MOCKBOARD 1 Flashcards
no
1
Q
In a distribution system, if the synchronous capacitors are to be used for
improving the power factor, the correct location would be
a. at the sending end
b. at the receiving end
c. in middle of the transmission line
d. none of these
A
at the sending end
2
Q
The phase shift between the current and voltage vectors is
due to the following except one
A. magnet coils
B. electric flat iron
C. power capacitors
D. fluorescent lamp
A
electric flat iron
3
Q
Assuming the constant efficiency transmission, if the voltage is
increased n times, the size of the conductor would be
a. reduced to 1/n2 that of the original
b. increased to n2 that of the original
c. reduced to 1/n that of the original
d. increased to n times that of the original
A
reduced to 1/n2 that of the original
4
Q
Find the average current during the half cycle given the
instantaneous maximum value of 20 amperes.
A. 12.73 amperes
B. 14.14 amperes
C. 20 amperes
D. 10 amperes
A
12.73
5
Q
- If a fixed amount of power is to be transmitted over a certain length wit
fixed power loss, it can be said
a. the volume of conductor required is inversely proportional to the squar
of voltage and that of the power factor of load
b. the volume of the conductor is inversely proportional to voltage and
that of power factor of load
c. the volume of the conductor is proportional to square of the voltage
and directly proportional to power factor of load
d. the volume of the conductor required is proportional to voltage only
A
the volume of conductor required is inversely proportional to the squar
of voltage and that of the power factor of load
6
Q
- The transmission of power by overhead lines is much costlier than the
underground transmission.
a. true
b. false
c. it depends
d. always
A
True
7
Q
- If A, B, C and D are the constants of the medium transmission line,
which of the following relation is correct?
a. AB - CD - -1
b. AD BD - 1
c. BC - AD = -1
d. AC - BD = 1
A
BC - AD = -1
8
Q
- The capacitance in the medium transmission line is
a. lumped
b. distributed over the entire length of line
c. a or b depending on the transmission voltage
d. variable non-linearly over line
A
distributed over the entire length of line
9
Q
- The surge impedance of the underground cable is __
surge impedance of the overhead transmission line.
-__ than the
a. less
b. more
c. equal
d. no relation
A
more
10
Q
- The surge impedance of the long transmission line is given by
a. Zc = V(L/C)
b. Zc - V(Z/Y)
c. Zc - V(Y/Z)
d. Zc - V(R/Y)
A
Zc - V(Z/Y)
11
Q
The approximate surge impedance of a transmission line is
a. L/C
b. LC
c. V(L/C)
d. V(LC)
A
√(L/C)
12
Q
- Ferranti Effect states that under certain conditions the sending end
voltage is
a. less than receiving end voltage
b. greater than receiving end voltage
c. equal to receiving end voltage
d. abnormally high
A
greater than receiving end voltage
13
Q
- If the receiving end voltage is assumed same as the sending end
voltage, and the impedance of the line is the resistance of the line. What
will be the maximum steady state power transmitted over the line?
a. Vr2/Z
b. Vs2
c. zero
d. very high
A
zero
14
Q
- If Vs = VR = 33 kV for three phase transmission and reactance is 13 ohms
per phase. What will be the maximum power transmission per phase?
