This set of Power Systems Multiple Choice Questions & Answers (MCQs) focuses 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
Explanation: 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
Explanation: 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
Explanation: 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
Explanation: 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
Explanation: 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
Explanation: 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.
Explanation: 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
Explanation: 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
Explanation: 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.
Explanation: 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.
Sanfoundry Global Education & Learning Series – Power Systems.
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