Category: Power Systems Objective Questions

Power Systems Multiple Choice Questions on “Gas Turbine Power Plants & Types of Tariffs”.

1. The installation time for a gas turbine power plant is ______________
A. Comparatively less than thermal power plant
B. Comparatively more than thermal power plant
C. Equal to thermal power plant
D. Very much longer than thermal power plant
Answer: A
Clarification: Gas turbine power plant is comparatively simpler in construction than thermal power plant. So, its installation time is less than a thermal power plant for same capacity.

2. Which of the following is not used in gas turbine power plant?
A. Compressor
B. Turbine
C. Combustion chamber
D. Condenser
Answer: D
Clarification: Natural gas itself or mixture of natural gas and air is used as working medium in gas turbine power plant. Condenser is a device or arrangement used to condense low pressure steam already used by turbine. There is no steam in gas turbine power plant so no condenser is required.

3. Which component of gas turbine power plant is main cause of its low efficiency?
A. Gas turbine
B. Combustion chamber
C. Compressor
D. Starting motor
Answer: C
Clarification: The overall efficiency of gas turbine is low, because a greater part of power developed by the turbine ( about 65%) is used in driving the compressor.

4. What is intercooling in gas turbine power plant?
A. Removal of heat from combustion gas between stages of turbine
B. Removal of heat from compressor between stages of compressor
C. Removal of heat from intake air
D. Removal of heat from exhaust air
Answer: B
Clarification: Intercooling means removal of heat from compressed air between low pressure and high pressure compressor. Cooling the low pressure compressed air reduces the air volume and improves the thermal efficiency, air rate and work ratio.

5. What is the function of regenerator?
A. Eatery compresses the exhaust gases
B. It heats the compressed air
C. It regenerates the combustible gas from exhaust gas
D. It regenerates the combustible oil from exhaust gas
Answer: B
Clarification: Regenerator is usually of shell and tube construction. Regenerator uses the heat of exhaust gas to heat compressed air before it is sent to combustion chamber. This reduces the fuel consumption and improves the cycle thermal efficiency.

6. Fuel other than natural gas i.e. solid and liquid fuels can be used in _______
A. open cycle gas turbine power plant
B. closed cycle gas turbine power plant
C. open and closed cycle gas turbine power plant
D. only natural gas is used in gas turbine power plant
Answer: B
Clarification: In closed cycle gas turbine power plant the working medium is heated externally and the fuel is not mixed with working fluid. This ensures the use of any fuel such as inferior type or solid type fuel.

7. Which of the following gas turbine power plant can use working medium of required property?
A. Closed cycle gas turbine power plant
B. Open cycle gas turbine power plant
C. Open and closed cycle gas turbine power plant
D. No gas turbine power plant can use working medium of required property.
Answer: A
Clarification: A working medium with physical properties superior to those of air such as helium and hydrogen can be used in closed cycle gas turbine power plant. This is because of airtight construction of this plant.

8. What is the tariff in case of power system?
A. The taxes which a power plant pay to Indian government
B. The taxes which a power plant pay to state government
C. The taxes which a Power Grid pay to Indian government
D. The schedule of rates are charged of supply of electricity for consumers
Answer: D
Clarification: Tariff means the schedule of rates are charges tariff. In case of electric supply means the schedule of rates framed for supply of electrical energy to different classes of consumer.

9. An electricity supplier is charging for the electricity as per the total load connected, fixed number of hours. This type of tariff will be a ___________
A. Simple tariff
B. Flat demand tariff
C. Flat rate tariff
D. Block rate tariff
Answer: B
Clarification: When the use of Electricity was mainly restricted to very few applications such as for lamps it is ee and the number of hours of use of lamp were fixed they were charged on the basis of total load connected in Kilowatt and the fixed number of hours of use district is known as flat demand tariff.

10. Which statement about simple tariff is true?
A. Charges are made as per the total load connected and of fixed duration of use
B. Charges are made on the basis of units consumed in a certain period
C. Different types of consumers are charged differently
D. Charges per kilowatt decreases with increase in unit consumed
Answer: B
Clarification: In simple tariff cost of energy is charged on the basis of unit consumed cost per KWh is given by summing annual fixed cost and annual operating cost and dividing it by total number of units applied to the consumer per annum.

11. Identify the type of tariff the consumer is charged Rs 4 per unit if the consumer does not exceed 50 KWh, Rs 3.50 per unit if the consumer does not exceed 50 KWh but less than 200 kilowatt hour, and Rs 3 per KWh if consumer exceeds 200 kilowatt hour.
A. Flat demand tariff
B. Simple tariff
C. Flat rate tariff
D. Step rate tariff
Answer: D
Clarification: Step rate tariff is a group of flat rate tariff of decreasing unit charges for higher range of conception. Charges per KWh are reduced for increas in power consumption above different predefined step levels. This type of tariff takes into account the fact of lower generation cost going to higher energy consumption consequent to improvement of load factor.

12. What is demand factor of commercial consumers?
A. Low
B. Low
C. High
D. More than 1
Answer: C
Clarification: Demand factor is the ratio of maximum demand to connected load. As we know maximum demand cannot be greater than connected load so demand factor is always less than one. Commercial consumer generally used as most of disconnected loads so their demand factor is high.

13. If an industrial consumer consumes 50KW for 4 hours, 300KW for 15 hours and 60KW for 5 hours daily and the tariff rate is Rs 5/KWh. What is the energy consumption in a month of 30 days?
A. Rs 750000
B. Rs 475000
C. Rs 755000
D. Rs 470000
Answer: A
Clarification: Energy Consumed in one day = (50×4 + 300×15 + 60×5)KWh = 5000 KWh
Energy Consumed in one month = 5000× 30
= 150000 KWh
Hence, Charge on one month = 150000 × 5
=750000 Rupees.

