Power Systems MCQ Set 1
1. Which of the following power plant causes highest amount of air pollution?
a) Thermal power plant
b) Hydroelectric power plant
c) Nuclear power plant
d) Geothermal power plant
Answer
Answer: a [Reason:] The major contribution of electrical power generation is from thermal power plant. The thermal power plant definitely contribute to economic growth but they bring with it like air and water pollution. Thermal power plant mostly causes air pollution by the emission of flue gases into air.
2. Which of the following gas is not emitted during combustion of coal?
a) Oxides of sulphur
b) Oxides of Nitrogen
c) Oxides of Mercury
d) Oxides of carbon
Answer
Answer: c [Reason:] Thermal power plant emit large amount of harmful gases such a Sulphur dioxide, nitrogen oxide, CO, CO2, certain hydrocarbons and particulates during the combustion of fossil fuels. There is no any emission of oxides of mercury.
3. Which of the following pollutants emitted by thermal power plant causes irritation in Eyes?
a) Oxides of sulphur
b) Oxides of Nitrogen
c) Oxides of Mercury
d) Oxides of carbon
Answer
Answer: b [Reason:] At high temperatures existing in the flame core of high power boilers, the nitrogen of fuel and air may partially be oxidised to form nitrogen oxides. These are toxic and produce a sharp irritating effect especially on the mucous membrane of the eye.
4. Which of the following pollutants emitted by thermal power plant is a cause of global warming?
a) NO
b) CO2
c) SO2
d) NO2
Answer
Answer: b [Reason:] Carbon monoxide and carbon dioxide are also emitted during the combustion of coal. Carbon monoxide is very toxic pollutant but it gets converted into carbon dioxide in open atmosphere surrounding the power station. On the other hand carbon dioxide has been identified as major cause of global warming.
5. Which of the following pollutant causes acid rain?
a) NO
b) CO2
c) SO2
d) NO2
Answer
Answer: c [Reason:] The Sulphur Dioxide emitted by thermal power plant gradually oxides to sulphur trioxide under the influence of Sunlight. This in turn interact with atmospheric moisture and forms sulphuric acid. This sulphuric acid later causes acid rain.
6. Which of the following is mostly affected by thermal power plant pollutants?
a) Lithosphere
b) Atmosphere
c) Hydrosphere
d) Exosphere
Answer
Answer: b [Reason:] The thermal power plant mostly causes air pollution by the emission of harmful flue gases. So, it can be said that thermal power plant mostly pollutes our atmosphere.
7. Hydroelectric power plants with limited storage are suitable to supply ____
a) Base load
b) Peak load
c) Base load and Peak load
d) Average load
Answer
Answer: c [Reason:] The hydropower plant should be employed for supplying base load. But hydro power plants with limited water storage cannot supply base load. Hence they are suitable for peak loads.
8. Nuclear power plants are suitable only for load factor over ___
a) 0.5
b) 0.7
c) 0.3
d) 0.8
Answer
Answer: d [Reason:] Nuclear power plant is not suitable for variable load operation as the reactor cannot be easily controlled to respond quickly to load variations. Such a plant is used as base load plant only operating at high load factors of over 0.8.
Power Systems MCQ Set 2
1. For the given circuit diagram for the substation the voltage between the two outer conductors is
____
Answer
Answer: b [Reason:] The maximum voltage levels between the two outer conductors is double the supply fed to it and the its rms is √2 V.
2. For the given circuit diagram for the substation fed with 315 kV, the voltage between the two outer conductors is ______
a) 445.5 kV
b) 890 kV
c) 630 kV
d) 223 kV
Answer
Answer: a [Reason:] The maximum voltage levels between the two outer conductors are double the supply fed to it and its rms is √2V.
Voltage between the two outer conductors is √2*315 kV = 445.5 kV.
3. If a 2-wire ac single phase distribution system operating at ‘P’ MW and ‘V’ kV, operating at the power factor of 0.8, then the current in the outer wire in kA is ______
a) 0.8P/V
b) 1.131P/V
c) 1.88P/V
d) 0.088P/V
Answer
Answer: a [Reason:] I = P/(√2 V Cos Ø) = 0.88P/V.
