I.E.

S-(OBJ) 1999 1 of 14

ELECTRICAL ENGINEERING

PAPER–II
1. A thermal generating station has an d. 0.1 pu
installed capacity of 15 MW and supplies a 5. A short transmission line has a total
daily load of 10 MW for 12 hours and 5 resistance of 2Ω, reactance of 3Ω, current
MW for remaining 12 hours. The plant of 125 A and pf of 0.8. Regulation in
capacity factor for this station is percentage is equal to
a. 1 a. 1.9
b. 0.75 b. 0.38
c. 0.67 c. 3.8
d. 0.5 d. 0.19
2. Power output (in kW) of a hydro power 6. A star-connected 3-phase 11 kV. 25 MVA
station is equal to (Q = discharge in m3/s, q alternators with its neutral grounded
overall. efficiency of the plant, h = head in through a 0.033 Pu reactance (based on the
m, ω = density of water) alternator rating) has positive negative and
75 Qω h zero-sequence reactance’s of 0.2 pu, 0.1 pu
a.
0.736 η and 0.1 pu respectively. A single line to
ground fault on one of its terminals would
0.736
b. Qω hη result in a fault current of
75 a. 150 MVA
750 Qθη b. 125 MVA
c.
0.736 h c. 100 MVA
0.736 Qhη d. 50 MVA
d.
750 ω 7. Compared to Gauss-Seidel method,
3. Consider following moderators used in Newton-Raphson method takes
nuclear reactors: a. less number of iterations and more
1. Graphite time per iteration
2. Beryllium b. less number of iterations and less time
3. Heavy water per. iteration
Their correct sequence in increasing order c. more number of iterations and more
of their neutron absorption cross-sections time per iteration
is d. more number of iterations and less
a. 1, 3, 2 time per iteration
b. 2, 1, 3 8. An infinite bus of 1 Pu is fed from a
c. 3, 1, 2 synchronous machine having E = 1.1 Pu.
If the transfer reactance between them is
d. 3, 2, 1
0.5 pu, the steady stat? power limit will be
4. 3-phase alternator rated at 50 MVA, 22 kV
a. 1.1 pu
has a synchronous reactance per phase of 5
Pu on its thermal rating. The pu value of b. 0.5 pu
this reactance on a base of 100 MVA and c. 2.2 Pu
220 kV is d. 1 pu
a. 25 pu 9. The positive sequence current for a L - L
b. 12.5 Pu fault of a 2 kV system is 1400 A, and
c. 1 pu corresponding current for a L - L - G fault
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is 2220 A. The zero sequence impedance
of the system is
a. 62.75 Ω
b. 4.5275 Ω
c. 5.275 Ω
d. 0.5275 Ω
10. The inertia constant of a 100 MVA, 50 Hz,
4-pole generator is 10 MJ/MVA. If the
The equivalent capacitor arrangement of a
mechanical input to the machine is
two-string insulator is shown in the above
suddenly raised from 50 MW to 75 MW
figure. The maximum voltage that each
the rotor acceleration will be equal to
unit can withstand should not exceed 17.5
a. 225 electrical degree/s2 kV. The line-voltage of the complete string
b. 22.5 electrical degree/s2 is
c. 125 electrical degree/s2 a. 17.5 kV
d. 12.5 electrical degree/s2 b. 33 kV
11. A surge of 260 kV traveling in a line of c. 35 kV
natural impedance of 500Ω arrives at a d. 37.3 kV
junction with two lines of natural
16. Consider the following statements:
impedances of 250Ω and 50Ω
1. By using bundle conductors in an
respectively. The voltage transmitted in
overhead line, the corona loss is
the branch lines is
reduced.
a. 400kV
2. By using bundle conductors, the
b. 260 kV inductance of transmission line
c. 80 kV increases and capacitance reduces;
d. 40 kV 3. Corona loss causes interference in
12. Insulation coordination of UHV lines adjoining communication lines.
(above 500 kV) is, done based on Which of these statements are correct?
a. lightning surges a. 1 and 2
b. lightning surges and switches surges b. 2 and 3
c. switching surges c. 1 and 3
d. None of the above d. 1, 2 and 3
13. The number of discs in a string of 17. Which one of the following sequences of
insulators for 400 kV ac overhead operations represents the rated operating
transmission line lies in the range of duty cycle of a circuit breaker?
a. 32 to 33 (O - open; C - close; t = 3 sec.; T = 3 mm.)
b. 22 to 23 a. O – t - C0 – T - CO
c. 15 to 16 b. O – CO – t – CO – T – C
d. 9 to 10 c. O – C – T – OC – T
14. The insulation resistance of a single-core d. O – CO – T – CO – T - C
cable is 200 MΩ/km. The insulation 18.
resistance for 5 km length is
a. 40 MΩ
b. 1000 MΩ
c. 200MΩ
d. 8 MΩ
15.
