Power Systems MCQ Set 1
1. Based on the below given phasor diagram, the condition for the zero voltage regulation occurs at ________
a) OC = OA
b) OC > OA
c) OC = OD
d) DC = AB
Answer
Answer: a [Reason:] Zero VR occurs when both the emf and the load voltage are equal.
2. In the below given phasor diagram representation, the angle sine(AOD) for the condition of zero voltage regulation will be given by _____
Answer
Answer: a [Reason:] Geometrically sin(AOD) = AD/OA = (AC/2)/|Vr|
The below given phasor diagram is for question number 3, 4 and 5
3. In the phasor diagram representation, the angle (AOD) for the condition of zero voltage regulation will be given by ___
Answer
Answer: a [Reason:] It is geometrically sin(AOD) = AD/OA = (AC/2)/|Vr|
4. In the phasor diagram, the angle Фr such that zero voltage regulation occurs at the receiving end of a transmission line for a leading load, is given as ____
Answer
Answer: a [Reason:] It is geometrically sin(AOD) = AD/OA = (AC/2)/|Vr|.
5. In the phasor diagram, the angle Фr such that zero voltage regulation occurs at the receiving end of a transmission line for a lagging load, is given as _____
Answer
Answer: b
6. 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
Answer: a [Reason:] It is a short transmission line as the capacitance considered is zero and so the line charging current is also zero.
7. 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
Answer: a [Reason:] Current, I = 5000/(10*0.8)
=625 A
Vs = |Vr|+|I|*(RcosФr + XsinФr)
= 10000+625(0.39*0.8+3.96*0.6)
= 11.68kV.
8. 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
Answer: a [Reason:] Increasing the frequency decreases the reactance and thus charging current increases and so the MVAR.
9.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
Answer: a [Reason:] Due to Ferranti effect, the voltage will be more at receiving end in a LTL.
10. 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
Answer: a [Reason:] In the nominal pi method, the losses are minimum.
Power Systems MCQ Set 2
1. Which of the following is not an advantage of stoker firing?
a) Zero capital investment
b) Greater combustion capacity
c) Uniform feeding of coal into furnance
d) Saving in labour cost
Answer
Answer: a [Reason:] Stokers are the mechanical arrangement which is used to feed coals into the furnace. Due to the mechanical equipment combustion capacity increases with uniform feeding of coal of into furnace, also labour cost is reduced. Stoker firing requires installation of mechanical stoker hence, capital investment requires.
2. In case of underfeed stokers fuel is supplied in the furnace ___
a) below the point of air admission
b) above the point of air admission
c) beside the point of air admission
d) by shovels
Answer
Answer: a [Reason:] Mechanical stokers are of two types namely underfeed stokers and overfeed stokers. The two differ in manner of feeding of coal below or above the level at which primary air is admitted in the furnace. In case of underfeed stokers fuel is supplied into the furnace below the point of air admission.
3. Which of the following is most advantageous and most widely method of solid fuel firing?
a) Stoker firing
b) Underfeed firing
c) Spreader stoker firing
d) Pulverised fuel firing
Answer
Answer: d [Reason:] The advantages of using pulverised fuel outweigh the disadvantages and all the modern power plants uses pulverised fuel firing method. In pulverised fuel firing better combustion is achieved. Pulverization is a means of exposing a large surface area to the action of oxygen and consequently helping the combustion.
4. What is the main disadvantage of spreader stoker?
a) Poor control
b) Difficult operation
c) More unwanted fly ash
d) Dangerous operation
Answer
Answer: c [Reason:] In spreader stoker the coal is not fed into the furnace by means of grate. Coal is fed by means of hopper, and function of grade is only to collect and remove the ash out of furnace. Spreader stokers can burn any type of coal from lignite to samianthracite, whether they are free burning or cocking. Their disadvantage is that fly ash is more.
5. Which do you mean by pulverization?
a) Burning of crushed coal
b) Burning of uncrushed coal
c) Crushing of coal into small partials
d) Breaking coal into small particsl
Answer
Answer: c [Reason:] Pulverization is crushing of coal into fine particles. This exposes large surface area to the action of oxygen and consequently helps the combustion. Solids fuels can be used in a powderd and burn like oil and gas.
6. What is the amount of air required to burn the pulverised coal?
a) Less than air required to burn lumped coal
b) More than air required to burn lumped coal
c) More than air required to burn lumped coal
d) No air required to burn the lapped coal
Answer
Answer: a [Reason:] The surface area of pulverised coal is increased in almost the ratio of 400:1, therefore high rates of combustion are possible. Moreover a smaller quantity of air is required than when the fuel is burnt in lumped form.
7. Capital cost of pulverised fuel firing is less than hand firing.
a) True
b) False
Answer
Answer: b [Reason:] Hand firing does not require any capital investment. For pulverised fuel firing separate coal preparation plant is required which makes the installation expensive.
8. What is the main requirement of good coal burner?
a) Minimum operating and maintenance cost
b) Production of uniform flame with complete combustion
c) The burner should be easy to handle and control
d) Attainment of proper designed
Answer
Answer: b [Reason:] Main requirement of good coal burner is complete combustion with production of uniform flame. Minimum operating and maintenance cost, simplicity in operation, attainment of proper design all are requirements of complete combustion.
