POWER SYSTEMS MCQS
1)
A 3-ph, 4-wire system is commonly used for
a) primary
distribution
b) secondary
distribution
c) primary
transmission
d) secondary
transmission
ANS: B
2)
The rated voltage of a 3-ph power system is given as
a) rms
phase voltage
b) peak
phase voltage
c) rms
line to line voltage
d) peak
line to line voltage
ANS: C
3)
Which of the following is usually not the generating voltage
a) 6.6kv
b) 9.9kv
c) 11kv
d) 13.2kv
ANS: B
4)
In a transmission system the feeder supplies power to
a) Transformer
substation
b) Service
mains
c) Distribution
d) All
of the above
ANS: C
5)
Feeder is designed mainly from the point of view of
a) Its
current carrying capacity
b) Voltage
drop in it
c) Operating
voltage
d) Operating
frequency
ANS: A
6)
Distributers are designed from the point of view of
a) Its
current carrying capacity
b) Operating
voltage
c) Voltage
drop in it
d) Operating
frequency
ANS: C
7)
Transmission and distribution of electric power by underground system is
superior to overhead system in respect of
a) Appearance
and public safety
b) Maintenance
cost
c) Frequency
of faults, power failure and accidents
d) All
of the above
ANS: D
8) By increasing the transmission voltage double of
its original value, the same power can be despatched keeping the line loss
a) Equal
to its original value
b) Half
of original value
c) Double
the original value
d) One-forth
of original value
ANS: D
9)
In a transmission system, the weight of copper used is proportional to
a) E2
b) E
c) 1/E2
d) 1/E
ANS: C
10)
The volume of copper required for an ac transmission line is inversely
proportional to
a) Current
b) Voltage
c) Pf
d) Both
(b) and (c)
ANS: D
11)
Improving power factor
a) Reduces
current for a given output
b) Increases
losses in line
c) Increases
the cost of station equipment
ANS: A
ANS: A
12)
which of the following distribution systems is preferred for good efficiency
and high economy
a) Single-phase,
2-wire system
b) 2-ph,
3-wire system
c) 3-ph,
3-wire system
d) 3-ph,
4-wire system
ANS: D
13)
The approximate cost ratio of a 220 kv, underground cable transmission and
220kv/ O/H transmission is
a) 50
b) 25
c) 13
d) 5
Ans: C
14)
The main reason for using high voltage for long distance power transmission is
a) Reduction
in transmission losses
b) Reduction
in time of transmission
c) Increase
in system reliability
d) None
of the above
ANS: A
15)
66 kv is suitable for transmission of power over
a) 30km
b) 60km
c) 120km
d) 200km
ANS: B
16)
If 3 MW power is to be transmitted over a distance of 30km, the desired
transmission voltage will be
a) 11kv
b) 33kv
c) 66kv
d) 3.3kv
ANS: C
17)
The highest transmission voltage used in India is
a) 400
kv
b) 220
kv
c) 132
kv
d) 765
kv
ANS: D
18)
For high-voltage transmission lines, conductors are suspended from towers so as
to
a) Increase
clearance from ground
b) Reduce
clearance from ground
c) Take
care of increase in length
d) Reduce
wind and snow effects
ANS: A
19)
The wooden poles well impregnated with creosote oil or any preservative
compound have life of
a) 25-30
years
b) 20-25
years
c) 10-15
years
d) 5-10
years
ANS: A
20)
Steel poles for transmission lines need protection against
a) Borer
b) Termites
c) Corrosion
d) All
of the above
ANS: C
21)
RCC poles usually have the spans of
a) 250-400
m
b) 80-150
m
c) 50-80
m
d) 25-50
m
ANS: B
22)
In india for distribution of electric power we usually use
a) Wooden
poles
b) Steel
poles
c) RCC
poles
d) Both
(b) and (c)
ANS: D
23)
Conductors used in ht transmission lines are stranded because of
a) Increased
tensile strength
b) Ease
in handling
c) Cheaper
in cost
d) Reduced
resistivity
ANS: B
24)
Which of the following properties has got higher value for aluminium in
comparison to that of copper
a) Electrical
resistivity
b) Melting
point
c) Thermal
conductivity
d) Specific
gravity
ANS: A
25)
ACSR is used in place of copper in overhead lines because of
a) Higher
current carrying capacity
b) Being
lighter in weight
c) Economy