4. If a 2-wire ac single phase distribution system operating at ‘30’ MW and ‘315’ kV, operating at the power factor of 0.8, then the current in the outer wire in kA is _____
a) 0.0838
b) 83.8
c) 8.38
d) 1.131
Answer
Answer: a
5. For a 2-wire ac single phase distribution system operating at ‘30’ MW and ‘315’ kV, operating at the power factor of 0.8 having 15Ω of resistance of each wire, then the copper loss at the substation in kW will be _____
a) 210.67
b) 105.33
c) 240.87
d) 108.27
Answer
Answer: a [Reason:] Current in the line, 
Power losses = 2*I2*R = 2*83.822*15 = 210.673 kW.
6. For a 2-wire ac single phase distribution system operating at ‘30’ MW and ‘315’ kV, operating at the power factor of 0.8 having 15Ω of resistance of each wire, then the power received at the consumer end will be ______
a) 29.79 MW
b) 29.895 MW
c) 29.76 MW
d) 29 MW
Answer
Answer: a [Reason:] Current in the line,
Power losses = 2*I2*R = 2*83.822*15 = 210.673 kW
Power received = 30-210.67 = 29.79 MW.
7. For a 2-wire ac single phase distribution system operating at ‘P’ MW and ‘V’ kV, operating at the power factor of 0.8. The copper losses of the system will be proportional to _____
Answer
Answer: a
8. The maximum rms voltage between one phase and ground neutral for a three phase 4-wire ac system will be ______
a) 221.32 kV
b) 313 kV
c) 442 kV
d) 127 kV
Answer
Answer: a [Reason:] The maximum rms phase voltage = Vph/√2 = 313/√2 = 221.32 kV.
9. The maximum rms voltage between one phase and ground neutral for a three phase 4-wire ac system will be ___
a) 171.46 kV
b) 242.5 kV
c) 221 kV
d) 127 kV
Answer
Answer: a [Reason:] The maximum rms phase voltage = Vph/√2 = 420/√(2*3) = 221.32 kV.
10. For the circuit diagram as depicted in the figure, the current per phase under balanced condition with a consumer end load of 90 kW, 414V operating at a power factor of 0.65 is _____
a) 157.66 A
b) 152 A
c) 111.4 A
d) 193.1 A
Answer
Answer: a [Reason:] Current per phase in the line, I = P/(√2 V/√3 CosØ) = 90000/(√2*414/√3*0.65) = 157.66 A.
Power Systems MCQ Set 3
1. The unvarying load, which occurs almost the whole day on the power plant is called ___
a) Base load
b) Peak load
c) Average load
d) Discrete load
Answer
Answer: a [Reason:] The load on any power plant can be conveniently considered into two parts namely ‘base load’ and ‘peak load’. The unvarying load which occurs almost the whole day on the power plant is called base load.
2. If there is one power plant only, the installed capacity of that power plant should be equal to ____
a) Average load
b) Base load
c) Peak load
d) Minimum load
Answer
Answer: c [Reason:] If the load is to be supplied from one power plant only then the installed capacity of the plant should be equal to the peak load or more. Otherwise during peak load period the plant will not be able to meet the load demand.
3. The various peak demands of the load above the base load of power plant is called ___
a) Base load
b) Over load
c) Extra load
d) Peak load
Answer
Answer: d [Reason:] Various peak demands of the load over and above the base load of the power plant is called peak load. The unvarying load which occurs almost the whole day on the power plant is called base load.
4. The system supplying base and peak loads will be more economical if power is supplied by ___
a) Only gas turbine power plant
b) Only thermal power plant
c) Only Deasel power plant
d) Combined operation of various power plants.
Answer
Answer: d [Reason:] The system containing only one power plant would be uneconomical since. Gas turbine and Diesel power plants operate economically only for peak load and Thermal power plant is suitable only for base load. Hence such power loads should not be supplied from single power plant.
5. Power plants to be employed as base load plants are not required to have _____
a) Capability of working continuously
b) Low operating cost
c) Capability of quick start
d) Economical and speedy repair
Answer
Answer: c [Reason:] Capability of quick start is the essential requirement for peak load plant. Base load plants are started once and operated for long time so capability of quick start is not an essential requirement for base load plants.
6. Which of the following is an essential requirement for a peak load plant _____
a) Capability of working continuously
b) Low operating cost
c) Capability of quick start
d) Economical and speedy repair
Answer
Answer: c [Reason:] The power plants to be employed as peak load plant should only have the capability of quick start, synchronization and taking up of system load and quick response to load variations.