a. 29 MW
b. 28 MW
c. 30 MW
d. 60 MW
A
28 MW
15
Q
- The size of the feeder is determined primarily by
a. the current it is required to carry
b. the percentage variation of voltage in the feeder
c. the voltage across the feeder
d. the distance over which the transmission is made
A
the current it is required to carry
16
Q
- If the voltage is increased n times, the current in the feeder is reduced
to (for a given power delivered)
a. 1/n times of the original
b. 1/n2 times of the original
c. 1/ n times of the original
d. n times of the original
A
1/n times of the original
17
Q
- The power transmission capacity of the transmission line is
a. proportional to the square of the operating voltage
b. inversely proportional to the voltage
c. proportional to the voltage
d. inversely proportional to the square of the voltage
A
proportional to the square of the operating voltage
18
Q
- The inductive interference between power and communication line
can be minimized by
a. increasing the distance between the conductors
b. transposition of the power line
c. transposition of the communication line
d. using aluminum
A
transposition of the power line
19
Q
- For a 11 kV underground system, it is possible to work upon a length of
a. 800 miles
b. 100 miles
C. 400 miles
d. none of these
A
100 miles
20
Q
- Series capacitors are used to
a. improve line voltage
b. compensate line inductive reactance
c. compensate line capacitive reactance
d. none of these
A
compensate line inductive reactance
21
Q
- A long transmission line is energized at then sending end and is kept
open circuited at the receiving end. The magnitudes of the sending end
voltage Vs and of the receiving end voltage Vr satisfy the following
relationship
a. Vs -Vr - o
b. Vs is greater than Vr
c. Vs is less than Vr
d. Vs =Vr
A
Vs =Vr
22
Q
- Voltage regulation of a short transmission line is
a. always positive
b. always negative
c. either positive, negative, or zero
d. always lagging
A
either positive, negative, or zero
23
Q
- Bundled conductors are used in EHV lines primarily for
a. reducing cost of the line
b. reducing corona loss and radio interference
c. increasing stability limit.
d. reduce internal inductance
A
reducing corona loss and radio interference
24
Q
- In a double-circuit line with hexagonal spacing .
a. The phases are balanced, but the conductors of each individual phase
are not balanced.
b. The conductors of each individual phase are balanced, but the phases
are not balanced
c. The phases, and the conductors of each individual phase are both
balanced
d. Is better for High voltage
A
The conductors of each individual phase are balanced, but the phases
are not balanced
25
46. The Self GMR considering the total effective outside radius method is
used to evaluate:
a. Inductance.
b. Capacitance
c. Inductance and Capacitance both.
d. None of these of the overhead transmission lines.
Capacitance
26
47. In EHV transmission lines, efficiency of transmission can be increased
by decreasing the corona loss. This is achieved by:
a. Increasing the distance between the line conductors.
b. Using bundled conductors.
c. Using thick conductors.
d. Using thin conductors.
Using bundled conductors
27
48. When two conductors are "bundled":
a. The potential gradient in space is increased.
b. Corona losses are eliminated.
c. The potential gradient around them is equivalent to that which would
exist with one large-diameter conductor.
d. Capacitive reactance remains the same
The potential gradient around them is equivalent to that which would exist with one large-diameter conductor.
28
53. Transmission voltages in the range 230 kV - 765 kV are known as
a. High voltage
b. Extra High Voltage
c. Ultra High Voltage
d. Very High Voltage
Extra High Voltage
29
54. Which one of the following statements is false? As the transmission
voltage increases,
a. Corona loss increase
b. Conductor copper loss decreases
c. Cost of insulators, transformers, switches
d. Corona Loss decreases
Corona Loss decreases
30
55. The internal inductance of a solid conductor of radius r and carrying a
current I is equal to
a. 0.5l x 10-7 H/m
b. 0.5l x 10-7 exp(-1/4) x r H/m
C. 0.5 X 10-7 H/m
d. 1.5 | x 10-7 exp(-1/4) x r H/m
0.5 X 10-7 H/m
31
56. Which one of the following statements is not true?
a. The GMD method of finding inductance does not apply to ACSR
conductors
b. Current density in ACSR conductors is not uniform due to skin effect
c. The GMD between two circular areas, each of different diameters, is
equal to the distance between their centers.
d. ACSR is better than TZACSR
ACSR is better than TZACSR
32
57. Expanded ACSR conductors are used
a. To increase the tensile strength of the line
b. To reduce corona loss
c. To reduce I2R loss
d. To minimize galloping
To reduce corona loss
33
58. A conductor with 19 strands, each of same diameter and each having
an inductance of L Henries is used for a transmission line. The total
inductance of the conductor will be
a. L
b. L/361
C. 19L
d. L/19
L/19
34
59. In a double-circuit line with hexagonal spacing .
a. The phases are balanced, but the conductors of each individual phase
are not balanced.
