ONGC Previous Paper 2009
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Transcript of ONGC Previous Paper 2009
ONGC Previous Paper 2009
ELECTRICAL ENGINEERING
1. A single phase transformer is connected to a supply of voltage V and frequency f and is supplying a load, connected across its secondary winding. If the supply voltage is reduced from V to V/2, the flux established in the core will
1. decrease by nearly 50%
2. increase by nearly 50%
3. remain unchanged
4. be affected by amount of load and not by the applied voltage
2. Under magnetic saturation of the core of a transformer, the reactance parameters of its equivalent circuit are affected such that
1. X1 and X2 increase while Xm does not change
2. X1 and X2 do not change while Xm decreases
3. X1 and X2 do not change while Xm increases
4. X1 and X2 decreases while Xm does not change
3. A single phase 2000/200 V, 10 kVA, two winding transformer is reconnected as a step-up autotransformer with 2000 V winding as primary. The kVA rating of the autotransformer shall be
1. 10 kVA
2. 11 kVA
3. 110 kVA
4. 220 kVA
4. The power factor at which power is drawn by a transformer is
1. very low under O.C. test but high under S.C. test
2. high under O.C. test but low under S.C. test
3. low both under O.C. and S.C. tests
4. high both under O.C. and S.C. tests
5. The O.C.C. of a shunt d.c. generator is represented by E = 12+66I. If the field resistance is 70 ohms, the no-load voltage of the generator will be
1. 144 V
2. 210 V
3. 220 V
4. 288 V
6. In d.c. shunt motors, the developed torque is proportional to
1. induced e.m.f.
2. armature current
3. output power
4. line current
7. The speed of a separately excited d.c. motor can be controlled below base speed by (a) armature resistance control and (b) supply voltage control. What happens to the slope of modified speed-torque characteristics under the two methods?
1. It changes in both types of control
2. It remains unchanged in both types of control
3. It remains unchanged in armature resistance control while changes in supply voltage control
4. It remains unchanged in supply voltage control while changes in armature resistance control
8. The polarity of interpoles used in d.c. machines is
1. same as the main pole ahead in generators while opposite of the main pole ahead in motors
2. same as the main pole ahead ion motors while opposite of the main pole ahead in generators
3. same as the main pole ahead in both motors and generators
4. opposite of the main pole ahead in both motors and generators
9. In synchronous generators, examine the following statements about voltage regulation:
1. Synchronous impedance method gives pessimistic results
2. MMF method gives optimistic results
3. In unsaturated machine both methods (synchronous impedance and MMF) give same result
Which of the statements are correct?
1, 2 and 3
Only 1 and 2
Only 3
Only 2 and 3
10. Under symmetrical short circuit of a synchronous generator, the armature reaction is
1. magnetizing
2. demagnetizing
3. cross-magnetising
4. mainly magnetising
11. In synchronous generators, the fifth harmonic in induced emf can be eliminated by using coils show chorded by an angle
1. 9o
2. 18o
3. 27 o
4. 36o
12. In induction motor operation, a slip greater than 1 refers to
1. regenerative braking
2. motoring in reverse direction
3. plugging
4. dynamic braking
13. As the applied voltage to an induction motor, operating under no-load, is reduced to half
1. its speed reduced and stator current increases
2. its speed reduced and stator current also reduces
3. its speed reduces but there is not change in stator current
4. there is no change in speed but stator current reduces
14. A 3-phase induction motor is delivering a load of 10 kW at a lagging p.f. of 0.5. If a 3-phase capacitor bank of 7.3 kVAR is connected at its input, the resulting kVA drawn from supply shall be (approximately)
1. 26.5
2. 24.5
3. 20.0
4. 14.0
15. An electric motor developing a starting torque of 10 Nm starts with a load of 6 Nm at its shaft. If the acceleration at start is 2 rad/sec2 , the moment of inertia of the system must be
1. 2 kg-m2
2. 2 N-m2
3. 0.5 kg-m2
4. 0.5 N-m2
16. A synchronous motor works as a synchronous condenser if
1. underexcited
2. overexcited
3. excited with 100% excitation
4. unexcited
17. In relation to damper bar winding in a synchronous motor, examine the following statements:
1. Damper bars are provided in slots on poles
2. Damper bars improve excitation
3. Damper bars help the motor self start
4. Damper bars minimize hunting.
Which of the statements are correct?