d) Higher
tensile strength
ANS: C
26)
ACSR conductors have
a) All
conductors made of aluminium
b) Outer
conductors made of aluminium
c) Inner
conductors made of aluminium
d) No
conductors made of aluminium
Ans: B
27)
The function of steel wire in an ACSR conductor is to
a) Compensate
for skin effect
b) Take
care of surges
c) Provide
additional mechanical strength
d) Reduce
inductance
ANS: C
28)
The material used for the manufacture of ground wire is
a) Aliminium
b) Galvanized
steel
c) Cast
iron
d) Stainless
steel
ANS: B
29)
Guy wire is employed for
a) Providing
protection against surges
b) Providing
emergency earth route
c) Supporting
the pole
d) All
of the above
ANS: C
30)
Effect of temperature rise in overhead lines is to
a) Increase
the sag and decrease the tension
b) Decrease
the sag and increase the tension
c) Increase
both
d) Decrease
both
ANS: A
31)
The sag of a transmission line conductor in summer is
a) Less
than that in winter
b) More
than that in winter
c) Same
as in winter
d) More
than that in winter
32)
In a transmission line sag depends upon
a) Span
length
b) Tension
in conductor
c) Weight
of the conductor per unit length
d) All
of the above
ANS: D
33)
Wind loading in coastal regions in the range of
a) 40-50
kg/m2
b) 150
kg/m2
c) 96
kg/m2
Ans: B
34)
Stringing chart is useful
a) For
finding the sag in the conductor
b) In
the design of tower
c) In
the design of insulator string
d) Finding
the distance between towers
Ans: A
35)
Which type of insulators is used on 132 kv transmission lines
a) Pintype
b) Disc
type
c) Shackle
type
d) Pin
and shackle type
Ans: B
36)
Post type insulators are generally used in lines operating
a) Above
100 kv
b) Below
33 kv
c) At
any voltage level, hv or ehv
Ans: C
37)
The number of discs in a string of insulators for 400 kv ac overhead
transmission line lies in the range of
a) 32
to 33
b) 22
to 23
c) 15
to 16
d) 9
to 10
ANS: B
38)
The voltage across the various discs of a string of suspension insulators
having identical discs is different due to
a) Surface
leakage currents
b) Series
capacitance
c) Shunt
capacitance to ground
d) Series
and shunt capacitances
ANS: C
39)
The string efficiency of a string of suspension insulators is dependent on
a) Size
of the insulators
b) Number
of discs in the string
c) Size
of tower
ANS: B
40)
The string efficiency of a high-voltage line is around
a) 100%
b) 80%
c) 40%
d) 10%
ANS: B
41)
The ratio of puncture voltage to the flash-over voltage of a line insulator is
a) Equal
to 1
b) Lower
than 1
c) Much
greater than 1
ANS: C
42)
The insulator may fail due to
a) Flash
over
b) Short-circuits
c) Deposition
of dust
d) Any
of the above
ANS: D
43) Corona is
a)
Partial breakdown of air
b)
Complete breakdown of air
c)
Sparking between lines
ANS: B
44) Corona loss in a transmission line is dependent
on
a)
Diameter of a conductor
b)
Material of the conductor
c)
Height of the conductor
ANS: A
45) Hollow conductors are used in transmission lines
to
a)
Reduce weight of copper
b)
Improve stability
c)
Reduce corona
d)
None of the above
ANS: C
46) In hv transmission, the spacing between
subconductors of a bundle is approximately
a)
20cm
b)
40cm
c)
60cm
d)
3.5cm
ANS: B
47) For a standard conductor the ratio of GMR to
actual radius is
a)
Equal to 1
b)
More than 1
c)
Equal to 0.7788
d)
Less than 0.7788
ANS: C
48) Transmission lines are transposed to
a)
Reduce corona loss
b)
Reduce skin effect
c)
Prevent interference with neighbouring
telephone lines
d)
Prevent short-ckt between any two lines
ANS: C
49) Transposition of transmission line is done to
a)
Reduce line loss
b)
Reduce skin effect
c)
Balance line voltage drop
d)
None of the above
ANS: C
50) Which of the following is neglected while
analyzing the performance of transmission line of
a)
50 km length
b)
150 km length
c)
250 km length
d)
All of the above
ANS: C
51) The capital cost on a HVDC converter is
a)
Less than ac substation
b)
More than ac substation
c)
Same as that of ac substation
