Power Systems MCQ Set 1
1. In stranded conductor of 6 layers, what will be the total number of individual wire?
a) 75
b) 85
c) 84
d) 74
Answer
Answer: b [Reason:] Standard conductors usually have the central wire around with there at successive layers of wires. For n layers the number of individual wire is 3n (n+1)+1. Where ‘n’ is number of layers.
2. A standard conductor have three layers of wire. What will be the diameter of stranded conductor if diameter of each strand is 5 mm?
a) 38 mm
b) 15 mm
c) 20 mm
d) 35 mm
Answer
Answer: d [Reason:] If the diameter of each strand is ‘d’ then diameter of the standard conductor will be (2n + 1)d. ‘n’ is number of layers.
3. What is the disadvantage of using Stranded Hard Drawn Copper for overhead transmission lines?
a) Low tensile strength
b) Due to electrolytic troubles
c) Corrosion
d) High cost
Answer
Answer: d [Reason:] Hard Drawn Copper have good tensile strength, does not corrodes in normal atmosphere and is not subject to electrolytic troubles. Owing to the difficulty of importing copper due to lack of foreign exchange in our country, cost of copper is higher than aluminium. The trend now days is to use aluminium in place of copper.
4. Which of the following conductors are most suitable for short lines supplying rural areas and operating at voltage of about 11 Kv?
a) Hard Drawn Copper Conductor
b) ACSR Conductor
c) Galvanized steel
d) Phosphor Bronze
Answer
Answer: c [Reason:] Galvanized steel have great tensile strength and so it can be used for extremely long spans,or for short line section exposed to normally high stresses due to climatic conditions. These conductors are most suitable for lines supplying rural areas and operating at voltages of about 11 Kv where cheapness is the main consideration.
5. Which of the following conductive material will be preferred when harmful gases such as ammonia are present in atmosphere?
a) Cadmium copper
b) Phosphor bronze
c) Galvanized steel
d) Aluminium
Answer
Answer: b [Reason:] When harmful gases such as Ammonia are present in atmosphere and the spans are extremely long, phosphor bronze is most suitable material for an overhead line conductor for such situation.
6. What is the amount of Corona losses in ACSR conductors in comparison to copper conductors?
a) Low
b) High
c) Same
d) No Corona loss
Answer
Answer: a [Reason:] The ACSR conductors has a largest diameter than any other type of conductor of same resistance, so corona losses are low in ACSR conductors.
7. What is the advantage of cadmium copper over hard drawn copper?
a) Higher conductivity
b) Higher tensile strength
c) Low cost
d) Low conductivity
Answer
Answer: b [Reason:] Addition of 1 or 2% of cadmium in copper increases the tensile strength by about 40% and reduces the conductivity only by 17% below that of pure copper. However, cadmium copper is costlier than pure copper, its use will be economical for a line with long spans and small cross section.
8. In extra High Voltage lines, which conductor material is used for ground wire provided above the line conductors for protection against lightning?
a) Hard drawn copper
b) Cadmium copper
c) Stranded galvanized steel
d) ACSR
Answer
Answer: c [Reason:] Due to very poor conductivity, about 30% of copper and higher eddy current and hysteresis losses. Application of galvanized steel wire is limited to telecommunication lines stay wire Earth wire and guard wires. Stranded galvanized steel wires are used as guy wires and earth wires.
9. Which of the following conductor is needed to use with shortest span?
a) ACSR Conductors
b) All Aluminium Conductors
c) Hard Drawn Copper Conductors
d) Cadmium Copper Conductors
Answer
Answer: b [Reason:] All aluminium conductors have low tensile strength. Linear coefficient of expansion of Aluminium is 1.4 times that of copper and so sag is greater in aluminium wires. Due to these characteristics, aluminium stranded conductors are mainly used for low voltage distribution overhead lines having shorts spans of up to 65 m.
