EE Correlations Subject: Reviewer:
Electrical Circuit 1_2_3 Dr !lberto ! "ava
Septer termber 1, 2016
1.
An exist existing ing indu industr strial ial plan plantt has an an averag averagee load load of 900 900 kW at at 0.6 0.6 pf laggi lagging. ng. To raise raise the the overal overalll power power facto factorr to 0.92 0.92,, a snchronous !otor driving a "# generator is to $e installed. %f the input of the snchronous !otor will $e 2&0 kW, calculate its k'A input rating. A. (&) k'A *. (++ k'A #. (2) k'A ". (1& k'A
2.
Two alter alternat nators ors A and and * deli deliver verss 100 and and 1&0 1&0 A, A, respec respectiv tivel el to to a load. load. %f%f these these curr current entss are out out of phase phase $ )0 )0 electr electrica icall degrees, deter!ine the total current drawn $ the load. A. 201.& A *. 2&0.0 A #. 21&. A ". 21.+ A
).
Three Three loads loads,, units units A, * and # are connec connected ted in in parall parallel el aand nd take take curre currents nts that that are are respe respecti ctivel vel 12, 10 and and 1& 1& A o o respectivel. respectivel. Assu!ing la to $e the reference phasor. l $ leads la $ )0 and lc lags $ehind la $ 6& , calculate the total -resultant current. A. 2+.)) A *. )0.21 A #. 26.6 A ". )2.10 A
.
An indu industr strial ial coil coil has a resist resistanc ancee of )2 )2 oh!s oh!s and and a reac reactan tance ce of 2 oh!s oh!s and rated rated 0 0 volts volts at at 60 /. A factor factor will will connect the coil to a 0 ', ', &0 / suppl. olve for the value of a series resistor needed to avoid overcurrent condition. A. 2.0( Ω *. 2.6 Ω #. 2. Ω ". 2.2& Ω
&.
An indu inducti ctive ve coil coil take takess a curre current nt of of 2 A and and cons consu!e u!ess 160 W when when conne connecte ctedd to a 20 ' A# A# suppl suppl.. A second second coil coil when when connected across the sa!e suppl takes ) A and &00 W. ind the total power when the two coils are connected in series to this suppl. A. 1.&6 W *. 1).)1 W #. 1&0.22 W ". 12+.)& W
6.
A coil coil draws draws 1+(& 1+(& watt wattss when when conne connecte ctedd to a 1&0 ' "# sour source. ce. %t%t consu! consu!es es )0(2 )0(2 watt wattss when when used used on 20 20 ', ', 60 / / A# A# source. ind the inductance of the coil. A. 0.02&& / *. 0.0)1 / #. 0.01&) / ". 0.020 /
(.
3iven th the fo following cu currents4 l a 5 60 7 0 A l$ 5 8)6 7+ A olve for the ero se:uence co!ponent of la. A. 10 7 *. + 76
lc 5 8+ 7)6 A #.
8 + 7
".
12 76
+.
ind ind the powe powerr angle angle when when a 1&008 1&008 k' k'A, 6.6 6.6 k', k', )8 phase phase,, ;8 ;8 connect connected ed alter alternat nator or havin havingg a resist resistanc ancee of 0. 0. oh! oh! and a reactance of 6 oh! per phase delivers full8 load current at nor!al rated voltage and 0.+ pf lag. A. °1&< *. (°10< #. a. +°20< ". 9°)0<
9.
The voltage applied across an => circuit is e:ual to ????? of '= and '>. A. arith!etic su! *. alge$raic su! #. phasor su!
". su! of s:uares
10.
A )8 )8 phase phase altern alternato atorr has gener generate atedd e!f per per phase phase of 2)0 2)0 ' with with 10 per per cent cent third third har!on har!onic ic and 6 per per cent cent fifth fifth har! har!oni onicc content. #alculate the r!s line voltage for s tar connection. A. 299 ' *. )99 ' #. 9 9 ' ". &90 '
11.
"eter! "eter!ine ine the the power power angle angle in the the series series circui circuitt which which consis consists ts of =52& =52& oh!s oh!s,, >50.2 >50.2 / across across a power power suppl suppl of 200 volts volts,, )0 /@ A. )6.° *. &2.° #. 6.° ". &6.°
12.
A 8 pole, pole, )8 )8 phase, phase, &08 &08 /, /, star8 star8 conn connect ected ed alter alternat nator or has has 60 slots slots,, with with condu conducto ctors rs per slot. slot. #oils #oils are are short short88 pitche pitchedd $ o ) slots. %f the phase spread is 60 , find the line voltage induced for a flux per pole of 0.9) W$ distri$uted sinusoidall in space. All the turns per phase are in series. A. 11,0&0 ' *. 12,1&0 ' #. 1),1+& ' ". 1),21& '
1).
