ONGC Previous Paper 2009 (Source: Engineers Institute)
ELECTRICAL ENGINEERING
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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
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
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
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
The O.C.C. of a shunt d.c. generator is represented by E = 12+66I. If the field resistance is 70 ohms, the noload voltage of the generator will be
1. 144 V
2. 210 V
3. 220 V
4. 288 V
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
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
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
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?
o
o
1, 2 and 3
Only 1 and 2
o
o
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
o experience dynamic braking
o experience regenerative braking
o experience no braking but will slow down due to its inertia
o 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
o 100 h.p. in both cases
o
o
o
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)
A single phase full controlled rectifier can work as inverter, if the firing angle is between
o 0o and 90o
o 60o and 90o
o 90o and 180o
o 0o and 60o
When d.c. voltage is converted to a.c. by an inverter, PWM technique is used to
o control only the output voltage from within the inverter
o control both the output voltage and frequency from within the inverter
o control the output current
o reduce losses in the inverter
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):
o Forward current can continue to flow if the circuit is purely resistive
o Forward current can continue to flow if the circuit is dominantly inductive
o Forward current can continue to flow if the circuit is dominantly capacitive
o Forward current will immediately stop flowing.
Which of the above statements are correct?
Only 4
Only 1
Only 2 and 3
Only 2
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
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
The grading capacitors are provided across the series connected interrupters in EHV circuit breakers for
o reducing short circuit current
o improving power factor
o equalizing distribution of recovery voltage across the interrupters
o preventing inductive current chopping.
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
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 exponent
31. In an N-bus power system with M-PV buses, the size of the Jacobian matrix for load flow calculation is
1. N×N
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
o (Dab + Dbc + Dca)/3
o (Dab * Dbc * Dca)/3
o (Dab + Dbc + Dca)1/3
o (Dab * Dbc * Dca)1/3
41. For calculating fault current for a double line to ground fault in an ungrounded system
o positive, negative and zero sequence networks are connected in series
o positive, negative and zero sequence networks are connected in parallel
o positive and negative sequence networks are connected in parallel
o positive and negative sequence networks are connected in series
42. The unit of R, the regulation constant of turbine speed governor, is
o Hz/MW
o MW/sec
o MW/Hz
o 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
o
o
o
o
44. The pumped storage hydro plants are used as
o Base load plants
o Peak load plants
o Mid-range plants
o 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
o 1 sec period
o 1 min period
o 10 min period
o 1 hr period
46. If a network has b branches and n nodes, then the number of independent KVL equations for the network are
o b-n
o n-b+1
o b-n-1
o b-n+1
47. What will be the value of ZL for maximum power transfer condition in the circuit shown in Fig. Q.47?
o
o
o
o
(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?
o The current and the admittance are maximum at resonance
o The phase angle of the impedance changes from +90o to –90o as the frequency is varied from 0 to ¥
o
o
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
o
o
o
o
zero
50. A two port network is reciprocal and symmetrical, if ABCD parameters satisfy the conditions:
o AB-CD = 1 and A = D
o AD-BC = 1 and A = D
o AC-BD = 1 and A = D
o AD-BC = 1 and B = C
51. Tellegen’s theorem is applicable to
o linear time invariant networks only
o non-linear time invariant network only
o any network satisfying Kirchoff’s current and voltage laws
o 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
o linear element
o irreversible element
o bilateral element
o unilateral element
53. A fundamental cut set contains
o only one tree branch and minimum number of links
o only one link and minimum number of tree branches
o only tree branches
o 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
o
o
o
o
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
o
o
Networks A and B are coupled
A is an active network
o
o
B is a passive network
B is a non-linear network
56. If X×Y= 0 then XÅY is equal to
o X+Y
o
o
o
1
57. The value of base x will be
(101)x + (110)7 = (101)8 + (29)16
o
o
o
o
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
o
o
o
o
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
o Incremented by 2 whenever data is pushed on to stack
o Incremented by 2 whenever data is popped from stack
o Incremented by 1 whenever data is pushed on the stack
o 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
o It is possible only if device is interfaced using memory mapped I/O
o It is possible only if device is interfaced using I/O mapped I/O
o Instead of LDA 0805H, the instruction STA 0805H should be used
o only IN PORT instruction can be used in 8085 A mp.
61. The macro RTL implemented by INR M in 8085 A microprocessor is
o (M)¬ (M) +1
o (H,L)¬(H,L) + 1
o M(H,L) ¬M(H,L) +1
o (H) ¬ (H) + 1, (L) ¬ (L) +1
62. In an 8085 A microprocessor when INTR interrupt, becomes active, the control will be transferred to
o 0024 H memory location
o 003C H memory location
o anywhere in the memory decided by the interrupting device
o 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
o 16
o 4
o 3
o 2
64. The meaning of direct addressing mode is
o
o
o
o
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
o
o
o
o
Zener diode
Esaki diode
Varistor
Varactor
66. The V-I characteristic shown in Fig. Q. 66 is that of
o
o
o
o
PN junction diode
Tunnel diode
Zener diode
Varactor
67. In a four variable V-K Map shown in Fig. simplified expression for X is
o
o
o
o
68. In following circuit assuming voltage drop of LED as 2 V, the LED current when transistor is saturated will be
o
o
o
o
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)
o
o
o
o
-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
o
o
o
o
71. The method of absolute measurement of resistance is
o Ohm method
o Potentiometer method
o Lorenz method
o 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
o absolute instrument
o secondary instrument
o recording instrument
o integrating instrument
73. The current passing through a resistor of (50±0.2)W is (4.0±0.02)A. The limiting error in the computed value of
power will be
o 0.2 %
o 0.4 %
o 0.9 %
o 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
o 40×10–6 N-m
o 20×10–6 N-m
o 40×10–3 N-m
o 20×10–3 N-m
75. In thermocouple element, heat energy transferred to the hot junction is converted to electrical energy by
o Johnson’s effect
o Seebeck effect
o Hall effect
o Faraday’s effect
76. The scale of dynamometer type instrument marked in terms of RMS value would be
o uniform throughout
o non-uniform, crowded near full scale
o non-uniform, crowded at the beginning
o non-uniform, crowded around mid-scale
77. The harmonic distortion percentage is accurately measure with
o V.T.V.M.
o An oscilloscope
o Harmonic distortion meter
o 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?
o 100oC
o 50oC
o 35oC
o 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
o digital ramp converter
o dual slope converter
o successive approximation converter
o 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. Maxwell’s
2. Hay’s
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.
6.
7.
8.
1 and 3 are correct
1 and 2 correct
2 and 3 are correct
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
i.
j.
4
3
B
1
4
C
D
2
2
3
1
k.
l.
1
1
3
3
2
4
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 inertia
B = viscous damping coefficient
K = system gain
The transient response specification which is not affected by variation of system gain is the
a.
b.
c.
d.
peak overshoot
damped frequency of oscillations
setting time
rise time
91. The second order system X = AX has
frequency wn are respectively
a. 0.5 and 1
. The value of its damping factor x and natural
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.
b.
c.
d.
0 £ K £ 40
0 £ K £ 10
0£K£¥
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 > 0
If 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.
2.
3.
dead zone can be classified as single valued non-linearity
hysteresis and backlash can be classified as double valued non-linearity
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
Consider the system
.
The condition for complete state controllability and complete observability is
.
a.
d1 > 0, b2 > 0, b1 and d2 can be anything
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
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
The pole-zero configuration of a phase lead compensating network is given by
.
a.
b.
c.