Hydroelectric Power PlantSolar Lounge

Nishkam Dhiman

Asst Prof : Electrical and Electronics Engineering

Chitkara University, Punjab

Introduction

• Hydroelectric power (often called hydropower) is considered a renewable energy source. A renewable energy source is one that is not depleted (used up) in the production of energy. Through hydropower, the energy in falling water is converted into electricity without “using up” the water. Hydroelectric power (hydropower) systems convert the kinetic energy in flowing water into electric energy.

1. Source of power.

2. Interconnected with steam power plants, base load is supplied by the hydro power plants while the peak load is supplied by steam power plant, when stream flow is less than maximum flow demand.

3. When stream flow is more than the maximum flow demand, base load is supplied by the steam power plants while the peak load is supplied by hydro power plant.

Applications

Advantages

1. No fuel charges.

2. Any hydro electric plant is highly reliable

3. Maintenance and operation charges are very low.

4. Running cost of plant is low.

5. It has no standby losses.

6. The plant efficiency doesn’t change with age.

7. It take a few minutes to run and synchronize the plant.

8. Less supervising staff is required.

9. No fuel transportation problem.

10. No ash problem.

11. In addition to power generation these plants are also used for flood control and irrigation purposes.

12. The have long life (100-125yrs, 20-45yrs of thermal plant)

Disadvantages

• The initial cost is very high.• It takes considerable time for the erection of such

plants.• Such plants are usually located in hilly areas far

away from the load centre and as such they require long transmission lines to deliver power, hence the cost of transmission linear and losses in them will be more.

• Power generation by the hydro-electric plants depend upon quantity of water hence rain.

Selection of Site

• Availability of water• Water storage• Water head• Accessibility of the site• Distance from the load centre• Type of the land of site

Essential Features/Elements of Hydro – electric Power Plant.

1. Catchment Area

2. Reservoir

3. Dam

4. Spillways

5. Conduits

6. Surge tanks

7. Prime movers

8. Draft Tubes

9. Powerhouse and Equipment

1. Catchment area: The whole area behind the dam draining into the stream.

2. Reservoir: Used to store water.

A. Natural (lake)

B. Artificial (dam, called pondage)

Types of dams:

A. Fill Dams : Earth dams, Rock Fill Dams

B. Masonary Dams: Solid gravity dams, Butteress dams, Arch dams.

C. Timber Dams

Selection of type of Dam

1. Nature of foundation

Sound rock formation in foundation: any type of dam

Poor rock and earth foundation: earth dam

2. Nature of valley

Narrow valley : arch dam

Rocky bed: Solid gravity dam

Wide valley weak foundation: Buttress dam

Any width of valley, good foundation : Steel Dam

T y p es o f D am s

• Fill Dams

1. Earth fill dams: earth fill dam, also called Earth Dam, or Embankment Dam,  dam built up by compacting successive layers of earth, using the most impervious materials to form a core and placing more permeable substances on the upstream and downstream sides. A facing of crushed stone prevents erosion by wind or rain, and an ample spillway, usually of concrete.

• A rockfill dam is a type of embankment dam which comprises primarily compacted rock materials.Used in mountainous locations where rock is available.

Masonry Dams• Solid Gravity Dam: Massive and

bulky and depends upon its weight on stability.

• It requires strong rock foundation• Bhakra Dam is the highest Concrete

Gravity dam in Asia and Second Highest in the world.

• Bhakra Dam is across river Sutlej in Himachal Pradesh

• It is 740 ft. high above the deepest foundation as straight concrete dam being more than three times the height of Qutab Minar.

• Length at top 518.16 m (1700 feet); Width at base 190.5 m (625 feet), and at the top is 9.14 m (30 feet)

B u tteress D am

• Is a gravity dam reinforced by structural supports.

• A buttress dam or hollow dam is a dam with a solid, water-tight upstream side that is supported at intervals on the downstream side by a series of buttresses or supports. The dam wall may be straight or curved.