14. Monthly consumption of a consumer is 500KWh. What will be the monthly bill at the following rate?
First 100 unit Rs 0.6/KWh
Next 100 units Rs 0.5/KWh
Remaining units Rs 0.4/KWh
A. Rs 250
B. Rs 25
C. Rs 230
D. Rs 23
Answer: C
Clarification: 500 KWh = (100 +100 + 300) KWh
Bill for one month consumption
= (100×0.6 + 100×0.5 + 300×0.4) Rupees
= 230 Rupees.

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Power Systems Multiple Choice Questions on “Bundled Conductors”.

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: D
Clarification: 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: B
Clarification: For open circuited end, ρ(v) = 1; ρ(i) = -1.

3. 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: A
Clarification: Vt = 2Vi(1-e^(-t/ZC.) = 2*240*1000(1-e^{-2*10-6/3*350*10-9}).

4. 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: A
Clarification: The feeders have bulk power and they have no tappings. They feed to the distributors.

5. 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: A
Clarification: Distributors work based on the voltage drops measured across them.

6. 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: A
Clarification: Feeders do not have tappings and they are designed on the basis of current flowing through them.

7. 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: D
Clarification: All the points are advantageous with respect to overhead transmission line in an underground power transmission system.

8. 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: B
Clarification: Underground installation takes a lot of initial cost.

9. 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: A
Clarification: Weight of the copper is proportional to voltage and power factor.

10. 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: D
Clarification: For a reliable system, the distribution system should be 4 wire, in case a fault occurs.

11. 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: C
Clarification: The most commonly used poles are steel and RCC poles.

12. Copper has got higher resistivity than aluminium which makes it less used in transmission system.
A. True
B. False

Answer: B
Clarification: Aluminium has higher resistivity over copper.

13. _______ 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: A
Clarification: Galvanised steel is used in the ground wire.

14. 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: A
Clarification: Guy wire as the earth route in the emergency earth route.

Power Systems Multiple Choice Questions & Answers on “Short Transmission Line – 2”.

1. What is the value of charging current in short transmission lines?
A. Less than medium transmission lines
B. Equal to medium transmission lines
C. More than medium transmission lines
D. More than long transmission lines
Answer: C
Clarification: Line to Earth capacitance of short transmission line is less than that in medium and long transmission line and is negligable. Because of this the charging current of short transmission line is less than that in medium and long transmission line and is negligable.

2. What is the value of Inductive reactance in short transmission lines?
A. More at reciving end
B. More at sending end
C. Uniformly distributed over entire length
D. More in middle of sending end and reciving end
Answer: C
Clarification: Actually the inductive reactance of line is uniformly distributed over its entire length. To make calculations simple this reactance is assumed to be lumped and connected in series with the line.

3. Regulation of short transmission lines depends:
A. Only on line resistance
B. Only on line inductance
C. Only on line capacitance
D. On line inductance and line resistance
Answer: D
Clarification: The expression of voltage regulation of short transmission line shows that, its voltage regulation depends on line resistance and line inductive reactance. Capacitance of short transmission line is negligible so it does not cause its effecting it.

4. What is the percentage voltage regulation of short transmission line if its sending end and reciving end voltages are 160 KV and 132 KV respectively?
A. 30 %
B. 21.21 %
C. 12.12 %
D. 38.22 %
Answer: B
Clarification: % Voltage Regulation = (Sending end voltage -Reciving end voltage) ÷ Reciving end voltage
= [( 160 – 132 ) × 100] ÷ 132
= 21.21 %.

5. A single phase transmission line is transmitting 1,100 KW power at 11 KV and at unity power fector. If it has a total resistance of 5 Ω, what is the efficiency of the transmission line?
A. 80 %
B. 89.65 %
C. 97.24 %
D. 99.54 %
Answer: C
Clarification: Efficiency (η) = Power delivered ÷ (Power Delivered + line losses)
Line current (I) = P/V
= (1100 × 1000/11000)
= 100 Amp.
Line losses = I2 R
= (100)2 5
= 50 KW
η = [11000/(11000+50)] × 100
= 99.54 %.

6. Voltage regulation of a transmission line should be ________
A. Minimum
B. Maximum
C. Greater than 50 %
D. Less than 50 %
Answer: A
Clarification: More value of voltage regulation means more voltage fluctuations and this is undesirable. So the value of voltage regulation should be as low as possible.

7. Which of the following is like equivalent circuit of short transmission line?
A. Series RLC circuit
B. Parallel RLC circuit
C. Series RL circuit
D. Parallel RL circuit
Answer: C
Clarification: Due to smaller distance and lower line voltage, the shunt capacitance effects are extremely small and also the shunt conductance effects are very low. So both of them are neglected and equivalent circuit contains only series inductance(L) and resistance(R).

8. In single phase transmission lines resistance and inductance are considered only up to neutral.
A. True
B. False
Answer: B
Clarification: In case of single phase transmission lines the total loop resistance and inductance is to be taken into account. Resistance and inductance only up to neutral are taken into account for 3 phase transmission lines.

all areas of Power Systems, .

Power Systems Multiple Choice Questions on “Conductor Materials”.

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: B
Clarification: 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: D
Clarification: 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: D
Clarification: 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: C
Clarification: 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: B
Clarification: 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: A
Clarification: 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: B
Clarification: 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: C
Clarification: 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: B
Clarification: 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: B
Clarification: 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.

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