Category: Power Systems Objective Questions

250+ TOP MCQs on Constituents of Steam Power Plant and Answers

Power Systems Multiple Choice Questions on “Constituents of Steam Power Plant”.

1. What is the principle of operation of steam power plant?
A. Carnot cycle
B. Brayton cycle
C. Stirling cycle
D. Rankine cycle
Answer: D
Clarification: 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: B
Clarification: 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: B
Clarification: 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: B
Clarification: 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: C
Clarification: 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: A
Clarification: 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: C
Clarification: 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: C
Clarification: 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.

.

250+ TOP MCQs on Economics of Power Generation and Answers

Power Systems Multiple Choice Questions on “Economics of Power Generation”.

1. What is the advantage of sectionalizing of power plant?
A. High reliability
B. Low capital cost
C. Low maintenance
D. Easy operation

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

250+ TOP MCQs on Effect of Earth on the Three Phase Transmission Line Capacitance – 1 and Answers

Power Systems Multiple Choice Questions on “Effect of Earth on the Three Phase Transmission Line Capacitance – 1”.

1. Transmission efficiency of a transmission line increases with the _____________
A. decrease in power factor and voltage
B. increase in power factor and voltage
C. increase in power factor but the decrease in voltage
D. increase in voltage only power factor remains constant

Answer: B
Clarification: Increasing the power factor and voltage reduces the losses and hence improves the efficiency.

2. Surge impedance of a transmission line is the impedance at the time of breakdown of voltage.
A. True
B. False

Answer: B
Clarification: Surge impedance is the characteristic impedance of a TL.

3. When the transmission line is lousy, then its characteristic impedance will not depend on which of the following?
A. Length
B. Operating frequency
C. Sub synchronous frequency
D. Length and Sub synchronous frequency

Answer: D
Clarification: For a lousy line, the characteristic impedance will be independent of its sub synchronous frequency and length.

4. If the transmission line is lossless, then its characteristic will be _________
A. √(L/C.
B. √LC
C. √(L+C.
D. √(C/L)

Answer: A
Clarification: The characteristic impedance for the lossless lines is given by √(L/C. because the resistance is zero.

5. The surge impedance of multiple conductor lines as compared to single line is _______
A. higher
B. lower
C. same
D. length dependent

Answer: B
Clarification: Due to the reduced GMD, the impedance decreases and so the surge impedance.

6. When ______ then the transmission line will act as a distortion less line.
A. RC = GL
B. RG = LC
C. R = G
D. Cannot be determined

Answer: A
Clarification: When both the time constants become same, then the transmission will behave like distortion less line.

7. It is intended to increase the power despatch of the existing transmission line. Then what can be the most appropriate solution for improving it?
A. Installing series capacitors
B. Installing shunt capacitor
C. Installing shunt reactor
D. Installing series reactor

Answer: A

8. Which of the following situations is very useless when the series capacitors to the transmission line are of little use?
A. When the VAR requirement is small
B. When the VAR requirement is large
C. When the VAR requirement is varying
D. Cannot be determined

Answer: A
Clarification: Because capacitance is usually neglected for a small transmission line.

9. Reactive power requirement of a power transmission system depends on __
A. Power angle δ
B. |Vs|-|Vr|
C. Vs
D. Vr

Answer: B

10. When do we use conduit pipe in the transmission of power?
A. Unsheathed cables
B. Armoured cables
C. PVC sheathed cables
D. All of the mentioned

Answer: A
Clarification: It is used in protection of wires and cables for underground transmission.

250+ TOP MCQs on Symmetrical Component Transformation – 2 and Answers

Power Systems online quiz on “Symmetrical Component Transformation – 2”.

1. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters.
Vs = A*Vr+B*Ir
Is = C*Vr+D*Ir

A. 1+YZ, Z
B. Z,Y
C. Y, 1+YZ
D. 1+YZ, Y-1+Z

Answer: A
Clarification: Using KVL to the line diagram,
Vs = (1+YZ)*Vr+Z*Ir
Is = Y*Vr+Ir.

2. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and C parameters.
Vs = A*Vr+B*Ir
Is = C*Vr+D*Ir

A. 1+YZ, Z
B. Z,Y
C. 1+YZ, Y
D. 1+YZ, Y-1+Z

Answer: C
Clarification: Using KVL to the line diagram,
Vs = (1+YZ)*Vr+Z*Ir
Is = Y*Vr+Ir.

3. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and D parameters.
Vs = A*Vr+B*Ir
Is = C*Vr+D*Ir

A. 1+YZ, 1
B. 1+YZ, Z
C. Y, 1+YZ
D. 1+YZ, Y-1+Z

Answer: A
Clarification: Using KVL to the line diagram,
Vs = (1+YZ)*Vr+Z*Ir
Is = Y*Vr+Ir.

4. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify B and A parameters.
Vs = A*Vr+B*Ir
Is = C*Vr+D*Ir

A. 1+YZ, Z
B. Z,YZ+1
C. Z, 1+YZ
D. 1+YZ, Y-1+Z

Answer: B
Clarification: Using KVL to the line diagram,
Vs = (1+YZ)*Vr+Z*Ir
Is = Y*Vr+Ir.

5. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify C and A parameters.
Vs = A*Vr+B*Ir
Is = C*Vr+D*Ir

A. 1+YZ, Z
B. Z,Y
C. Y, 1+YZ
D. 1+YZ, Y-1+Z

Answer: C
Clarification: Using KVL to the line diagram,
Vs = (1+YZ)*Vr+Z*Ir
Is = Y*Vr+Ir.

6. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify D and A parameters.
Vs = A*Vr+B*Ir
Is = C*Vr+D*Ir

A. 1+YZ, Z
B. 1+ZY, 1
C. Y, 1+YZ
D. 1, 1+YZ

Answer: A
Clarification: Using KVL to the line diagram,
Vs = (1+YZ)*Vr+Z*Ir
Is = Y*Vr+Ir.

7. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters and find AB value.
Vs = A*Vr+B*Ir
Is = C*Vr+D*Ir

A. (1+YZ)* Z
B. 1+YZ* Z
C. Y*( 1+YZ)
D. (1+YZ)*Y-1+Z

Answer: A
Clarification: Using KVL to the line diagram,
Vs = (1+YZ)*Vr+Z*Ir
Is = Y*Vr+Ir.

8. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters and find ‘A*C’ value.
Vs = A*Vr+B*Ir
Is = C*Vr+D*Ir

A. (1+YZ)* Y
B. (1+YZ)* Z
C. Y*( 1+YZ)
D. (1+YZ)*Y-1+Z

Answer: A
Clarification: Using KVL to the line diagram,
Vs = (1+YZ)*Vr+Z*Ir
Is = Y*Vr+Ir.

9. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters and find ‘A*D’ value.
Vs = A*Vr+B*Ir
Is = C*Vr+D*Ir

A. (1+YZ)
B. (1+YZ)* Z
C. 1
D. 0

Answer: A
Clarification: Using KVL to the line diagram,
Vs = (1+YZ)*Vr+ Z*Ir
Is = Y*Vr + Ir
AD = (1+YZ).

10. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters and find ‘B*D’ value.
Vs = A*Vr+B*Ir
Is = C*Vr+D*Ir

A. (1+YZ)
B. (1+YZ)* Z
C. Z
D. YZ

Answer: C
Clarification: Using KVL to the line diagram,
Vs = (1+YZ)*Vr + Z*Ir
Is = Y*Vr + Ir
BD = Z.

11. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters and find ‘B*C’ value.
Vs = A*Vr + B*Ir
Is = C*Vr + D*Ir

A. (1+YZ)
B. (1+YZ)* Z
C. 1
D. YZ

Answer: A
Clarification: Using KVL to the line diagram,
Vs = (1+YZ)*Vr+Z*Ir
Is = Y*Vr+Ir
BC = YZ.

12. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters and find ‘C*D’ value.
Vs = A*Vr+B*Ir
Is = C*Vr+D*Ir

A. (1+YZ)
B. (1+YZ)* Z
C. Z
D. Y

Answer: A
Clarification: Using KVL to the line diagram,
Vs = (1+YZ)*Vr+Z*Ir
Is = Y*Vr+Ir
CD = Y*1 = Y.

13. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters and find ‘AB-CD’ value.
Vs = A*Vr+B*Ir
Is = C*Vr+D*Ir

A. Z-Y+YZ2
B. (1+YZ)* Z
C. 1+YZ+YZ2
D. 1-YZ+ZY2

Answer: A
Clarification: Using KVL to the line diagram,
Vs = (1+YZ)*Vr+Z*Ir
Is = Y*Vr+Ir
AB-CD = (1+YZ)*Z-Y.

14. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters and find ‘AD-BC’ value.
Vs = A*Vr+B*Ir
Is = C*Vr+D*Ir

A. Z-Y+YZ2
B. (1+YZ)* Z
C. YZ+YZ2
D. 1

Answer: D
Clarification: Using KVL to the line diagram,
Vs = (1+YZ)*Vr+Z*Ir
Is = Y*Vr+Ir
AD-BC = (1+YZ)-YZ = 1.

15. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters and find ‘A*C*D’ value.
Vs = A*Vr+B*Ir
Is = C*Vr+D*Ir

A. ZY+(YZ)2
B. (1+YZ)* Z
C. YZ+YZ2
D. 1-YZ+ZY2

Answer: A

250+ TOP MCQs on Switchgear and Protection – 3 and Answers

Tricky Power Systems Questions on “Switchgear and Protection – 3”.

