# Irrigation Engineering Questions and Answers – Hydro Electric Power – Turbines Types and their Selection

This set of Irrigation Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Hydro Electric Power – Turbines Types and their Selection”.

1. Which of the following is an example of an impulse turbine?
a) Pelton turbine
b) Francis turbine
c) Kaplan turbine
d) Propeller turbine

Explanation: In the impulse turbine, all the potential energy or head is converted into kinetic energy or velocity head by passing the water through a contracting nozzle or by guide vanes before it strikes the buckets. Some types of impulse turbine are Pelton wheel, Turgo impulse wheel, and Girard turbine.

2. Which of the following is turbine is used for medium heads ranging from 25 to 150 meters?
a) Pelton turbine
b) Kaplan turbine
c) Francis turbine
d) Propeller turbine

Explanation: For high heads over 150 meters, a low-speed turbine like Pelton wheel is suitable. Francis turbine is used for medium heads varying from 25 to 150 meters and for low heads, Kaplan and propeller turbines are used.

3. An impulse turbine is essentially a __________________
a) low-speed turbine and is used for high heads
b) low-speed turbine and is used for low heads
c) high-speed turbine and is used for high heads
d) high-speed turbine and is used for low heads

Explanation: It is a low-speed wheel and is relatively used for high heads over 150 meters. It works under high heads so comparatively less quantity of water is required. Pelton’s turbine is an important example of an impulse type of turbine.

4. Kaplan turbines are found to be more versatile and costly in their initial cost as compared to propeller turbines.
a) True
b) False

Explanation: Kaplan turbines have an additional arrangement of adjusting the inclination of the runner blades or vanes on the hub. This causes the Kaplan turbine to give higher efficiency even under part-load conditions although both the turbines look alike and behave hydraulically in a similar fashion.

5. An impulse turbine like a Pelton’s turbine is __________________________
a) an open body exposed to the atmosphere
b) a closed body not exposed to the atmosphere
c) a partially open and partially closed body
d) depends on the design requirements

Explanation: The water through a contacting nozzle or by guide vanes is made to strike on a series of buckets. The wheel revolves free in the air and the water is in contact with only a part of the wheel at a time and the pressure is atmospheric. A casing is provided in order to prevent splashing and to guide the water discharged from the buckets to the tail-race.
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6. In a reaction turbine like a Francis turbine or a Kaplan turbine ______________
a) the potential head of water is totally changed into the kinetic head
b) the potential head of water is partially changed into the kinetic head
c) the potential head of water is not at all changed into the kinetic head
d) the change of potential head of water totally or partially depends on other factors as well

Explanation: In a reaction turbine, only part of the available potential energy is converted into velocity head at the entrance to the runner. The balance portion remains as a pressure head. In Francis turbine, there is an inward radial flow of water and in Francis turbine, there is a mixed flow of water.

7. In a Francis turbine, the water flows through a closed draft tube.
a) True
b) False

Explanation: In Francis turbine, the water enters radially inward but leaves in a parallel direction to the shaft at the center, it is called mixed flow. In the case of a reaction turbine like Francis turbine, a draft tube is used to connect the outlets of the runner to the tailrace.

8. For a hydropower plant having 150 m head of stored water behind the dam. The water in the reservoir is clear and load on the powerhouse is not likely to fluctuate much. Which type of turbine will be suitable for the same?
a) Pelton turbine
b) Francis turbine
c) Kaplan turbine
d) Propeller turbine

Explanation: Francis turbines are cheaper than Pelton’s turbine and there is no special need for Pelton’s turbine because variable loads are not likely to come and water is not sandy which may certainly need Pelton’s turbines. Hence, Francis turbine will suffice to our needs.

9. For a hydropower plant working on 150 m head, the water is sandy and the load on the plant is highly variable. Which type of turbine will generally be recommended?
a) Pelton Turbine
b) Francis turbine
c) Kaplan turbine
d) Propeller turbine

Explanation: For variable loads (part loads) and sandy water, Pelton’s wheel is most suitable. These are preferred where the available water source has a relatively high head at low flow rates.

10. If two identical pumps each capable to deliver a discharge Q against a head H are connected ___________________________
a) in parallel, the resulting discharge is 2Q against a head H
b) in parallel, the resulting discharge is Q against a head of 2H
c) in series, the resulting discharge is 2Q against a head H
d) in series, the resulting discharge is Q against a head 2H

Explanation: Water pumps are installed in parallel as in the case of pumping water from a sump well using more than one pump. The head remains constant and the combined discharge of the two pumps is equal to the sum of the individual discharges for a specific head.

11. If the specific speed in revolution per minute of a turbine is in between 60 to 300, the type of the turbine is ________________
a) Pelton turbine
b) Francis turbine
c) Propeller turbine
d) Kaplan turbine

Explanation: The specific speed of a Pelton turbine ranges from 10 to 30. Francis turbine has a specific speed between 60 to 300 and the specific speed of Kaplan and propeller turbine lies in between 300 to 1000.

12. A draft tube is essentially required for impulse type turbines.
a) True
b) False

Explanation: The entire flow from head race to tail race takes place in a closed system as the water is under pressure. The wheels of the turbine are submerged and water enters all around the periphery of the wheel. A closed conduit or casing like the draft tube is absolutely necessary so as to prevent any access of atmospheric air into the turbine.

13. Pick the correct choice of turbine required to generate 10,000 HP under a head of 81 m while working at a speed of 500 rpm.
a) Pelton
b) Kaplan
c) Bulb
d) Francis

Explanation: The specific speed is given by the equation: Ns = N. Pt1/2 / H5/4
Where, N = the normal speed of turbine = 500 rpm
Pt = Turbine output in metric horsepower = 10,000 hp
H = effective head = 81 m
Ns = 500 x 100 / 815/4 = 205.76 rpm.
The turbine which is suitable for a head between 25 to 150 m and Ns of 60 – 300 is Francis turbine i.e reaction type turbine.

14. Consider the following statements.

```i. Runoff river plants can be located on any river
ii. Runaway speed of a turbine is generally 180% of normal speed
iii. Underground power stations are suited to areas susceptible to landslides
iv. Higher the specific speed, higher will be the discharge and the head
```

Which of these statements are correct?
a) i and ii
b) ii and iii
c) i and iv
d) ii and iv

Explanation: The specific speed is inversely proportional to the specific head, higher the specific speed, lesser will be the head. Run-off river plants are suitable only on a perennial river and are not suitable for the constant steady load.

15. The Pumps in series operation allow the head to increase and the pumps in parallel operation increase the flow rate.
a) True
b) False

Explanation: When two or more pumps are connected in series, the same discharge passes through all the stages. Each stage in pumping operation adds an additional head to the flow. Thus the combined head is equal to the sum of individual heads for a specific discharge. In parallel, the head remains constant and the combined discharge is equal to the sum of individual discharges for a specific head.

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