Hydraulic head - Revision history

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	[[Category:Done 2018-05-18]]		[[Category:Done 2018-05-18]]
			[[Category:Translated to French]]
			[[fr:Charge hydraulique]]
	<onlyinclude>The '''hydraulic head''' is a value that measures the amount of mechanical [[energy]] available in [[water]] in a river, stream or even lake. The hydraulic head is equivalent to the water level in a static (non-flowing) water body.</onlyinclude><ref name=boyle>G. Boyle. ''Renewable Energy: Power for a Sustainable Future'', 2nd ed. Oxford, UK: Oxford University Press, 2004.</ref> In its simplest form hydraulic head is a measurement of the height of a static water column above an arbitrary point, usually expressed in [[meter]]s (or [[foot\|feet]] in the US). The higher the water level or hydraulic head, the more [[energy]] that the water at a specific location has.<ref name="RE1">Turbine Generator. (August 31, 2015). ''Hydraulic Head'' [Online]. Available: http://turbinegenerator.org/hydro/hydroelectric-power/hydraulic-head</ref>		<onlyinclude>The '''hydraulic head''' is a value that measures the amount of mechanical [[energy]] available in [[water]] in a river, stream or even lake. The hydraulic head is equivalent to the water level in a static (non-flowing) water body.</onlyinclude><ref name=boyle>G. Boyle. ''Renewable Energy: Power for a Sustainable Future'', 2nd ed. Oxford, UK: Oxford University Press, 2004.</ref> In its simplest form hydraulic head is a measurement of the height of a static water column above an arbitrary point, usually expressed in [[meter]]s (or [[foot\|feet]] in the US). The higher the water level or hydraulic head, the more [[energy]] that the water at a specific location has.<ref name="RE1">Turbine Generator. (August 31, 2015). ''Hydraulic Head'' [Online]. Available: http://turbinegenerator.org/hydro/hydroelectric-power/hydraulic-head</ref>

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Jmdonev at 19:57, 11 May 2018

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← Older revision		Revision as of 19:57, 11 May 2018
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	[[Category:Done ~~2017~~-07-01]]		[[Category:Done 2018-05-18]]
	<onlyinclude>The '''hydraulic head''' is a value that measures the amount of mechanical [[energy]] available in [[water]] in a river, stream or even lake. The hydraulic head is equivalent to the water level in a static (non-flowing) water body.</onlyinclude><ref name=boyle>G. Boyle. ''Renewable Energy: Power for a Sustainable Future'', 2nd ed. Oxford, UK: Oxford University Press, 2004.</ref> In its simplest form hydraulic head is a measurement of the height of a static water column above an arbitrary point, usually expressed in [[meter]]s (or [[foot\|feet]] in the US). The higher the water level or hydraulic head, the more [[energy]] that the water at a specific location has.<ref name="RE1">Turbine Generator. (August 31, 2015). ''Hydraulic Head'' [Online]. Available: http://turbinegenerator.org/hydro/hydroelectric-power/hydraulic-head</ref>		<onlyinclude>The '''hydraulic head''' is a value that measures the amount of mechanical [[energy]] available in [[water]] in a river, stream or even lake. The hydraulic head is equivalent to the water level in a static (non-flowing) water body.</onlyinclude><ref name=boyle>G. Boyle. ''Renewable Energy: Power for a Sustainable Future'', 2nd ed. Oxford, UK: Oxford University Press, 2004.</ref> In its simplest form hydraulic head is a measurement of the height of a static water column above an arbitrary point, usually expressed in [[meter]]s (or [[foot\|feet]] in the US). The higher the water level or hydraulic head, the more [[energy]] that the water at a specific location has.<ref name="RE1">Turbine Generator. (August 31, 2015). ''Hydraulic Head'' [Online]. Available: http://turbinegenerator.org/hydro/hydroelectric-power/hydraulic-head</ref>