A current of 10 A and a power factor factor of 0.+ lagging lagging is taken fro! a single phase 2&0 volt suppl. suppl. The reactive reactive power of the the sste! is A. 1&00 *. 2000 #. 2& 00 ". one of these
1. 1.
%f p.f. p.f. of a cir circu cuitit is unit unit, its its reac reacta tanc ncee is is A. a !axi!u! *. e:ual to %2 =
1&.
#. ero
". a negative :uantit
A capacitor is rated 100 k'A=, k'A=, )+0 volts, &0 /. What will it
2.
The i!pedance coil a$sor$s 2&0 watts when connected across 220 ', 60 / !ains. %t is then connected across 110 ', 2& / !ains and also a$sor$s 2&0 watts. What is the conductance of the coil@ A. 0.12& / *. 0.19 / #. 0.1& / ". 0.16) /
).
The open circuit voltage across the output ter!inals of an A# power suppl is 1&.2 '. When these ter!inals are short8 circuited, a current of ).2 A flows. When a &8 oh! resistance is placed across these ter!inals, the current through it is 1.+ A. #alculate the series internal resistance of the power suppl. A. 2.)( oh!s *. 2.20 oh!s #. 2.12& oh!s ". 2.0& oh!s
.
A single8 phase load takes && kW at (0B pf lagging fro! a 20 ', &0 / suppl. %f the suppl is !ade 60 /, with the voltage re!aining the sa!e, what will $e the kW load at 60 /@ A. 2 kW *. + kW #. 0 kW ". & kW
&.
A load of 20 7)& oh!s is connected across a220 volts source. "eter!ine the power factor and the 'A=. A. 9.6 B, 102 'A= *. +&.) B, 9(& 'A= #. &2.2 B, 102) 'A= ". 2.) B, 10+( 'A=
6.
ind the total i!pedance in rectangular for the following three i!pedances4 12∠10o, 2&∠1&o and )∠26o A. 66.&2 7 2).6 *. 6+.) 7 20.& #. (.)1 7 21.&6 ". 6(.(0 7 22.0
(.
An i!pedance draws a current % 5 10 cos -wt )0o fro! a voltage, v 5 220 sin -wt )0 o. What is the i!pedance@ A. 1&.6 7 1&.6 *. 1&.6 7 1&.6 #. 19.1 7 11.1 ". 11.0 7 19.1
+.
A series resistance8 capacitance -=8 # circuit is connected to a 2)0 volt 60 ccle source. %f the power taken $ the circuit is , +00 watts and the voltage drop across the resistor is 11& volts, calculate the capacitance of the capacitor. A. &0 µ *. &)0 µ #. &&6 µ ". &0) µ
9.
A capacitance is connected to a 11&8 ', 2&8 / !ains and takes & A. What current will it take when the capacitance and the fre:uenc are $oth dou$led@ A. 2.& A *. &A #. 20 A ". 10 A
10.
A capacitor is rated 100 k'A=, )+0 volts, &0 /. What will it
12.
Two alternators are operating in parallel suppling a co!!on load of 2&0 kW at 0.+& power factor lagging. Alternator A contri$utes 600 k'A= at 0.92 power factor lagging. olve for the power factor of alternator *. A. 0.+1) lagging *. 0.+) lagging #. 0.+0 lagging ". 0.+20 lagging
1).
The difference $etween the half8power fre:uencies is called the4 A. :ualit factor *. resonant fre:uenc #.
$andwidth
".
cutoff fre:uenc
1.
A plant has a load of 290 kilowatt with an average power factor of (0B. The owner re:uests ou to correct the power factor to reduce its power consu!ption. /ow !uch capacitor k'A= is re:uired to increase the power factor to 90B@ A. 1&2.6 *. 1&&.)9 #. 1&0.) ". 1&.&+
1&
A three8 phase alternator has 6 slots per pole per phase. "eter!ine the distri$ution factor. A. 0.9(( *. 0.9&6 #. 0.96) ". 0.9+ #o$ %less &ou !lwa's(
1.
A capacitor, an electric resistance heater, and an i!pedance are connected in parallel to a 120 ', 60 / sste!. The capacitor draws &0 'A=, the heater draws 100 W and the i!pedance coil draws 269 'A at a pf of 0.( lagging. "eter!ine the sste! power factor. A. 0.9)) lagging *. 0.92+ lagging #. 0.916 lagging ". 0.911 lagging
2.
