Difference between revisions of "Hydro Power - Civil Engineering"

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<![endif]-->'''Intake'''
 
  
<span>The water intake must be located upstream so it will
+
[[Portal:Hydro|► Back to Hydro Portal]]
always supply the necessary and&nbsp; adequate amount of water to the turbine.
 
It must include a screen to prevent debris, fish, or rocks from entering the
 
turbine. A properly designed and constructed screen will be self-cleaning and
 
require little maintenance.&nbsp; A poorly designed screen will require upkeep
 
and will rob the system of power.&nbsp;</span>
 
  
&nbsp;&nbsp;
 
  
{| cellspacing="0" cellpadding="0" border="1"
+
== Weir and Intake ==
|-
 
|
 
&nbsp;
 
  
|-
+
A (overflow) weir maintains a constant water level in the river at this point. This allows to divert a constant amount of water from the river into canal, '''penstock''' and [[Wind_Turbine_Technology|turbine]]. If there is substantial silt in the water (muddy or sandy grounds) it requires a '''flush gate'''. Such gate can be opened to clear out silt which is usually transported with waters downstream but settles before a weir.
|
 
'''<u><span><!--[if gte vml 1]>
 
 
 
 
 
   
 
   
 
   
 
   
 
   
 
   
 
   
 
   
 
   
 
   
 
   
 
   
 
 
 
 
 
 
 
 
 
 
 
  <![endif]-->[[Image:&#124;Inletpipe.JPG]]</span></u>'''  
 
  
&nbsp;
+
Intake is the structure between river an canal. It consists of a gate to open/close the water feed. A rake prevents major debris to enter the system. The intake is located preferably on an outside of a river bend in a way that silt and debris is not “automatically” streamed in. Due to it’s location in/on the river it is to be designed to withstand floods.
  
|}
+
[[File:Weir construction.jpg|663px|Weir construction.jpg|alt=Weir construction.jpg]]
  
'''<u>&nbsp;</u>'''
+
<br/>
  
'''<u>&nbsp;</u>'''
 
  
'''<u>&nbsp;</u>'''
+
== Canal<br/> ==
  
'''<u>&nbsp;</u>'''
+
The canal transports the water towards the point where it drops steeply. To gain much height difference possible it is aligned with as little slope as possible. Canals usually lay on valley slopes. It is to be secured that no waters cross the canal uncontrolled (flushing above or under) from its side.. 1 - ½ meter path between hillside and canal allows its comfortable maintainance and prevents slides blocking the flow.
  
'''&nbsp;'''
+
<br/>
  
'''Forebay tank'''
+
== Sandtrap ==
  
<span>Forebay
+
The '''sandtrap''' separates silt and debris from the water before it enters penstock and turbine. It can be placed on the beginning or the end of the canal. The forebay is wider than the canal so the water goes slower. Therefore fine materials such as sand and mud settle at the bottom. A '''flush gate''' or a flush pipe at smaller installations is used to clean the sandtrap during maintainance intervals. A '''spillway''' ensures controlled overflow in case of flooding of canal.
tank filters&nbsp;&nbsp;debris and prevents it from being drawn into
 
turbine and penstock pipe. This type of settling tank is not necessary but is
 
highly advisable. This serves as an area for the water from the intake to
 
“decelerate” and for any fine materials such as sand and gravel that passed
 
through the intake screen to settle and not flow into the turbine. As a general
 
rule, the settling tanks capacity should be about 20 times the turbines water
 
usage in one minute. So for example if your turbine uses 100 gallons per
 
minute, the tank should hold at least 2000 gallons of water. The inlet and
 
outlet from the settling tank should include a sluice gate/ shut-off so the
 
debris that settles to the bottom can be cleaned out. The outlet should also
 
include screens as a double check against debris from entering the turbine,
 
should the inlet for some reason fail to perform it’s intended task.&nbsp;
 
</span>
 
  
<br>
+
[[File:Sand trap forebay.jpg|left|546px|Sand trap forebay.jpg|alt=Sand trap forebay.jpg]]
  
<br>
+
== Forebay and Trash Rack ==
  
'''Pipeline (Penstock)'''  
+
In the '''forebay''' tank the connection towards the '''penstock''' must not be the lowest point. The lowest point is towards a flush pipe. At such sand and mud can be flushed out during maintenance intervals. The '''forebay''' is closed by a '''trash rack'''. It's preventing any debris entering the penstock!<br/>'''Trash rack''' Features: As wide as possible to prevent quick blocking by debris. Grid should be cleanable by a rake from the top. Easy access and comfortable handling make regular cleaning more probable.
  