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With the usual notation, the impedance
matrix for the system shown in the above
figure is
⎡3 1 ⎤
a. ⎢ ⎥
⎣1 3⎦
⎡ 3 / 8 −1/ 8⎤ The distribution system shown in the
b. ⎢ ⎥ above figure is to be protected by over-
⎣ −1/ 8 3 / 8 ⎦ current system of protection. For proper
⎡ 6 / 5 4 / 5⎤ fault discrimination, directional over-
c. ⎢ ⎥
⎣ 4 / 5 6 / 5⎦ current relays will be required at locations
a. 1 and 4
⎡5 4⎤
d. ⎢ ⎥ b. 2 and 3
⎣4 5⎦ c. 1, 4 and 5
19. A 3-phase circuit breaker is rated at 2000 d. 2, 3 and 5
MVA, 33 kV; its making current will be
23. If the fault current is 2 kA, the relay
a. 35 kA setting is 50% arid the CT ratio is 400/5,
b. 49 kA then plug setting multiplier will be
c. 70 kA a. 25
d. 89 kA b. 15
20. Line trap at coupling capacitors are used c. 50
for carrier current protection in which d. 12.5
a. line trap has high impedance to 50 Hz 24. A three-phase 11/66 kV, delta/star
signal but low impedance to carrier transformer, protected by Merz-price
current signal whereas a coupling scheme has CT ratio of 400/5 on L.T. side.
capacitor has low impedance to 50 Hz Ratio of C.T. on H.T. side will be equal to
signal but high impedance to carrier
a. 1 : 23
signal
b. 23 : 1
b. line trap has low impedance to 50Hz
signal but high impedance to carrier c. 23 : 3
current signal, whereas a coupling d. 3 : 23
capacitor has high impedance to 50 Hz
signal but low impedance to carrier 25. Which one of the following statements in
signal respect of HVDC transmission line is not
correct?
c. both line trap and coupling capacitor
have low impedance to 50 Hz signal a. the power transmission capability of
but high impedance to carrier current bipolar line is almost the same as that
signal of single circuit ac line
d. both line trap and coupling capacitor b. HVDC link line can operate between
have high impedance to 50 Hz signal two ac systems whose frequencies
but low impedance to carrier current need not be equal
signal c. There is no distance limitation for
21. Four alternators, each rated at 5 MVA, 11 HVDC transmission by UG cable
kV with 20% reactance are working in d. Corona loss is much higher in HVDC
parallel. The short-circuit level at bus bars transmission line
is 26. In a 3-phase converter used in HVDC
a. 6.25 MVA transmission, the three anodes conduct
b. 20 MVA sequentially. Due to overlap caused by the
circuit inductance, two anodes conduct
c. 25 MVA simultaneously during the overlap period
d. 100 MVA The output voltage waveform during this
22. period is the
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a. voltage of the 1st anode, because the firing angle α min = φ where
2nd anode has not completely taken
φ = tan −1 (ω L / R ) .
over
b. mean of the two anode voltages, as Reason (R): In an ac voltage regulator
they conduct together feeding R — L load, control is lost if
c. voltage of the 2nd anode, because the α min < φ .
voltage of this anode is greater than a. Both A and Rare true and R is the
that of the 1st correct explanation of A
d. sum of the 1st and the 2nd anode b. Both A and R are true but R is NOT
voltages, because both the anodes are the correct explanation of A
conducting c. A is true but R is false
27. If, for a given alternator in economic d. A is false but R is true
operation mode, the incremental cost is 32. Assertion (A): A 64 input MUX can be
given by (0.012P +8) Rs./mwh, dPL / dP = built by using eight 8 input multiplexers
0.2 and plant λ = 25, then the power
Reason (R): Any six variable functions can
generation is
always be implemented by a multiplexer
a. 1000 MW with six address lines.