	In a hydroelectric facility, the amount of energy harnessed depends on the difference between the headwater level in the [[hydroelectric reservoir\|reservoir]] upstream of the dam and the [[tailwater]] level below the [[hydroelectric dam]]. This is known as the hydraulic head difference and it represents the amount of energy that can be transformed into electricity by the turbines and generators. More detailed calculations show that not only the difference in height of the water determines how much energy can be harnessed, but there are a variety of losses known as head losses. These head losses occur as a result of [[friction]] in pipes. When head losses are accounted for, the actual amount of energy that can be harnessed is reduced. This reduced value for hydraulic head with the losses accounted for is known as the '''[[effective head]]'''.		In a hydroelectric facility, the amount of energy harnessed depends on the difference between the headwater level in the [[hydroelectric reservoir\|reservoir]] upstream of the dam and the [[tailwater]] level below the [[hydroelectric dam]]. This is known as the hydraulic head difference and it represents the amount of energy that can be transformed into electricity by the turbines and generators. More detailed calculations show that not only the difference in height of the water determines how much energy can be harnessed, but there are a variety of losses known as head losses. These head losses occur as a result of [[friction]] in pipes. When head losses are accounted for, the actual amount of energy that can be harnessed is reduced. This reduced value for hydraulic head with the losses accounted for is known as the '''[[effective head]]'''.

	The water in the reservoir, which is at a higher altitude has more [[gravitational potential energy]] because it is at a higher vertical position than the [[tail race]]. The energy used to generate electricity by moving the turbines arises from the utilization of gravitational potential energy of the reservoir water as it moves down through the penstocks. The use of [[Bernoulli's equation]] can help illustrate this process. Overall, hydraulic head is a way to represent the energy of energy of stored a fluid - in this case water - per unit weight.		The water in the reservoir, which is at a higher altitude has more [[gravitational potential energy]] because it is at a higher vertical position than the [[tail race]]. The energy used to generate electricity by moving the turbines arises from the utilization of gravitational potential energy of the reservoir water as it moves down through the penstocks. The use of [[Bernoulli's equation]] can help illustrate this process. Overall, hydraulic head is a way to represent the energy of energy of stored a [[fluid]] - in this case water - per unit weight.

	[[File:hydroelectricdam.png\|400px\|framed\|center\|Figure 1. A labelled diagram of a hydroelectric plant, including the hydraulic head.<ref>Wikimedia Commons. (August 31, 2015). ''Hydroelectric Dam'' [Online]. Available: https://upload.wikimedia.org/wikipedia/commons/thumb/5/57/Hydroelectric_dam.svg/2000px-Hydroelectric_dam.svg.png</ref>]]		[[File:hydroelectricdam.png\|400px\|framed\|center\|Figure 1. A labelled diagram of a hydroelectric plant, including the hydraulic head.<ref>Wikimedia Commons. (August 31, 2015). ''Hydroelectric Dam'' [Online]. Available: https://upload.wikimedia.org/wikipedia/commons/thumb/5/57/Hydroelectric_dam.svg/2000px-Hydroelectric_dam.svg.png</ref>]]
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	*<math>\Delta h</math> is the hydraulic head difference across the dam or turbine, expressed in meters (m)		*<math>\Delta h</math> is the hydraulic head difference across the dam or turbine, expressed in meters (m)
	*<math>ρ</math> is the [[density]] of the fluid, measured in [[kilogram]]s per unit [[volume]] (kg/m<sup>3</sup>)		*<math>ρ</math> is the [[density]] of the fluid, measured in [[kilogram]]s per unit [[volume]] (kg/m<sup>3</sup>)
	*<math>Q</math> is the volumetric [[flow rate]] of the fluid, measured in volume per unit time (m<sup>3</sup>/s)		*<math>Q</math> is the volumetric [[hydroelectric discharge]] (the [[flow rate]]) of the fluid, measured in volume per unit time (m<sup>3</sup>/s)
	*<math>g</math> is [[acceleration due to gravity]], measured in meters per second (m/s)		*<math>g</math> is [[acceleration due to gravity]], measured in meters per second (m/s)

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Jmdonev at 22:35, 16 August 2017