ANS: B
52) In an HVDC link, power flows
a)
From rectifier end to the inverter end
b)
From the inverter end to the rectifier
end
ANS: A
53) HVDC transmission needs
a)
Pulse converters
b)
Dc generators
c)
Ac filters
d)
Dc filters
ANS: A
54) The pu impedance of a line to 50 MVA, 132 kv
base is 0.4, the pu impedance to a 100 MVA, 132 kv base will be
a)
0.2
b)
0.4
c)
0,8
d)
1.6
ANS: C
55) A dc line carries
a)
Less power than an equivalent ac line
b)
More power than the ac line
c)
Same power as an ac line
ANS: B
56) In the case of an HVDC system, there is
a)
Charging current but no skin effect
b)
No charging current but skin effect
c)
Neither charging current nor skin effect
d)
Both charging current and skin effect
ANS: C
57) For bulk power transmission over long distance
HVDC transmission is
a)
Is economically and technically superior
to ac transmission
b)
Not good alternative to ac transmission
c)
Not economically viable
ANS: A
58) Bulk power transmission over long HVDC lines are
preferred an account of
a)
Low cost of an HVDC terminal
b)
No harmonic problem
c)
Minimum line power losses
d)
Simple protection
ANS: C
59) As compared to ac transmission dc transmission
is free from
a)
Inductance
b)
Capacitance
c)
Phase displacement
d)
All of the above
ANS: D
60) Insulation coordination for UHV lines (above 500
kv) is done based on
a)
Lightning surges
b)
Lightning surges and switching surges
c)
Switching surges
d)
None of the above
ANS: C
61)
The most accurate and versatile method of achieving reactive power compensation
is by using
a) Switched
capacitors
b) Fixed
capacitor with controlled reactor
c) Saturable
reactor with capacitor bank
d) Switched
capacitor with controlled reactors
ANS: D
62)
Series capacitors
a) Increase
the power transmission capability of an EHV long line
b) Provide
voltage control
c) Increase
the shunt admittance of the line
ANS:
A
63)
Series capacitor is used in a transmission line to
a) Compensate
the voltage drop
b) Reduce
line loss
c) Limit
short ckt current
d) Improve
load power factor
ANS: A
64)
With bundled conductors
a) The
corona inception voltage increases
b) The
corona inception voltage decreases
c) The
corona inception voltage remain unaffected
ANS: A
65)
The conductor of an EHV line is selected on the basis of
a) Current
carrying capacity
b) Corona
and RI performance
c) Line
voltage
d) none
of these
ANS: B
66) frequency of resonant vibration lies in the range of
a) 10-20
hz
b) 100-200
hz
c) 50-100
hz
d) 200-300
hz
ANS: C
67)
On what basis is the insulation level of a 400 kv, EHV overhead transmission
line decided?
a) Lightning
over voltage
b) Corona
inception voltage
c) Switching
over voltage
d) Radio
and TV interference
ANS: C
68)
In order to reduce the inductive interference to parallel communication
circuits to the minimum
a) The
conductors are transposed at regular intervals
b) Bundle
conductors are used
c) Thick
conductors are used
d) Either
(a) or (b)
ANS: D
69)
Extra high voltage transmission means
a) Voltage
less than 400kv
b) Voltage
in the range of 400-750kv
c) Voltage
grater than 750
ANS: A
70)
Bundled conductors are used for EHV transmission lines primarily for reducing
the
a) Corona
loss
b) Surge
impedance
c) Voltage
drop across the line
d) None
of the above
ANS: A
71)
The medium sized induction motor will operate at minimum power factor while
operating at
a) Full
load
b) 50%
full load
c) 25%
full load
d) Any
load
ANS: A
72)
An industrial installation has a power factor of 0.8 lagging. It would be
economical to improve p ftp
a) Unity
b) About
0.8 leading
c) About
0.95 lagging
d) About
0.95 leading
ANS: C
73)
The most economical limit of power factor correcting is governed by
a) Original
power factor
b) Relative
costs of the supply and power factor correction equipment
c) Both
a and b
d) None
of the above
ANS: B
74)
Advantage of the improved power factor are
a) Increase
in operating efficiency of the power system
b) Improvement
in voltage regulation