b. 1250 MW a. Both A and Rare true and R is the
c. 750 MW correct explanation of A
d. 1500 MW b. Both A and R are true but R is NOT
28. Load frequency control uses the correct explanation of A
a. proportional controllers alone c. A is true but R is false
b. integral controllers alone d. A is false but R is true
c. both proportional and integral 33. Assertion (A): The input resistance of a
controllers silicon JFET is of the order of tens or
d. either proportional or integral huntlreds of megaohms.
controllers Reason (R): The gate-source junction of
29. Two generators rated at 200 MW and 400 JFET is a reverse biased silicon diode and
MW are operating in parallel. Both the hence only a very small leakage current
governors have a drop of 4%, when the flows through the gate.
total load is 300 MW They share the load a. Both A and Rare true and R is the
as (suffix ‘1’ is used for generator 200 correct explanation of A
MW and suffix ‘2’ is used for generator b. Both A and R are true but R is NOT
400 MW) the correct explanation of A
a. P1 = 100 MW and P2 = 200MW c. A is true but R is false
b. P1 = 150 MW and P2 = 150 MW d. A is false but R is true
c. P1 = 200 MW and P2 = 100 MW 34. Assertion (A): The per unit impedance of a
d. P1 = 200 MW and P2 = 400 MW synchronous machine is the reciprocal of
30. Assertion (A): dc series motors are used short-circuit ratio of the machine
to drive electric locomotives. Reason (R): For the computation of the
Reason (R): dc series motor develop high short-circuit ratio, the field excitation to
torque at high speed. generate rated voltage on open-circuit
a. Both A and Rare true and R is the should be read from the open-circuit
correct explanation of A characteristic of the machine.
b. Both A and R are true but R is NOT a. Both A and Rare true and R is the
the correct explanation of A correct explanation of A
c. A is true but R is false b. Both A and R are true but R is NOT
the correct explanation of A
d. A is false but R is true
c. A is true but R is false
31. Assertion (A): If an ac-voltage regulator is
feeding and R — L ked, the minimum d. A is false but R is true
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35. Assertion (A): The switching function F = b. 22.22 mA, 8.61 mA and 12.3mA
Σ(0 - 3, 12 - 15) does not have a unique c. 28.33 mA, 14.61 mA and 13.33 mA
minimal sum of product form. d. 40 mA, 20 mA and 25 mA
Reason (R) The switching function F = 39. The transition capacitance of a diode is 1
Σ(0 - 3, 7, 12 - 15) has cyclic prime nF and it can withstand reverse potential of
implicants. 400 V.A capacitance of 2 nF which can
a. Both A and Rare true and R is the withstand a reverse potential of 1 kV is
correct explanation of A obtained by connecting
b. Both A and R are true but R is NOT a. two 1 nF diodes in parallel
the correct explanation of A b. six parallel branches with each branch
c. A is true but R is false comprising three 1 nF diodes in series
d. A is false but R is true c. two 1 nF diodes in series
36. Assertion (A): The maximum possible d. three parallel branches with each
output frequency of the basic series branch comprising six 1 nF diodes in
inverter, using SCR’s T1 and T2 is limited series
to the resonant frequency. 40.
Reason (R): Thyristor T2 can only be fired
when thyristor T1 is OFF and vice-versa,
otherwise a dead short-circuit will take
place across the dc supply.
a. Both A and Rare true and R is the
correct explanation of A
b. Both A and R are true but R is NOT
the correct explanation of A The circuit of a class B push-pull amplifier
c. A is true but R is false shown in the above figure. If the peak
d. A is false but R is true output voltage VO is 16 V, the power
37. drawn from the dc source would be
a. 10 W
b. 16 W
c. 20 W
d. 32 W
41. An FET source follower circuit has gm of
2 m band rd of 50 k . If the source
resistance RS is 1 kΩ, the output resistance
of the amplifier will be
A 5 V reference is drawn from the circuit a. 330 Ω
shown in the above figure. If the zener b. 450 Ω
diode is of 5 mV and 5 V, then RZ will be
c. 500 Ω
a. 50 Ω
d. 1 k Ω
b. 500 Ω
42. If the counters of INTEL 8253
c. 5000 Ω (programmable interval timer) are loaded
d. 50000 Ω with a hew value while counting, then
38. A voltage of 200 cos 100 t is applied to a a. the counter will stop counting
half-wave rectifier with a load resistance b. the counter will ignore the new. loaded
of 5 kΩ. The rectifier is represented by an value d continue to count as per
ideal diode in series with a resistance of 1 previous loaded value
kΩ. The maximum value of current, dc c. the counter will start counting
component of current and rms value of backwards
current will be respectively d. counting will restart from the new
a. 33.33 mA, 10.61 mA and 16.67 mA value of count which has been loaded
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43.