2. 1, 2, 3
3. 2, 3
4. 1, 4
5. 1, 3, 4
18. In large power ratings, synchronous motor is considered superior to induction motor, since
1. it is less expensive
2. its efficiency is better
3. it can be operated at better power factor
4. its speed regulation is superior.
19. An induction motor drive is designed for two speed operation. For this purpose, the motor is provided with two windings on its stator corresponding to 4 poles and 8 poles. While the motor was running on 4 pole winding, a changeover to 8 pole winding is made. The motor will
experience dynamic braking
experience regenerative braking
experience no braking but will slow down due to its inertia
draw dangerously high current
20. A d.c. shunt motor drive of 100 h.p. is run (a) at half the rated speed by armature voltage control and (b) at 1.5 times the rated speed by field control. Its power rating in the two cases shall be modified as
100 h.p. in both cases
50 h.p. in case (a) and 150 h.p. in case (b)
50 h.p. in case (a) and 100 h.p. in case (b)
100 h.p. in case (a) and 150 h.p. in case (b)
21. A single phase full controlled rectifier can work as inverter, if the firing angle is between
0o and 90o
60o and 90o
90o and 180o
0o and 60o
22. When d.c. voltage is converted to a.c. by an inverter, PWM technique is used to
control only the output voltage from within the inverter
control both the output voltage and frequency from within the inverter
control the output current
reduce losses in the inverter
23. A thyristor which is in ON state is to be switched OFF. For this purpose a reverse bias is applied across it. Examine the following statements regarding flow of current from anode to cathode (forward current):
Forward current can continue to flow if the circuit is purely resistive
Forward current can continue to flow if the circuit is dominantly inductive
Forward current can continue to flow if the circuit is dominantly capacitive
Forward current will immediately stop flowing.
Which of the above statements are correct?
Only 4
Only 1
Only 2 and 3
Only 2
24. In a 3-phase full controlled thyristor bridge rectifier operating under continuous conduction mode, each thyristor conducts for
180o and two thyristors conduct at a time
120o and three thyristors conduct at a time
180o and three thyristors conduct at a time
120o and two thyristors conduct at a time
25. A single phase fully controlled rectifier is feeding a d.c. motor. At a = 0o, the armature voltage is 200 V and motor speed is 1000 rpm. Neglecting armature resistance and considering continuous conduction, the armature voltage and speed at a = 60o will be
100 V and 500 rpm
100 V and 1000 rpm
200 V and 500 rpm
100 V and speed will depend upon load
26. The grading capacitors are provided across the series connected interrupters in EHV circuit breakers for
reducing short circuit current
improving power factor
equalizing distribution of recovery voltage across the interrupters
preventing inductive current chopping.
27. The minimum cost operating condition for a thermal plant is that
the larger units should generate more power as compared to smaller units
the smaller units should generate more power as compared to larger units
the incremental cost rate of the units be proportional to their rating
the incremental cost rate of all the units be equal
28. The effect of earth on a three-phase transmission line is to
increase its capacitance and decrease inductance
decrease its capacitance and increase inductance
increase its capacitance without affecting inductance
increase its inductance without affecting capacitance.