A 2&0 ', )0 / generator supplies power to a parallel circuit consisting of a 20 hp !otor whose efficienc is 90B at 0.+0 pf lagging and a second load that draws an apparent power of ( k'A at unit pf. "eter!ine the sste! power factor. A. 0.+2+ lagging *. 0.+)1 lagging #. 0.+02 lagging ". o.++ lagging
).
Two i!pedances A and * are connected in parallel across a 1208 ' A# suppl. The total current and the current in each i!pedance are ad7usted to 20 A. The power drawn $ A is dou$led that of * and the power factor is lagging. "eter!ine power factor of A. A. 0.6&0 lagging *. 0.(0 lagging #. 0.+1 lagging ". 0.6(( lagging
.
%f ad!ittance ; 5 0.06 7 0.0+ !ho, then conductance 3 e:uals, A. 0.06 *. 0.06 #. 0.0+
". 0.0+
&.
A parallel circuit consists of a resistor having a conductance of !hos, an inductive reactor having a susceptance of + !hos and a capacitive reactor having a susceptance of & !hos. What is the i!pedance of the circuit@ A. 0.11 70.1) *. 0.1) 70.11 #. 0.12 70.16 ". 0.16 70.12
6.
#apacitor of )08!icrofarad capacitance is in series with a coil across an +,0008ccle suppl. What inductance is re:uired for resonance@ A. 1.) µ/ *. 10.& µ/ #. 1).19 µ/ ". 12.&& µ/
(.
A loud speaker whose inductance is 1.1& henries is coupled to a power tu$e through a condenser of 2 µ capacit. To what fre:uenc will the co!$ination $e resonant@ A. 110 / *. 10+ / #. 10& / ". 100 /
+.
What capacitance !ust $e placed in series with an inductance of 0.0& / so that at 100 /, the i!pedance $eco!es e:ual to the oh!ic resistance@ A. &0.( µ *. )&.& µ #. (0.( µ ". +(.0 µ
9.
A non8 inductive resistor = is connected in parallel with an inductive reactance of 10 oh!s. The co!$ination is then connected in series with a capacitive reactance of & oh!s. olve for = at which the power factor of the given circuit would $e unit. A. 10 Ω *. 12 Ω #. 1) Ω ". 11 Ω
10.
A )008 oh! inductive reactance is connected across a series co!$ination of a resistor = and a capacitive reactance Cc. olve for = if the e:uivalent i!pedance of the co!$ination is a pure resistance of 100 oh!s. A. 92 oh!s *. ++ oh!s #. (+ oh!s ". 90 oh!s
11.
Two i!pedances D1 5 1& 720 and D 2 5 & 7 C c are connected in parallel. olve for the value of C c so that the total current drawn $ the co!$ination will $e in phase with an suppl voltage. A. 2+.& Ω *. )0.) Ω #. )).12 Ω ". 29.&& Ω
12.
Three i!pedances Da, Dc, Dr are connected in parallel. %f at 60 /, D a 5 0 7+, D c 5 0 72 and D r 5 & 70 oh!s. olve for the fre:uenc at resonance. A. )0 / *. ) / #. )6 / ". 2+ /
1).
A generator supplies three8phase power to $alanced load. The voltage is 2)0 volts, the current is 1+ A and the power factor is +&B. What is the power@ A. ).6 kW *. 1.6 kW #. 6.1 kW ". 1. kW
1.
"eter!ine the ratio of the line current drawn $ three identical i!pedances connected in we to the line current drawn $ the sa!e i!pedances connected in delta. *oth connections $eing i!pressed with the sa!e $alance )8φ voltages. A. 142 *. )4 #. 24) ". 14)
1&.
The input power factor to a three8phase, 68poles, 60 volts, 60 /, &08hp induction !otor is 0.62 as 20 A is drawn $ the !otor. ind the power input to the !otor. A. 9,++0 W *. 9,6(& W #. 9,+9& W ". 9,(+ W #o$ %less &ou !lwa's(
1.
3iven the following line voltages and two load i!pedancesE 'a$ 511(∠0° ' Dac 5& 712 F '$c 511(∠20° ' olve for the line current in line c. A. 1(.1 A *. 1(.9& A #. 16.62 A
D$c 5 1) 70 F
'ca 511(∠120° '
". 1+.6 A
2.