In the circuit shown in the above figure,

the value of output ‘vo’ is
a. + 3 V
Assume VBE = 0.7 V and β = 50 for the b. - 3 V
transistor in the circuit shown in the above c. - 7 V
figure. For VCE = 2 V, the value of RB is d. + 7 V
a. 200 kΩ 48.
b. 242 kΩ
c. 283 kΩ
d. 300 kΩ
44. In the shunt series feedback amplifier, the
basic amplifier and the feedback network
are parallel connected at the input and
series connected at the output. The signal
sampled and the summing done will be
The Op-amp in the above circuit shows a
respectively
unity-gain bandwidth of 1 MHz and a
a. current and current dominant pole at 10 Hz. The bandwidth of
b. current and voltage the non-inverting amplifier will be
c. voltage and current a. 10 MHz
d. voltage and voltage b. 1 MHz
45. A transistor amplifier has a voltage gain of c. 250 kHz
50, input resistance of 1 kΩ and output d. 200 kHz
resistance of 40 kΩ. The amplifier is now 49. The speed of rotation of a shaft is
provided 10% negative voltage feedback measured by using a 120 teeth wheel and
in series with the input. With feedback, the an inductive pick up. The reading on a
voltage gain, input resistance and output digital frequency meter is 3000 with a
resistance will be respectively gating period of 10 micro-seconds. The
a. 8,7 kΩ and 3 kΩ shaft speed would be
b. 8.33, 6 kΩ and 6.66 kΩ a. 750 rpm
c. 5.33, 8.33 kΩ and 8.66 kΩ b. 1500 rpm
d. 6.66, 8.86 kΩ and 6.66 kΩ c. 3000 rpm
46. In an inverting amplifier, the two input d. 3600 rpm
terminals of an ideal Op-amp are at the 50. Consider the following statements
same potential because 1. A NAND gate is equivalent to an OR
a. the two input terminals are directly gate with its inputs inverted.
shorted internally 2. A NOR gate is equivalent to an AND
b. the input impedance of the Op-amp is gate with its inputs inverted.
infinity 3. A NAND gate is equivalent to an OR
c. CMRR is infinity gate with its outputs inverted.
d. the open-loop gain of the Op-amp is 4. A NOR gate is equivalent to an AND
infinity gate with its output inverted.
47. Which of these statements are correct?
a. 1 and 2
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b. 2 and 3 Consider the following statements:
c. 3 and 4 The circuit in the above figure is the high
d. 1 and 4 frequency equivalent of a CE amplifier,
51. lithe upper cut-off frequency ωH = 1/ T
where T = RC, then
1. R = RS = rπ
2. R = RS parallel rπ
3. C = Cπ + Cμ
4. C = Cπ + Cμ (1 + gm RL)
Which of these statements are correct?
a. 1 and 3
An Op-amp with an open-loop gain of b. 1 and 4
10,000. Rm =2 kΩ and RO = 5000 is used
c. 2 and 3
in the non-inverting configuration as
shown in the above figure. The output d. 2 and 4
resistance Rof is 55.
a. 250.5 Ω
b. 21 Ω
c. 2 Ω
d. 0.998 Ω
52.