10. Which of the following wire is used as stay wire?
a) All Aluminium Conductors
b) Standard Galvanized Steel Conductors
c) Cadmium Copper Conductors
d) Phosphor Bronze Conductors
Answer
Answer: b [Reason:] Stay wires are used for supporting poles and towers. Standard galvanized steel conductors have great tensile strength and superior mechanical properties. So standard galvanized steel wires are widely used as stay wire and earth wire.
Power Systems MCQ Set 2
1. What is the principle of operation of steam power plant?
a) Carnot cycle
b) Brayton cycle
c) Stirling cycle
d) Rankine cycle
Answer
Answer: d [Reason:] The Rankine cycle is an idealized thermodynamic cycle of heat engine. Under this cycle heat energy is converted into mechanical energy while undergoing phase change. The heat is supplied externally to the closed loop which usually uses water as working fluid.
2. Read the following statement about boilers.
I. Water tube boiler is capable of generating steam of pressure more than 50 kg/cm2 .
II. Fire tube boiler is suitable for generating steam of pressure less than 17.5 kg/cm2 .
III. Water tube boiler occupy comparatively less space.
a) Only statement I is true
b) Statement I, II and III are true
c) I and II are true but III is false
d) I and III are true but II is false
Answer
Answer: b [Reason:] In fire tube boiler water and steam are in same shell so higher pressure is not possible. In water tube boiler comparison to fire tube boiler, the drum do not contain any tabular heating surface so they can be built in smaller diameter and consequently they will withstand higher pressure.
3. Fire tube boilers are safer than water tube boilers.
a) True
b) False
Answer
Answer: b [Reason:] In event of sudden and major tube failure steam explosion may occur in furnace of fire tube boiler due to rush of high pressure water into hot combustion chamber. Water tube boiler does not contain such tubular heating surfaces so no such problem arises there.
4. Which of the following material is not used in the boiler furnace walls?
a) Fire clay
b) Concrete
c) Silica
d) Kaolin
Answer
Answer: b [Reason:] Fire clay, Silica and Kaolin have property of resisting change in shape, weight or physical property at higher temperature. Concrete have no such properties at higher temperature so it is not suitable for that. The construction of boiler furnace varies from plain refractory walls to completely water cooled walls depending upon the characteristics of fuel used and firing methods.
5. Which of the following statement about economiser of steam power plant is wrong?
a) Economiser increases the Boiler Efficiency about 5 to 15%
b) It uses the heat of flue gases used by boiler going to the chimney.
c) Economiser increases the temperature of intake air
d) It require regular maintenance and cleaning
Answer
Answer: c [Reason:] Economiser is used to rise the temperature of feed water. Air preheater is used to raise the temperature of intake air. Flue gases after heating boiler water Still possesses sufficient heat energy which if not used will waste. Economiser and air preheater uses that heat energy to work and hence increase the thermal efficiency of power plant about 15%.
6. Which of the following are the most widely used condensers in modern thermal power plants?
a) Surface condensers
b) Low level counter flow type jet condenser
c) High level counter flow type jet condenser
d) Parallel flow type jet condenser
Answer
Answer: a [Reason:] Power plants mostly use surface condensers because from these condensers condensate can be used as feed water requiring less pumping power. In case of jet condensers exhaust steam mixes with the cooling water hence condenses and cooling water are mixed so condensing cannot be recovered for the use of feed water.
7. Read the following statements about feed water heaters
I. Open or contact heaters are also called Deaerator.
II. Open or contact heaters constructed to remove non-condensable gases from feed water.
a) Only statement I. is correct
b) Only statement II. is correct
c) I. and II. are correct
d) I. and II. are wrong
Answer
Answer: c [Reason:] Dissolved gases can cause corrosion inside the boiler so they must be removed from feed water. Feed water heaters are used to heat the feed water by means of bled steam before it is supplied to the boiler. The amount of non-condensable gases decreases with increase in temperature of water in open heaters hence called Deaerator.
8. Which of the following is a part of air and fuel gas circuit?
a) Condenser
b) Economiser
c) Air preheater
c) Cooling tower
Answer
Answer: c [Reason:] In air and fuel gas circuit air is drawn from the atmosphere by a forced draught fan or induced draught fan through the air preheater. In air preheater that air is heated by the heat of flue gases passing to the chimney and then admitted to the furnaces. Cooling tower and Condenser are parts of Cooling water circuit and Economiser is part of Feed water and steam circuit.