• Most buttress dams are made of reinforced concrete and are heavy, pushing the dam into the ground. Water pushes against the dam, but the buttresses are inflexible and prevent the dam from falling over

• Buttress - a support that transmits a force from a roof or wall to another supporting structure

• It has a relatively thin structure. Because of this, these dams often use half as much concrete as gravity dams can be used for weaker foundation.

Arch dam

• An arch dam is a solid dam made of concrete that is curved upstream in plan. The arch dam is designed so that the force of the water against it, known as hydrostatic pressure, presses against the arch, compressing and strengthening the structure as it pushes into its foundation or abutments.

• An arch dam is most suitable for narrow gorges or canyons with steep walls of stable rock to support the structure and stresses .Since they are thinner than any other dam type, they require much less construction material, making them economical and practical in remote areas.

Arch Dam

• Timber Dams • When wood in plentiful and more durable

material are not accessible timber is used for low dams 12m.

S p illw ay s

• A spillway is an integral part of a Dam.• A spillway is usually used to remove water from a reservoir to

prevent overflow and to release pressure on a dam from increasing quantities of water. It is normally composed of three major

components: • The approach facility admits flow to the spillway. • The discharging conduit evacuates the flow from the approach

facility to an outlet structure. • The outlet structure (tailwater channel) dissipates the excessive

energy of the flow from the discharging conduits and conveys tranquil flow to the downstream.

O v erflo w S p illw ay

• Overflow spillways are also called ogee-shaped

(S-shaped) spillways. • This type of spillways allows

the passage of the flood wave over its crest

(which is S-shaped). • Can be classified under

controlled or uncontrolled. • Widely used on Gravity

dams, Arch dams, and Buttress dams.

Chute spillways

• Chute spillways are common and

basic in design as they transfer excess water from behind the dam down a smooth decline into the river below. • The spillway’s slope and its sides

are lined with concrete. • In case of having sufficient stiff

foundation conditions at the spillway

location, a chute spillway may be used instead of overflow spillway due to economic consideration.

Side Channel Spillway

• It is employed when valley is too narrow in case of solid gravity dams and when non rigid dams are adopted.

• The side channel spillway is different from chute spillway in the sense that after crossing over the spillway crest. Water flows parallel to the crest length in former, whereas the flow is normal to the crest in the later.

Side Channel Spillway

S ad d le S p illw ay

• There may be natural depressions or saddle on the periphery of the reservoir basin away from the dam. The depressions may be used as spillway.

• The bottom of the depression should be at full reservoir level.

S ip h o n S p illw ay

• Crest is fixed at Full Reservoir Level. When the water level in the reservoir rises over F.R.L water starts spilling over the crest.

C o n d u it

• A headrace is a channel which leads water to a turbine and a tailrace is a channel which conducts water from the wheels.

• Open Conduit: Canals and Flumes • Close conduits: Tunnels, pipelines and penstock

P en sto ck

• Closed conduit for supplying water under pressure to a turbine.

• Thinkness of penstock is given by:• T = pd/2fn

p = pressure due to water

d = diameter of the penstock

f = Permissible circumferential stress

n = Joint efficiency

Surge Tanks

• A surge tank is small reservoir or tank in which water level rises of falls to reduce the pressure swings so that they are not transmitted in full to closed circuit.

1. They reduce the distance between the free water surface and turbine thereby reducing water hammer effect ( the change in in pressure rapidly above or below normal pressure caused by sudden changes in the rate of water flow through the pipe according to the demand of the primemover) on the penstock.

2. To serve as supply tank to the turbine in case of increased load conditions, and storage tank in case of low load conditions.

Surge Tank

Prime movers

• Impulse Turbines: Pressure energy of water is converted to kinetic energy when passing through nozzle and forms velocity of high head.