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	[[Category:Done ~~2016~~-01~~-15~~]]		[[Category:Done 2017-07-01]]
	<onlyinclude>The '''hydraulic head''' is a value that measures the amount of mechanical [[energy]] available in [[water]] in a river, stream or even lake. The hydraulic head is equivalent to the water level in a static (non-flowing) water body.</onlyinclude><ref name=boyle>G. Boyle. ''Renewable Energy: Power for a Sustainable Future'', 2nd ed. Oxford, UK: Oxford University Press, 2004.</ref> In its simplest form hydraulic head is a measurement of the height of a static water column above an arbitrary point, usually expressed in [[meter]]s (or [[foot\|feet]] in the US). The higher the water level or hydraulic head, the more [[energy]] that the water at a specific location has.<ref name="RE1">Turbine Generator. (August 31, 2015). ''Hydraulic Head'' [Online]. Available: http://turbinegenerator.org/hydro/hydroelectric-power/hydraulic-head</ref>		<onlyinclude>The '''hydraulic head''' is a value that measures the amount of mechanical [[energy]] available in [[water]] in a river, stream or even lake. The hydraulic head is equivalent to the water level in a static (non-flowing) water body.</onlyinclude><ref name=boyle>G. Boyle. ''Renewable Energy: Power for a Sustainable Future'', 2nd ed. Oxford, UK: Oxford University Press, 2004.</ref> In its simplest form hydraulic head is a measurement of the height of a static water column above an arbitrary point, usually expressed in [[meter]]s (or [[foot\|feet]] in the US). The higher the water level or hydraulic head, the more [[energy]] that the water at a specific location has.<ref name="RE1">Turbine Generator. (August 31, 2015). ''Hydraulic Head'' [Online]. Available: http://turbinegenerator.org/hydro/hydroelectric-power/hydraulic-head</ref>

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	The value for hydraulic head is used in the [[hydroelectric power equation]] to determine the [[available power]] of a [[hydroelectric facility\|hydroelectric system]]. It is one of the main components in this equation, represented by:<ref name=boyle/>		The value for hydraulic head is used in the [[hydroelectric power equation]] to determine the [[available power]] of a [[hydroelectric facility\|hydroelectric system]]. It is one of the main components in this equation, represented by:<ref name=boyle/>

	<center><m>P = \rho Q g \Delta h</m></center>		<center><math>P = \rho Q g \Delta h</math></center>

	where:		where:

	*<m>P</m> is the amount of [[power]] being calculated, measured in [[joule]]s per [[second]] (J/s) which is also known as a [[watt]] (W)		*<math>P</math> is the amount of [[power]] being calculated, measured in [[joule]]s per [[second]] (J/s) which is also known as a [[watt]] (W)
	*<m>\Delta h</m> is the hydraulic head difference across the dam or turbine, expressed in meters (m)		*<math>\Delta h</math> is the hydraulic head difference across the dam or turbine, expressed in meters (m)
	*<m>~~\rho~~</m> is the [[density]] of the fluid, measured in [[kilogram]]s per unit [[volume]] (kg/m<sup>3</sup>)		*<math>ρ</math> is the [[density]] of the fluid, measured in [[kilogram]]s per unit [[volume]] (kg/m<sup>3</sup>)
	*<m>Q</m> is the volumetric [[flow rate]] of the fluid, measured in volume per unit time (m<sup>3</sup>/s)		*<math>Q</math> is the volumetric [[flow rate]] of the fluid, measured in volume per unit time (m<sup>3</sup>/s)
	*<m>g</m> is [[acceleration due to gravity]], measured in meters per second (m/s)		*<math>g</math> is [[acceleration due to gravity]], measured in meters per second (m/s)

