Water as Power

8/8/2019 Water as Power

1/13

An Introduction to the History and

Application of Hydropower


2/13

Table of Contents

page

1 Introduction...2

2 The early days....3

3 Basic hydropower system..43.1 Types of water wheels.4

3.2 Mechanical System..7

4 History of hydroelectric power..74.1 Modern hydropower systems...8

5 The basic generator....8

6 Summary & conclusion....11

7 References....12

List of Figures

Figure 1.Persian Wheel driven by a camel.3Figure 2.Overshot water wheel...4Figure 3.Breast water wheel5

Figure 4.Backshot water wheel...5Figure 5.The undershot Wheel....6Figure 6.The Pelton wheel..6Figure 7.A simple water wheel powered snuff mill....7Figure 8.An elementary AC generator....9Figure 9.Output voltage of an elementary generator during one revolution.10

2


3/13

1 Introduction

Hydropower (a.k.a. hydraulic or water power) relates to the power that is derivedfrom the force or energy of moving water, which may be harnessed for useful purposes [1].

It is one of the oldest sources of power known to man. From its humble beginnings, it

was used for irregation, mining, and as a useful source of power for driving many typesof machines. Water power soon replaced many of the streneous tasks that were

previously accomplished only by manual labor performed either by man or beast.

Today, hydropower plays a significant role in producing a clean, natural, andrenewable source of power that may be harnesed to provide useful energy for human

utilization.

Hydroelectricity eliminates the gas emissions that occur from fossil fuel

combustion, such as sulfur dioxide, nitric oxide, carbon monoxide, dust, and mercury incoal. Additionally, hydroelectricity also avoids the hazards of coal mining and the

indirect health effects of coal emissions[2].

Unlike nuclear power, hydroelectricity generates no nuclear waste and has none

of the dangers associated with uranium mining, or nuclear leaks

[2]

.Compared to wind farms, hydroelectric power plants have a more predictable load

factor. If the plant has a storage reservoir, it can be activated to generate power whenrequired. Additionally, Hydroelectric plants can be easily regulated to follow variations

in power demand[2].

However, Hydro-powered electricity is not without its drawbacks, such as:

When a dam is constructed it raises the water level in the area and floods

large areas of land. This situation forces the local population to beresettled elsewhere - often on less fertile land[2].

Dam failures can be very hazardous. Since large conventional dammed-

hydro facilities hold back large volumes of water, a failure due to poorconstruction, terrorism, or other causes can lead to catastrophic damage todownriver settlements and infrastructures[2].

Hydroelectric power plants lower the levels of oxygen in the surrounding

water, creating a threat to animal and plant life. Current means ofreducing this problem include the installation of fish ladders to ensure safe

passage for fish around the area, and regular water aeration to maintain

adequate oxygen levels[2].

This work begins with a discussion of the earliest uses for waterpower. Then,

descriptions of early hydropower systems are analyzed, including descriptions of the

various types of waterwheels employed and the simple machinery that harnessed theirrotational energy. Next, a brief history on the origin of hydropower is revealed along

with various examples of how hydropower is harnessed today. Subsequently, an

explanation of how hydropower can be utilized to provide the mechanical force necessaryto operate an elementary AC generator is presented detailing how the electrical power is

generated. Finally, a summary of the material and concluding remarks are made on the

practicality of hydropower and its role on generating renewable energy for the future areexamined.

3


4/13

2 The early days

Although the origin of the idea for using running water for pratical purposes is

unknown, it is believed that its initial use was applied to irrigation [3]. Early irrigationsystems date back to Mesopotamia and ancient Egypt since the 6th millennium BC[1].

Various techniques were employed in ancient times to elevate the water from rivers to ahigher level on the bank, from where it would flow through canals and ditches to the

fields. One such technique employed the Persian wheel or saqia (see Figure 1) thismechanism consisted of a large wheel mounted on a horizontal axle with buckets

attatched to its rim. The driving force for the Persian wheel was generally a buffalo,

donkey, or camel. It is suspected that someone once noticed long ago that when the beastwas unharnessed, the river current caused the wheel to rotate in the opposite direction,

therby revealing the potential for water to perform work[3].

Figure 1: Persian Wheel driven by a camel [3].

By about 80 B.C. water wheels were geared to milstones for the purpose ofgrinding corn. Although this device minimized the manual labor necessary to process

corn, it was not used extensively by the Romans, whom relied upon the traditional

manner of having their corn ground by hand using slaves in stone querns[3].

