This set of Power Systems Multiple Choice Questions & Answers (MCQs) focuses on “Elements of Hydroelectric Power Plant”.
1. Which element of hydroelectric power plant prevents the penstock from water hammer phenomenon?
a) Valves and Gates
b) Draft tubes
d) Surge Tank
Explanation: Sudden increase in water pressure in penstock due to closing of gates is called water hammer. Surge tank is a tank at sufficient height , connected to penstock through riser pipe. It takes the rejected water and relives the penstock from excessive water hammer pressure.
2. Dam having very wide base as compared to its height is called _________
a) buttress dam
b) arch dam
c) earth dam
d) solid gravity dam
Explanation: Buttress dams are the concrete dams supported on downstream side by buttresses. Arc dams are concrete dams curved from upstream side. Earth dam is a type of embankment dam and have rock filled inside the structure.
3. Spillway discharges the overflow water to the downstream side when the reservoir is full.
Explanation: A condition may arise during flood periods when water level increases beyond the capacity of reservoir. In such conditions spillway acts as safety valve.
4. Trash racks are built for ___________
a) discharging the water freely from the turbine exit to tailrace
b) preventing the turbine from ingress of floating and other materials
c) creating artificial head to store sufficient potential energy of water
d) controlling the opening of valves
Explanation: Heavy solid materials flowing with water can damage the turbine blades if not stopped. Trash racks are closely spaced flat bars which provides narrow path from which such unwanted materials cannot pass.
5. Penstock in a hydroelectric power plant is _____________
a) a pipe connected to runner outlet
b) nozzle that release high pressure water on turbine blades
c) a conduit connecting forebay to scroll case of turbine
d) a pipe connecting surge tank to dam
Explanation: Penstocks are the conduit built of steel or reinforced concrete. Penstock connects forebay or surge tank to scroll case of turbine. Their main function is to carry water from dam to the turbine.
6. The pressure at the inlet or exit of the draft tube should not be _________
a) less than one third of atmospheric pressure
b) greater than one third of atmospheric pressure
c) less than one atmospheric pressure
d) greater than one atmospheric pressure
Explanation: Decrease in pressure in any portion of turbine below one third of atmospheric pressure may cause vapour bubbles or cavities to form. This phenomenon is called cavitation. Also to maintain continuity of flow without vaporisation the pressure should not fall below vapour pressure of water.
7. Draft tube increases the operating head on the turbine.
Explanation: Draft tubes are the pipes of suitable diameter attached to the runner outlet. Draft tube converts the pressure developed by water leaving from turbine into kinetic energy. This in turn increases the operating head on turbine.
8. Which statement about surge tank is wrong?
a) Ideal location of surge tank is at the turbine inlet
b) A decrease in load demands cause a rise in water level in surge tank
c) Surge tanks are totally closed to avoid entry of unwanted objects to penstock
d) Surge tanks are installed to reduce harm effects of water hammer phenomenon
Explanation: Function of surge tank is to relieve the penstock from excessive water hammer pressure. It does so by receiving rejected flow of water into the tank. A totally closed tank can not release pressure so usually surge tanks are left open at the top.
9. Trash racks are located _____________
a) near tailrace
b) at the entrance of turbine
c) inside penstock
Explanation: Intake includes headworks at the entrance of conduit. Those headworks include different structures, trash racks are one of them. Trash racks are fitted directly at the intake to prevent the floating and other materials from going into the conduit.
10. What is the function of booms?
a) It supports the dam
b) It supports the penstock
c) It divert the Icebergs from flowing into the penstock
d) To hold the turbine structure
Explanation: Booms are the one of those structures made at the intake. They are constructed to prevent unwanted solid materials from flowing into the penstock. Solid materials like icebergs, wood logs or other heavy materials which may cause damage to the turbine blades if reached there.
Sanfoundry Global Education & Learning Series – Power Systems.
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