	Note that the larger the head difference in the expression above, the more potential mechanical energy the water in the reservoir has.		Note that the larger the head difference in the expression above, the more potential mechanical energy the water in the reservoir has.
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	The height difference between the water reservoir and the [[tail race]] in a hydroelectric facility is termed the gross head and it determines the maximum amount of power that can be produced. However, energy losses occur whenever water flows through pipes due to friction and this reduces the actual rate of power production. These losses reduce the overall head and result in a number known as the '''effective head''' or net head. Effective head is equal to the gross head minus the sum of all head losses.<ref name=boyle/> Head losses occur in all hydroelectric facilities, and are classified as major and minor head losses. These hydraulic head losses are measured, calculated, and expressed in the same way hydraulic head is, in the equivalent height of water in meters. In this case, you subtract the amount of power lost through head losses from the overall gross power to get the actual net power one can obtain. The equation can be shown as:		The height difference between the water reservoir and the [[tail race]] in a hydroelectric facility is termed the gross head and it determines the maximum amount of power that can be produced. However, energy losses occur whenever water flows through pipes due to friction and this reduces the actual rate of power production. These losses reduce the overall head and result in a number known as the '''effective head''' or net head. Effective head is equal to the gross head minus the sum of all head losses.<ref name=boyle/> Head losses occur in all hydroelectric facilities, and are classified as major and minor head losses. These hydraulic head losses are measured, calculated, and expressed in the same way hydraulic head is, in the equivalent height of water in meters. In this case, you subtract the amount of power lost through head losses from the overall gross power to get the actual net power one can obtain. The equation can be shown as:

	<center><m>P_{net} = P_{gross} - P_{loss}</m></center>		<center><math>P_{net} = P_{gross} - P_{loss}</math></center>

	Types of head losses include:<ref name="RE2">The Engineering Toolbox. (August 31, 2015). ''Total Pressure or Head Loss in Pipe or Duct Systems'' [Online]. Available: http://www.engineeringtoolbox.com/total-pressure-loss-ducts-pipes-d_625.html</ref>		Types of head losses include:<ref name="RE2">The Engineering Toolbox. (August 31, 2015). ''Total Pressure or Head Loss in Pipe or Duct Systems'' [Online]. Available: http://www.engineeringtoolbox.com/total-pressure-loss-ducts-pipes-d_625.html</ref>
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	==References==		==References==
	{{reflist}}[[Category:Uploaded]]		{{reflist}}
			[[Category:Uploaded]]

Jmdonev: 1 revision imported

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Jmdonev at 23:30, 16 February 2016

2016-02-16T23:30:44Z

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	<onlyinclude>The '''hydraulic head''' is a value that ~~represents~~ the ~~height that~~ [[~~water~~]] ~~'falls' from a higher elevation~~ [[~~hydroelectric reservoir\|reservoir~~]] ~~where it~~ is ~~stored~~ to the ~~[[hydro turbine\|turbines]] where it is used to [[electricity generation\|generate electricity]]~~.</onlyinclude><ref name=boyle>G. Boyle. ''Renewable Energy: Power for a Sustainable Future'', 2nd ed. Oxford, UK: Oxford University Press, 2004.</ref> ~~This~~ is ~~simply~~ a measurement of the ~~difference in~~ height ~~as the~~ water ~~moves through the system~~, usually expressed in [[meter]]s~~. This height difference includes the distance down through the~~ [[~~penstock~~]]~~s and into~~ the ~~turbine itself~~. The ~~larger the height of~~ the hydraulic head, the more [[energy]] that the ~~flowing~~ water has.<ref name="RE1">Turbine Generator. (August 31, 2015). ''Hydraulic Head'' [Online]. Available: http://turbinegenerator.org/hydro/hydroelectric-power/hydraulic-head</ref> The water in the reservoir, which is at a higher altitude has more [[gravitational potential energy]] because it is at a higher vertical position than the [[tail race]]. The energy used to generate electricity by moving the turbines arises from the transformation from gravitational potential energy of the reservoir water to kinetic energy of falling water as it moves down through the penstocks.		<onlyinclude>The '''hydraulic head''' is a value that measures the amount of mechanical [[energy]] available in [[water]] in a river, stream or even lake. The hydraulic head is equivalent to the water level in a static (non-flowing) water body.</onlyinclude><ref name=boyle>G. Boyle. ''Renewable Energy: Power for a Sustainable Future'', 2nd ed. Oxford, UK: Oxford University Press, 2004.</ref> In its simplest form hydraulic head is a measurement of the height of a static water column above an arbitrary point, usually expressed in [[meter]]s (or [[foot\|feet]] in the US). The higher the water level or hydraulic head, the more [[energy]] that the water at a specific location has.<ref name="RE1">Turbine Generator. (August 31, 2015). ''Hydraulic Head'' [Online]. Available: http://turbinegenerator.org/hydro/hydroelectric-power/hydraulic-head</ref>