The counter shown in the above figure has
initially Q2Q1 Q0 = 000. The status of Q2
Q1 Q0 after the first pulse is
a. 001
b. 010
Which one of the gates labelled 1, 2, 3 and c. 100
4 in the network shown in the above figure d. 101
is redundant? 56. A system which accepts as M-bit word and
a. 1 establishes the state “1” on one and only
b. 2 one of 2M output lines is called
c. 3 a. decoder
d. 4 b. demultiplexer
53. In a JK flip-flop, J is connected to Q and K c. multiplexer
is connected to Q outputs. The JK flip-flop d. encoder
converrts into a 57. The number of comparators needed in a 4-
a. R — S flip-flop bit flash-type A/D converter is
b. D flip-flop a. 32
c. T flip-flop b. 15
d. clocked R — S flip-flop c. 8
54. d. 4
58. in 8085 microprocessor whenever the POP
H instruction is executed
a. data bytes in the HL pair are stored in
the stack
b. two data bytes at the top of the stack
are transferred to the HL pair
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c. two data bytes at the top of the stack II (their function) and select the correct
are transferred to PC answer:
d. two data bytes horn the HL registers List I
that were previously stored on the A. 8255 A
stack on transferred back to the HL B. 8254
pair
C. 8259
59. A 3-bit resistance ladder D/A (R-2R
D. i 8096
network) has resistor values of R = 10 kΩ
List II
and 20 kΩ. If Vref = 8 V. I0 for a digital
input of 111 will be 1. Interrupt controller
a. 0.1 mA 2. Microcontroller
b. 0.2 mA 3. Counter
c. 0.7mA 4. Pripheral interface
d. 1 mA Codes;
60. Which one of the following is a correct A B C D
statements in connection with commands a. 3 4 2 1
of CMP and CPI b. 4 3 2 1
a. CMP takes less number of m/c cycles c. 4 3 1 2
compared to CP1 d. 3 4 1 2
b. CMP takes more number of m/c cycles 65.
compared to CPI
c. Both CMP and CPI take the same
number of m/c cycles
d. CMP takes either less or the same
number of m/c cycles as compared to
CPI
61. The instruction queue length in INTEL Consider a signal f(x) sampled at t = 0, 1,
8086 and 8088 are 2, 3, ……. as shown in the above figure.
a. 6 bytes in both processors. The expression for the sampled signal is
b. 4 bytes in both processors. a. {f(x).n} where n = number of samples
c. 4 bytes in 8086 and 6 bytes in 8088 b. {f(x)δ(t, n)} where δ(t, n) kronek or
d. 6 bytes in 8086 and 4 bytes in 8088 delta n = 0, 1,2, ………
62. A four-bit BCD(DCBA) for numeral 9 can c. {f(x).Δn} where Δ = constant equal to
be decoded most economically by the sample duration
logic operation d. not possible to write
a. AD 66. If the clock has a frequency of 5 MHz,
b. ABD then the execution time for ADD memory
c. ACD to register instruction using based indexed
relative addressing (result put in register)
d. ABCD required is
63. A program accesses ten continuous
a. 4.8 μs
memory locations. The CPU will take less
time if the addressing mode used is b. 4.9 μs
a. direct c. 5 μs
b. implicit d. 5.1 μs
c. register indirect 67. In conventional AM super heterodyne
d. immediate receivers, the detectors employed to
extract intelligence include
64. Match List I (chips related to
microprocessors and controllers) with List a. peak detectors
b. ratio detectors
 9 of 14
c. phase locked loops a. depends upon the sampling frequency
d. slope detectors employed
68. The characteristic impedance of a b. is independent of the value of n
transmission line with series impedance Z c. decreases with increasing value of n
ohms per unit length and shunt admittance d. increases with increasing value of n
Y mhos per unit length, is given by 74. A PWM signal can be generated by
(Z +Y )
2
a. a. an astable multivibrator
b. a monostable multivibrator
b. ( Z .Y ) c. integrating a PPM signal
c. (Z / Y ) d. differentiating a PPM signal
75. Medium wave radio signal can be received
(Z / Y )
2
d. at far off distances at night because
69. The suitable programmable counter for a. radio waves travel faster at night
8086 microprocessors is b. ground wave attenuation is lower at
a. 8253 chip night
b. 8254 chip c. sky wave is stronger at. Night
c. 8259A chip d. there is no fading at night
d. 8251 chip 76. The fetch and execute instructions are
repeatedly executed by the microprocessor
70. 70. If two stages with noise figures F1 and
until the power is switched OFF The
F2 and gall-is G1 and G2 are cascaded, the
microprocessor enters into a loop
resultant noise figure F will be
described by while power is on do
F −1
a. F1 + 2 begin
G1
fetch the next instruction
F2 − 1 execute this instruction
b. F1 +
G2 end
F1 − 1 These two tasks are sequential. Which one
c. + F2 of the following microprocessors does not
G2
follow this sequence?