Power Systems MCQ Set 3
1. Which of the following costs come under semi fixed cost?
a) Salaries of high officials
b) Salaries of operational and maintenance staff
c) Salaries of Management and clerical staff
d) Annual cost of fuel
Answer
Answer: c [Reason:] The semi fixed cost is due to annual interest, the capital cost of generating plant transmission and distribution network building and other civil works, all types of taxes and insurance charges and salaries of Management and clerical staff. Salaries of higher officer is a fixed cost and salaries of operation and maintenance staff is running or operating cost.
2. Which power plant has minimum operating cost?
a) Hydroelectric power plant
b) Thermal power plant
c) Nuclear power plant
d) Gas Turbine Power Plant
Answer
Answer: a [Reason:] Hydroelectric power plant has lowest running cost because it does not needs any fuel and can be operated by few number of persons. Nuclear gas and thermal power plant requires fuels also the handling cost of fuels is added with the total cost.
3. Which of the following is most likely to nuclear power plant?
a) Thermal power plant
b) Hydroelectric power plant
c) Gas turbine power plant
d) Nuclear power plant
Answer
Answer: d [Reason:] Most of the parts of nuclear power plants are similar to the thermal power plant, except the heat generating system. In thermal power plant heat energy is produced by the combustion of fossil fuels like coal, Oil or gas. In nuclear power plant the heat energy is produced by Nuclear Fission of nuclear fuels like Uranium or plutonium in reactor.
4. Which of the following have highest operating cost?
a) Hydroelectric power plant
b) Thermal power plant
c) Nuclear power plant
d) Solar electric power plant
Answer
Answer: b [Reason:] Operating cost of hydroelectric and Solar Power Plant are very low because they don’t need fuel. In nuclear power plant fuel required is of very small quantity as compared to coal required by thermal power plant. Due to above the cost of transportation of fuel and also the cost of fuel itself is low for nuclear power plant.
5. Which of the following least affect the cost of electricity produced in thermal power plant?
a) Cost of fuel
b) Cost of transportation
c) The load factor
d) Salaries of higher officials
Answer
Answer: d [Reason:] Change in fuel cost by 20% main cause about 8% variation in total cost per KWh generated. Cost of transportation and the load factor changes and also cause variation in fuel cost. The salaries of higher officials comes under fixed cost and so it does not affects the cost of fuel.
6. Which of the following power plant have longest physical life?
a) Thermal power plant
b) Nuclear power plant
c) Hydroelectric power plant
d) Diesel power plant
Answer
Answer: c [Reason:] Thermal and diesel power plants are so constructed that their efficiency Falls over time faster as compared to hydroelectric power plant. Nuclear power plant also needs maintenance over time. The components of hydroelectric power plant including turbine, generator and the concrete Dam are so rugged in construction that their life maybe as long as 80 years or even longer.
7. When load factor and diversity factor increases _____
a) cost of electricity decreases
b) cost of electricity also increases
c) cost of electricity remains same
d) cost of electricity increases exponential
Answer
Answer: a [Reason:] Load factor and diversity factor playes an important role in cost of supply of electrical energy. Higher the value of load factor and diversity factor, lower will be the cost per unit generated.
8. Which of the following has highest diversity factor?
a) Domestic lightning
b) Commercial lightning
c) Industrial power
d) Domestic power
Answer
Answer: a [Reason:] Diversity fector of all of the options rangers from 1.5 to 2. The diversity factor of domestic lightning upto 1 kilo watt rangers from 3 to 5.
Power Systems MCQ Set 4
1. A transmission and distribution engineer needed to design the sub transmission substation. The tapping component needed will be ___
a) feeder
b) distributor
c) transmitter
s) tap-changing transformer
Answer
Answer: a [Reason:] For the sub transmission level, there is no tapping at various level does not take place. For this a feeder is used.
