Electrical Engineering

Transcription

1 A SET Bklet N. : EE - 5 Electrical Engineering Duratin f Test : Hurs Max. Marks : 0 Hall Ticket N. Name f the Candidate : Date f Examinatin : OMR Answer Sheet N. : Signature f the Candidate Signature f the Invigilatr INSTRUCTIONS. This Questin Bklet cnsists f 0 multiple chice bjective type questins t be answered in 0 minutes.. Every questin in this bklet has 4 chices marked,, and fr its answer. 3. Each questin carries ne mark. There are n negative marks fr wrng answers. 4. This Bklet cnsists f 6 pages. Any discrepancy r any defect is fund, the same may be infrmed the Invigilatr fr replacement f Bklet. 5. Answer all the questins n the OMR Answer Sheet using Blue/Black ball pint pen nly. 6. Befre answering the questins n the OMR Answer Sheet, please read the instructins printed n the OMR sheet carefully. 7. OMR Answer Sheet shuld be handed ver t the Invigilatr befre leaving the Examinatin Hall. 8. Calculatrs, Pagers, Mbile Phnes, etc., are nt allwed int the Examinatin Hall. 9. N part f the Bklet shuld be detached under any circumstances. 0. The seal f the Bklet shuld be pened nly after signal/bell is given. EE-5-A

2 . If A = 0 0 ELECTRICAL ENGINEERING (EE), then which ne f the fllwing is true? A 3 5A + 7A + 3I = 0 A 3 + 5A + 7A 3I = 0 A 3 5A + 7A 3I = 0 A 3 + 5A + 7A + 3I = 0. The directinal derivative f xy + yz + zx at the pint (,, 0) in the directin f i + j + k is (u, v) 3. If u = xy, v = x + y, then (x, y) = (x y) (y z) (z x) x + y + z xyz (x y) (z y)(z x) 4. The P.I. f (D + 6)y = cs 4x is x 8 cs 4x x 8 sin 4x x cs 4x x sin 4x 5. The half range Furier sine series f f(x) =, 0 < x < π is ( ) f(x) = Σ n sin nx f(x) = nπ ( ) n f(x) = sin nx nπ n = Σ n = 6. The slutin f 3 u x + u y = 0, u(x, 0) = 4e x is Σ n = ( ) n + nπ sin nx f(x) = ( ) n Σ n sin nx = nπ u(x, y) = 4e x 3 y u(x, y) = 4e x 3 y u(x, y) = 4e x + 3 y u(x, y) = 4e x + y 7.. (z + ). (z dz, where c : z = is ) c πi πi/ πi πi 8. If f(x) = k( x ) fr 0 < x < 0 elsewhere represents the prbability density f a randm variable X, then k = /3 3/ / 9. The crrelatin cefficient f twelve pairs f data having Σx = 730, Σy = 07, Σx = 4493, Σy = 8680 and Σxy = 635 is Set - A EE

3 0. The slutin f y' = x + y, y(0) = at x = 0., using Euler s methd, is A tree f a netwrk graph cnsists f (n-) ndes n branches ne r tw ndes left in islated psitin n clsed paths. The pwer delivered by the current surce in the circuit shwn in Figure. Ω 6 +_.5A 4 Ω 9 W W 8.5 W.5 W 3. The vltage acrss the Ω resistr in the circuit shwn in Figure. Ω A Ω +_ The current thrugh 6 surce in the circuit shwn in Figure. Ω Ω 6 +_ A +_ 0.5 A.0 A.5 A A Set - A 3 EE

4 5. The current thrugh the circuit shwn in Figure, if switch, S is clsed at time, t = 0 kω S 5 +_ mf t e t e t e t e 6. The damping rati f an under damped R-L-C circuit with step respnse is R R R R L / C L / C L / C C / L 7. The Thevenin equivalent acrss X-Y fr the circuit shwn belw : Ω X 0 A j3 Ω j Ω 45, (+ j) Ω 45, (+ j) Ω 45, ( + j) Ω 45, ( j) Ω Y 8. The Z parameters f Tee netwrk shwn in Figure. + Z a Z b + Z c Z a + Zc Z c Z a Zc Z c Zc Zb + Z c Zc Zb Zc Z a + Z _ c Z c Zc Zb + Z Z c Za Z c c Zc Zc Za Set - A 4 EE