9. Coal burners are employed to fire the pulverised coal along with primary air in the furnace.
a) True
b) False
Answer
Answer: a [Reason:] Coal burner’s fire pulverised coal with stream of primary air into the furnace. Secondary air is then admitted separately below the burner, around the burner or elsewhere.
10. Spread stockers can be employed for boiler capacitors of ___
a) 1000 kg/hr – 14000 kg/hr
b) 586 kg/hr – 1086 kg/hr
c) 1500 kg/hr – 40000 kg/hr
d) 70,000 kg/hr – 140,000kg/hr
Answer
Answer: d [Reason:] In spreader stoker coal is fed from the coal hopper into the path of the rotor by means of a conveyor and rotor throws the coal into the furnace. Grate collects the ash and moves it out of the furnace.
Power Systems MCQ Set 3
1. Which of the following is correct arrangement of different types of coals according to their increasing carbon content?
a) Peat, bituminous, lignite, anthracite
b) Peat, lignite, bituminous, anthracite
c) Bituminous, peat, lignite, anthracite
d) Peat, anthracite, bituminous, lignite
Answer
Answer: b [Reason:] Coal is the most commonly used fuel in thermal power plant. Coal contain moisture, carbon, hydrogen, sulphur, Nitrogen, Oxygen and ash. Coals are classified according to their calorific value and carbon content.
2. Which of the following is most suitable fuel for thermal power plant?
a) Peat coal
b) Lignite coal
c) Bituminous coal
d) Anthracite coal
Answer
Answer: c [Reason:] Peat and lignite coals have low calorific value and high ash content. Anthracite coals are found in small quantities and are therefore costlier for power generation. Bituminous coals have enough calorific value, low moisture and ash content so most suitable for power generation.
3. Read the below statements.
I. Sulphur is one of the combustible elements
II. The Sulphur content of coal should be less than 1%
a) Only I is correct
b) Only II is correct
c) I and II are correct
d) I and II are incorrect
Answer
Answer: c [Reason:] Sulphur content is one of the factors taken into account while selecting coal for steam power plant. Sulphur is combustible element and can produces energy. But its primary combustion product, Sulphur dioxide, is a health hazard due to which sulphur content in coal should be low.
4. Which of the following coal has highest moisture content?
a) Sub-bituminous coal
b) Bituminous coal
c) Anthracite coal
d) Peat coal
Answer
Answer: d [Reason:] Peat is the first stage in the process of transformation of buried vegetation into coal. It has about 60% to 90% moisture content and low carbon content (about 5% to 20%). Peat coal is not suitable for use in power plants.
5. Which of the following coal has highest enthalpy of combustion?
a) Peat coal
b) Sami-bituminous coal
c) Semi-anthracite coal
d) Lignite coal
Answer
Answer: b [Reason:] Peat and lignite coals have enthalpy of combustion about 3000 KJ/kg and 17600 KJ/kg. Semi-anthracite coals are harder than bituminous coals and have enthalpy of combustion up to 34750 KJ/kg while sami bituminous coals have that up to 35000 KJ/kg.
6. What is the main drawback of liquid fuel in thermal power plant?
a) High handling cost
b) Hard and Adhesive oil slag
c) Difficult to store
d) High cost of liquid fuel
Answer
Answer: d [Reason:] Handling and storing cost of oil fuels are less, load fluctuations can be made easily and few operations are needed. There is no disposal of ash. Superheaters are subjected to hard and adhesive oil slag which is often difficult to remove, but other heating surfaces are almost trouble free.
7. A minimum of 4 to 6 percent of ash is required in coal.
a) True
b) False
Answer
Answer: a [Reason:] This 3 to 6% of ash is required on hand fire grates and some stokers for protection of grades against overheating.
8. Grindability of coal should be low.
a) True
b) False
Answer
Answer: b [Reason:] Grindability index is inversely proportional to the power required to grind the coal to a certain fineness. Higher the grind ability factor index better the coal is.
9. The selection of coal for power plant does not depends on ___
a) Calorific value
b) Nitrogen content
c) Sulphur content
d) Grindability index
Answer
Answer: b [Reason:] The selection of coal for power plant depends on the number of factors such as calorific value, weather ability, sulphur content, ash content, particle size, grindability index, and caking characteristics. Nitrogen content is not needed for the selection of coal for power plants.
10. Read the following statements about coals.
I. Lignite coals can be used in thermal power plants
II. Super-anthracite coal are best for thermal power plants
a) Only I is correct
b) Only II is correct
c) I and II are correct
d) I and II are incorrect
Answer
Answer: a [Reason:] Lignite have 30 to 50% moisture and 20 to 40% carbon content and can be used in power generation. Super-anthracite coals are very hard with shiny black surface. It is non cooking and is very difficult to ignite and so, it has little importance in power generation.
Power Systems MCQ Set 4
1. Which of the system would require more insulation, a 400 kV ac line or 400 kV dc line?
a) 400 kV ac
b) 400 kV dc
c) Both will need same level of insulation
d) Data is insufficient to decide
Answer
Answer: a [Reason:] In ac system, the peak value attained will be 400*√2= 564 kV.