b. The conductors of each individual phase are balanced, but the phases
are not balanced
c. The phases, and the conductors of each individual phase are both
balanced
d. Is better for High voltage
The phases, and the conductors of each individual phase are both
balanced
35
60. Which one of the following statements is true?
a. Skin effect at 50 Hz is negligible for larger diameter conductors but
becomes appreciable for smaller conductor.
b. Skin effect at 50 Hz is negligible whatever the diameter of the
conductor.
c. Resistivity of soil does not have any effect on zero sequence resistance
d. Skin effect at 50 Hz is negligible for the smaller diameter conductors
but becomes appreciable for the larger conductor conductor.
Skin effect at 50 Hz is negligible for the smaller diameter conductors
but becomes appreciable for the larger conductor conductor
36
61. Which one of the following statements is true?
a. Resistance of a conductor decreases and the internal inductance
increases as the frequency is increased
b. Resistance and internal inductance of a conductor both increase with
increase of frequency
c. At UHV the line is inductive
d. Resistance of a conductor increases and the internal inductance
decreases as the frequency is increased
Resistance of a conductor increases and the internal inductance
decreases as the frequency is increased
37
62. The surge impedance of a double-circuit power transmission line is
a. 40 ohms
b. 200 ohms
c. 400 ohms
d. 800 ohms
200 ohms
38
63. The surge impedance of a telephone line is
a. 50 ohms
b. 75 ohms
c. 200 ohms
d. 400 ohms
200 ohms
39
64. Bundle conductors are preferred in EHV transmission lines because
a. It is easy to fabricate thin conductors and combine them to make a
bundle
b. Inductance of the line is reduced, and the corona loss, and radio
Inductance of the line is reduced, and the corona loss, and radio interference
40
65. The percentage regulation of an overhead transmission line can be
zero when the load power factor is
a. Lagging
b. Unity
c. Leading
d. zero
Leading
41
66. Which one of the following statements is true?
a. Skin effect increases the resistance of a conductor ,but proximity effect
decreases the resistance
b. Both skin effect and proximity effect increase the resistance of a
conductor
c. Both skin effect and proximity effect increase the internal inductance of
a conductor
d. Proximity effect is not consider in Medium voltage application
Both skin effect and proximity effect increase the resistance of a
conductor
42
69. Mutual inductance between a three -phase power line and a
telephone line due to third harmonic current in the power line is
a. The algebraic sum of mutual inductances from individual phase wires
b. The arithmetic sum of mutual inductances from individual phase wires
c. Zero
d. Always positive
The arithmetic sum of mutual inductances from individual phase wires
43
78. In a lightly loaded transmission line of such a length that the
capacitive reactance is appreciable, the receiving end voltage
a. Is always less than the sending end voltage
b. May exceed the sending end voltage
c. Is always equal to the sending end voltage
d. zero
May exceed the sending end voltage
44
80. Ferranti effect on long overhead lines is experienced when it is:
a. Lightly loaded.
b. On full load at unity p.f.
c. On full load at o.8 p.f. lag.
d. In all these cases.
Lightly loaded.
45
83. The Self GMD method is used to evaluate:
a. Inductance.
b. Capacitance.
c. Inductance and Capacitance both.
d. None of the above of the overhead transmission lines.
Inductance and Capacitance both.
46
91. Arcing on transmission lines is prevented by connecting a suitable:
a. Circuit breaker.
b. Protective relay.
c. Inductor in the neutral.
d. Capacitor in the neutral.
Capacitor in the neutral.