29. In case of a transmission line if the voltage regulation is negative, then the load power factor is
1. zero
2. lagging
3. unity
4. leading
30. The voltage gradient at the surface of a cable, having a conductor of radius r and a sheath of radius R, is minimum when
1. R = r/e
2. R = r
3. R =er
4. R = er
where e = natural exponent31. In an N-bus power system with M-PV buses, the size of the Jacobian matrix for load flow calculation is
1. NN
2. (N-M) (N-M)
3. (N-1) (N-1)
4. (N-M-1) (N-M-1)
32. The zero-sequence equivalent circuit of a delta-star transformer, with solidly grounded neutral, is
1. 2. 3. 4. 33. The plug setting multiplier of a 5 Amp. IDMT relay for a fault current of 4000 Amp. and a relay setting of 125%, with a C.T. ratio of 80 will be
1. 1
2. 2
3. 4
4. 8
34. If the cost of electricity generation is to be reduced then
1. the diversity factor and load factor both should be low
2. the diversity factor and load factor both should be high
3. the diversity factor should be high while the load factor should be low
4. the diversity factor should be low and the load factor should be high
35. The coefficients of reflection for voltage and current for an open ended line are respectively
1. -1.0 and -1.0
2. -1.0 and 1.0
3. 1.0 and 1.0
4. 1.0 and -1.0
36. If G is the MVA rating of a synchronous machine with inertia constant H sec. and operating frequency f, then the angular momentum M of the machine, in MJ-sec/electrical degree, is
1. 2. 3. 4. 37. Circular grooves are provided underneath the insulator disc for
1. reducing the weight of the disc
2. improving disc strength
3. increasing cooling of the disc
4. increasing the creepage distance
38. The arc formation in vacuum circuit breaker is initiated by
1. field emission
2. thermal emission
3. photo emission
4. secondary emission
39. The series reactors are used to
1. limit over voltages
2. control Ferranti effect
3. limit fault current
4. improve stability
40. If the spacings Dab, Dbc and Dca between the phases a, b, and c of a three phase transmission line are not equal, then the equivalent spacing Deq can be calculated as
(Dab + Dbc + Dca)/3
(Dab * Dbc * Dca)/3
(Dab + Dbc + Dca)1/3
(Dab * Dbc * Dca)1/3
41. For calculating fault current for a double line to ground fault in an ungrounded system
positive, negative and zero sequence networks are connected in series
positive, negative and zero sequence networks are connected in parallel
positive and negative sequence networks are connected in parallel
positive and negative sequence networks are connected in series
42. The unit of R, the regulation constant of turbine speed governor, is
Hz/MW
MW/sec
MW/Hz
MW-Hz
43. If in a power system the line to line base voltage is VB kV and the 3-phase base MVA is SB, then the base impedance of the system is
44. The pumped storage hydro plants are used as
Base load plants
Peak load plants
Mid-range plants
both (A) and (B)
45. The specified operating criteria for the proper operation of interconnected power system is , that Area Control Error (ACE) must be zero at least once in a
1 sec period
1 min period
10 min period
1 hr period
46. If a network has b branches and n nodes, then the number of independent KVL equations for the network are
b-n
n-b+1
b-n-1
b-n+1
47. What will be the value of ZL for maximum power transfer condition in the circuit shown in Fig. Q.47?
(2-j2)W
(2+j2)W
(3-j2)W
(3+j2)W
48. Which of the following statements does not apply to series RLC circuit?
The current and the admittance are maximum at resonance
The phase angle of the impedance changes from +90o to 90o as the frequency is varied from 0 to
The total stored energy in the circuit is constant at resonance
The power factor is unity at resonance
49. The average value of a sine wave over a full cycle is
zero
50. A two port network is reciprocal and symmetrical, if ABCD parameters satisfy the conditions:
AB-CD = 1 and A = D
AD-BC = 1 and A = D
AC-BD = 1 and A = D
AD-BC = 1 and B = C
51. Tellegens theorem is applicable to
linear time invariant networks only
non-linear time invariant network only
any network satisfying Kirchoffs current and voltage laws
linear time variant network only
52. The circuit element having identical properties for forward and reverse direction of current flow through it, is called a
linear element
irreversible element
bilateral element
unilateral element
53. A fundamental cut set contains
only one tree branch and minimum number of links
only one link and minimum number of tree branches
only tree branches
only links
54. In the circuit shown in Fig. Q. 54 if the switch is opened at t = 0 and the initial current through the switch and L1 is 10 A, then the current i(t) and the voltage v(t) of t > 0 are