F1 − 1
d. + F2 a. 8085
G1 b. Z 80
71. In TV systems, the modulation methods c. 8086
employed for video and audio signals are d. 68000
a. both amplitude modulation 77. Which one of the, following layers is the
b. both frequency modulation service provider for transport layer of OSI
c. respectively amplitude modulation and model?
frequency modulation a. Network layer
d. respectively frequency modulation and b. Session layer
amplitude modulation c. Transport layer of another station
72. For an AM wave having a power of 800 W d. Physical layer
at its carrier frequency and modulation
78. A 4-bit Johnson counter is initialized to
index of 90%, the power content of each
0101. Whenever the state 1011 is reached
side-band is
the counter is reinitialized to 0000 at the
a. 81W next closed active edge. Again when the
b. 162W state 0001 s reached, the counter is
c. 200W initialized back to 0101 at the next clock
d. 400W active edge. The cycle length of the
73. The signal to quantization noise ratio in an counter is
n-bit PCM system a. 6
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b. 8 a. 3 (V + V
1
2
3
2
)
c. 16
d. 32 b. 3V1
79. ⎛ V ⎞
c. 3 ⎜ V1 + 3 ⎟
⎝ 3⎠
V32
d. V12 +
3
82.
1.
An electromechanical energy conversion
device is shown in the above figure. The
instantaneous values of armature induced
emf, bus bar voltage and armature current
are respectively e, v and i, Te, Ta and ωr
present external torque, armature
developed torque and angular velocity of
shaft respectively. Assume that the given 2.
directions of parameters in the figure are
positive. If the device is working in
generating mode then
a. all parameters will have the positive
direction
b. e, v, Te and ωr will have negative
direction and others will remain in 3.
positive direction
c. Ta and i will have negative direction
and others will remain in positive
direction
d. Te and ωr will have negative direction
and others will remain in positive
Three singly-excited electromagnetic
direction
structures are shown in the above figures
80. A torroidal ferromagnetic ring is uniformly labelled 1, 2 and 3 (R - Rotor, S - Stator).
wound with copper wire of certain turns. A The reluctance torque can be developed in
dc voltage V1 is applied across the
a. 1 and 3
winding to cause a uniform flux density in
the ring. If the linear dimensions of the b. 1 alone
ring, number of turns and length of a mean c. 2 and 3
turn are doubled without changing the d. 2 alone
gauge of the wire, the dc voltage required 83. Consider the following statements
to be applied across the new winding to regarding the magnetisation characteristics
produce the same flux density will be of a dc generator:
a. V1/2 1. It represents the variation of field flux
b. V1 with field current.
c. 2V1 2. Variation of open-circuit terminal
d. 4V1 voltage with field current is
81. In a 3-phase star connected generator, if independent of speed.
the fundamental and third harmonic rms 3. It is non-Linear from zero to rated field
voltages in each phase are respectively V1 current.
and V3, the line voltage of he generator 4. It helps to determine critical field
will be resistance at a given period.
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5. It always starts from the origin. d. rich in third harmonic and its
Which of these statements are correct? fundamental would lag the voltage by
a. 1 and 4 less than 90°
b. 1, 2 and 5 89. The zero power factor characteristic for
the Potier’s diagram can be obtained by
c. 2, 3 and 4
loading the alternator using
d. 3 and 5
a. lamp load
84. If two 8-pole & machines of identical
b. synchronous motor
armatures are wound one with lap winding
arid the other with wave winding, then c. water load
a. wave wound machine will have more d. dc motor
rated current and more voltage 90. If all other requirements for parallel
b. lap wound machines will have more operation of transformer are fulfilled,
rated voltage and more current which one of following pairs of three-
phase transformers, with given VECTOR
c. lap wound machine will have more
GROUPS, can be operated in parallel?
rated voltage and less current
a. Y d 1 and Yy 0
d. wave wound machine will have more
rated voltage and less current b. Y d 1 and Dy 11
85. If the speed of a dc motor increases with c. Dd 6 and Dy 1
load torque, then it is a d. Dd 0 and Dy 11
a. series motor 91. When short-circuit test on a transformer is
b. permanent magnet motor performed at 25 V, 50 Hz, the drawn
current ‘I1’ is at a lagging p.f. angle of φ1.
c. differentially compounded motor
If the test is performed at 25 V, 25 Hz and
d. cumulatively compounded motor the drawn current “I2’ is at a lagging p.f.