5 9. In a 3-phase balanced system the phase vltages with a-b-c phase sequence are = p 0 and = p 0. The line vltages are an bn ab = L 30, bc = L ab = L 30, bc = L ab = L 30, bc = L ab = L, bc = L Set - A 5 EE Tw parallel cnductrs are separated by a distance, d carrying a current, I in the same directin. The magnetic field alng a line running parallel t the cnductrs and midway between them is zer prprtinal t I prprtinal t d prprtinal t the permeability f the medium.. A cil f N turns is placed in a medium f reluctance, S. The inductance is N N N N S S S S. A dielectric material is said t be linear if the electric flux density varies nn-linearly with electric field linearly with electric field linearly with the permittivity nn-linearly with electric ptential 3. The capacitance f a caxial cnductr f length L, having inner radius, a, uter radius, b and permittivity, π L π L π L π L a + b a b ln ln ln (a + b)/ b a 4. If x (t) is an even signal then the cnditin t prve that the prduct f the signals, y(t) is dd and y(t) = y(t) even and y( t) = y(t) dd and y( t) = y(t) even and y(t) = y(t) 5. A cntinuus time signal x(t) is sampled and the peridic impulse train f perid τ is n= given by s(t) = δ ( t nτ ). If ω s is the sampling frequency, then the Furier Transfrm S ( j ω π ) = δ ( kωs ) τ S ( jω ) = π δ ( kωs ) n= n= S ( j ω π ) = δ ( ω kωs ) τ π S ( jω ) = δ ( ωs ) n= τ n= 6. The current thrugh a circuit is expressed as, transfer functin f the circuit is s + s s + 3s + s + 3s + s t i( t) = 3e e 5s + 3s + t. The crrespnding s 5s + + 3s +

6 7. The Z-Transfrm f a discrete time signal x(n) is = n x ( n) z n 0 n= x ( n) z n= n ( n z n= Set - A 6 EE x ) x( n) z 8. The magnetizing reactance f a 4 k/ 400, 50 Hz single-phase transfrmer n lw vltage side is 35 Ω. The magnetizing reactance n the high vltage side is 0.35 Ω 3.5 Ω 350 Ω 3500 Ω 9. At maximum efficiency f a single-phase transfrmer, the lad pwer factr is unity lagging leading zer 30. The per unit I R lsses and per unit reactance f a transfrmer at 0.8 leading pwer factr is 0. and 0.03, respectively. The per unit regulatin f the transfrmer is In star-star cnnectin f 3-phase transfrmer, the triplen harmnics are suppressed by using star cnnected tertiary windings delta cnnected tertiary windings neutral cnductr additinal insulatin fr the phases 3. If tw 3-phase transfrmers with unequal vltage ratis are cnnected in parallel, the result is circulating current n n-lad n circulating current n n-lad dead shrt-circuit equal n-lad secndary emfs 33. In a 6-ple wave wund dc machine the number f cnductrs is 70. The back pitch and cmmutatr segments, respectively, are and 35 and 34 3 and 35 4 and The number f brushes in a 6-ple duble-layer lap wund dc machine is Equalizer rings are used in a dc machine t prvide mechanical balance balance the flux prduced by the ples prvide path fr the circulating currents vercme armature reactin 36. The demagnetizing AT/ple f a 4-ple dc generatr is 480. The number f cnductrs is 480 and the current in each cnductr is 40 A. Then the required brush shift in mechanical degrees In a dc shunt generatr critical field circuit resistance line is the line drawn abve the OCC belw the OCC tangent t the saturatin curve tangent t the linear prtin f OCC 38. A 00 dc mtr takes a field current f A t generate a back emf f 80. If the field winding resistance is 80 Ω, the resistance f the shunt field regulatr is 0 Ω 0 Ω 00 Ω 80 Ω n

7 39. The statr mmf and rtr mmf f a 3-phase inductin mtr are equal rtate with slip speed are ppsite but rtate with synchrnus speed rtate with the same rtr speed 40. The mechanical pwer develped and the rtr cpper lsses f a 3-phase inductin mtr in terms f slip, s are in the rati f s : s s : s + s : s ( s)/s : s 4. In a single-phase inductin mtr the slip with respect t frward and backward rtating magnetic fields, respectively, are s and ( s) s and ( + s) s and ( s) ( s) and ( s) 4. The number f slip-rings in a turb-alternatr are zer T eliminate n th harmnic vltage in the generated vltage f a 3-phase synchrnus generatr, the cil span f the statr winding is π/n π ( /n) π ( + /n) n π ( /n) 44. The rati f air-gap line vltage frm pen-circuit characteristic and armature current frm shrt-circuit characteristic fr a particular value f the field current in a synchrnus generatr is synchrnus reactance synchrnus impedance unsaturated synchrnus reactance unsaturated synchrnus impedance 45. When tw synchrnus machines are cnnected in parallel the synchrnizing pwer tends t accelerate the faster machine retard the faster machine retards the slwer machine pull the faster machine ut f step 46. The maximum pwer transferred by a 3-phase, 400 synchrnus generatr with synchrnus reactance f 5 Ω and at an excitatin vltage f 650 is 5 kw 78 kw 04 kw 5 3 kw 47. The pwer factr f a synchrnus machine is cntrlled by cnnected lad generated vltage field current lad angle 48. In a nn-salient ple synchrnus generatr E csδ X d X d Set - A 7 EE, where = generated vltage, E = back emf, X d = direct axis synchrnus reactance, and δ = lad angle, represents active pwer reactive pwer reluctance pwer ttal pwer

