250+ TOP MCQs on Principal Components of a Hydro Electric Scheme and Answers

Irrigation Engineering Multiple Choice Questions on “Principal Components of a Hydro Electric Scheme”.

1. Forebay provides temporary storage before the water goes to the turbine. Following perform the function of forebay ____________________
a) river
b) tailrace channel
c) reservoir
d) approach channel
Answer: c
Clarification: The reservoir itself acts as a forebay when it is constructed by building a dam. The water is taken to the powerhouse directly from the reservoir through penstocks. Following are some functions of forebay:
• To temporarily store water and to meet the instantaneous demand
• Absorbs the short interval variations and fluctuations.

2. The surge tank serves which of the following purposes?

i. It allows the sediment to settle down
ii. It prevents debris from entering powerhouse
iii. It controls pressure variations in pipelines
iv. It regulates flow in the pipelines

a) i and ii
b) ii and iii
c) iii and iv
d) i, ii and iii
Answer: c
Clarification: The cylindrical chamber which is connected to the penstocks and open to the atmosphere is the simplest one. It serves the following functions i.e. to reduce the pressure fluctuations in the pipe and helps in eliminating additional water hammer pressure.

3. Identify the correct statement in regard to hydropower.
a) Hydropower stations are generally labour-oriented
b) The gestation period for hydro-power plant is usually small
c) The hydro generators give high efficiency over a wide range of load
d) In a hydropower scheme, the firm power is usually high as compared to tidal power
Answer: c
Clarification: Hydroelectric power plants are the most efficient means of producing energy and the efficiency of today’s hydroelectric plant is about 90%. Large hydropower plants usually have a gestation period of about 7 years whereas for smaller plants it is 2 to 5 years.

4. To avoid the possible damage to the wicket gates and turbine runners _________________ is provided.
a) trash racks
b) surge chamber
c) floating boom
d) racks and trolley arrangement
Answer: a
Clarification: Intakes should be provided with trash racks so as to prevent the entry of debris into the penstocks or to prevent choking up of the nozzles of the impulse turbines. Trash racks are made up of thin flat steel bars placed 10 to 30 cm apart and the permissible velocity of water entering these is 0.6 to 1.6 m/s.

5. In case of long penstocks, ___________________ is generally provided so as to absorb water hammer pressure.
a) trash racks
b) surge chamber
c) floating boom
d) racks and trolley arrangement
Answer: b
Clarification: The surge tank is mostly employed in a water power plant or in a large pumping plant to control the pressure variations resulting from rapid changes in the flow. It is done by admitting a large mass of water in the surge tank otherwise it would have flown out of the pipeline and returns to the tank due to closure of pipe end.

6. Sharp bends must be avoided in penstocks while designing components of the hydroelectric scheme.
a) True
b) False
Answer: a
Clarification: Sharp bends cause loss of head and requires special anchorages. It may be buried under the ground or kept exposed. The penstock can be replaced by constructing a tunnel through a hill if a considerable saving in length can be gained.

7. The retarding and accelerating heads are developed more promptly in ________________
a) simple surge tank
b) restricted orifice surge chamber
c) differential surge chamber
d) multi surge chamber
Answer: c
Clarification: The differential surge chamber has a central riser pipe in addition to the main outer tank and the retarding and accelerating heads are developed more promptly. The capacity of a different type of surge chamber may be less than that of a simple elementary type for a given amount of stabilizing effect.

8. The correct sequence in the direction of the flow of water for installations in a hydropower plant is _______________________
a) Reservoir, Surge tank, Turbine, Penstock
b) Reservoir, Penstock, Surge tank, Turbine
c) Reservoir, Penstock, Turbine, Surge tank
d) Reservoir, Surge tank, Penstock, Turbine
Answer: b
Clarification: The main components of a hydropower plant is Forebay, intake arrangement, Penstock, Surge tank, turbines and generators, powerhouse and tailrace. The water is taken from a reservoir or forebay and is taken down to the powerhouse by penstock. A surge tank is fitted at some opening made on a penstock to receive the rejected flow when the pipe is suddenly closed.