0 A, 0 V
0 A, V
6 A, 12 V
10 A, 20 V
55. The Thevenin and Norton equivalents of network A at points X, Y (Fig. Q.55) can not be found if
Networks A and B are coupled
A is an active network
B is a passive network
B is a non-linear network
56. If XY= 0 then XY is equal to
X+Y
1
57. The value of base x will be
(101)x + (110)7 = (101)8 + (29)16
2
7
8
10
58. Consider the counter circuit shown in Fig. Q.58.
If the present state QA QB of the counter is QA = 1 & QB = 0, the next state of the counter will be
QA = 1, QB = 1
QA = 1, QB = 0
QA = 0, QB = 1
QA = 0, QB = 0
59. In 8085 A mp, stack pointer is a 16 bit register which is
Incremented by 2 whenever data is pushed on to stack
Incremented by 2 whenever data is popped from stack
Incremented by 1 whenever data is pushed on the stack
Neither incremented nor decremented a result of PUSH and POP operation
60. The instruction LDA 0805H is used to input a data from an I/O device. Choose the correct statement
It is possible only if device is interfaced using memory mapped I/O
It is possible only if device is interfaced using I/O mapped I/O
Instead of LDA 0805H, the instruction STA 0805H should be used
only IN PORT instruction can be used in 8085 A mp.
61. The macro RTL implemented by INR M in 8085 A microprocessor is
(M) (M) +1
(H,L)(H,L) + 1
M(H,L) M(H,L) +1
(H) (H) + 1, (L) (L) +1
62. In an 8085 A microprocessor when INTR interrupt, becomes active, the control will be transferred to
0024 H memory location
003C H memory location
anywhere in the memory decided by the interrupting device
0034 H memory location
63. In an 8255 programmable peripheral interface both the groups are programmed in made 0. The possible number of combination in which the ports can be programmed is
16
4
3
2
64. The meaning of direct addressing mode is
The address of operand is available in register pair
The address of operand is available in PC
The data is directly available in the instruction itself
The address of the operand is available in the instruction itself.
65. The schematic symbol shown in following Fig. Q. 65 is that of
Zener diode
Esaki diode
Varistor
Varactor
66. The V-I characteristic shown in Fig. Q. 66 is that of
PN junction diode
Tunnel diode
Zener diode
Varactor
67. In a four variable V-K Map shown in Fig. simplified expression for X is
68. In following circuit assuming voltage drop of LED as 2 V, the LED current when transistor is saturated will be
12 mA
9.7 mA
6 mA
5.8 mA
69. In the following circuit the collector voltage VC is (assume VBE = 0.7 V)
-17.4 V
5.6 V
12.3 V
17.4 V
70. From the following V-K map the simplified expression for Z is
71. The method of absolute measurement of resistance is
Ohm method
Potentiometer method
Lorenz method
Rayleigh method
72. The instrument which gives the value of the quantity to be measured in terms of instrument constants and its deflection is called the
absolute instrument
secondary instrument
recording instrument
integrating instrument
73. The current passing through a resistor of (500.2)W is (4.00.02)A. The limiting error in the computed value of power will be
0.2 %
0.4 %
0.9 %
1.4 %
74. The coil of an instrument has 40 turns. The mean length of the coil is 25 mm and the axial length of the coil is 20 mm. If the flux density is 0.1 T and the coil current is 20 mA, the torque on the moving coil will be
40106 N-m
20106 N-m
40103 N-m
20103 N-m
75. In thermocouple element, heat energy transferred to the hot junction is converted to electrical energy by
Johnsons effect
Seebeck effect
Hall effect
Faradays effect
76. The scale of dynamometer type instrument marked in terms of RMS value would be
uniform throughout
non-uniform, crowded near full scale
non-uniform, crowded at the beginning
non-uniform, crowded around mid-scale
77. The harmonic distortion percentage is accurately measure with
V.T.V.M.
An oscilloscope
Harmonic distortion meter
Square wave generator
78. A thermometer has a time constant of 3.5 s. It is quickly taken from a temperature 0oC to water bath at 100oC. What temperature will be indicated after 1.5 s?
