Category: Power Systems Objective Questions

Power Systems Multiple Choice Questions on “Nuclear Reaction”.

1. In nuclear power stations which nuclear reaction is performed?
A. Nuclear fission
B. Nuclear fusion
C. 90% fission and 10% fusion
D. 90% fusion and 10% fission
Answer: A
Clarification: Nuclear fission is the process in which heavy nucleus is split when it is bombarded by certain partials. Huge amount of energy is released during nuclfclear fission in form of heat and radiation.

2. Which particle is bombarded on heavy nucleus of nuclear fuel?
A. Electron
B. Proton
C. Neutron
D. Photon
Answer: C
Clarification: Nuclear fission involvs bombardment of certain particles on heavy nucleus causing it to split. All modern fission reactors uses neutron particles for this purpose because they are neutral in charge and so, they can make their way through the shells of electrons and then through the nucleus at low energy.

3. The critical mass for U235 fission reaction is about _____________
A. 100Kg
B. 200 Kg
C. 50 kg
D. 10 kg
Answer: D
Clarification: For a chain reaction to occur the sample of the fissionable material should be large enough to capture the neutron internally. The minimum mass of fissionable material required to sustain a chain reaction is called the Critical Mass”. The critical mass varies for each reaction, for U235 fission reaction it is about 10 Kg.

4. The fuel mainly used in nuclear fission reactors are:
A. U235
B. U239
C. U233
D. U238
Answer: A
Clarification: The materials U235,U233 and Pu239 are called fissionable materials. From all the above mentioned fuels only U235 will fission in chain reaction.

5. Which fissionable nuclear fuel occur in nature?
A. Plutonium
B. Thorium
C. Uranium
D. 94239 Pu
Answer: C
Clarification: The only natural fissionable fuel occurring in our nature is Uranium, of which 99.3% is U238 and 0.7% is U235 and U234 is only a trace. Out of these isotopes only U235 will fission in chain reaction.

6. Which of the following has high fission percentage?
A. Pu239
B. U233
C. U235
D. U234
Answer: C
Clarification: U235 has higher fission percentage in comparison to others. U235 is only fissionable nuclear fuel found in nature, Pu239 and U233 are produced artificially. They are fissionable.

7. Reactors used for converting fertile materials to fissile materials are called _____
A. research and development reactor
B. production reactor
C. power reactors
D. slow reactors
Answer: B
Clarification: Research and development reactors are used for testing new reactor designs and research. Production reactors are used for converting fertile materials into fissile materials and Power reactors are used for generation of electrical energy.

8. Which statement about fast reactor is true?
A. These reactors are big in size so not easier to shield
B. Fast reactors can convert fertile materials to fissile materials
C. Fast reactors are easy to control
D. Heat transfer and cooling is very easy and simple
Answer: B
Clarification: Fast reactors can convert more fertile material to fissile materials with the result that the net fuel consumption for such reactors is much less. These reactors are small and compact and so easier to shield. Heat transfer and cooling problems in the core are accomplished due to high power density.

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Power Systems Questions on “Inductance of Composite Conductor Lines – 2”.

1. For a transmission line under study of failure analysis, it is observed that the current at the receiving end is same as that of the sending end, then what can be concluded about the nature of the transmission line?
A. It is short TL
B. It is medium TL
C. It is long TL
D. Current is always same at the receiving end and the sending end.

Answer: A
Clarification: It is a short transmission line as the capacitance considered is zero and so the line charging current is also zero.

2. A single phase 50 hz, generator supplies an inductive load of 5 MW at a power factor of 0.8 lagging using OHTL over 20 km. The resistance and reactance are 0.39Ω and 3.96 Ω. The voltage at receiving station is maintained at 10 KV. The sending end voltage is ______
A. 11.68 kV
B. 7.62 kV
C. 14.4 kV
D. 12.2 kV

Answer: A
Clarification: Current, I = 5000/(10*0.8)
=625 A
V_s = |V_r|+|I|*(RcosФ_r + XsinФ_r)
= 10000+625(0.39*0.8+3.96*0.6)
= 11.68kV.

3. When the frequency of the system is increased, the charging MVAR of a system will __________
A. increase
B. decrease
C. remain constant
D. cannot be said

Answer: A
Clarification: Increasing the frequency decreases the reactance and thus charging current increases and so the MVAR.

4.Taking a case study for the long line under no load condition, the receiving end voltage is ____________
A. more than the sending-end voltage
B. less than the sending-end voltage
C. equal to the sending-end voltage
D. it will not be affected by the loading

Answer: A
Clarification: Due to Ferranti effect, the voltage will be more at receiving end in a LTL.

5. While given receiving-end voltage for a long transmission line, the sending-end voltage is more than the actual is found out using _____________
A. Nominal-pi method
B. Nominal-T method
C. Load end capacitance method
D. Any of the mentioned

Answer: A
Clarification: In the nominal pi method, the losses are minimum.

Power Systems Multiple Choice Questions on “One-Line Diagram and Impedance or Reactance Diagram”.

1. What is the main purpose of reactance diagram?
A. Load flow analysis
B. Falt analysis
C. Calculation of ratings of Alternators
D. Calculation of ratings of Transformers
Answer: B
Clarification: The main purpose of reactance diagram is fault analysis. Load flow analysis is done by the help of Impedance diagram. All these diagrams are made using symmetrical component analysis method on per phase basis.