8 49. As the speed increases, the trque develped by a dc serv mtr decrease with a negative slpe increases with a psitive slpe remain cnstant becmes unstable 50. A plant with 0 MW installed capacity prduces an annual utput f 6 remains in peratin fr 000 hurs in a year. The Plant Use Factr is 0.33 % 3.33 % 5 % 30 % 5. In a medium transmissin line, the cmplex A, B, C, D cnstants are related as A = B, C = D A = D, C = 0 AB CD = 0 A = C, B = D 6 0 kwh and 5. The sending end current and receiving end current f a medium transmissin line are (0 j 5) A and (80 j 90) A, respectively. The charging current is (300 j 05) A ( 60 + j 75) A (60 j 75) A 35 A 53. The minimum ptential gradient f a single-cre cable with cre diameter, d, internal sheath diameter, D and the ptential difference between the cnductr and sheath, is D D D D D lg e d lg e d lg e D lg e d d d d 54. The verhead radial distributin is preferred t reduce vltage fluctuatins increase service reliability distribute pwer at lw vltage distribute pwer t lng distances 55. The base k and base MA are halved and the per unit impedance new value is 0.5. The per unit impedance f the riginal circuit element is The necessary cnditin fr an n n Z bus and Y bus matrices is, if Z bus is symmetric, Y bus is diagnal Z bus is diagnal, Y bus is symmetric Z bus is symmetric, Y bus is symmetric Z bus is symmetric, then Ybus is transpse f Z bus 57. In the lad flw analysis, a Jacbian is a matrix f size n n with cnstant elements upper triangular cnstant elements first partial derivative elements secnd partial derivative elements Set - A 8 EE

9 58. In a pwer flw prgram the input and utput data, respectively, at the P k, k and Q k, δ k P k, Q k and k, δ k (C ) k, δ k and P k, Q k P k, δ k and k, Q k 59. The effect f crna is less by using verhead lines f large cnductr size under grund cable f small cnductr size verhead lines having less spacing between cnductrs verhead lines f higher vltages th k lad bus are 60. A synchrnus cndenser is used at the receiving end f a transmissin line fr supplying lagging ka vltage cntrl frequency cntrl maintaining a higher vltage than at the sending end 6. Real pwer flw in transmissin lines is cntrlled by tap changing transfrmer vltage regulating transfrmer phase-angle regulating transfrmer bster transfrmer 6. The injected cmplex pwer fr a given bus system, given Ybus, Zbus, bus vltage fr i =,,.n n m= Y im m i n m= Y im m * i 63. The vltage prfile f a n-bus pwer system can be imprved by cntrlling the lad angles active pwer flws reactive pwer flws cmplex pwer flws 64. Given 3-phase vltages a, b, c, and the transfrmatin matrix ( a = 0 ), T = a a, the matrix equatin fr psitive, negative and zer sequence currents is a a,,0 = T a, b, c,,0 = T a, b, c 3 0,, = T a,,0 = T a, b, c, b, c 65. Tw 3-phase synchrnus generatrs with reactance 60% and 40% feed a fault current f 00 A up t shrt-circuit fault pint. The shrt-circuit current is 00 A 400 A 4000 A 5000 A Set - A 9 EE n m= Z im m * i n m= Y im * m i