100oC
50oC
35oC
15oC
79. A digital voltmeter employees an ADC which requires a start pulse, uses an analog comparator and has a relatively fixed conversion time independent of applied voltage. The ADC is
digital ramp converter
dual slope converter
successive approximation converter
flash type
80. In measurements made using Q-meter, impedance elements should be connected in
1. star
2. delta
3. series
4. parallel
81. The measured values of iron losses of a magnetic specimen are 15 W and 25 W at, 40 Hz and 60 Hz respectively at constant flux density. The respective hysteresis and eddy current losses at 50 Hz are
1. 14.584 W and 5.208 W
2. 7.5 W and 12.5 W
3. 5.208 W and 14.548 W
4. 5 W and 10 W
82. The most common and best bridge method for precise measurement of inductance over a wise range is
1. Maxwells
2. Hays
3. Wien
4. Anderson
83. The AC bridge that can be used for accurate determination of excitation frequency is
1. Wien bridge
2. Schering bridge
3. Anderson bridge
4. De Sauty bridge
84. A thermo-couple arrangement is to be used to measure temperature in the range of 700-800oC. Point out the pair that would be most suitable for this application
1. Copper-constantan
2. Chromel-alumel
3. Platinum-platinum rhodium
4. Iron-constantan
85. Rotameter is employed for measuring
1. flow
2. rotation
3. specific gravity
4. viscosity
86. Consider the following statements regarding the stability of a control system
1. Gain margin and phase margin are negative
2. Gain margin and phase margin are positive
3. All roots of characteristic equation must lie in left half of s-plane
4. Gain margin is positive and phase margin is negative
Out of these statements
5. 1 and 3 are correct
6. 1 and 2 correct
7. 2 and 3 are correct
8. 3 and 4 are correct
87. In the feedback system shown below, if the steady state error for a step input is 0.05, then the value of K is
1. 0.05
2. 0.95
3. 1.9
4. 19
88. Match List I with List II and select the correct answer using the codes given below the lists:
List I (Location of poles on s-plane)1. 2. 3. 4. List II (Impulse Response)5. 6. 7. 8. Codes: A B C D
i. 4 1 2 3
j. 3 4 2 1
k. 1 3 2 4
l. 1 3 4 2
89. The Nyquist plot for a control system is shown in Fig. Q.89. The Bode plot of |G| for the same system will be
a. b. c. d. 90. A unity feedback second order control system is characterized by where J = moment of inertiaB = viscous damping coefficientK = system gainThe transient response specification which is not affected by variation of system gain is the
a. peak overshoot
b. damped frequency of oscillations
c. setting time
d. rise time
91. The second order system X = AX has . The value of its damping factor x and natural frequency wn are respectively
a. 0.5 and 1
b. 1 and 1
c. 0.707 and 2
d. 1 and 2
92. A negative unit feedback system has forward path transfer function as Ks/(s2+2s+25). The break in point(s) of root locus occur at
a. s=5
b. s=-5
c. both A & B
d. s = 25
93. In an electrical analog of mechanical system of rotational motion, using torque-voltage analogy, inertial and viscous damper are respectively analogous to
a. Inductance and capacitance
b. Capacitance and resistance
c. Inductance and resistance
d. Capacitance and inductance
94. The characteristic equation of a feedback system is given by
For this system, stable closed loop behavior can be ensured when gain K is such that
a. 0 K 40
b. 0 K 10
c. 0 K
d. 0 K 20
95. The eigen values of the matrix are
a. (a+1), 0
b. a, 0
c. (a-1), (a-1)
d. 0, 0
96. A first order linear system is initially relaxed. For a unit step signal u(t), the response of the system is
(1-e-3t), t > 0If a signal 3. u(t) + d(t) is applied to the same initially relaxed system, the response will be
a. 3(1-e-3t) .u(t)+ e-3t. d(t)
b. (1-3e-3t) .u(t)
c. 3(1+e-3t) .u(t)
d. 3.u(t)
97. Consider the following statements regarding the non linear system
1. dead zone can be classified as single valued non-linearity
2. hysteresis and backlash can be classified as double valued non-linearity
3. Coulomb friction can be classified as double valued non-linearity
Out of these statements
d. 1 and 3 are correct
e. all three are correct
f. 1 and 2 are correct
g. 2 and 3 are correct
a. Consider the system
.The condition for complete state controllability and complete observability is
. d1 > 0, b2 > 0, b1 and d2 can be anything
a. d1 > 0, d2 > 0, b1 and b2 can be anything
b. b1 > 0, b2 > 0, d1 and d2 can be anything
c. b1 > 0, b2 > 0, d1 < 0 and d2 can be anything
a. The semilog plot of gain characteristic (BODE plot) of a network is shown in the Fig. Q.99.
The gain cross over frequency wc is
. 20 rad/sec
a. 30 rad/sec
b. 40 rad/sec
c. 25 rad/sec
a. The pole-zero configuration of a phase lead compensating network is given by
. a. b. c.