86. Full-load voltage regulation of a power angle of φ, then
transformer is zero, when power factor of
a. I2 > I1 and φ2 < φ1
the load is neat
a. unity and leading b. I2 > I1 and φ2 < φ1
b. zero and leading c. I2 < I1 and φ2 > φ1
c. zero and lagging d. I2 < I1 and φ2 > φ1
d. unity and lagging 92. A synchronous motor with negligible
armature resistance runs at a load angle of
87. In a single-phase transformer, the
20° at the rated frequency. If supply
magnitude of leakage reactance is twice
frequency is increased by 10%, keeping
that of resistance of both primary and
other parameters constant, the new load
secondary. With secondary short-circuited,
angle will be
the input power factor is
a. 16°
a. 1/ 2
b. 18°
b. 1/ 5 c. 20°
c. 2/ 5 d. 22°
d. 1/3 93. A synchronous motor is running from an
88. If a sinusoidal voltage source is connected infinite bus of voltage Vt in steady-stat, at
to a power transformer, its no-load current about 50% of its rated load with a power-
would be angle δ1, between Vt and Ef (induced
a. sinusoidal and lagging the voltage by voltage). The load is suddenly decreased to
90° 25%. Ef attains its new steady-state power-
angle δ2 with Vt by initially,
b. sinusoidal and lagging the voltage by
less than 90° a. falling behind and making a complete
rotation
c. rich in third harmonic and its
fundamental would lag the voltage by b. advancing and making a complete
90° rotation
 12 of 14
c. falling behind, followed by oscillation 97. A 3-phase induction motor is driving a
about δ2 content torque load of 1 Pu at 5% slip. It
d. advancing, followed by oscillation has a maximum torque of 2 Pu at 10% slip.
about δ2 Torque-speed variation in stable zone is
assumed to be linear. For the stable
94. The two-reaction phasor diagram of a
operation of the motor, the minimum pu
salient-pole synchronous generator is
supply volt- age is approximately
considered, where
a. 0.25
Ia = armature current per phase, X1 =
armature leakage reactance per phase, Xd = b. 0.50
direct-axis synchronous reactance, Xq = c. 0.707
quadrature-axis synchronous reactance and d. 0.80
V = generator terminal voltage, taken as 98. Slip test is performed to determine
reference. a. Slip
The voltage in phase with the direct-axis b. direct axis reactance and quadrature
will be the phasor-sum of axis
a. V + Iara + IaX1 c. positive sequence reactance and
b. V + Iara + IaXd negative sequence reactance
c. V + Iara + IaXq d. sub-transient reactance
d. V + Iara + Ia(Xd + Xq) 99. Match List I (methods of full-load
95. Consider the following statements : The regulation of 25 MVA alternator at 0.8
syunchronous generators used in thermal Power factor lagging) with list II (%
power stations have regulation):
1. cylindrical rotors List I
2. slip rings and brushes A. emf
3. laminated rotor B. mmf
4. stator slots in multiples of 6 C. ZPF
5. 3-phase star connected stator windings List II
Which of these statements are correct? 1. 13%
a. 1, 2, 3 and 4 2. 18%
b. 1, 2, 3 and 5 3. 32%
c. 3, 4 and 5 A B C
d. 1, 2, 4 and 5 a. 3 1 2
96. Match List I with List II and select the b. 1 3 2
correct answer: c. 2 3 1
List I d. 1 2 3
A. Single-phase inductor motor 100. 100. As compared to DOL starting, a cage
B. 3-phase slip ring induction motor induction motor with star-delta starting
C. 3-phase squirrel cage induction motor shall have
List II a. more starting torque
1. Rotor resistance starting b. more starting time
2. Not self-starting c. reduced starting current
3. Auto-transformer starting d. smoother acceleration
Codes; 101. The speed of a 3-phase induction motor is
A B C controlled from 1 pu to 2 pu using a
variable frequency inverter. The equivalent
a. 2 1 3
circuit parameter most likely to vary is
b. 1 2 3
a. stator leakage inductance
c. 2 3 1
b. rotor leakage inductance
d. 3 1 2
c. magnetizing inductance
 13 of 14
d. core loss resistance a. one resistor across the suing
102. b. resistors of different values across each
SCR
c. resistors of the value across each SCR
d. one resistor in series with the string
107. An SCR has half cycle surge current of
rating-of 3000 A for 50 Hz supply. One
cycle urge current rating will be
The phasor diagram of a synchronous
a. 1500 A
machine connected to an infinite bus is
shown i above figure The machine is b. 2121.32A