Three une:ual single8phase loads so connected across the lines of a $alanced, )8phase, 2)0 volts circuit. The first takes 106 A at 0.(+ pf lagging and is connected across lines 1 G 2. The second takes 12 A, at 0.+2 pf lagging and is connected across a lines 2 G ). And the third takes 2+. kW at 0.(( pf lagging and is connected across lines ) G 1. find the three lines currents. A. 2&.0 A, 211.)+ A, 2&2 A *. 2)1.26 A, 21&.20 A, 26+ A #. 2&.0 A, 21&.20 A, 2&2 A ". 2)1.26 A, 211.)+ A, 26+ A
).
Three resistors 10, 1& and )0 oh!ic values are connected in we8configuration to a $alanced 20+8volt three8phase suppl. #alculate the total power of the sste!. A. 26 W *. 2++0 W #. )0+0 W ". )2+0 W
.
Three i!pedances, Dan 5 20 70, D $n 5 16 712, D cn 5 & 71& oh!s are connected in we across a 2)0 ' -line to line, )8 phase, 8 wire source. The phase se:uence is a8$8c, counterclockwise. "eter!ine the current passing thru the neutral. A. (.& A *. 9.12 A #. +.+1 A ". +.02 A
&.
%n a snchronous !otor, the !otor #u losses are !et $ A. !otor input *. ar!ature input #. suppl lines
". d.c. source
6.
A )8phase, ) wire feeder has the following line currents and line voltages4 'a$ 5220∠0° ' %aa 5 )087)0 A '$c 5220∠20° v %cc 5297)9.+ A "eter!ine the reactive power supplied $ the feeder. A. (.(& k'A= *. (.) k'A= #. +.)2 k'A= ". +.& k'A=
(.
A )8phase, )8wire load draws the following line currents4 %a 5 60∠ ))0o A %$ 5 (+.∠ 21o A %c 5 (&∠ +0o A %f the voltages i!pressed on the load are $alanced )8 phase. /aving a !agnitude of 10 volts line to line, solve for the total power in kW. A. &&6.1& *. &06.+& #. &)6.& ". &20.1+
+.
3iven the following load i!pedances in delta and is i!pressed voltages as follows4 'a$ 5 220∠ 0o ', Da$ 5 + 76 F ' $c 5 220∠ 20o ', D$c 5 +.66 7& F 'ca 5 220∠ 120o ', Dca 5 10 F What will $e the reading of the two watt!eters connected to !easure total power. Hse line a as the co!!on potential point. A. ).+69 kW, 9.0)1 kW *. 2.&6 kW, +.)&( kW #. ).12& kW, 6.((+ kW ". .0&& kW, 9.++ kW
9.
A $alanced )8 phase load draws 120 a!peres line current at 2)0 volts line to line 0.++ pf lagging current. olve for the readings of the two watt!eters used to !easure the )8 phase power. A. 2&.&) kW, 1&.0+( kW *. 2+.1&& kW, 12.)+& kW #. 2.)6& kW, 16.1(& kW ". 2(.&+) kW, 12.9&( kW
10.
%f the field of a snchronous !otor is under8excited, the power factor will $e A. lagging *. leading #. unit
".
!ore than unit
11.
The power drawn $ a three8 phase $alanced load is !easured using two watt!eters properl connected. At what power factor will the reading of one of the watt!eters $e ero@ A. 0.+66 *. 1.0 #. 0.& ". 0.(0(
12.
A )0008 k'A, 68 pole alternator runs at 1000 rp! in parallel with other !achines on ))008 ' $us8$ars. The snchronous reactance is 2&B. #alculate the snchroniing power for one !echanical degree of displace!ent. A. &6. kW *. &6(.6 kW #. 62+. kW ". 6&(.+ kW
1).
A three8 phase feeder carries two lagging $alanced loads. The power o$served $ each is !easured $ two watt!eters !ethod, giving the following readings4 irst load4 W1 5 160 kW W2 5 96 kW econd load4 W1 5 90 kW W2 5 + kW What is the co!$ined k'A load on the feeder@ A. ).6+ *. 62.)6 #. &0.2 ". 20.12
1.
Three i!pedances, 8710, 710 and 10 oh!s are we connected. "eter!ine the i!pedance of an e:uivalent delta. A. &, 7&, 87& oh!s *. 10, 710, 8710 oh!s #. 7+.&, 8712.&, + oh!s ". 12.&, 712.&, 812.& oh!s
1&.
Dero power factor !ethod of an alternator is used to find its A. efficienc *. voltage regulation #. ar!ature resistance #o$ %less &ou !lwa's(
". snchronous i!pedance