2. Which of the following is not neglected during formation of reactance diagram from impedance diagram?
A. Resistance of various power system components
B. Static loads
C. Shunt component of Transformers
D. Reactance of alternators
Answer: D
Clarification: Reactance diagram is drawn by the help of symmetrical network of various power system components by neglecting resistance of various components, static loads like induction motors and shunt component of Transformers.

3. Impedance diagram is used for analysis of __________
A. Load flow
B. Alternator
C. Fault
D. Transmission Line
Answer: A
Clarification: Impidance diagram is made for the analysis of load flow. Fault analysis is doen by the help of reactance diagram. All these diagrams are made using symmetrical component analysis method on per phase basis.

4. Reactance diagram contains which of the following ?
A. Resistance of Alternator
B. Resistance of transformer winding
C. Induction motor’s equivalent corcuit
D. Inductive reactance of transmission lines
Answer: D
Clarification: Reactance diagram contains only reactance of synchronous machines, transmission line and Transformers. Static loads like induction motors are neglected in diagram.

5. Single line diagram does not represents:
A. Star connection of transformer winding
B. Delta connection of transformer winding
C. Neutral wire of transmission lines
D. Ratings of machines
Answer: C
Clarification: Single line diagram is a representation of balanced power system on per phase basis with neutral eliminated. Neutral wire is not shown in single line diagram. Winding connections (star or neutral) is represented beside the symbol of transformer with its Impidance and rating.

6. Single line diagram of which of the following power system is possible?
A. Power system with LLG fault
B. Power system with LG fault
C. Power system with LL fault
D. Balanced power system
Answer: D
Clarification: Only balanced power system can be represented by a single line diagram. Single line diagram is drawn on per phase basis. A power system with LLG, LG and LL faults becomes unbalanced and can not be represented in per phase basis.

7. In impedance diagram different power system elements are represented by symbols.
A. True
B. False
Answer: B
Clarification: In reactance diagram different power system elements are represented by their symmetrical networks.

8. A three phase transformer has a nameplate rating of 30 MVA, 230Y/69Y kV with a leakage -reactance of 10% and the transformer connection is wye-wye. Choosing a base of 30MVA and 230 kV on high voltage side, the transformer reactance referred to the low voltage side will be _______(in ohms).
A. 15.87 Ω
B. 157.8 Ω
C. 176.33 Ω
D. 17.67 Ω
Answer: A
Clarification: X Ω = Xpu*X_b(LV) = 0.1*158.87 = 15.87 Ω.

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Power Systems Multiple Choice Questions on “Nuclear Reactor Main Parts and their Functions”.

1. In which part of nuclear power plant steam is produced?
A. Boiler
B. Heat exchanger
C. Chamber across the reactor
D. Air preheater
Answer: B
Clarification: There is no boiler in nuclear power plant. The heat energy released in the reactor during nuclear fission is utilised to heat the coolant. This coolant is circulated through the heat exchanger to produce steam.

2. What is the main function of moderator?
A. It absorb the extra neutrons
B. It divert extra neutrons
C. It slow down the speed of fast neutrons
D. It absorb the heat energy caused by nuclear reaction
Answer: d
Clarification: Neutrons rejected during the fission process at a very high velocity of about 1.5 × 107 m/s. For more effective use in nuclear reactor it is desirable to slow down the fast neutrons to speed corresponding to the speed of molecules of gas at normal temperature and pressure. This is accomplished with the help of moderator.

3. Which of the following material is not used as moderator?
A. Oxygen
B. Ordinary water
C. Heavy water
D. Graphite
Answer: A
Clarification: At present the common moderator materials used are graphite, ordinary water and heavy water. Oxygen is not suitable to use due to its low density and the consequent small number of collision.

4. Which of the following part of nuclear reactor is used to control the rate of reaction.
A. Moderator
B. Control rods
C. Reflector
D. Coolant
Answer: B
Clarification: In a reactor the chain reaction is to be maintained at steady value during the operation of reactor. Also the reactor must be able to shutdown automatically under emergency conditions. All these requires control rods for control of reactor so as to prevent the melting of fuel rods, disintegration of coolant and destruction of reactor as the amount of energy released is enormous.

5. Which of the following is the most essential requirement of control rod material?
A. It must be light weight
B. It must be cheap
C. It must have high absorption capacity for neutrons
D. It must be very reflective to neutrons
Answer: C
Clarification: The function of control rod is to control the rate of nuclear reaction by absorption extra release neutrons. Chain reaction is controlled either by removing or inserting neutron absorbing materials. The materials used for control rods must have very high absorption capacity for entrance.

6. Which of the following can be used as both as coolant and moderator ?
A. Helium
B. Molten sodium
C. Lithium
D. Ordinary water
Answer: D
Clarification: A good coolant should not absorb neutrons, should be non-oxidizing, non-toxic, non corrosive, should have high chemical and radiation stability and good heat transfer ability. Ordinary water is used as both as coolant and moderator in boiling water reactor and pressurized water is used as both as coolant and moderator in pressurized water reactor.

7. In thermal reactors control is very easy in comparison to other reactors.
A. True
B. False
Answer: A
Clarification: In thermal reactor control his very easy because of relatively low power densities and longer in neutron lifetime.

8. The main body of reactor is called ____________
A. Thermal shielding
B. Reactor vessel
C. Reflector
D. Biological shielding
Answer: B
Clarification: The reactor core, reflector and thermal shielding are all enclosed in the main body of reactor and is called reactor vessel or tank. It is strong walled container and provides the entrance and exit for the coolant. It also provides the passage for flow of coolant through and around the reactor core.

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