Power Systems Test - 1

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GATE
EEE

Power
Systems

Test-01Solutions

POWER SYSTEMS
1. Match List-I (Power Plant) with List-II (Application) and

select the correct answer:
List-I
A. Nuclear
B. Diesel
C. Gas turbine
D. Hydro
List-II
1. Base load
2. Stand-by
3. Base load or peak load
4. Peak load
Codes:

ABC D
a) 1 3 4 2
b) 4 2 1 3
c) 4 3 1 2
d) 1 2 4 3
Answer: (d)
Solution:
Nuclear → Always base load due to safety issues
Diesel → Standby as power very costly
Hydro → Base as well as peak load
Gas → Peak load

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2. The tariff most suitable for large industrial consumers is:
a) Flat demand rate
b) Block meter rate
c) Two part tariff
d) All the above
Answer: (c)
Solution:
Two part tariff means a lump sum fee as well as a per unit
charge.

3. The selection of size of conductors for a distributor in a
distribution system is governed by
a) Corona loss
b) Temperature rise
c) Radio interference
d) Voltage drop
Answer: (d)
Solution:
Resistance of a conductor � = �,
Where, A = area of cross section of conductor.
In a distribution system, if the drop of voltage (IR) is more,
means the current [(or) Load] is more for a given length of
conductor. The size of conductor must be increased, so that the
resistance of conductor is reduced and hence the voltage drop.
Hence rated voltage is maintained at the load terminal.

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4. What is the purpose of the moderator in a nuclear power plant?
a) To control the flow of water inlet
b) To control the amount of nuclear fuel into the reactor
c) To control the nuclear fission or fission rate by slowing down
the neutrons
d) To control the steam flow to the turbine
Answer: (c)
Solution:
Moderator slow down the speed of neutron produced in fission
by absorbing kinetic energy. It increases the chances of fission.
It controls the fission. D2o is one of the moderator used in
Indian pressured heavy water reactor (PHWR).

5. Differential relays are used to protect the equipment against:
a) internal faults
b) reverse current
c) over voltage
d) over current
Answer: (a)
Solution:
Differential relay is used for the localized faults or internal
faults. It is generally used to protect the transformers and
generators.

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6. For harnessing low variable water heads, which is the most
suitable hydraulic turbine?
a) Kaplan Turbine
b) Francis Turbine
c) Pelton Turbine
d) Impeller Turbine
Answer: (a)
Solution:
Low head → Propeller or Kaplan turbine

7. The moderator used in fast breeder reactor is:
a) Heavy water
b) Graphite
c) Ordinary water
d) Any of the above
Answer: (a)
Solution:
Some reactors such as CANDU reactor are fast breeder reactor
and uses heavy water as moderator.

8. A fault involving all the three phases of a power system is
known as
a) line to line to ground fault
b) symmetrical fault
c) unsymmetrical fault
d) unbalanced fault
Answer: (b)

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Solution:
The fault involving all the three phases of a power system is
known as symmetrical fault.
9. The insulation level of a 400 kV, EHV overhead transmission
line is decided on the basis of
a) Lightning over voltage
b) Switching over voltage
c) Corona inception voltage
d) Radio and TV interference
Answer: (b)
Solution:
In any transmission line lightning over voltages is more severe
compared to switching over voltages. The lighting voltages are
external voltages. Hence the insulation is provided for switching
over voltage.
10. In Gauss-Seidel method of power flow problem, the number of
iterations may be reduced if the correction in voltage at each bus
is multiplied by
a) Gauss constant
b) Acceleration constant
c) Deceleration constant
d) Blocking factor
Answer: (b)
Solution:
In G-S method, convergence is slow.

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It can be speed up by α → acceleration constant

α = 1.6 (Generally)

11. Location of lightning arrester should be near a

a) generator

b) transformer

c) bus-bar

d) circuit breaker

Answer: (b)

Solution:

Lightning arrestor should be located close to the equipment that

is expected to be protected. So, location of lightning arrestor

should be near a transformer.

12. In designing lighting scheme, utilization factor is used. It is

defined as

a) utilization factor = total lumens utilized on working plane
total lumens radiated by lamp

b) utilization factor = total lumens utilized on working plane
illumination when everything is clean

c) utilization factor = illumination under normal working condition
illumination when everything is clean

d) utilization factor = total lumens radiated by lamp
total lumens utilized on working plane

Answer: (a)

Solution:

Utilization factor (or)coefficient of utilization =

Lumens actually received by a particular surface
Total lumens emitted by a luminous source

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= total lumens utilized on working plane
total lumens radiated by lamp

13. What is/are the disadvantage(s) of Gauss-Seidel method over

Newton's method in load-flow programmes?

a) More iteration

b) More memory requirement and less accuracy

c) Less iterations but more memory

d) More accuracy and more memory

Answer: (a)

Solution:

Number of iteration in G.S. > N.R. But time per iteration in G.S.

< N.R.

14. At times of peak loads, a power system needs

a) injection of lagging vars

b) injection of leading vars

c) none of (a) and (b)

d) both of (a) and (b) alternately

Answer: (a)

Solution:

At times of peak loads, which are mainly lagging power factor

load the power system needs injection of lagging VARs.