10 66. A single-line-t-grund fault n a verhead transmissin line creates vltage sag vltage swell ver vltage vltage flicker 67. Rati relay by using line-t-neutral vltage prtect 3-phase faults duble line faults duble-line-t-grund faults generatr bus earth faults 68. Prtectin f transfrmer frm all types f faults is by using ver current relay differential relay distance relay Buchhlz relay 69. The vltage that appears acrss the cntacts f the circuit breaker after the arc extinctin is called as arc vltage recvery vltage re-striking vltage extinctin vltage 70. Differential relays detect internal faults in 3-phase transfrmers by zer sequence currents psitive sequence currents negative sequence currents bth psitive and negative sequence currents 7. Fr a synchrnus machine swing curve, the lad angle swings between δ min and δ max, if the damping cnstant is equal t zer greater than zer less than zer equal t nrmalized inertia cnstant 7. The breakeven distance fr HDC transmissin is 00 km 50 km 500 km 800 km Abve 000 km 73. A hm-plar HDC link cnsists f single-cnductr with psitive plarity tw cnductrs with ne psitive and anther negative plarity (C ) tw cnductrs having the same plarity with a grund return single cnductr with negative plarity and grund as psitive plarity 74. A static AR cmpensatr is a series cnnected thyristr based cntrller shunt cnnected thyristr based cntrller energy strage device cmbined series shunt cnnected cntrller 75. The Interline Pwer Flw Cntrller in a transmissin system injects vltage by static series cnverters injects current by static shunt cnverters injects vltage and current by the static series and shunt cnverters prvides real and reactive pwer cmpensatin by static shunt cmpensatr Set - A 0 EE

11 + st 76. The system given by the transfer functin, G( s) = + st nn-minimum phase system minimum phase system (C ) system with transprt lag unstable system 77. The clsed-lp transfer functin f unity feedback system with ( K R G s) = and G ( s) = in the frward path is s RCs + KR KRs + s + RC RCs + s RCs + s + KR RC RCs + s + KR KR RCs + s + KR 78. K p K The pen-lp transfer functin f a unity feedback system is. The steady state Ts + errr in the unit-step respnse is Zer + K p K K p K K p K 79. Fr a unity feedback system with a transfer functin G(s) and input R(s), the steady state errr is sr( s) R( s) R( s) lim lim lim lim s 0+ G( s) s 0+ G( s) s 0+ G( s) s 0 s( + G( s)) A system represented by the characteristic equatin s + s + 3s + s + K stable if K > 0 > K > 0 > K > 0 K > is said t be 8. The Nyquist plt f a unity feedback minimum phase system is drawn fr different values f gain, K. The system is stable if the plt des nt enclse the ( + j 0) pint passes thrugh the ( + j 0) pint enclses the ( + j 0) pint passes thrugh the ( + j 0) pint 8. Fr unity feedback cntrl system, the magnitude f G(jω ) at the phase crss-ver frequency, ω is measured as /3 frm the Bde plt. The gain margin is /3 3/ (C ) 4/9 9/4 83. A lag-lead cmpensatr fr a secnd rder system imprves steady state errrs, reduces relative stability marginally imprves steady state errrs, increases relative stability reduces steady state errrs, increases relative stability imprves bth transient respnse and steady state respnse Set - A EE

12 84. The pint f intersectin f tw asympttes in a plt is called crner frequency in unifrm scale crner frequency in lgarithmic scale phase crss-ver frequency in unifrm scale phase crss-ver frequency in lgarithmic scale 85. In the Bde plts, the magnitude and phase angle f the factr ( + j ω T) are 0lg+ jωt, tan 0lg, tan ωt ωt + jωt + jωt, cs ωt 0lg, 0 + jωt 86. Fr the state equatin X & = AX where X = n-vectr and A = n n cnstant matrix. Given the initial state X(0), the slutin f the state equatin At X ( t) = e X (0) X ( t) = A X (0) At X ( t) = e X (0) T X ( t) = A X (0) 87. The mathematical mdel f a system is & y + 3& y + y = u, where u = input, and y = utput. The matrix state equatin fr y = x, is x& x& x& x& 0 = 0 = x 3 x x - 3 x 0 + [ u] x& x& x& x& 0 = 0 = x - 3 x x - 3 x 0 + [ u] 88. The state transitin matrix f a state equatin, X & = AX + Bu ( si A) ( si A) L [ ] [ ] L [( si A) ] L [( A si ) ] 89. Given X & = AX + Bu where A is a matrix and B is a matrix. The cnditin fr cntrllability is AB AB A AB : B [ A : ] [ B : ] [ AB : ] [ ] 90. Given X & = AX + Bu, y = CX where A = matrix, B = matrix and C = matrix. The cnditin fr bservability is * * CAB AB * : A B * * * C : A C [ CB : ] [ ] B : [ B ] [ ] 9. A Wien bridge is used t measure quality factr f a cil audi frequency f a signal capacitance f a capacitr inductance f a cil 9. The full scale range f PMMC vltmeter is 00 and its sensitivity is 000 Ω/. If the meter reads 50, the current thrugh the vltmeter is 0.05 ma 0.5 ma 5 ma 50 ma Set - A EE