1. A power system network is connected as shown in the figure below.

Sd1=15+j5 pu
Sd2=25+j15 pu
Zcable = j0.05pu
|V1|=|V2|=1 pu. The torque angle for the system will be _______
A. 14.4
B. 22.1
C. 16.2
D. 18.2

Answer: A

2. A single phase distributor of 1 km long has resistance and reactance per conductor of 0.1Ω and 0.15 Ω respectively. If the far end voltage Vb=200V and current is at 100A at 0.8 lag. At the midpoint a current of 100A is tapped at a pf of 0.6 pf with ref to voltage Vm at mid point. The voltage magnitude at M is __________
A. 218V
B. 200V
C. 232V
D. 220V

Answer: A
Clarification: Drop in MB= (100ʟ-36.67)(0.1+j0.15)= 18.027ʟ19.44
VM= 200+18.027 = 218.027 V.

3. A single phase motor is connected to 400V, 50Hz supply. The motor draws a current of 31.7A at a power factor 0.7 lag. The capacitance required in parallel with motor to raise the power factor of 0.9 lag (in micro farads) is ___________
A. 94.62
B. 282.81
C. 108.24
D. 46.87

Answer: A
Clarification: Active power drawn by the motor=VIcosФ = 400*31.7*0.7 = 8876 W
Reactive power = VIsinФ=400*31.7*sin(45.57.29) = 9055.3 VAR
New power factor=cosθ2 = 0.9
θ2=cos-1(0.9)
Q2=8876*tan(25.84) = 4298.855 VAR
Change in reactive power=9055.3-4298.855 = 4756.4 VAR
Qc = V2/Xc = V2*2πfC
C=4756.4/(4002*2π*50) = 94.62μF.

4. A single phase motor is connected to 400V, 50Hz supply. The motor draws a current of 31.7A at a power factor 0.7 lag. The additional reactive power (in VAR) to be supplied by the capacitor bank will be ___________
A. 4756
B. 4873
C. 4299
D. 9055.3

Answer: A
Clarification: Active power drawn by the motor=VIcosФ = 400*31.7*0.7 = 8876 W
Reactive power = VIsinФ=400*31.7*sin(45.57.29) = 9055.3 VAR
New power factor=cosθ2 = 0.9
θ2=cos-1(0.9)
Q2=8876*tan(25.84) = 4298.855 VAR
Change in reactive power=9055.3-4298.855 = 4756.4 VAR.

5. A 275 kV TL has following line constants A=0.85ʟ5o, B=200ʟ75o. The active power received if the voltage to be maintained is 275kV will be ______________
A. 117.63
B. 220
C. 120
D. 115.25

Answer: A

6. A 275 kV TL has following line constants A=0.85ʟ5o, B=200ʟ75o. The active power angle such that the voltage to be maintained at the other end will be 275 kV ______________
A. 22
B. 16
C. 18
D. 24

Answer: A

7. A power system has a maximum load of 15 MW. Annual load factor is 50%. The reserve capacity of plant is _____ if the plant capacity factor is 40%.
A. 3.75 MW
B. 4.75 MW
C. 18.75 MW
D. 5.75 MW

Answer: A

8. A 100 MVA synchronous generator operates on full load at a frequency of 50 Hz. The load is suddenly reduced to 50 MW. Due to time lag in governor system, the steam valve begins to close after 0.4s. The change in the frequency (H=5 kW-s/KVA. is ___________
A. 1
B. 0.5
C. -1.5
D. 0.8

Answer: A

9. A 50 Hz four pole turbo-generator rated 100 MVA, 11 kV has an inertia constant of 8 MJ/MVA. If the mechanical input is suddenly raised to 80 MW for an electrical load of 50MW, then the rotor acceleration is __________
A. 337.5
B. 3.375
C. 457.5
D. 4.57

Answer: A
10. A single phase TL has copper conductor of 0.775 cm2 cross section through which 200 kW at UPF at 330 V is to be maintained. If the efficiency of transmission line is 90%, then the minimum length of TL is _________(in km and take specific resistance to be 1.785 μΩ/cm).
A. 13.6 km
B. 14 km
C. 136 km
D. 16.4 km

Answer: A
Clarification: Pr=200 kW, efficiency=0.9
Ps= 200/0.9=222.22 kW
Losses=22.22 kW
Current, I=200000/3300 = 60.60 A
Line losses=2I2R ( for a 2 wire line)
R=22.22/(2*60.602)=3.02 Ω
R=ρl/a
Length, l = (3.025*0.775)/(1.785*10-6) = 13.6 km.