c) Reduction
in overall cost per unit
d) Better
utilization of kw capacities of prime movers, transformers, switchgear and the
lines
ANS: D
75)
For power factor improvement static capacitors have the drawback of
a) Short-service
life
b) Getting
damaged by high voltage
c) Not
repairable
d) All
of the above
ANS: D
76)
For power factor improvement static capacitors have the advantage of
a) Small
losses
b) Easy
installation
c) Low
initial cost and little maintenance
d) All
of the above
ANS: D
77)
Static capacitors are rated in terms of
a) kVAR
b) kW
c) kVA
d) kWh
ANS: A
78)
For a consumer the most economical power factor is usually
a) 0.25-0.5
lagging
b) 0.25-0.5
leading
c) 0.85-0.95
lagging
d) 0.85-0.95
leading
ANS: C
79)
The primary reason for low power factor is owing to installation of
a) Synchronous
motors
b) Dc
motors
c) Induction
motors
d) Commutator
furnaces
ANS: A
80)
Low power factor is usually not due to
a) Discharge
lamps
b) Incandescent
lamps
c) Arc
lamps
d) Induction
furnaces
ANS: B
81)
Doherty rate tariff is applied to
a) Domestic
consumers
b) Medium
industrial consumers
c) Bulk
supplies
d) Municipal
loads
ANS: C
82)
The penalty for low power factor is imposed on
a) Residential
and commercial consumers
b) Industrial
consumers
c) Agricultural
consumers
d) All
of the above
Ans: B
83)
Two part tariff is charged on the basis of
a) Connected
load
b) Units
consumed
c) Maximum
demand
d) Both
a and b
ANS: D
84)
Domestic consumers are usually charged
a) Flat
demand tariff
b) Block
rate tariff
c) Flat
rate tariff
d) Off
peak tariff
ANS: B
85)
Flat rate tariff can be charged on the basis of
a) Connected
load
b) Units
consumed
c) Maximum
demand
d) Both
a and b
Ans: B
86)
As the load factor of a generating plant increases, the generation cost per kWh
generated
a) Reduces
the installation cost
b) Increases
the installation cost
c) Does
not effect the installation cost
ANS: A
87)
A power plant has a maximum demand of 15 MW, The load factor is 50% and the
plant factor is 40%, The operating reserve is
a) 3.75
MW
b) 3
MW
c) 6
MW
d) 7
MW
ANS: A
88)
The power which must be available ever under emergency conditions is known as
a) Spinning
reserve
b) Cold
reserve
c) Firm
reserve
d) Hot
reserve
ANS: C
89)
The knowledge of diversity factor helps in computing
a) Plant
capacity
b) Average
load
c) Units
(kWh) generated
d) Peak
demand
ANS: A
90)
Diversity factor * maximum demand is
a) Average
demand
b) Sum
of consumers maximum demand
c) Installed
capacity
d) Generated
power
ANS: B
91)
The power system experiences peak demand from
a) Midnight
to 8 A.M.
b) 8
A.M. to 2 P.M.
c) 2
P.M. to 6 P.M.
d) 6
P.M to 10 P.M.
ANS: D
92)
During which season the load on a power system is maximum
a) Autumn
b) Rainy
c) Summer
d) Winter
ANS: C
93)
The load duration curve for unity load factor will be of
a) Rectangular
shape
b) Triangular
shape
c) L-shape
d) I-shape
Ans: A
94)
Load curve of power generating station is of always
a) Negative
slope
b) Zero
slope
c) Positive
slope
d) Any
combination of a, b, and c
ANS: D
95)
The efficiency of a boiler used in a
modern steam power plant is of the order of
a) 30%
b) 50%
c) 85%
d) 100%
ANS: C
96)
In bleeder turbines, part of the steam is extracted for
a) Condensation
b) Reheating
c) Feed
water heating
d) Secondary
air heating
ANS:C
97)
The average load factor of thermal power plants in India is
a) 100%
b) 80-95%
c) 50-60%
d) 35-45%
ANS: C
98)
As the size of a thermal generating unit increases, the capital cost per kW of
installed capacity
a) Increases
b) Decreases
c) Remains
the same
d) May
increase or decrease
ANS: B
99)
In thermal power plants, the pressure in the working fluid cycle is developed
by
a) Condenser
b) Superheater
c) Feed
water pumps
d) Turbine
ANS: C
100)
In a thermal power plants, the feed water coming to the economizer is heated
using
a) HP
steam
b) LP
steam
c) Direct
heat in the furnace
d) Flue
gases
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