13 93. The pwer in a 3-phase lad is measured by tw watt meters. If ne watt meter reads zer, then the lad pwer factr is Zer 0.5 (C ) unity 94. The burden f the instrument transfrmers is A rating secndary winding current secndary winding vltage (secndary winding current) resistance f secndary winding 95. Digital meters are superir ver analgue meters because less expensive utput reading is binary in nature utput impedance is less installatin is easy as panel meters 96. The mst accurate instrument fr measuring phase difference between tw signals is X Y pltter scillscpe phase sensitive detectr electrnic cunter/timer 97. Measurement f pwer by vltmeter and ammeter methd in a circuit resulted in calculated maximum errrs f ± % and ± %, respectively. The likely errr in calculated pwer is ± 3 % ± 0.0 % ±.5 % ± 0. % 98. Majr cause fr creeping in inductin type energy meter is due t nly current cil is energized under cmpensatin fr frictin ver cmpensatin fr frictin ver lading f meter 99. The semicnductr device that perates in the reverse breakdwn regin light emitting dide zener dide field effect transistr biplar junctin transistr 00. The regin cnsisting f hles and electrns near the p-n junctin f a dide is diffusin regin neutral zne recmbinatin regin depletin regin 0. A BJT s vltage stand-ff capability when the base current is zer cllectr-emitter breakdwn vltage minimum cllectr-emitter vltage cllectr-base breakdwn vltage emitter-base vltage 0. The utput vltage change in µs f a certain peratin amplifier is ± 8 in the linear regin. The slew rate is 4 /µs 4 /µs 8 /µs 6 /µs Set - A 3 EE

14 03. The critical frequency f a single-ple active lw-pass filter with RC netwrk is π RC RC πrc π π RC 04. An 8-bit analgue-t-digital cnverter returns fr an analgue input signal a cntinuus set f discrete values 6 discrete values 0 discrete values 8 discrete values 05. The IC used fr : multiplexer is IC 7450 IC 745 IC 7453 IC In a sample-and-hld circuit, the aperture time is time required fllwing a sample time required fr the switch t pen transitin time interval between sample and hld time frm the hld cmmand t the pening f the switch 07. A bi-stable multi-vibratr can be built by using NAND gates AND gates AND r OR gates Excusive-NOR gates 08. Semicnductr devices are prtected by a fuse and the material used is silver gld cpper tin 09. The pwer lss in a transistr is a functin f the prduct f base current and cllectr-emitter vltage cllectr current and base current cllectr current and saturatin vltage cllectr current and cllectr-emitter vltage 0. A TRIAC can be switched int n-state by psitive gate current nly negative gate current nly psitive r negative gate current sinusidal gate current. The cnducting SCR turns-ff when the n-state current is belw the latching current belw the hlding current equal t the reverse leakage current zer Set - A 4 EE

15 . The pwer factr f input surce current f a single-phase semi-cnverter perating at a firing delay angle, α and feeding a dc lad, is cs α cs α unity cs α 3. A fully cntrlled single-phase bridge cnverter is supplied at 0, 50 Hz and the firing delay angle f the SCRs is 45. The average utput lad vltage fr cntinuus current is 0 π 0 π 4. The duty rati f a step-up chpper with an utput vltage f 00 frm a 80 dc surce, is (C ) The fundamental cmpnent f rms utput vltage f a full-bridge single-phase squarewave inverter with dc as input vltage, is 4 π dc π dc Set - A 5 EE 40 π 4 dc π 0 π 4 dc 3π 6. The starting trque f a /f cntrlled inverter-fed 3-phase inductin mtr perating at 5 Hz as cmpared with the same mtr perating at 50 Hz is mre duble equal less 7. Regenerative breaking f ac-dc cnverter fed dc mtr is pssible when firing delay angle f SCRs is (C ) In slip-energy recvery scheme f cnverter-fed 3-phase inductin mtr, super synchrnus speeds are pssible by injecting vltage int the statr injecting vltage int the rtr extracting vltage frm the statr extracting vltage frm the rtr. 9. The vltage cllected by the pantgraph f electric lcmtive is DC vltage single-phase AC, 50 Hz 3-phase AC, 50 Hz single-phase AC, 5 Hz 0. Fast acceleratin and high-speed cruising electric tractin drive mtr is separately excited dc mtr DC series mtr AC series mtr 3-phase squirrel cage inductin mtr

16 SPACE FOR ROUGH WORK Set - A 6 EE