Water power also found applications in the mining industry. It was realized thatthe power of a wave of water released from a tank could impart enough force to extract

metal ores from the earth in a method known as hushing. To perform the hushing

operation, tanks and reservoirs were built near the suspected veins and filled with water

4


5/13

from an aqueduct. Then, the water was suddenly released using a sluice-gate onto the

hillside below, resulting in a man-made erosion effect that would reveal the bedrock and

any mineral veins in the affected area[4]. Hushing was first employed at the Dolaucothigold mine in Wales from 75 AD onwards. Hushing was also widely used in Britain in the

Medieval and later periods to extract lead and tin ores. This procedure later evolved into

hydraulic mining during the California gold rush (18481855)[1]

.Later applications of hydropower were used to drive other various machines, such

as watermills, textile machines, sawmills, dock cranes, and domestic lifts[1].

3 Basic hydropower system

A basic hydropower system consists of two main components the water wheel

and the mechanical machine. The water wheel is responsible for converting the falling orpassing water into rotational energy which can be put to service to drive a machine. This

mechanical energy can then be transformed into some desirable action in order to reduce

the manual labor that would normally be required to accomplish a specific task.

3.1 Types of water wheels

An efficiently operating water wheel relies on two engineering disciplines, civil

and mechanical. The civil engineer is responsible for ensuring that a sufficient supply of

water is availabe at the right level and to the right location. Mechanical engineers

responsibility pertains to the construction of the wheel and its ancillary works so that itcan extract the maximum amount of energy from the water[3].

Water wheels are classified by five main types-overshot, breast, backshot,

undershot, and the Pelton wheel.The overshot wheel utilized the weight of falling water coming from slightly

forward of its axis to apply force to one side of the wheel, causing it to revolve (see

figure 2). The diameter of the overshot wheel is generally from 2 to 3 feet less than thetotal fall available[5]. Where total fall or Head is defined as the vertical difference in

level by the water above the wheel (headrace) and that immediately below it (tailrace).

This configuration results in a full 180-degree rotation of the waterwheel; representingthe most efficient design (rated at 55 to 70% efficient[6]).

Figure 2: Overshot water wheel[7].

5


6/13

When the head was not sufficient for a large diameter overshot wheel, the breast

wheel (as illustrated in figure 3) was commonly used. In this arrangement, the falling

water imparts only a 90-degree rotation of the wheel [8]. The efficiency of the breastwheel is generally less than that of the overshot wheel (due to the reduction in rotation

angle for the falling water) and is rated at 30 to 65%[6].

Figure 3: Breast water wheel[7].

A backshot (a.k.apitchback) wheel is a variety of overshot wheel where the water

falls just behind the summit of the wheel causing the water to descend along the back ofthe wheel (figure 4). This particular arrangement causes the wheel to continue to

function untill the water in the wheel pit rises well above the height of the axle, a

condition that would stop or may even damage the overshot wheel. The efficiency of thepitchback wheel is comparable to that of the overshot wheel and is rated at 55 to 65%[6].

Figure 4: Backshot water wheel[9].

The undershot wheel (a.k.a. stream wheel[7]) as depicted in figure 5 is a vertically

mounted wheel that is rotated by water striking paddles or blades at the bottom of the

wheel. This arrangement is generally the least efficient (efficiency rating of only 15 to25% or less[6]), and represents the oldest type of wheel.

6
http://upload.wikimedia.org/wikipedia/commons/c/c9/Breastshot_water_wheel_schematic.png


7/13

Figure 5: The undershot Wheel[9]

The advantage of the undershot wheel is that it is cheaper and simpler to build,however, it is less powerful and efficient than any other type of wheel. Additional

disadvantages of the undershot wheel include: they can only be utilized where the flow

rate is sufficient to provide torque, and they gain no advantage from head[9].The Pelton wheel, invented by Lester Allan Pelton in the 1870s, represents the

most efficient type of water turbine[10]. This wheel rotates around its axis when a high

velocity jet of water is directed through a nozzle toward several cup-shaped wheelsmounted around its periphery[11]. The geometry of Peltons paddles were designed sothat the rim runs at the speed of the water jet, causing the water toleave the wheel with very little speed, extracting almost all of itsenergy into the wheel, allowing for a very efficient turbine[10]. Anillustration of an old Pelton wheel, recovered from the Walchenseepower plant is presented in figure 6.

Figure 6: The Pelton wheel[10].

7


8/13

3.2 Mechanical System

Power from the rotating waterwheel was transmitted to the machines through a

series of gears and shafts called the power train. Figure 7 displays the working

machinations for an automated snuff mill. In this illustration, two gears turn a lanternpinion, which in turn provides power to the snuff-grinding machine. Through the use of

gearing, the snuff grinder could be turned at a different rate than that of the waterwheel

itself.This simple system could easily be expanded to power many machines from a

single waterwheel[12].

Figure 7: A simple water wheel powered snuff mill[12].

