Power Systems Test - 5 - PDF Flipbook
Power Systems Test - 5
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GATE
EEE
Power
Systems
Test-05Solutions
POWER SYSTEMS
1. When bundle conductors are used in place of single conductors,
the effective inductance and capacitance will respectively
a) increase and decrease
b) decrease and increase
c) decrease and remain unaffected
d) remain unaffected and increase
Answer: (b)
2. The interrupting time of a circuit breaker is the period between
the instant of
a) Initiation of short circuit and the arc extinction on an opening
operation
b) Energizing of the trip circuit and the arc extinction on an
opening operation
c) Initiation of short circuit and the parting of primary arc
contacts
d) Energizing of the trip circuit and the parting of primary arc
contacts
Answer: (b)
3. For a transmission line with negligible losses, the lagging
reactive power (VAR) delivered at the receiving-end, for a given
receiving-end voltage is directly proportional to the
a) square of the line voltage drop
b) line voltage drop
c) line inductive reactance
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d) line capacitive reactance
Answer: (d)
4. In a 3-pin plug
a) all the three pins are of the same size.
b) two pins are of the same size but third one is thicker.
c) two pins are of the same size but third one is thicker and
longer.
d) all the three pins are different sizes.
Answer: (c)
Solution:
In a 3 pin plug, two pins are of the same size but third one is
thicker and longer because, the earth pin on a plug is longer
than: the live and neutral pins. This means the earth pin is first
to connect and the last to disconnect. When inserting the plug,
the earth connection is made before the current carrying contacts
of the plug become live. When with-drawing the plug, the
current carrying contacts shall separate before the earth
connection is broken.
5. Which of the following equipments is installed in steam power
plants to reduce air pollution?
a) Desuper heater
b) Air filter
c) Air electrostatic precipitator
d) Stock
Answer: (c)
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6. If the reference bus is changed in two load flow runs with same
system data and power obtained for reference bus taken as
specified P and Q in the latter run
a) The system losses will be unchanged but complex bus
voltages will change.
b) The system losses will change but complex bus voltages
remain unchanged.
c) The system losses as well as complex bus voltage will
change.
d) The system losses as well as complex bus voltage will be
unchanged.
Answer: (a)
Solution:
The losses are remain same.
The reference bus is taken as load bus.
Hence the complex bus voltage will change.
7. The proximate analysis of coal gives percentage by weight of
a) moisture and voltaic matter
b) moisture, voltaic matter, fixed carbon and ash
c) carbon, hydrogen, oxygen, nitrogen, Sulphur and ash
d) carbon, hydrogen and oxygen
Answer: (b)
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8. The undesirable property of an electrical insulating material is
a) high dielectric strength
b) high relative permittivity
c) high thermal conductivity
d) high insulation resistivity
Answer: (b)
Solution:
High Relative Permittivity
9. If two synchronous generators are connected, loss of
synchronism will result in
a) stalling of generators
b) wild fluctuations in current
c) wild fluctuations in current and voltage
d) none of these
Answer: (c)
10. The annual load duration curve of a power supply system may
be considered as a straight line from 40 MW to 80 MW. The
load factor of the system is
a) 20 %
b) 40 %
c) 60 %
d) 83.33%
Answer: (b)
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11. Steady state stability of a power system is the ability of the
power system to
a) Maintain voltage at the rated voltage level.
b) Maintain frequency exactly at 50Hz
c) Maintain a spinning reserve margin at all times.
d) Maintain synchronism between machines and on external tie
lines.
Answer: (d)
12. In a 100 bus power system, there are 10 generators. In a
particular iteration of Newton Raphson load flow technique (in
polar coordinates), two of the PV buses are converted to PQ
type. In this iteration
a) the number of unknown voltage angles increases by two and
the number of unknown voltage magnitudes increases by two.
b) the number of unknown voltage angles remains unchanged
and the number of unknown voltage magnitudes increases by
two.
c) the number of unknown voltage angles increases by two and
the number of unknown voltage magnitudes decreases by
two.
d) the number of unknown voltage angles remains unchanged
and the number of unknown voltage magnitudes decreases by
two.
Answer: (b)
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Solution:
Total no.of buses = 100
Generator bus = 10 – 1 = 9
Load buses = 90, Slack bus = 1
If 2 buses are converted to PQ from PV it will add 2 unknown
voltages to iteration but unknown angles remain constant
13. Element that can be used as the interconnecting elements is
a) vector
b) capacitor
c) resistor
d) resistor and capacitor
Answer: (b)
14. For an unbalanced fault, with paths for zero sequence currents,
at the point of fault
a) The negative and zero sequence voltages are minimum.
b) The negative and zero sequence voltages are maximum.
c) The negative sequence voltage is minimum and zero
sequence voltage is maximum.
d) The negative sequence voltage is maximum and zero
sequence voltage is minimum.
Answer: (b)
Solution:
Normally in an alternator negative and zero sequence
components doesn’t exist, only positive sequence components
exist. Negative sequence components exist due to unbalanced
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fault (or) unbalanced load, whereas zero sequence components
exist only during grounded faults.