11. An isolated generator connected to a turbine with its continuous maximum power of 20 MW, 50 Hz. Generator connected with two loads of 8 MW, each operate at 50 Hz.. Generator has 5% droop characteristic. If an additional load of 6 MW is added then frequency will be ___________
A. 50.25
B. 40.75
C. 49.75
D. 48.75

Answer: A

250+ TOP MCQs on Steam Turbines and Answers

Power Systems Multiple Choice Questions on “Steam Turbines”.

1. Which of the following is not a type of steam turbine?
A. Impulse turbine
B. Reaction turbine
C. Pelton wheel turbine
D. Axial flow type turbine
Answer: C
Clarification: Pelton wheel turbine is a water turbine. Impulse and reaction turbines are the steam turbines characterized by the action of steam on moving blades. Axial and radial flow turbine and steam turbines are characterized by type of flow of steam over blades.

2. Which statement about impulse turbine is true?
A. Steam expands over blades
B. Steam expends completely in stationary nozzels
C. Steam expends partially over nozzle and turbine blades
D. Steam expends over blades incompletely
Answer: B
Clarification: In an impulse turbine the steam expands completely in the stationary nozzles. No pressure drop occurs over the moving Blade Runner. During expansion steam attains a high velocity and impinges against the blades fixed on the rotor Periphery resulting in the impulsive force on the moving blades which sets the rotor rotating.

3. Which statement about reaction turbine is false?
A. Steam does not expand in nozzle
B. Blades acts like nozzles
C. Steam expands as flows over the rotor blades
D. Steam continuously losses its heat as flows over the rotor blades
Answer: D
Clarification: The expansion of steam in reaction turbine totally occurs when it flows over the turbine blades. The expansion of steam as it flows over the blades is adiabatic any friction losses between the steam and the blades are converted into heat which in turn will reheat the steam.

4. Reaction turbines are characterized by ___________
A. relatively low RPM and steam expension over nozzle
B. relatively high RPM and steam expension over nozzle
C. relatively low RPM and steam expension over rotor blades
D. relatively high RPM and steam expansion over rotor blades
Answer: C
Clarification: In reaction turbine steam does not expand in nozzle but expands as flows over the rotor blades. Reaction turbines are characterized by relatively low RPM. As steam expands over the turbine blades, causes the reaction force over the turbine which rotates the turbine.

5. In condensing turbine what is the back pressure of the turbine?
A. Very high
B. Above atmospheric pressure
C. Equal to atmospheric pressure
D. Below atmospheric pressure
Answer: D
Clarification: According to the back pressure steam turbines are classified into condensing and non condensing turbines. Where there is no use of exhaust steam, turbine is built as a pure condensing type turbine. In condensing turbine steam is reduced in pressure down to a vacuum pressure which is in accordance with the cooling water temperature.

6. The turbine in which steam enters the blade tip nearest the axis of the wheel and flows towards the circumference is called _____________
A. axial flow turbine
B. radial flow turbine
C. impulse turbine
D. non-condensing turbine
Answer: B
Clarification: According to type of flow of steam the steam turbines used are of two types namely axial flow turbine and radial flow turbine. In axial flow turbine steam flows over the blades in a direction parallel to the axis of wheel. In radial flow turbine steam enters from blade tip near the axis of wheel and flows towards the circumference.

7. Majority of the turbines are axial flow type.
A. True
B. False
Answer: A
Clarification: In axial flow type turbines the steam flows over the blades in a direction parallel to the axis of the wheel. In radial flow turbines the blades are arranged radially so that the steam enters at the blade tip nearest the axis of the wheel and flows towards the circumference.

8. Which turbines are employed for driving alternator at synchronous speed?
A. Central Station turbine
B. Reheating turbine
C. Extraction turbine
D. Extraction induction turbine
Answer: A
Clarification: Central turbines are for driving the alternator at synchronous speed. In Reheating turbine steam is returned back to the boiler after partial expansion for superheating and then allowed to expand to back pressure. In extraction turbines steam leaves the turbine casing before the exhaust, for feed water heating.

9. Read the statements below.
I. The built up rotor is cheaper and easier to manufacture.
II. The high pressure and intermediate pressure rotors are always of integral type.
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: C
Clarification: A built-up rotor consists of a forged steel shaft on which separate forged steel discs are shrunk and keyed. In an integral rotor the wheels and shaft are formed from the solid forging. The built-up rotor is cheaper and easier to manufacture.

10. In velocity compounding the steam is expanded from the boiler pressure to condenser pressure in one set of stationary blades on nozzle.
A. True
B. False
Answer: A
Clarification: In compounding a number of rotors in series, keyed on the same shaft, are employed and the steam pressure or the jet velocity is absorbed in steps as it was over the moving blades. Compounding is necessary for obtaining reasonable blade tip speed in turbines.

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