	[[File:~~2000px-Hydroelectric_dam.svg~~.png\|400px\|framed\|center\|Figure 1. A labelled diagram of a hydroelectric plant, including the hydraulic head.<ref>Wikimedia Commons. (August 31, 2015). ''Hydroelectric Dam'' [Online]. Available: https://upload.wikimedia.org/wikipedia/commons/thumb/5/57/Hydroelectric_dam.svg/2000px-Hydroelectric_dam.svg.png</ref>]]		In a hydroelectric facility, the amount of energy harnessed depends on the difference between the headwater level in the [[hydroelectric reservoir\|reservoir]] upstream of the dam and the [[tailwater]] level below the [[hydroelectric dam]]. This is known as the hydraulic head difference and it represents the amount of energy that can be transformed into electricity by the turbines and generators. More detailed calculations show that not only the difference in height of the water determines how much energy can be harnessed, but there are a variety of losses known as head losses. These head losses occur as a result of [[friction]] in pipes. When head losses are accounted for, the actual amount of energy that can be harnessed is reduced. This reduced value for hydraulic head with the losses accounted for is known as the '''[[effective head]]'''.

			The water in the reservoir, which is at a higher altitude has more [[gravitational potential energy]] because it is at a higher vertical position than the [[tail race]]. The energy used to generate electricity by moving the turbines arises from the utilization of gravitational potential energy of the reservoir water as it moves down through the penstocks. The use of [[Bernoulli's equation]] can help illustrate this process. Overall, hydraulic head is a way to represent the energy of energy of stored a fluid - in this case water - per unit weight.

			[[File:hydroelectricdam.png\|400px\|framed\|center\|Figure 1. A labelled diagram of a hydroelectric plant, including the hydraulic head.<ref>Wikimedia Commons. (August 31, 2015). ''Hydroelectric Dam'' [Online]. Available: https://upload.wikimedia.org/wikipedia/commons/thumb/5/57/Hydroelectric_dam.svg/2000px-Hydroelectric_dam.svg.png</ref>]]

	The value for hydraulic head is used in the [[hydroelectric power equation]] to determine the [[available power]] of a [[hydroelectric facility\|hydroelectric system]]. It is one of the main components in this equation, represented by:<ref name=boyle/>		The value for hydraulic head is used in the [[hydroelectric power equation]] to determine the [[available power]] of a [[hydroelectric facility\|hydroelectric system]]. It is one of the main components in this equation, represented by:<ref name=boyle/>

	<center><m>P = \rho Q g h</m></center>		<center><m>P = \rho Q g \Delta h</m></center>

	where:		where:

	*<m>P</m> is the amount of [[power]] being calculated, measured in [[joule]]s per [[second]] (J/s) which is also known as a [[watt]] (W)		*<m>P</m> is the amount of [[power]] being calculated, measured in [[joule]]s per [[second]] (J/s) which is also known as a [[watt]] (W)
	*<m>h</m> is the hydraulic head, expressed in meters (m)		*<m>\Delta h</m> is the hydraulic head difference across the dam or turbine, expressed in meters (m)
	*<m>\rho</m> is the [[density]] of the fluid, measured in [[kilogram]]s per unit [[volume]] (kg/m<sup>3</sup>)		*<m>\rho</m> is the [[density]] of the fluid, measured in [[kilogram]]s per unit [[volume]] (kg/m<sup>3</sup>)
	*<m>Q</m> is the volumetric [[flow rate]] of the fluid, measured in volume per unit time (m<sup>3</sup>/s)		*<m>Q</m> is the volumetric [[flow rate]] of the fluid, measured in volume per unit time (m<sup>3</sup>/s)
	*<m>g</m> is [[acceleration due to gravity]], measured in meters per second (m/s)		*<m>g</m> is [[acceleration due to gravity]], measured in meters per second (m/s)

	Note that the larger the ~~h value~~ in the expression above, the more ~~gravitational~~ potential energy the water in the reservoir has.		Note that the larger the head difference in the expression above, the more potential mechanical energy the water in the reservoir has.