7. Which of the following is not suitable to uses as peak plant?
a) Hydroelectric power plant
b) Gas power plant
c) Diesel elected plant
d) Nuclear power plant
Answer
Answer: d [Reason:] The power plants to be employed as peak load plant should have the capability of quick start and quick response to load variations. Nuclear power plant is not suitable for variable load operation as the reactor cannot be easily controlled to respond quickly to load variations.
8. Which of the following power plant cannot be used as base load plant?
a) Hydroelectric power plant
b) Nuclear power plant
c) Diesel elected plant
d) Thermal power plant
Answer
Answer: c [Reason:] The power plant to be employed as base load plant should have low operating cost. Diesel power plants have very high operating cost and so it is not suitable to use as base load plant.
Power Systems MCQ Set 4
1. The larger power can be transmitted over a line with fixed voltage profile when ______
a) compensators are installed
b) negative VAR is fed
c) positive VAR is fed
d) compensators are installed and postive VAR is fed
Answer
Answer: d [Reason:] Compensators allow the flow of a large power through the TL by feeding positive VAR into the system.
2. A rectangular voltage wave is impressed on a long overhead line, with the far end of the line being open circuited. After reaching line end, the current is ___
a) current is reflected back with positive but voltage with negative sign
b) current is reflected back with negative but voltage with positive sign
c) both current and voltage are reflected with negative sign
d) both current and voltage are reflected with positive sign
Answer
Answer: b [Reason:] For open circuited end, ρ(v) = 1; ρ(i) = -1.
3. If OH transmission line of impedance Z1, is terminated with a cable of impedance Z2. The transmission coefficient of the voltage for the travelling wave at the junction of line and cable is ________
Answer
Answer: a
4. A 240 kV 2μs rectangular pulse surge on a transmission line has surge impedance of 350 ohms. It approaches a generating station with capacitance of 3000 pF. The transmitted voltage will be ______
a) 340.5 kV
b) 280 kV
c) 400 kV
d) 480 kV
Answer
Answer: a [Reason:] Vt = 2Vi(1-e(-t/Zc)) = 2*240*1000(1-e-2*10-6/3*350*10-9).
5. In a transmission line system, the feeders act as input to ___
a) distributors
b) service mains
c) transformer sub stations
d) all of the mentioned
Answer
Answer: a [Reason:] The feeders have bulk power and they have no tappings. They feed to the distributors.
6. One needs to design the distributors, the parameter which will be considered for the design of it?
a) voltage drop in it
b) current flowing
c) operating voltage
d) operating frequency
Answer
Answer: a [Reason:] Distributors work based on the voltage drops measured across them.
7. One would design the feeders of the transmission system based on its ______
a) current capacity
b) voltage drop
c) operating voltage
d) all of the mentioned
Answer
Answer: a [Reason:] Feeders do not have tappings and they are designed on the basis of current flowing through them.
8. The underground transmission and distribution of power is better than the corresponding overhead transmission and distribution in respect of ___
a) appearance and safety
b) maintenance cost
c) frequency of faults
d) appearance, safety, maintenance, frequency
Answer
Answer: d [Reason:] All the points are advantageous with respect to overhead transmission line in an underground power transmission system.
9. Before installing any transmission system, one has to decide about the type of the transmission system to be employed. Considering a monetary shortage and economical setup, one would take up _______
a) underground system
b) overhead system
c) underground or overhead system
d) can be chosen randomly.
Answer
Answer: b [Reason:] Underground installation takes a lot of initial cost.
10. The volume of copper required in a transmission system is proportional to ___
a) voltage and power factor
b) power factor
c) voltage
d) current
Answer
Answer: a [Reason:] Weight of the copper is proportional to voltage and power factor.
11. While deciding an efficient and economical transmission and distribution system, the preferred distribution system will be _______
a) single phase, 2 wire
b) two phase, 3 wire
c) three phase, 3 wire
d) three phase, 4 wire
Answer
Answer: d [Reason:] For a reliable system, the distribution system should be 4 wire, in case a fault occurs.
12. In India, the preferred poles used in the transmission and distribution is ______
a) Steel poles
b) RCC poles
c) Steel and RCC poles
d) Wood poles
Answer
Answer: c [Reason:] The most commonly used poles are steel and RCC poles.
13. Copper has got higher resistivity than aluminium which makes it less used in transmission system.
a) True
b) False
Answer
Answer: b [Reason:] Aluminium has higher resistivity over copper.
14. _______ material is used for the making of the ground wire in the transmission system.
a) Galvanised steel
b) Steel
c) Cast iron
d) Aluminium
Answer
Answer: a [Reason:] Galvanised steel is used in the ground wire.
