1. 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
2. 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
3. Majority of the turbines are axial flow type.
a) True
b) False
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.
4. 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.
5. 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.
6. 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
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.
7. 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
Explanation: 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
8. 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
Explanation: 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
9. 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
Explanation: 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
10. What is the main disadvantage of spreader stoker?
a) Poor control
b) Difficult operation
c) More unwanted fly ash
d) Dangerous operation
Explanation: 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.