	==Classifications==		==Classifications==
	There are three main classifications of hydraulic head: high, medium, and low. The characteristics of these types are described below.		There are three main classifications of dames based on the hydraulic head differences: high, medium, and low. The characteristics of these types are described below.

	===High Head===		===High Head===
	~~Elevations~~ 100 meters or higher are considered high head. In this type of plant, water travelling through the turbine comes from a significantly higher elevation, meaning that the system ~~requires~~ a smaller volume of water to ~~operate since the water gains more [[momentum]] simply by falling~~.<ref name=boyle/> These systems generally also require smaller turbines since there is less water flowing through the turbine.		Head differences of 100 meters or higher are considered high head. In this type of plant, water travelling through the turbine comes from a significantly higher elevation, meaning that the system needs a smaller volume of water to produce an equivalent amount of energy.<ref name=boyle/> These systems generally also require smaller turbines since there is less water flowing through the turbine.

	In addition to a smaller turbine, a ~~larger~~ penstock is needed to guide the water down from the high elevation reservoir. Generally, large hydroelectric installations are either high or medium head.<ref name="RE1"/>		In addition to a smaller turbine, a longer penstock is needed to guide the water down from the high elevation reservoir. Generally, large hydroelectric installations are either high or medium head.<ref name="RE1"/>

	===Medium Head===		===Medium Head===
	Medium head systems ~~are an in-~~between between ~~high~~ and ~~low head systems~~. ~~Like high head dams,~~ medium head ~~dams contain a penstock that transports water from a reservoir down to the turbine. However, this penstock~~ is slightly shorter as there is less of an elevation drop. This type of [[hydroelectric dam\|dam]] relies both on a significant volume of water flowing and a significant drop in height of the water.		Medium head systems generally have head differences between between 10 and 100 meters. The penstock in a medium head dam is slightly shorter than a high head dam as there is less of an elevation drop. This type of [[hydroelectric dam\|dam]] relies both on a significant volume of water flowing and a significant drop in height of the water.

	===Low Head===		===Low Head===
	Low head is usually classified as systems with ~~elevations~~ of around 10 meters. These low head hydro turbines are generally used in [[run-of-the-river systems]] where there is a flowing river with little elevation change~~. In these dams, there is no penstock as there isn't enough of a water drop to justify its installation~~.<ref name="RE1"/>		Low head dams are usually classified as systems with head differences of around 10 meters or less. These low head hydro turbines are generally used in facilities such as [[run-of-the-river systems]] where there is a flowing river with little elevation change.<ref name="RE1"/>

	These low head systems usually transport large volumes of water and thus require larger ~~turbine [[generator]]s~~ to efficiently convert water energy into [[electricity]]. A dam isn't ~~always~~ needed ~~in these low head systems,~~ as there is very little water storage.<ref name=boyle/>		These low head systems usually transport large volumes of water and thus require larger turbines to efficiently convert water energy into [[electricity]]. In these installations, a large dam isn't needed to barricade water as there is very little water storage.<ref name=boyle/>

	==Head Losses==		==Head Losses==
	~~Although there is a set~~ height difference between the water reservoir and the [[tail race]] in a hydroelectric ~~facilities~~, ~~there are some~~ losses ~~that~~ occur whenever water flows through the ~~pipes~~. These losses reduce the overall head and result in a number known as the [[effective head]].<ref name=boyle/> Head losses occur in all hydroelectric facilities, and are classified as major and minor head losses~~. A head loss occurs in inefficiencies of the hydroelectric facility that reduce the total hydraulic head that can be used for hydroelectric generation~~. These hydraulic head losses are measured, calculated, and expressed in the same way hydraulic head is, in meters. ~~Once hydraulic~~ head losses ~~are known they can simply subtracted~~ from the ~~hydraulic head~~ to get the ~~total hydraulic head~~.		The height difference between the water reservoir and the [[tail race]] in a hydroelectric facility is termed the gross head and it determines the maximum amount of power that can be produced. However, energy losses occur whenever water flows through pipes due to friction and this reduces the actual rate of power production. These losses reduce the overall head and result in a number known as the '''effective head''' or net head. Effective head is equal to the gross head minus the sum of all head losses.<ref name=boyle/> Head losses occur in all hydroelectric facilities, and are classified as major and minor head losses. These hydraulic head losses are measured, calculated, and expressed in the same way hydraulic head is, in the equivalent height of water in meters. In this case, you subtract the amount of power lost through head losses from the overall gross power to get the actual net power one can obtain. The equation can be shown as:

			<center><m>P_{net} = P_{gross} - P_{loss}</m></center>

	Types of head losses include:<ref name="RE2">The Engineering Toolbox. (August 31, 2015). ''Total Pressure or Head Loss in Pipe or Duct Systems'' [Online]. Available: http://www.engineeringtoolbox.com/total-pressure-loss-ducts-pipes-d_625.html</ref>		Types of head losses include:<ref name="RE2">The Engineering Toolbox. (August 31, 2015). ''Total Pressure or Head Loss in Pipe or Duct Systems'' [Online]. Available: http://www.engineeringtoolbox.com/total-pressure-loss-ducts-pipes-d_625.html</ref>
	* '''Major head losses''': Major head losses arise from ~~factors such as surface~~ friction ~~from~~ the pipes, ~~length~~ of the ~~pipes, and size of pipes~~		* '''Major head losses''': Major head losses arise mainly from friction in the pipes, and occur over long lengths of pipe, such as in the penstock.
	* '''Minor head losses''': Minor head losses arise from friction ~~at bends and valves~~, ~~flow rate in~~ the pipe, ~~and blockages such as trash racks~~		* '''Minor head losses''': Minor head losses arise from any other place ''besides'' friction in the pipes. Essentially, any place that the pipe bends or the velocity of the water changes, minor losses exist.

	~~Major~~ head losses are ~~typically expected to be larger then~~ minor head losses~~. The~~ minor head losses ~~can actually contribute more to~~ the ~~total head loss than the major head losses do. These arise fromthe design~~ of the hydroelectric ~~facility, limitations in the local geography, river flow, size of river, and type of river~~.<ref name="RE2"/>		Despite the names, major head losses are not always greater than minor head losses - it is simply the combination of both minor and major head losses that are important in determining what the net power of the hydroelectric power plant is.<ref name="RE2"/>

	==References==		==References==
	{{reflist}}		{{reflist}}[[Category:Uploaded]]

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2015-09-03T16:07:17Z

New page

[[Category:Done 2015-09-05]]
<onlyinclude>The '''hydraulic head''' is a value that represents the height that [[water]] 'falls' from a higher elevation [[hydroelectric reservoir|reservoir]] where it is stored to the [[hydro turbine|turbines]] where it is used to [[electricity generation|generate electricity]].</onlyinclude><ref name=boyle>G. Boyle. ''Renewable Energy: Power for a Sustainable Future'', 2nd ed. Oxford, UK: Oxford University Press, 2004.</ref> This is simply a measurement of the difference in height as the water moves through the system, usually expressed in [[meter]]s. This height difference includes the distance down through the [[penstock]]s and into the turbine itself. The larger the height of the hydraulic head, the more [[energy]] that the flowing water has.<ref name="RE1">Turbine Generator. (August 31, 2015). ''Hydraulic Head'' [Online]. Available: http://turbinegenerator.org/hydro/hydroelectric-power/hydraulic-head</ref> The water in the reservoir, which is at a higher altitude has more [[gravitational potential energy]] because it is at a higher vertical position than the [[tail race]]. The energy used to generate electricity by moving the turbines arises from the transformation from gravitational potential energy of the reservoir water to kinetic energy of falling water as it moves down through the penstocks.