2. The amount of dc compensation needed by a 400 kV dc line for transmitting the data over 300 km having resistance as 5 ohms?
a) 400 var
b) 564 var
c) 600 VAR
d) None of the mentioned
Answer
Answer: a [Reason:] A dc line does not require any reactive compensation.
3. Steady state problem is not very serious problem in dc transmission line system due to which of the following systems?
a) No reactive compensation
b) Only resistance drop
c) Stable voltage regulation
d) No reactive compensation, resistance drop, voltage regulation
Answer
Answer: a [Reason:] Due to all the above reasons, mainly the reactive power compensation there is very less variation in stability.
4. DC line transmission can be used to provide _______ link.
a) asynchronous
b) synchronous
c) lossless
d) none of the mentioned
Answer
Answer: a [Reason:] As dc link provides to connect to different frequencies of the operating buses. It can transfer power frequency independent.
5. (i) Low short circuit current is required in dc system
(ii) Fast control of the converter switches cannot effectively control the damping of the oscillations.
Choose the most appropriate.
a) (i) and (ii) both are true
b) Only (ii) is false
c) Only (i) is false
d) Both statements are false
Answer
Answer: b [Reason:] It’s an advantage the using converters in dc link can control the fast damping of the oscillations which occur in ac systems.
6. The reactive power demand of the converters in HVDC can be provided by _____
a) AC filters
b) Shunt Capacitors
c) SVC
d) AC Filters, Shunt Capacitors and SVC
Answer
Answer: d [Reason:] Reactive power demand by the HVDC system can be fulfilled by all the mentioned equipment’s.
7. As compared to the HVDC line, the corona and radio interference in a HVAC line are ____
a) more
b) lesser
c) same
d) cannot be determined
Answer
Answer: a [Reason:] The corona and radio interference losses are more in ac system.
8. What of the below mentioned statements are incorrect as compared to the HVDC system?
a) Back to back connection is possible
b) More corona losses
c) Distance limitation
d) Extra reactive power compensation
Answer
Answer: b [Reason:] Out of all the corona losses are less in HVDC system.
9. It is required to implement the HVDC system using the thyristors in large numbers. Why it becomes necessary to use a large number of thyristor switches?
a) Due to low voltage rating of thyristor switches
b) Due to low current rating of thyristor switches
c) Due to lack of response for open circuit fault
d) Cannot be determined
Answer
Answer: a [Reason:] Thyristors have low voltage rating and to achieve high voltage, a series of switches that have to used.
10. The corona loss on a particular system at 50 Hz is 1 kW/phase per km. The corona loss on the same system in case of DC transmission will be ______
a) Zero
b) 0.5 kW/phase/km
c) 0.33 kW/phase/km
d) 0.6 kW/phase/km
Answer
Answer: c
Power Systems MCQ Set 5
1. Consider the figure as shown below:-
The line capacitance will be given by ______
Answer
Answer: a [Reason:] For the given configuration,
2. Consider the figure as shown below:-
The phase capacitance will be given by ______
Answer
Answer: b [Reason:] For the given configuration,
3. The per unit value of any quantity is usually given by _______
a) (The actual value in any units)/(The base base value in same in same units)
b) (The base base value in same in same units)/(The actual value in any units)
c) The actual value in any units* The actual value in any units
d) 1/(The base base value)
Answer
Answer: a [Reason:] The per unit value is given as (The actual value in any units)/(The base base value in same in same units).
4. If Xa is the armature reactance of a synchronous machine and Xl is the leakage reactance of the same machine, then the synchronous reactance is ______
a) Xa+Xl
b) ½(Xa)
c) 1/2(Xa+Xl)
d) None of the mentioned
Answer
Answer: a [Reason:] Xs = Xa+Xl
5. A large bus system whose voltage and frequency remain constant independent of the power exchange between the synchronous machine and the bus is called ____
a) infinite bus
b) load bus
c) generator bus
d) cannot be determined
Answer
Answer: a [Reason:] It is infinite bus.
6. The power delivered by a synchronous generator to an infinite bus is given by ______
Answer
Answer: a [Reason:] 
7. In a three phase system the three-phase fault MVA is always higher than the LG fault MVA at a bus.
a) True
b) False
Answer
Answer: a [Reason:] Yes, at the bus three phase system the three-phase fault MVA is always higher than the LG fault.
8. The charging current of a 400 kV is _____ that of 220 kV line of the same length.
a) more than
b) less than
c) equal to
d) none of the mentioned
Answer
Answer: a [Reason:] Line charging current is proportional to voltage.
9. Voltage regulation in the power system is ____
a) rise in voltage at receiving end
b) dip in voltage at receiving end
c) rise in voltage at sending end
d) dip in voltage at sending end
Answer
Answer: a [Reason:] VR is rise in voltage at receiving end for a transmission line.
10. Voltage regulation becomes negative for a ______load.
a) leading
b) lagging
c) zero power factor
d) unity power factor
Answer
Answer: a [Reason:] VR will be negative for a leading load at a receiving end.