47
95. When alternating current is passing through a conductor there is a
tendency to the current to crowd near the surface of the conductor. This is
known as
a. corona
b. magnetization
c. skin effect
d. resistivity
skin effect
48
96. When alternating current is passing through a parallel conductor there
is a tendency that there will exist an induced current between the surface
of the conductor. This is known as
a. edge effect
b. proximity efect
c. skin effect
d. Kelvin effect
proximity efect
49
97. The two conductors of a single phase transmission line suspended in
air carry currents in opposite direction. The force per unit length on each
conduct or varies:
a. directly as the distance between the conductors
b. directly as the current in either conductor
c. directly as the square of the current in either conductor
d. inversely as the square of the distance between the conductors
directly as the square of the current in either conductor
50
98. A medium length transmission line problem can be solved using the
_______circuit.
a. exact equivalent
b. nominal wye
c. nominal T
d. any of these
nominal T
51
19. EE Board Exam April 1995
Ideal transformer assumptions do not include
A. no leakage flux
B. no saturation of core
C. zero resistance of the winding
D. zero reactance of the winding
zero reactance of the winding
52
21. REE Board Exam October 1998
Which of the following given below is the eddy current loss not proportional to?
A. square of the thickness
B. square of the frequency
C. square of the load current of the laminated core
D. square of the flux density
square of the load current of the laminated core
53
23. EE Board Exam April 1992
When the emf in the two windings of a transformer are opposite in
direction, the polarity is
A. positive
B. additive
C. negative
D. subtractive
subtractive
54
24. EE Board Exam October 1991
The copper loss of the transformer will
A. not be affected by a change in the power factor
B. decrease with a lowering of the power factor
C. increase with an increase of the power factor
D. increase with the lowering of the power factor
increase with the lowering of the power factor
55
25. EE Board Exam June 1990
Power lost due to alternating magnetization and
demagnetization of the core material
A. copper loss
B. eddy current loss
C. hysteresis loss
D. rheostat loss
hysteresis loss
56
26. EE Board Exam June 1990
In the open circuit test of the transformer the wattmeter
reading is equal to
A. eddy current loss
B. current loss
C. hysteresis loss
D. core loss
core loss
57
30. EE Board Exam June 1990
Transformer connection that can transform threephase
system to two-phase system and vice versa
A. Scott or T-connection
B. open delta
C. autotransformer connection
D. wye-delta connection
Scott or T-connection
58
31. EE Board Exam June 1990
Which transformer has only one winding?
A. distribution transformer
B. power transformer
C. autotransformer
D. isolated winding transformer
autotransformer
59
32. EE Board Exam April 1990
When the primary and secondary windings take the form of a
common ring which is encircled by two or more rings of
magnetic materials distributed around its periphery, the
transformer is termed as
A. grounding transformer
B. regulating transformer
C. core type transformer
D. shell type transformer
shell type transformer
60
36. The main purpose of using core in a transformer is to
A. decrease iron losses
B. prevent eddy current loss
C. eliminate magnetic hysteresis
D. decrease reluctance of the common magnetic circuit
decrease reluctance of the common magnetic circuit
61
37. Transformer cores are laminated in order to
A. simplify its construction
B. minimize eddy current loss
C. reduce cost
D. reduce hysteresis
minimize eddy current loss
62
39. The primary and secondary induce e.m.fs. E1 and Ez in a
two-winding transformer are always
A. equal in magnitude
B. anti-phase with each other
C. in-phase with each other
D. determined by load on transformer secondary
in-phase with each other
63
41. The primary and secondary windings of an ordinary 2-
winding transformer always have
A. different number of turns
B. same size of copper wire
C. a common magnetic circuit
D. separate magnetic circuits
a common magnetic circuit
64
42. In a transformer, the leakage flux of each winding is
proportional to the current in that winding because
A. Ohm's law applies to magnetic circuits
B. leakage paths do not saturate
C. the two windings are electrically isolated
D. mutual flux is confined to the core
leakage paths do not saturate
65
43. In a two-winding transformer, the e.m.f. per turn in
secondary winding is always _..._ the induced e.m.f. power
turn in primary.