[[File:2000px-Hydroelectric_dam.svg.png|400px|framed|center|Figure 1. A labelled diagram of a hydroelectric plant, including the hydraulic head.<ref>Wikimedia Commons. (August 31, 2015). ''Hydroelectric Dam'' [Online]. Available: https://upload.wikimedia.org/wikipedia/commons/thumb/5/57/Hydroelectric_dam.svg/2000px-Hydroelectric_dam.svg.png</ref>]]

The value for hydraulic head is used in the [[hydroelectric power equation]] to determine the [[available power]] of a [[hydroelectric facility|hydroelectric system]]. It is one of the main components in this equation, represented by:<ref name=boyle/>

<center><m>P = \rho Q g h</m></center>

where:

*<m>P</m> is the amount of [[power]] being calculated, measured in [[joule]]s per [[second]] (J/s) which is also known as a [[watt]] (W)
*<m>h</m> is the hydraulic head, expressed in meters (m)
*<m>\rho</m> is the [[density]] of the fluid, measured in [[kilogram]]s per unit [[volume]] (kg/m<sup>3</sup>)
*<m>Q</m> is the volumetric [[flow rate]] of the fluid, measured in volume per unit time (m<sup>3</sup>/s)
*<m>g</m> is [[acceleration due to gravity]], measured in meters per second (m/s)

Note that the larger the h value in the expression above, the more gravitational potential energy the water in the reservoir has.

==Classifications==
There are three main classifications of hydraulic head: high, medium, and low. The characteristics of these types are described below.

===High Head===
Elevations 100 meters or higher are considered high head. In this type of plant, water travelling through the turbine comes from a significantly higher elevation, meaning that the system requires a smaller volume of water to operate since the water gains more [[momentum]] simply by falling.<ref name=boyle/> These systems generally also require smaller turbines since there is less water flowing through the turbine.

In addition to a smaller turbine, a larger penstock is needed to guide the water down from the high elevation reservoir. Generally, large hydroelectric installations are either high or medium head.<ref name="RE1"/>

===Medium Head===
Medium head systems are an in-between between high and low head systems. Like high head dams, medium head dams contain a penstock that transports water from a reservoir down to the turbine. However, this penstock is slightly shorter as there is less of an elevation drop. This type of [[hydroelectric dam|dam]] relies both on a significant volume of water flowing and a significant drop in height of the water.

===Low Head===
Low head is usually classified as systems with elevations of around 10 meters. These low head hydro turbines are generally used in [[run-of-the-river systems]] where there is a flowing river with little elevation change. In these dams, there is no penstock as there isn't enough of a water drop to justify its installation.<ref name="RE1"/>

These low head systems usually transport large volumes of water and thus require larger turbine [[generator]]s to efficiently convert water energy into [[electricity]]. A dam isn't always needed in these low head systems, as there is very little water storage.<ref name=boyle/>

==Head Losses==
Although there is a set height difference between the water reservoir and the [[tail race]] in a hydroelectric facilities, there are some losses that occur whenever water flows through the pipes. These losses reduce the overall head and result in a number known as the [[effective head]].<ref name=boyle/> Head losses occur in all hydroelectric facilities, and are classified as major and minor head losses. A head loss occurs in inefficiencies of the hydroelectric facility that reduce the total hydraulic head that can be used for hydroelectric generation. These hydraulic head losses are measured, calculated, and expressed in the same way hydraulic head is, in meters. Once hydraulic head losses are known they can simply subtracted from the hydraulic head to get the total hydraulic head.

Types of head losses include:<ref name="RE2">The Engineering Toolbox. (August 31, 2015). ''Total Pressure or Head Loss in Pipe or Duct Systems'' [Online]. Available: http://www.engineeringtoolbox.com/total-pressure-loss-ducts-pipes-d_625.html</ref>
* '''Major head losses''': Major head losses arise from factors such as surface friction from the pipes, length of the pipes, and size of pipes
* '''Minor head losses''': Minor head losses arise from friction at bends and valves, flow rate in the pipe, and blockages such as trash racks

Major head losses are typically expected to be larger then minor head losses. The minor head losses can actually contribute more to the total head loss than the major head losses do. These arise fromthe design of the hydroelectric facility, limitations in the local geography, river flow, size of river, and type of river.<ref name="RE2"/>

==References==
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