti cloc:wise c

either a or b

-3

In a gener generato ator, r, what what elimi eliminat nates es any any possib possible le spar: spar:ing ing to to the brus brush h guides guides caus caused ed by the the movem movement ent o  o  brushes within the holder? a the pigtail b brush spring tension c under cutting the mica on commutator d lubricating the brush sides

-5

%he level level o compou compoundi nding ng in cumu cumulat lativ ive e compou compound nd dc dc gene generat rator or is usuall usually y ad0ust ad0usted ed byC byC a alternating series ield b changing shunt ield current c connecting it long shunt d connecting in short shunt

/8

In vibra vibrator tor type type voltag voltage e regulat regulator or,, relay relay contac contacts ts in each each section section ie ie .volt .volt regula regulator tor,, curren currentt regulat regulator or and <;;<) normallyC a close, open, close b close, close, close c close, close, open d open, open, close

/1

>enera >enerator tor with with vibra vibrator tor type type volta voltage ge regu regulat lator or and and its its [email protected]' [email protected]' is luc luctua tuate te due due toC toC a pitting on contact point b tension o ad0ustment spring is low c regulating resistor burn d all

5

/2 /2

/\$ /\$

/( /(

ibr ibrat ator or type type volt voltag age e reg regul ulat ator or used used or or a high ield current c both a and b

b d

%wo %wo curre current nt car carry ryin ing g paral paralle lell cond conduc ucto torr .in .in same same dir direc ecti tion) on) a tends to repel b tends to attract Motor otor used used or or ac ac eng engiine star starti ting ng a shunt motor b induction motor ;han ;hange ge the the dir direc ecti tion on o rota rotati tion on o shad shaded ed pole pole IM IM a rev revers ersing ing the the conn connec ecti tion on to sta starrting ting windi inding ng b rev revers ersing ing the conn connec ecti tion on to mai main windin nding g c either a or b d none

//

&lip phase motor is a not sel starting

/

/3 /3

sel starting

A; series motor   a also :nown as universal motor c not an induction motor

c

c series motor

/- /-

b

low ield current none

b d

c

no result

d

synchronous motor

e#ternal e#citation is re4uired

operated on dc all

When When moto motorr or gene genera rato torr oper operat atin ing g prop proper erly lyFF FF  indi indica cate tes s a :noc:ing b evenly hum c armature dragging

d

none

/5

I <;;< <;;< conta contact ct .<eve .<everse rse curr current ent cut cut out rela relay) y) conta contact ct points points ail ail to to open ate aterr the gener generato atorr [email protected]' has dropped below battery volt current will low through the gene rator armatureC a in the the nor norma mall dire direct ctio ion n and and thro throug ugh h shun shuntt iel ield d oppos opposit ite e the the norm normal al dir direc ecti tion on b oppos opposit ite e the the norm normal al dir direc ecti tion on and and thr throu ough gh the the shu shunt nt ie ield ld in in the the same same dir direc ecti tion on c opposite in shunt ield

8 8

*umb *umber er o alte altern rnat atio ion n in [email protected][email protected] (88 (88 6 a c a 288 b 388

c

(88

In diagram generator isC a series wound b

shunt wound

c

compound wound

&ide &ides s o the the loo loop p mov moves es par paral alle lell to to lin line e o o lu lu# # a ma# volt induced c ma# positive volt included

b d

volt induced ma# negative volt induced

1

2 2

d

1/88

\$

%he neutra neutrall plane plane is the the posi positi tion on wher where e the the plan plane e o the two two oppos opposite ite coil coil isC isC o a parallel b at (c perpendicular

(

;ompensating winding a connected in in ser seriies wi with iield wi winding b connected in in se series wi with ar armature c as in in b and and mag mag ie ield ld pro produ duce ced d by comp compen ensa sati ting ng win windi ding ng wil willl aid aid to to mag mag iel ield d prod produc uced ed by by armature d as in in b and and mag mag ie ielld prod produc uced ed by by comp compen ensa sati ting ng win windi ding ng wil willl coun counte terr race race the the mag mag iel ield d produced by armature

-

Inter poles a coun countter acts acts the e eect ects o o ar armatu maturre wi windi nding

6

b c d / /

 

3

minimie ield distortion as in a and and ten tends ds to :eep :eep the the neu neutr tral al plan plane e in in sam same e pos posit itio ion n or or all all load loads s all

I serie eries s iield eld ai aids the shunt hunt iel ield d a plane compound c cumulative compound

b d

In elec electr tric ic arc arc wel weldi ding ngF F gen gener erat ator or is used usedCC a dierential compound b

shunt

Gcoming in inHC speed means a produced over volt than rated volt c pro produc duced very low volt than rated

dierentially compound over compound

c

b

cumulative compound

produced normal volt

5 5

;han ;hange ge the the dir direc ecti tion on o rota rotati tion on o sing single le phas phase e mot motor  or  a rev revers ersing ing the conn connec ecti tion on to mai main windin nding g b rev revers ersing ing the the conn connec ecti tion on to sta starrting ting windi inding ng c either a or b d bother a and b

38

In a vibr vibrato atorr conta contact ct type type voltag voltage e regul regulato atorr is connec connected ted with with gene generat rator or outp output ut in in a series b parallel c series!parallel d

either a or b

7

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