15. In emergency cases, another wire is installed in the system, that is widely known as ____
a) Guy wire
b) Earth wire
c) Line wire
d) Neutral wire
Answer
Answer: a [Reason:] Guy wire as the earth route in the emergency earth route.
Power Systems MCQ Set 5
1. For a given system consisting of two generators
Units Rating(MW) Speed Drop(%R)
1. 400 0.04
2. 800 0.05
The units share load of P1=200MW and P2=600MW. The units are operating in parallel to share a load of 700 MW at 50 HZ. The load is increased by 130MW with B=0. Then the value new steady state frequency variation is ________
a) 49.75 Hz
b) 51.25 Hz
c) 49.25 Hz
d) 48.75 Hz
Answer
Answer: a
2. A 50 bus power system Ybus has 80% sparsity. The total number of transmission lines will be _____
a) 225
b) 500
c) 475
d) 100
Answer
Answer: a [Reason:] Number of non zero elements = 50*50*20/100 = 500 non zero
Number of TL = (500-50)/2 = 225 transmission lines.
3. The given graph is the depiction of ________ on a large power system network.
a) L-G fault
b) Three phase motor getting short
c) Fault in feeder
d) Any of the mentioned
Answer
Answer: a [Reason:] A LG fault will create a sudden dip in the voltage profile and it will be recovered.
4. A single core cable is graded by using three dielectrics with relative permittivity 5,4,3 respectively. The diameter of the conductor is 2cm and the overall diameter is 8 cm. If the three dielectric work at the same maximum stress of 40kV/cm, then the safe working rms voltage of cable is ______ kV
a) 57.72
b) 81.63
c) 84.67
d) 71.63
Answer
Answer: a [Reason:] d=2cm, d1 = ?, d2= ?, D = 8cm
Ԑ1 = 5; Ԑ2 = 4; Ԑ3 = 3
gmax =40 kV/cm
Ԑ1d1 = Ԑ2d2 = Ԑ3d3
d1 = 2.5cm, d2 = 3.33 cm
Rms value of the peak voltage = 81.63/√2 = 57.72 kV.
5. A generator delivers power of 1 pu to an infinite bus through a purely reactive network. The maximum power that could be delivered by generator is 2 pu. A three phase fault occurs at the generator which reduces the generator output to zero. The fault is restored after ‘tc’ seconds. The maximum swing of rotor angle is found to be δmax = 110o electrical. The rotor angle at ‘tc’ is ________ electrical deg.
a) 69.14o
b) 159.14o
c) 63.08o
d) 65.7o
Answer
Answer: a
6. A system consists of an alternator having reactance of 0.5pu connectedto an infinite bus through a series of reactance of 1 pu. The generator terminal voltage of IBB is 1 pu and that of 1.2 pu. The steady state power system limit (in pu) is _____
a) 1.152
b) 1.167
c) 1.765
d) 1.729
Answer
Answer: a
7. A system consists of an alternator having reactance of 0.5pu connected to an infinite bus through a series of reactance of 1 pu. The generator terminal voltage of IBB is 1 pu and that of 1.2 pu. The Steady state occurs at power angle of ________degree.
a) 0
b) 90
c) 180
d) 45
Answer
Answer: a [Reason:] It occurs at δ=90o.
8. A system consists of an alternator having reactance of 0.5pu connectedto an infinite bus through a series of reactance of 1 pu. The generator terminal voltage of IBB is 1 pu and that of 1.2 pu.The emf induced in the alternator for the maximum power transfer will be ____
a) 1.729
b) 1.152
c) 1.2
d) 1.6
Answer
Answer: a
9. A system consists of an alternator having reactance of 0.5pu connected to an infinite bus through a series of reactance of 1 pu. The generator terminal voltage of IBB is 1 pu and that of 1.2 pu. The emf induced in the alternator will have the phase difference with respect to reference for the maximum power transfer is ___
a) 90
b) 0
c) 73.87
d) 86.25
Answer
Answer: a [Reason:] It occurs at δ=90o for the maximum power transfer.
10. A three phase transmission line is having a three unit suspension insulation string. The voltage at the insulator unit nearest to the line is 20kV and that across the adjacent unit is 15 kV. The ratio of mutual to ground capacitance is ____
a) 0.18
b) 0.2
c) 0.333
d) 0.16
Answer
Answer: a