4.0 History of hydroelectric power

In 1864, Dr. Pacinotti suggested that a device similar to the electric motor could

be made to generate an electric current if the rotor were rotated by mechanical means.This idea was proven practical at the Vienna University Exhibition of 1873, where a

pump was powered by an electric motor; which received its electrical power from asimilar electric motor which had its rotor revolved by a gas engine[13].

This idea lead to the first operating water turbine and electric generator powered

house, which was built at Cragside, Northumberland, in 1879. This facility operated an 8

horsepower turbine using a head of 30 feet and delivered a potential of 90 volts one mile

away to power incandescent lamps[13].It is believed that the first commercial hydroelectric plant ever built was erected

in September 1883, in Northern Ireland. This plant, which was located at Salmon Leap

8


9/13

Falls on the river Bush, was used to supply power to a railway, which ran from Portrush

to Bushmills and later extended to the famous Giants Causeway- a total distance of eight

miles. At this plant, a head of 27 feet operated two 52 horsepower turbines; which in turngenerated a maximum current of 100 amperes at 250 volts[13].

The passion for water generated electricity rose quickly resulting in about 45

hydroelectric power plants in the U.S. and Canada by 1886 and by 1889, there were 200hydroelectric power plants in the U.S. alone. By 1920, 40% of the powerproduced in the United States was hydroelectric[2].

Hydroelectric power plants continued to increase in sizethroughout the twentieth century. The Hoover Dams power plant wasconstructed in 1936 and generated 1,345 MW of hydroelectric power.This monument was soon eclipsed by the 6,809 MW Grand Coulee Damin 1942 and again by the Brazil's and Paraguay's Itaipu Dam in 1984which generated 14,000 MW of hydroelectric power and finally by the Three Gorges Dam in China. This Dam was erected in 2008 andgenerated 22,500 MW of power[2].

4.1 Modern hydropower systems

Today, there are several forms of waterpower currently in use or in development.Some, like their predecessors, are used for purely mechanical purposes, but generally

their primary purpose is to generate electricity. Broad categories of modern waterpower

usage include[1]:

Damless hydro - used to capture the kinetic energy in rivers, streams and oceans.

Hydroelectricity - such as hydroelectric dams, or run-of-the-river setups (e.g.

hydroelectric-powered watermills).

Marine current - systems that captures the kinetic energy from marine currents. Ocean thermal energy conversion (OTEC) - exploits the temperature difference

between deep and shallow waters.

Osmotic power - channels river water into a container separated from sea water

by a semipermeable membrane.

Tidal power - captures energy from the tides in a horizontal direction.

Tidal stream power - captures energy from the tides in a vertical direction.

Waterwheels - used for hundreds of years to power mills and machinery.

Wave power - uses the energy in waves.

5 The basic generator

The elementary AC generator as depicted in figure 8 consists of a wire loop

positioned so that it can be rotated (by a mechanical force such as a manual crank or

flowing/falling water) in a stationary magnetic field. This rotation will produce aninduced electromotive force (emf) in the loop. The generated emf is then transferred to

the load (such as a voltmeter) through a series of slip rings and brushes.

9


10/13

Figure 8: An elementary AC generator[14].

The pole pieces (marked N and S) are shaped and positioned as shown in order toconcentrate their magnetic field as close to the wire loop (known as the armature) aspossible.

The fundamental principal in AC generation lies in an application of Faradays

Law. Faradays Law expressed mathematically as

V = - N d/ dt, [1]

states that the induced voltage in a conductor is proportional to the time rate of change of

the magnetic flux linked with it[15]. The minus sign is mandated by Lenzs law, which

states that the current flow in a conductor due to an induced voltage moves in a direction

that creates a magnetic flux, which opposes that which induced the voltageSince the magnetic flux linkage is given by = N , and the induced voltage is

the time rate of change of these linkages, the induced voltage can be derived in terms of

the velocity of the conductors by

V = N d/ dt = NBl ds/dt = NBlv, [2]

where

N is the number of conductors,

B is the magnetic flux density,l is the length of the conductor in the magnetic field, and

ds is the differential distance traveled by the conductor through the field.

Figure 9 illustrates how an AC voltage is generated when the armature is rotated

in a clockwise direction.

The initial or starting point occurs at position A (0). At the 0 position, the

armature loop is perpendicular to the magnetic field and does not cut any lines of fluxresulting in no emf being induced in the conductors and no voltage indication appearing

on the voltmeter. This position is called the neutral plane.

10


11/13

As the armature rotates from position A (0) to position B (90), the conductors

cut through an increasing number of magnetic flux lines, at a continually increasing

angle. During this rotation, the dark conductor cuts up through the field as the lightconductor cuts down through the field. At 90 they are cutting through the maximum

number of flux lines and at the maximum angle. The induced emfs in the conductors are

series aiding; meaning that the resultant voltage across the brushes is the sum of the twoinduced voltages. Thus, the voltmeter reads its maximum value at position B.