• Reaction Turbines: Water pressure combined with the velocity works on the runner, power is developed from the combined action of pressure and velocity of water, that completely fill the runner and water passage.

Draft Tubes

• It allows the turbine to be set above tail water level, without loss of head, to facilitate inspection and maintenance

• It regains, by diffuser action, the major portion of the kinetic energy delivered to it from the runner.

1. Conical Type: used on low powered units for all specific speeds and frequently od large head units. Side angle 4 to 6 deg.

2. Elbow Type: Mostly used, vertical portion is a conical section which gradually flattens in the elbow section and then discharges horizontally.

Draft Tubes

Types of Power Plants

H ig h H ead P o w er P lan t

Head: 100m to 2000m

Water is stored in the lake over the mountain during high rainy season or when snow melts.

Water should be available throughout the year.

Pelton Wheel turbine is used.

Medium Head Plants

• Head : 30 to 100m• Uses Francis Turbine• Forebay provided at the beginning of penstock at as reservoir.• Water is carried in open canals from main reservoir to forebay then to

powerhouse through penstock.

Low Head Power Plants

• They consist of dam across the river.• A sideway stream diverges from the river at the dam, powerhouse is

constructed over the stream, which further joins the river.• Vertical shaft Francis or Kaplan turbine

According to Nature of Load

Base Load Plants: they cater to the base load of the system, they need to supply constant power when connected to the grid.

Peak Load Plants: some of the plants supply average load but also some peak load. Other peak load plants are required to work only during peak load hours.

According to the quantity of water

1. Run of river plants without pondage: • No pondage.• No control on flow of water.

2. Run of river plants with pondage

May work as base load or peak load plants.

Storage for a week

3. Storage Type Plant

The storage is large.

Used as base load and peak load plants

Controlled flow .

4. Pumped Storage plants• These plants are employed

where quantity of water required is inadequate.

• Water passing through the turbine is stored in the tail race pond. During low load periods the water is pumped back to the reservoir, which can be used during peak load plants.

• Usually interconnected with steam or diesel power plants.

M in i an d M icro h y d el p lan ts

• Mini – 5m to 20 m head• Micro – below 5 m head

These plants are scattered in our country and estimated potential is 20,000MW.

Each plant generate about

100 to 1000kW per unit.

Hydraulic Turbines

According to the head and quantity of water

• Impulse Turbine: Requires high head and small flow of water.

• Reaction Turbine: Requires low head and high rate of flow of water.

According to the name of originator

• Pelton Turbine: It is an impulse type of turbine used for high head and low discharge.

• Francis Turbine: It is reaction type of turbine, used for medium high to medium low heads and medium small to medium large quantities of water.

• Kaplan Turbine: It is reaction type of turbine, used for low head and large quantities of flow.

According to action of water on the moving blades

• Impulse: Pelton• Reaction: Kaplan, Francis, Propeller.

According to direction of flow of water in runner

• Tangential flow turbine (Pelton Turbine) • Radial flow turbine ( not used) • Axial flow turbine (Kaplan Turbine) • Mixed (radial and axial ) flow turbine (Francis turbine)

According to the position of turbine shaft

• Shaft may be horizontal or vertical • Pelton has horizontal axis

According to specific speed

• The specific speed is defined as the speed of a geometrically similar turbine that would develop one brake power horsepower under the head of one meter.

Im p u lse T u rb in e-P elto n T u rb in e

• Tangential flow impulse turbine.• Rotor has equally spaced

hemispherical buckets, Water is transferred from high head source through penstock pipes.

• All the available potential energy is converted to kinetic energy before the jet strikes the buckets.

• The pressure all over the wheel is constant and equal to atmospheric pressure, energy transfer occurs due to purely impulse action.

R eactio n T u rb in e

• The runner utilizes both potential and kinetic energy.

• As the water flows through the stationary part of the turbine, whole of its pressure energy is not transferred to kinetic energy. When the water flows through the moving parts, there is a change both in the pressure and in the direction and velocity of flow of water.