A. equal to K times
B. equal to 1/K times
C. equal to
D. greater than
equal to
66
44. In relation to a transformer, the ratio 20:1 indicates that
A. there are 20 turns on primary one turn on secondary
B. secondary voltage is 1/ zoth of primary voltage
C. primary current is 20 times greater than the secondary
current
D. for every 20 turns on primary, there is one turn on
secondary
for every 20 turns on primary, there is one turn on
secondary
67
48. The primary reason why open-circuit test is performed on
the transformer is that it
A. draws sufficiently large no-load current for convenient
reading
B. requires least voltage to perform the test
C. needs minimum power input
D. involves less core loss
draws sufficiently large no-load current for convenient
reading
68
49. No-load test on a transformer is carried out to determine
A. copper loss
B. magnetizing current
C. magnetizing current and no-load loss
D. efficiency of the transformer
magnetizing current and no-load loss
69
50. The main purpose of performing open-circuit test on a
transformer is to measure its
A. Cu loss
B. core loss
C. total loss
D. insulation resistance
core loss
70
51. During short-circuit test, the iron lose of a transformer is
negligible because
A. the entire input is just sufficient to meet Cu losses only
B. flux produced is a small fraction of the normal flux
C. iron core becomes fully saturated
D. supply frequency is held constant
flux produced is a small fraction of the normal flux
71
53. In operating a 400 Hz transformer at 50 Hz
A. only voltage is reduced in the same proportion as the
frequency
B. only kVA rating is reduced in the same proportion as the
frequency
C. both voltage and kVA rating are reduced in the same
proportion as the frequency
D. none of these
only kVA rating is reduced in the same proportion as the
frequency
72
55. Transformers are rated in KVA instead of kW because
A. load power factor is often not know
B. KVA is fixed whereas kW depends on load p.f.
C. total transformer loss depends on voltampere
D. it has become customary
total transformer loss depends on voltampere
73
56. When a 400 Hz transformer is operated its kVA rating is
A. reduced to 1/8
B. increased 8 times
C. unaffected
D. increased 64 times
reduced to 1/8
74
57. At relatively light loads, transformer efficiency is low
because
A. secondary output is low
B. transformer losses are high
C. fixed loss is high in proportion to the output
D. Cu loss is small
fixed loss is high in proportion to the output
75
63. The all-day efficiency of a transformer depends primarily
on
A. its copper loss
B. the amount of load
C. the duration of load
D. both B and C
both B and C
76
64. The marked increase in kVA capacity produced by
connecting a 2 winding transformer as an autotransformer is
due to
A. increase in turn ratio
B. increase in secondary voltage
C. increase in transformer efficiency
D. establishment of conductive link between primary and
secondary
establishment of conductive link between primary and
secondary
77
65. The kVA rating of an ordinary 2-winding transformer is
increased when connected as an autotransformer because
A. transformation ratio is increased
B. secondary voltage is increased
C. energy is transferred both inductively and conductivity
D. secondary current is increased
energy is transferred both inductively and conductivity
78
66. The saving in Cu achieved by converting 2-winding
transformer into an autotransformer is determined by
A. voltage transformation ratio
B. load on the secondary
C. magnetic quality of core material
D. size of the transformer core
voltage transformation ratio
79
68. The essential condition for parallel operation of two 1-Ф
transformer is that they should have the same
A. polarity
B. kVA rating
C. voltage
D. percentage impedance
polarity
80
69. If the impedance triangles of two transformers operating
in parallel are not identical in shape and size, the two
transformers will
A. share the load unequally
B. get heated unequally
C. have a circulatory secondary current even when unloaded
D. run with different power factors
run with different power factors
81
100. REE Board Exam October 1998
Its primary function is to provide ground source
A. zigzag transformer
B. sectionalizer
C. surge arrester
D. tertiary transformer
tertiary transformer