As the armature continues rotating from position B (90) to position C (180), the

conductors again approach a perpendicular alignment with the magnetic field. Atposition C (180) the armature no longer cuts through any lines of flux, resulting in no

induced emf and thus a zero voltage reading returns on the voltmeter.

From position A (0) to position C (180) the conductors of the armature loop

have been moving in the same direction through the magnetic field causing the polarity ofthe induced voltage to remain the same. As the loop continues to rotate from position C

(180) to position D (270), and back to the initial or starting point at position A (0), the

direction of the cutting action of the conductors through the magnetic field reverses.

Now, as the armature rotates from position C (180) back to position A (0), the darkconductor cuts down through the field while the light conductor cuts up through the field

resulting in a reversal of the induced voltages. This is witnessed in the graph of thegenerators terminal voltage in figure 8 by points C, D, and A being equal in magnitude

but opposite in polarity from that of points A, B, and C.

Figure 9: Output voltage of an elementary generator during one revolution [14].

11


12/13

6 Summary & conclusion

The practical applications for hydropower continue to evolve with the technological

advancements of mankind. Starting from its simple beginnings, it was used toirrigate crops in order to sustain life. Later, waterpower found practical use in the

grinding of food as well as a power source used to drive various machines, such aswatermills, textile machines, sawmills, dock cranes, and domestic lifts. Today,

hydropower is primarily used to produce clean and renewable (Green) energywhich is consumed by the modern man.

Although the use of hydroelectric plants can play a significant role in producing

Green energy, it is not without its drawbacks (i.e. the flooding of fertile land and thedangers of collapsing dams). Therefore, it is imparative that the world does not only

exploit any one technique for producing Green energy as each technique produces it own

variety of advantages and disadvantages. Although the exclusive use of only onetechnique may amplify the advantages associated with that particular method, it also

compounds the disadvantages as well. Logically, it can be asssumed that a mixture of all

energy generating methods utilized in their most beneficial locations can proide for theworlds energy demand while minimizing the disadvantages associated with anyparticular method.

12


13/13

7 References

[1] Wikipedia. (2010, August 5).Hydropower[Online]. Available:http://en.wikipedia.org/wiki/Hydropower

[2] Wikipedia. (2010, August 8).Hydroelectricity[Online]. Available:

http://en.wikipedia.org/wiki/Water_Power

[3] T. Paton and J. Guthrie,Introduction, inPower from water, London, England:

Northumberland Press Ltd., 1960, pp. 1-4.

[4] Wikipedia. (2010, August 3).Hushing[Online]. Available:

http://en.wikipedia.org/wiki/Hushing

[5] Fitz Waterwheel Mills. (2008, October 17). General Information About OvershootWater Wheels[Online]. Available: http://www.fitzwaterwheel.com/OSgeneralnfo.html

[6] T. R. Hazen. (2002, April 22).Efficiency of Water Wheels[Online]. Available:http://www.angelfire.com/journal/millbuilder/efficiency.html

[7] Wikipedia. (2010, August 8). Water wheel[Online]. Available:

http://en.wikipedia.org/wiki/Water_wheel

[8] The waterwheel factory.(2010, April 20). Breast WaterWheel[Online]. Available:

http://www.waterwheelfactory.com/breast.htm

[9] Top-alternative-energy-sources.(2008). Water Wheel Design - Take a detailed look at

water wheel configurations[Online]. Available: http://www.top-alternative-energy-sources.com/water-wheel-design.html

[10] Wikipedia. (2010,July 30). Pelton wheel[Online]. Available:http://www.woonsocket.org/stuartwater.html

[11] T. Paton and J. Guthrie, Plant, inPower from water, London, England:

Northumberland Press Ltd., 1960, pp. 69-70.

[12] S. Water. Water Power[Online]. Available:

http://www.woonsocket.org/stuartwater.html

[13] T. Paton and J. Guthrie,The dawn of hydro-electric power, inPower from water,

London, England: Northumberland Press Ltd., 1960, pp. 10-13.

[14]Navy Electricity and Electronics Training Series, Module 5Introduction to

Generators and Motors, Naval education and training professional development and

technology center, Pensacola, FL, 1998, pp. (1-2) (1-4).

[15] J. Camara, Electromagnetic theory in Electrical Engineering Reference Manualfor the Electrical and Computer PE Exam, 6th ed. Belmont, CA: ProfessionalPublications, Inc.,2001, pp. 16-22.

13
http://en.wikipedia.org/wiki/Hydropowerhttp://en.wikipedia.org/wiki/Hydropower

Water as Power

Documents

Transcript of Water as Power