During unbalanced grounded faults negative and zero sequence
components exist at fault point, which are maximum in value.
15. To meet the reactive .power requirements at the load centres
usually
a) shunt capacitors are used
b) series capacitors are used
c) tap changing transformers are used
d) shunt reactors are used
Answer: (b)
16. For the same voltage drop, increasing the voltage of a
distributor n times
a) reduces the x-section of the conductor by n times
b) increasing the x-section of the conductor by n-times
c) reduces the x-section of the conductor by n2 times
d) increasing the x-section of the conductor by n2 times
Answer: (b)
17. An HVDC link consists of rectifier, inverter transmission line
and other equipments. Which one of the following is true for
this link?
a) The transmission line produces/supplies reactive power
b) The rectifier consumes reactive power and the inverter
supplies reactive power from/to the respective connected
consumes.
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c) Rectifier supplies reactive power and the inverted consumes
reactive power to/from the respective connected AC systems
d) Both the converters (rectifier and inverter) consume reactive
power from the respective connected AC systems.
Answer: (b)
Solution:
Rectifier acts as an inductor [for α < 900]
And inverter acts as a capacitor [for α > 900]
18. In which type of welding is a pool of molten metal used?
a) Electroslag
b) Submerged arc
c) MIG
d) TIG
Answer: (a)
Solution:
Electroslag welding is used for thick materials. It deposits weed
metal into weed cavity and uses a pool of molten metal.
19. In order to have lower cost of electrical energy generation it is
required to have
a) low load factor and low diversity factor
b) low load factor but high diversity factor
c) high load factor but low diversity factor
d) high load factor and high diversity factor
Answer: (c)
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20. By burden of relay we mean
a) volt-ampere rating of relay
b) current rating of relay
c) voltage rating of relay
d) watt rating of relay
Answer: (a)
Solution:
Burden of relay means VA rating of relay.
21. By increasing the transmission voltage to double of its original
value the same power can be dispatched keeping the line loss
a) equal to original value
b) half the original value
c) double the original value
d) one-fourth the original value
Answer: (b)
22. Dielectric heating is also called
a) volume heating
b) infrared heating
c) surface heating
d) eddy current heating
Answer: (a)
Solution:
In dielectric heating the generated power density is given in
terms of per unit volume. It is also called as volume heating.
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23. The inductance of line is minimum when
a) GMD is high
b) GMR is high
c) both GMD and GMR are high
d) GMD is low but GMR is high
Answer: (c)
24. Presence of earth in case of overhead lines
a) increases the capacitance
b) increases the inductance
c) decreases the capacitances and increases the inductance
d) does not affect any of the line constants
Answer: (c)
25. For a fixed value of complex power flow in a transmission line
having a sending end voltage V, the real power loss will be
proportional to
a) V
b) V2
c) 1/V2
d) 1/V
Answer: (c)
Solution:
P = I2R = �√3 �2 = 2
3 2
∝ 1
2
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26. Compound with a solid conductor of the same radius corona
appears on a stranded conductor at a lower voltage because
stranding
a) assists ionization
b) makes the current flow spirally about the axis of the
conductor
c) produces oblique sections to a plane perpendicular to the axis
of the conductor
d) produces surfaces of smaller radius
Answer: (a)
27. Consider a HVDC link which uses thyristor based line
commutated converters as shown in the figure. For a power flow
of 750 MW from system 1 to system 2, the voltages at the two
ends, and the current, are given by: V1 = 500 kV, V2 = 485 kV
and I = 1.5 kA. If the direction of power flow is to be reversed
(that is, from system 2 to system 1) without changing the
electrical connections, then which one of the following
combinations is feasible?
a) V1 = –500 kV, V2 = –485 kV and I = 1.5 kA
b) V1 = –485 kV, V2 = –500 kV and I = 1.5 kA
c) V1 = 500 kV, V2 = 485 kV and I = –1.5 kA
d) V1 = –500 kV, V2 = –485 kV and I = –1.5 kA
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Answer: (b)
Solution:
Initial case, V1 = 500 kV, V2 = 485 kV, I = 1.5 kA
Power delivered by system-1 is
P1 = V1I = 750 MW
To reverse power flow [from system (2) to system (1)] power
delivered by system (2) is, P2 = -V2I
For same current and same power values
V2 = − 750M = −500kV
1.5k
As I = 1.5 A ⇒ V1 = −4.85 kV (V1 > V2)
28. For a long distance hv transmission line the receiving end
voltage under unloaded conditions is
a) much lower than
b) lower than
c) equal to
d) higher than the sending and voltage
Answer: (b)
29. The sequence components of the fault current are as follows:
Ipositive = j1.5 pu, Inegative = –j0.5 pu, Izero = –j1 pu. The type of
fault in the system is
a) LG
b) LL
c) LLG
d) LLLG
Answer: (c)
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Solution:
For LLG fault, Ipositive = Inegative + Izero
Hence given data satisfies the above condition.
30. For average value of load current, current chopping occurs
more frequently in:
a) VCB’s
b) OCB’s
c) ACB’s
d) SF6 CB’s
Answer: (a)
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