• The water which acts on the runner blades is under pressure above the atmospheric.

Francis Turbine

• It is an inward mixed flow reaction turbine i.e. water under pressure , enters the runner form the guide vanes towards the centre in the radial direction and discharges out of the runner axially.

• It runs under medium heads and requires medium quantity of water. • Water is brought down to the turbine and directed to a number of

stationary guide vanes.• The head acting on the turbine is partly transformed into kinetic

energy and rest remains as pressure head.• The runner is always full of water. The movement of runner is

affected by the change of both the potential and the kinetic energies of water.

• The water is then discharged to the tail race, through draft tube.

Propeller and Kaplan Turbines

• Propeller turbine is a reaction turbine used for heads between 4m to 80 m and specific speed of 300 to 1000.

• Axial Flow Type • It consists of axial flow runner• With 4-6 or max 10 blades of air foil shape

In Propeller Runner blades are fixed and non adjustable as in Francis Turbine.

In Kaplan Turbine which is a modification of propeller turbine the runner blades are adjustable and can be rotated about pivots fixed to the base.

Kaplan Turbine

T u b u lar/B u lb T u rb in e

• It is a modified axial flow turbine, the turbo generator set using the bulb/tubular turbine has the outer casing of the shape of a bulb.

• The turbine generator set is called bulb set and turbine used is called bulb turbine. The bulb unit is a water tight assembly of turbine and generator with horizontal axis, submerged in a stream of water.

Turbine Efficiencies

Governing of Hydraulic Turbines

• Governing means the speed regulation. Under normal conditions the turbine should run at constant speed irrespective of changes in the load.

• This is achieved by means of a governor called oil pressure governor.

Governing of Impulse turbines

• The quantity of water rejected from turbine nozzle and from striking the buckets may be regulated in following ways:

• Spear regulation: To and fro motion of spear inside the nozzle alters the cross sectional area of the stream.

• Deflector regulation: the deflector is generally a plate connected to the oil pressure governor by means of levers. When it is required to deflect the jet, the plate can be brought in between the nozzles and buckets, thereby diverting the water away from the runner and directing into tailrace.

It is used when supply of water is constant but load fluctuates.• Combined spear and deflector regulation: the speed is

regulated by spear and pressure is regulated by deflector

Governing of Reaction Turbines

• The guide blades of reaction turbine are pivoted and connected by levers and links to the regulating ring.

• To the regulating ring are attached two long regulating rods connected to the regulating lever.

• The regulating ring is keyed to the regulating shaft which is turned by servomotor piston of oil pressure governor.

• The penstock which feeds the turbine inlet is has relief valve know as pressure regulator.

• When guide vanes have to be suddenly closed the relief valve opens and diverts the water to tailrace.

Hydrology

• It may be defined as the science which deals with the depletion and replenishment of water resources.

Measurement of run-off

3. Run off tables and curves

• Hydrograph: It is defined as graph showing discharge(run off) of flowing water with respect to time for a specified time.

• It indicates the power available from the stream at different times of day, week or year.

• Unit Hydrograph: It is a hydrograph which represents unit run off resulted from an intense rainfall of unit duration and specified areal distribution.

Flow Duration Curve

• Is a plot of discharge against the percentage of time the flow was equaled or exceeded.

• It is the curve plotted between the flow available during a period verses fraction of time.

• The area under the flow of the duration curve gives the total quantity of run-off during that period.

• A flow duration curve allows the evaluation of low levels of flow.

• It is highly useful in the planning and design of water recourses.

• It also finds use in the design of drainage system and in flood control studies.

Mass Curve

• Mass curve is the graph of cumulative values of water quantity (run off) against time. A mass curve is integral curve of the hydrograph which expresses the area under the hydrograph from one time to another.

List of Power Plants in India

• http://en.wikipedia.org/wiki/List_of_power_stations_in_India