acting as a c. 4242.64 A
a. generator and operating at a lagging d. 6000 A
power factor 108. The correct sequence of the given devices
b. generator and operating at a leading in the decreasing order of their speeds. of
power factor operation is
c. motor and operating at a leading power a. Power BJT power MOSFET, IGBT
factor SCR
d. motor and operating at a lagging power b. IGBT, power MOSFET, power BJT,
factor SCR
103. Which one of following statements c. SCR, power BJT, IGBT, MOSFET
regarding a capacitor start, capacitor run d. MOSFET, IGBT, power BJT, SCR
single-phase induction motor is correct? 109. Match List I (SMPS topology) with List II
a. One of the capacitors is in the circuit (output voltage) and select the correct
during starting and both are in the answer:
circuit during running List I
b. Both the capacitors are in the circuit A. Boost
during starting and one of them is in B. Buck
the circuit during running
C. Buck-Boost
c. Both the capacitors are in the circuit
D. Isolated Buck-Boost
during starting and running
List II
d. One of the capacitors is in the circuit
during starting and the other is in the 1. VO = VD
circuit during running 2. VO = -VD/1-D
104. ‘Crawling’ is an in4qction motor is due to 3. VO = V/1 - D
a. time harmonics in supply 4. VO = VD/a(1 - D)
b. slip ring rotor A B C D
c. space harmonics produced y winding a. 2 1 3 4
currents b. 3 1 2 4
d. insufficient starting torque c. 2 4 3 1
105. A two-phase servomotor develops d. 3 4 2 1
maximum torque at 110. Commutation overlap in the phase-
a. forward speed of one-half of the controlled ac to dc converter is due to.
synchronous speed a. load inductance
b. backward speed of one-half of the b. harmonic content of load current
synchronous speed c. switching operation in the converter
c. synchronous speed d. source inductance
d. a speed of twice the synchronous speed 111. A three-pulse converter has a freewheeling
106. Static voltage equalization in series- diode across its load. The operating range
connected SCRs is obtained by the use of of the converter is
 14 of 14
a. 0° ≤ α ≤ 150° Full-bridge inverter is shown in the above
b. 60° ≤ α ≤ 120° figure. The maximum rms output voltages
‘Vo’at fundamental frequency is
c. 30° ≤ α ≤ 150°
a. 24 V
d. 180° ≤ α ≤ 360°
b. 33.94 V
112. A single-phase ‘fully controlled Iin’
commutated ac to dc converter operates as c. 43.2 V
an inverter, when d. 48 V
a. 0° ≤ α ≤ 90°’ 117. Which one of the following controls
reduces the size of the transformer in a
b. 90° ≤ α ≤ 180°
switch mode ac power supply?
c. it supplies to a ‘back emf load
a. Resonant control
d. 90° ≤ α ≤ 180°’and there is a suitable b. bidirectional control
dc source in the load circuit
c. PWM control
113. A step up chopper is fed from a 220 V dc
d. Phase control
source to deliver a load voltage of 660 V.
If the non-conduction time of the thyristor 118. The output voltages e1 and e2 of two full-
is 100 μs, the required pulse width will be bridge inverters are added using output
transformer. In order to eliminate the 5th
a. 100 μs harmonic from output voltage, the phase
b. 200 μs angle between e1 and e2 should be
c. 220 μs a. π/3rad
d. 660 μs b. it/4rad
114. In a type -A chopper, given that source c. π/5rad
voltage = 100 V d, ON-period = 100 μs, d. π/6rad
OFF-period = 150 μs and load R = 2Ω, L
119. In single-phase cyclo-converter, if α1 and
=5 mH with back emf E = 10 V connected
in series for continuities conduction, α2 are the trigger angles of positive
average output voltage and average output converter and negative converter, then
current will be respectively a. α1 + α 2 = π / 2
a. 40V and 15 A b. α1 + α 2 = π
b. 66.66 V and 28.33 V c. α1 + α 2 = 3π / 2
c. 60 V and 25 A
d. α1 + α 2 = 2π
d. 40 V and 20 A
115. If an ac chopper is feeding an inductive 120. In a 3-phae to 1-phase cyclo-converter
load, the firing pulse to the SCR employing 6-pulse bridge circuit, if the
a. may have a width equal to turn ON input voltage is 200 V per phase the
time of the SCR fundamental rms value of output voltage
will be
b. should be a series of pulses of short
duration 600
a. V
c. should be a single pulse of long π
duration b. 300 3V
d. should be a train of pulses of duration 300 3
equal to the conduction period of the c. V
SCR π
116. 300
d. V
π