h. Hydro-electric Power Plant - Lecture

8/10/2019 h. Hydro-electric Power Plant - Lecture

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H.HYDRO-ELECTRIC POWER PLANT - LECTURE

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1.

Basic Elements in Hydro-Electric Power Plant.

1.1

Storage Reservoir or Reservoir

Reservoir used to store water during rainy days and supply the same during the dry season. Also stores the

water coming from the upper river or water falls.

1.2

Spillway

Spillwaya weir in the reservoir which discharges excess water so that the head of the plant will be maintained

1.3

Dam

Dam - the concrete structure that encloses the reservoir used for impounding the water for storage and for

creating head for the power plant.

1.4

Intake Structure or Equipment

Intake structureconsists of racks or screens to prevent trash or entry of debris into the turbine runners.

1.4.1

Silt Sluicea chamber used to collect and discharge mud.

1.4.2

Trash racka screen which prevents leaves, twigs, branches and other water contaminants to enter the

penstock.

1.5

Water way

1.5.1

Open channel

1.5.2

Penstocka pressure conduit which leads water from reservoir to turbine.

1.5.3

Tailracea channel which leads water from turbine to tailwater.

1.6

Surge Tank or Chamber

1.6.1

Surge Tank - is used to reduce the water hammer during decrease in turbine load.

1.6.2

Surge Chamber a standpipe connected to the atmosphere and attached to the penstock so that the

water will be at atmospheric.


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1.7

Powerhouse

Powerhouseconsists of building structure of hydraulic and electrical equipment which includes the following:

a.

Hydraulic turbines

b.

Speed governors

c.

Generators

d.

Switchgears

e.

Pressure relief valves

f.

Isolation valves

g.

Transformers

1.8

Draft Tube

Draft tube an integral part of reaction turbine used to recover energy head. It connects the turbine outlet to

the tailwater so that the turbine can be set above the tailwater level.

1.9

Forebay

1.10

Turbineconverts the energy of the water into mechanical energy.

1.11

Generatorconverts the mechanical energy of the turbine into electric energy output.

1.12

Tailwaterthe water that is discharged from the turbine.

2.

Types of Hydraulic Turbines

2.1

Impulse (Pelton) Turbine is also known as tangential wheel or Pelton wheel, it utilizes kinetic energy of high

velocity jet which acts upon a small part of the circumference at an instant.

2.2

Reaction turbine develops power from the combined action of pressure and velocity of the water tha

completely fills the runner and water passages.

2.2.1

Francis Turbinelow head and high efficiency.

2.2.2

Propeller-Type(Axial Flow)very low head and efficiency is lower than Francis

a.

Fixed Blade

b.

Adjustable blade or Kaplan


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3.

Classification of Hydro-Electric Power Plants according to the:

3.1

Available head for power generation.

a.

Low head6 m to 30 m

b.

Medium head30 m to 150 m

c.

High head150 m and above

3.2

Nature of load or function.a.

Base-load plant

b.

Peak-load plant

3.3

Quantity of water available for power generation.

a.

Run-of-river plant without pondage

b.

Run-of-river plant with pondage

c.

Storage reservoir hydro plant (most common in RP)

d.

Pumped storage hydro plant

4.

Run-of-the River (Low Head) Hydro-Electric Power Plant

Pondagethe water behind the dam of a run-of-the-river hydro-electric plant.

5.

Pumped Storage Hydro-Electric Plant or Hydraulic Accumulator

Pumped storage plantis a hydro-electric plant which involves the use of off-peak energy to store water and to use

the stored water to generate extra energy to cope with the peak load.


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6.

Performance of Hydro-Electric Power Plant.

6.1

Gross head, hg

Gross head, hgis the difference between the head water and tailwater elevation.

6.2

Friction head loss, hf

g

V

D

Lfhf

2

2

- Darcy Equation

where:

f= coefficient of friction.

L= total length of pipe, in meters

V= velocity, m/s

g=9.81 m/s2

D= inside diameter, meters

(Friction head loss is usually expressed as a percentage of the gross head).

6.3

Net head or effective head,h

fg hhh

6.4

Penstock efficiency or pipeline efficiency, ep

turbineimpulseonheadgross

turbineimpulseonheadeffectiveep

gp h

he

6.5

General flow equation

AVQ

where:

Q= volume flow rate, m3/s

A= cross-sectional area, m2

V= velocity, m/s


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6.6

Water power, WP

gQhQhWP kW

Where:

= specific weight of water = 9.81 kN/m3

= density of water = 1000 kg/m3

6.7

Turbine output, Wt

ttt gQhQhW kW

Where:

t = turbine efficiency

6.8

Generator output, EP

etet gQhQhEP kW

Where:

e = electrical or generator efficiency

6.9

Generator speed,N

p

fN

120

where:

N = speed, rpm

f= frequency (usually 60 Hz)

p= number of poles (even number)

6.10

Utilized head

hw hh

where:

h= hydraulic efficiency

6.11

Head of Pelton (impulse) turbine

g

Vph

2

2

where:

V= velocity of jetp= inlet gage pressure

g= 9.81 m/s2

6.12

Head of Reaction (Francis and Kaplan) turbine

g

VVZ

ph BA

2

22


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6.13

Peripheral coefficient (relative speed or speed ratio),

gh

DN

JetofVelocity

VelocityPeripheral

2

where:

D= diameter of runner, meters

N= speed of runner, rev/sec

g= 9.81 m/s2

h= net head, meters

6.14

Specific speed, Ns

Specific speeddefined as the number of revolutions per minute at which a given runner would revolve if it

were so reduced in proportions that it would develop 1 hp under one foot head; it serves to classify a

hydraulic turbine and to indicate its type.

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H

HPNNs

where:

N= turbine runner rotative speed, rpm

HP= horsepower output per runner

H= available head acting on turbine per stage in feet.

7.

Identification of hydraulic turbine type based on available head and specific speed.

Hydraulic Turbine Type Available Head, m Specific Speed

Impulse 800 and up 5.5 to 80

Reaction (Francis) 50 to 800 22 to 80

Reaction (PropellerKaplan) 15 to 100 85 to 170

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h. Hydro-electric Power Plant - Lecture