2. While designing the distribution to locality of one lac population with medium dense load requirement, we can employ _____
a) radial system
b) parallel system
c) ring main system
d) any of the mentioned
Answer
Answer: a [Reason:] A radial system is used for the medium requirement of loading and a medium dense population as it becomes easier to install and operate.
3. A ___ distribution system is more reliable than the ______ distribution system.
a) parallel, radial
b) parallel, ring
c) radial, parallel
d) ring, parallel
Answer
Answer: a [Reason:] A parallel distribution system has two end feeding and an alternative of parallel line, so in case there is a fault, the isolator can isolate the faulty part and let the healthy system operate.
4. For the figure shown, having a 2-wire dc system where mid point is earthed, having resistance of 20 ohms, with a power transmitted of 5 MW at the voltage level of 440 kV.
The power loss of the distribution system will be _____
a) 5165 W
b) 515 kW
c) 10330 W
d) 2583 W
Answer
Answer: a [Reason:] I = P/V = 5000000/440000 = 11.36 A
Power loss = 2I2*R = 2* 11.362*20 = 5165 W.
5. For the figure shown, having a 2-wire dc system where mid point is unearthed, having resistance of 20 ohms, with a power transmitted of 5 MW at the voltage level of 440 kV.
The power loss of the distribution system will be _____
a) 5165 W
b) 515 kW
c) 10330 W
d) 2583 W
Answer
Answer: d [Reason:] I = P/V = 5000000/440000 = 11.36 A
Power loss = I2*R = 2* 11.362*20 = 2583 W.
6. A DC 2-wire system with mid-point earthed having cross-sectional area of each conductor be ‘a’ and resistance ‘R1’. If the DC tow wire replaces the system, then the ratio of volume of each conductor V1/V2 will be _____
a) ¼
b) ½
c) 4
d) 2
Answer
Answer: a [Reason:] Let the power losses remain constant over the systems, then
2P2R/V2 = 2P2R1/2*V2
or, R = R1/4;
As R = lρ/a;
a1 = a/4;
So, V1/V1 = 1/4.
7. While designing the distribution sub stations by the designer, it is required to use the _______ for the discrete power tapping.
a) distributor
b) power transformer
c) distribution transformer
d) feeder
Answer
Answer: a [Reason:] For the discrete tapping of the power the consumer level it is the distributor which is employed at the sub stations and consumer levels.
8. A DC 2-wire system with mid-point earthed having cross-sectional area of each conductor be ‘a’ and resistance ‘R1’. If this is replaced by monopolar system, then saving of copper will be ______
a) ½
b)b¼
c) 2
d) 4
Answer
Answer: a [Reason:] Let the power losses remain constant over the systems, then
2P2R/V2 = 2P2R1/V2
or, R1 = R
As R = lρ/a;
a1 = a
So, V1/V1 = a1*2l/a1 = 1/2.
9. For the single phase 2-wire system, the maximum voltage between the outer wires and earth is ________
a) V/√2
b) √2V
c) V
d) 2V
Answer
Answer: a [Reason:] The midpoint voltage will be V/√2.
10. For the given distribution system the maximum voltage at the midpoint will be ________
a) 155.6 V
b) 311.12 V
c) 622 V
d) 220 V
Answer
Answer: a [Reason:] Vmax = V/√2 = (440/2)/√2 = 155.6 V.
Power Systems MCQ Set 5
1. What is the advantage of sectionalizing of power plant?
a) High reliability
b) Low capital cost
c) Low maintenance
d) Easy operation
Answer
Answer: a [Reason:] Sectionalizing means installing more number of small units rather than installing a big unit. Doing so enables us to maintain continuity of supply from rest of the units, when one or two units of plant fails. this makes the plant more reliable.
2. The area under the load curve represents ______
a) the average load on power system
b) maximum demand
c) number of units generated
d) load factor
Answer
Answer: c [Reason:] Load curve is obtained by plotting fluctuating load be keeping load on y axis and time in x axis. The area under the load curve represents the total number of units generated in a particular time.