15. How is a voltage control bus specified in load flow studies of a

power system?

a) By real power and reactive power

b) By real power and voltage magnitude

c) By voltage and voltage phase angle

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d) By reactive power and voltage magnitude
Answer: (b)
Solution:
Voltage controlled bus → P, |V|
16. Compared to the breaking capacity of a circuit breaker, its
making capacity should be
a) more
b) less
c) equal
d) the two are unrelated to each other
Answer: (a)
Solution:
Making capacity of a circuit breaker should be more than the
breaking capacity.
17. To reduce the cost of the electricity generated
a) the load factor and diversity factor must below.
b) the load factor must be low but diversity factor high.
c) the load factor must be high but diversity factor low.
d) the load factor and diversity factor must be high
Answer: (d)
Solution:
To reduce the cost of electricity generated, the load factor and
diversity factor must be high.

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18. Shunt resistor is connected across the contacts of circuit
breaker in order to
a) Damp out the re-striking transient
b) By pass the arc current.
c) Limit the short-circuit current.
d) Reduce the damage to the contacts due to arcing.
Answer: (a)
Solution:

Shunt resistors functions:
1. Reduces rate of rise of restriking voltage and reduces duties

of breaker.
2. Reduces transient voltages during switching.
3. In multi-break C.B. transient recover voltage uniform

distribution.
19. Which of the following equipments is used to limit short-

circuit current level in a substation?
a) Isolators
b) Lightning switch
c) Coupling capacitor
d) Series reactor

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Answer: (d)
Solution:
Series reactor is used to limit short circuit level in a substation.
20. The acceptable value of grounding resistance to domestic
application is
a) 0.1 Ω
b) 1 Ω
c) 10 Ω
d) 100 Ω
Answer: (b)
Solution:
The acceptable value of grounding resistance to domestic
application is 1 Ω.
21. Phase comparison relaying is
a) Used for providing back-up protection to transmission lines.
b) Immune to the effects of power surges.
c) Adversely affected by the currents flowing in the protected

line due to mutual induction from another nearby circuit.
d) Adversely affected by the loss of synchronism between

sources of generation beyond the ends of the protected line.
Answer: (b)
Solution:
• Phase comparison relaying (PCR) is differential relaying that

compares the phase angle of current entering one terminal of

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a transmission line with the phase angle of current entering
all remote terminals of same line.
• For internal fault phases of current entering in terminal would
be in 1800 phase.
• For external fault phases would be same.
• In case of loss of synchronism, phase angle of terminals are
different which PCR sees as external fault and is not affected.
So it is immune to be effect of power surges and loss of
synchronism.
• It is a primary protection.
22. For a 500 Hz frequency excitation, a 50 km short power line
will be modeled as
a) Short line
b) Medium line
c) Long line
d) Data insufficient for decision
Answer: (c)
Solution:
In order to get one full wave variation of voltage (or) current on
the line, the length of the line for 50 Hz supply will be given by

=
Where f = supply frequency

= wavelength i.e., the length of the line.
= velocity of wave = 3 × 108 /

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∴ = = 3×108 = 6000
50

For 6000 km wave length, the line with more than 160 km

length is treated as long line.

For 500 Hz,

= 3×108 = 600
500

Hence with 500 Hz supply, a line with more than 16 km length

is treated as long line, where line parameters are distributed.

23. The type of protection that does not respond to faults occurring

beyond its zone even though the fault current may pass through

the zone is:

a) Back-up protection

b) Busbar protection

c) Unit protection

d) Generator protection

Answer: (c)

Solution:

Unit protection does not respond to faults occurring beyond its

zone even though the fault current may pass through the zone.

24. Match List-I (Powers system components) with List-II

(Relaying schemes) and select the correct answer

List-I List-II

A. Power transformer 1. Differential relaying

B. Transmission lines 2. Distance relaying

C. Alternator

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Codes:
ABC

a) 1 1 2
b) 2 1 1
c) 1 2 1
d) 2 1 2
Answer: (c)
Solution:
Transmission line - Distance protection
Alternator and transformer - Differential protection
25. Regulation of an alternator supplying resistive or inductive
load is:
a) infinity
b) always negative
c) always positive
d) zero
Answer: (c)
26. Match List-I (Relays) with List-II (Protection) and select the
correct answer:
List-I
A. Buchholz relay
B. Translay relay
C. Carrier current phase comparison relay
D. Directional over current relay

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List-II
1. Feeder
2. Transformer
3. Ring main distributor
4. Long overhead transmission line
Codes:

ABC D
a) 2 3 4 1
b) 4 1 2 3
c) 2 1 4 3
d) 4 3 2 1
Answer: (c)
Solution:
• Buchhloz → Transformer
• Carrier current phase comparison → Long transmission line
• Direction O/C → Ring main distributors
• Translay → Feeders
27. In DC operation of fluorescent tube, the life of the tube
a) remain same
b) may increase or decrease
c) decreases by about 80% as that with AC operation.
d) increases by about 80% as that with AC operation.
Answer: (c)
Solution:
It decreases by about 80%.

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28. What are the typical values of percentage bias of differential
values used for generator and transformer protection?
a) 5% and 20%, respectively
b) Both 5%
c) Both 20%
d) 20% and 5%, respectively
Answer: (a)
Solution:
Generator → 5%
Transformer → 20%

29. The electric driver possess the following drawback
a) requires hazardous fuel requirement.
b) not adoptable to various environments.
c) not available with various rating.
d) requires a continuous power supply
Answer: (c)
Solution:
Various rating non-availability is the drawback.

30. Series capacitive compensation in EHV transmission lines is
used to
a) Reduce the line loading
b) Improve the stability of the system
c) Reduce the voltage profile
d) Improve the protection of the line.
Answer: (b)

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Solution:

Electrical power supplied by alternator = sin

By using series capacitor the effective value of reactance can be

reduced.

Hence for a given power transfer, we can operate the alternator

at lower values of ‘δ’ so that machine will not lose its

synchronism during abnormal conditions of operation.

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