This set of Thermal Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Steam Turbine Governing and Control”.
1. What is the objective of steam turbine governing?
a) To keep turbine load constant irrespective of the turbine speed
b) To keep turbine speed constant irrespective of the load
c) To enhance the output of the turbine
d) To reduce the losses in the turbine
View Answer
Explanation: The objective of steam turbine governing is to keep turbine speed constant irrespective of the load on the turbine shaft. The performance of a steam turbine is affected when the load changes. Turbine governing is important because in practical conditions the load frequently varies.
2. Which of the following is NOT a method of steam turbine governing?
a) By-pass governing
b) Throttle governing
c) Steam governing
d) Nozzle governing
View Answer
Explanation: Throttle governing, by-pass governing and nozzle governing are all different methods of steam turbine governing while there is no method called steam governing. The mentioned three methods are used to keep the turbine speed constant at varying load condition.
3. Which of the following statements about throttle governing is wrong?
a) It cannot be used in small turbines
b) It has a relatively simpler mechanism
c) Steam is throttled whenever the load falls below the design load
d) Its initial cost is less
View Answer
Explanation: Throttle governing is used particularly for small turbines. Its cost is less and it has a simple mechanism. In throttle governing the steam is throttled whenever the load falls below the design load to maintain turbine speed constant.
4. In case of throttle governing, the beat valve is operated using oil supply. The oil is supplies using a _____
a) centrifugal pump
b) servomotor
c) reciprocatory pump
d) diaphragm pump
View Answer
Explanation: The double beat valve in the throttle governing mechanism is operated by supply of oil. This supply of oil is carried out by an oil servomotor. When the steam turbine gains speed this valve is closed and supply to the nozzle is reduced.
5. The oil servomotor in case of throttle governing mechanism is controlled by a _____ governor.
a) centrifugal
b) reciprocatory
c) diaphragm
d) gear
View Answer
Explanation: In throttle governing mechanism, the oil servomotor is controlled by a centrifugal governor. The servomotor supplies oil for operating the double beat valve. The closing of the valve reduces the supply to the nozzle.
6. The relationship between steam consumption and load in throttle governing is given by _____
a) Wilson’s line
b) Wilkinson’s line
c) Willan’s line
d) Wilber’s line
View Answer
Explanation: Willan’s line gives the relationship between the steam consumption and load in throttle governing. In throttle governing the steam is throttled whenever the load falls below the design load. It is used mostly in small turbines.
7. Which of the following is the correct equation for Willan’s line?
a) ms0=KM+ms
b) ms0=M/K+ms
c) ms=KM+ms0
d) ms=M/K+ms0
View Answer
Explanation: Willan’s line gives the relationship between steam consumption and load in case of throttle governing. It’s given by –
ms=KM+ ms0
where, ms – Steam consumption at any load M (kg/h)
ms0 – Steam consumption at no load (kg/h)
M – Any load (kW)
K – Constant.
8. Carrying out throttle governing at low loads reduces the turbine efficiency.
a) True
b) False
View Answer
Explanation: The turbine efficiency is significantly reduced when throttle governing is carried out at low loads. To avoid this, nozzle governing is used. Governing by means of nozzle control is more efficient than throttle governing.
9. In nozzle governing, under full load condition what can be said about regulating valves?
a) They are fully open
b) They are fully closed
c) They are partially open
d) Depends on the input
View Answer
Explanation: In nozzle governing, around 3 to 5 or even more groups of nozzles are employed and the supply of steam to the nozzles is controlled by regulating valves. Under full load condition the regulating valves are fully open, allowing maximum flow through the nozzles.
10. In nozzle governing, when the load on the turbine deviates from the design load, steam supply to a group of nozzles could be varies to restore the original speed.
a) True
b) False
View Answer
Explanation: The objective of steam turbine governing it to maintain turbine speed constant irrespective of loading. In case of nozzle governing, the steam supply to a group of nozzles is varied when the load deviates from the design value to keep the turbine speed constant.
11. Which of the following statements is FALSE regarding nozzle-governing in steam turbines?
a) It can only be applied to the first stage of the turbine
b) Nozzle governing is more efficient than throttle governing
c) It can also be employed for large turbines having an impulse stage followed by an impulse reaction turbine
d) It is cannot be employed for simple impulse turbine
View Answer
Explanation: Nozzle governing is well suited for simple impulse turbine. it is more efficient than throttle governing and nozzle control can be applied only on the first stage of the turbine. Also it is used for large turbines having an impulse stage followed by an impulse reaction turbine.
12. Which of the following method of steam turbine governing is ideal for reaction turbines?
a) Throttle governing
b) Nozzle governing
c) By-pass governing
d) Combination of throttle and by-pass governing
View Answer
Explanation: In case of reaction turbines, pressure drop is required in case of moving blades and therefore, nozzle control governing is not possible. For this reason, combination of throttle and by-pass governing is considered ideal for reaction turbines.
13. Which of the following statements is FALSE about by-pass governing?
a) There is curving observed in Willan’s line
b) When the by-pass valve is opened efficiency is reduced
c) Opening of by-pass valve reduces the work output of lower stages
d) By-pass valve opens after throttle valve has opened to a definite threshold amount
View Answer
Explanation: The opening of by-pass valve reduces the effieincy of the turbine, but the work output of the lower stages is increased as the supply of steam has increased. By-pass valve opens only after the throttle valve has opened a definite amount.
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