3. Which of the following is equal to the maximum demand?
a) The ratio of area under curve to the total area of rectangle
b) The ratio of area under curve and number of hours
c) The peak of the load curve
d) The area under the curve
Answer
Answer: c [Reason:] The ratio of area under curve to the total area of the rectangle is called load factor. The ratio of area under the curve to the number of hours represents the average load. The peak of the curve represents the maximum demand.
4. Load duration curve indicates _______
a) the variation of load during different hours of the day
b) total number of units generated for the given demand
c) total energy consumed by the load
d) the number of hours for which the particular load lasts during a day
Answer
Answer: d [Reason:] The variation of load during different hours of the day is shown by load curve. Load duration curve is different from Load curve. Load duration curve indicates the variation of the load, but with the load arranged in descending order of magnitude. Load duration curve give the number of hours for which a particular load lasts during a day.
5. During which time the demand of electrical energy is maximum?
a) 2 A.M. to 5 A.M.
b) 5 A.M. to 12 P.M.
c) 12 P.M. to 7 P.M.
d) 7 P.M. to 9 P.M
Answer
Answer: d [Reason:] From the load curve it is obtained that during early morning demand is always low. Around 5 A.M. it starts increasing and around 9 A.M. load reaches a high value and remains almost constant till evening except for some Dip during lunch hours. The load again starts increasing in evening hours and reaches its peak around 7 to 9 P.M.
6. Size and cost of installation depends upon ______
a) average load
b) maximum demand
c) square mean load
d) square of peak load
Answer
Answer: b [Reason:] The greatest of all “short time interval averaged” during a given period, on the power system is called the maximum demand. Maximum demand represents the maximum amount of load that is active, out of total connected load. So the size and rating of power plant depends on Maximum demand.
7. What is Demand factor?
a) Ratio of connected load to maximum demand
b) Ratio of average load to connected load
c) Ratio of maximum demand to the connected load
d) Ratio of kilowatt hour consumed to 24 hours
Answer
Answer: c [Reason:] Demand factor is the ratio of actual maximum demand on the system to the total load connected to the system. The idea of demand factor was introduced due to the fact that all the equipments connected to the system does not work at a time in practice.
8. Which of the following represents the annual average load?
a) (KWh supplied in a day)/24
b) {(KWh supplied in a day)/ 24 } × 365
c) {(KWh supplied in a month)/(30 x 24)
d) (KWh supplied in a year) / (24 × 365)
Answer
Answer: d [Reason:] The average load on the power station is average of load occurring at the various events. It can also be stated as energy deliver in a given period divided by the number of hours in that period. Option d matches correctly to these statements.
9. The load factor is ____
a) always less than unity
b) less than or greater than 1
c) always greater than 1
d) less than zero
Answer
Answer: a [Reason:] Load factor is the ratio of average demand to the maximum demand. Average demand can not be greater than maximum demand. So the value of load factor is always less than unity.
10. In practice what is the value of diversity factor?
a) Less than Unity
b) Geater than Unity
c) Equal to or greater than Unity
d) Less than zero
Answer
Answer: b [Reason:] Maximum demand of different consumers never occurs at a time, due to this the total maximum demand of the load is always less than sum of individual maximum demands. And hence, demand factor e.i. the ratio of sum of individual maximum demand to the maximum demand of total load is always greater than unity.
11. Coincidence factor is reciprocal of _____
a) average load
b) demand factor
c) capacity factor
d) diversity factor
Answer
Answer: d [Reason:] Coincidence factor is the ratio of total maximum demand to the sum of individual maximum demands which is the reciprocal of diversity factor.
12. Which of the following is called as cold reserve?
a) Reserve capacity available but not ready for use
b) Reserve capacity available and ready for use
c) Generating capacity connected to bus and ready to take load
d) Capacity in service in excess of peak load
Answer
Answer: a [Reason:] Cold reserve is the generating capacity which is available for service but not normally ready for immediate loading. Reserved capacity available and ready to use are called hot reserve.