'''<u><br></u>'''
+
[[File:Ererti I forbay , trash rack and flush gate.JPG|thumb|left|180px|Ererti I forbay , trash rack and flush gate.JPG]]
  
<u></u>'''<span><!--[if gte vml 1]>
+
[[File:Penstock.jpg|right|338px|Penstock.jpg|alt=Penstock.jpg]]
 
<![endif]-->[[Image:|penstockfrombuilding.JPG]]</span>'''
 
  
<span>
+
== Pipeline (Penstock)<br/> ==
</span>  
 
  
Penstock pipeline carries water from forebay tank to the power house. The pipeline&nbsp;delivers water to the turbine from the settling tank and must be sized properly to prevent frictional losses from robbing available power. This will be a cost/benefit trade-off since a long penstock can cost more than the turbine. Penstocks should be buried if possible to protect them and prevent freezing in cold weather climates.&nbsp;The penstock should include a breather pipe, ideally near the settling tank. This will prevent the disastrous event known as an implosion. Depending upon the pipe chosen, and if the intake were to suddenly be shut off – a huge vacuum would develop in the pipe. This is caused by the water’s momentum and can be of a large enough magnitude to cause the pipe to collapse.  
+
Within the '''penstock''' pipeline the height difference creates pressure on the water. The pressurized water feeds the turbine. On top of the penstock a '''breather pipe''' prevents negative vacuum effects within the pipe during sudden shutting of the '''shutter valve'''. This valve is mounted directly before the turbine. It allows to close the water flow during maintenance or in emergency. This is to be done carefully to prevent a water hammer (strong pressure impulses). A pressure gauge mounted on the pipe before entering the turbine indicates the “'''net-head'''”. It also allows to monitor eventual irregularities within penstock or turbine.<br/><br/>The '''penstock''' is to be rested on '''supports''' in a way that they can slide on top due to heat/cold expansion/shrinking. '''Expansion joints''' are required to avoid changes in length to damage the structure. No forces from penstock must act on neither '''forebay''' nor turbine. Avoid steep angles (>135º) in pipe conduction. It reduces net-head and degrades much quicker than straight pipe (strengthening required on outer bend of an elbow).
  
&nbsp;
+
<br/>
  
<span>A pressure gauge should be installed at the end of the
+
== Powerhouse<br/> ==
penstock, right in front of the turbine shut-off valve. It will be a quick way
 
to monitor how the system and penstock are performing. A quick reading of the
 
pressure shows if there is a change or a problem. Additionally, by monitoring
 
this gauge&nbsp;when &nbsp;closing the turbine shut-off valve&nbsp;water hammer problems can be detected. Water
 
hammer is the opposite of the implosion issue noted above. If the valve is
 
closed too quickly, the momentum of the water can dramatically increase water
 
pressure to the point of bursting the penstock. Shutting down systems water
 
flow should be done carefully.</span>  
 
  
{| cellspacing="0" cellpadding="0" border="1"
+
[[File:Powerhouse 3.jpg|right|251px|Powerhouse 3.jpg|alt=Powerhouse 3.jpg]]
|-
 
| width="300" |
 
&nbsp;
 
  
|-
+
The turbine, generator, and electrical control have to be protected from: rain, theft and unauthorized access. Moving parts and electrical current can be dangerous for untrained people. The turbine should be nicely accessible, placed min. 1 ½ m from the walls. The location has to be dry even during floods. Rainwater from the hill is to be drained away from the house.
|
 
&nbsp;
 
  
|}
+
=== Tail Race (water outlet) ===
  
'''Shut-off Valve'''
+
below the powerhouse is the tail race where the turbine spills its water. Strong forces easily wash out such canal if its not prepared accordingly. The tail race usually feeds back the water to the river.
  
'''&nbsp;'''
+
<br/>
  
<span>A shut-off valve is necessary, and should be directly
+
 
in front of the turbine in case an immediate shutdown of the system is
+
== Poles (wood pole protection)<br/> ==
required. This valve should be of high quality and very durable. It is
+
 
recommended that to &nbsp;close and then open
+
The previously used Boucherie system has not proven successful in the tropics because it was not effective against termites. Experience with this system were made by GTZ in Burundi during the 70th. (one manufacturer of the chemical is/was[http://www.wolman.de/en/about_us/index.php?thisID=67 :]Wolmanit). The necessary 'Boucherie system' pole caps have long been out of industry production.
the valve slightly on a regular basis to insure they don’t become seized in the
+
 
open position and then don’t function when most needed.<u>  
+
 
</u></span> &lt;/meta&gt;&lt;/meta&gt;&lt;/meta&gt;&lt;/meta&gt;
+
 
 +
The only effective means (of wood protection) in the tropic is '''Creosote '''because it is also effective against termites.
 +
<div style="text-align: left"><div>The poles can be dipped - but this is not very effectively because only the outer sides of the mast is covered. After a short time the agent runs down the mast. What remains is the bare wood. The only advantage is that thickens the protection is thickend in the earth transition zone.</div><div></div><div>The only effective wood pole protection is the industrial pressure/vacuum process with creosote.</div><div><div><br/></div><div></div><div>Cylindrical steel poles are more durable but more expensive than wood poles.<br/></div><div>Several European manufacturer produce galvanized, octagonal steel poles that can be used.<br/></div><div>
 +
Alternatively and dependend from actual design,<br/>you may keep powerlines short, use local available materials and ensure mechanisms for regular maintenance.
 +
 
 +
 
 +
 
 +
Alternative low cost solutions may be concrete filled bamboo posts. If applicable and resources are available, a locally implemented maintainance system which replaces the posts if necessarymay be a solution too.
 +
</div></div></div>
 +
<br/>
 +
 
 +
 
 +
= Further Information =
 +
 
 +
*[http://www.energyservices.lk/forms/techspec.htm Technical specifications for MHP][http://www.energyservices.lk/forms/techspec.htm - Sri Lanka]
 +
*[http://practicalaction.org/civil-works-guidelines-for-micro-hydropower-in-nepal Civil Works Guidelines for Micro Hydropower in Nepal]<br/>
 +
*[[Portal:Hydro|Hydro portal on energypedia]]
 +
 
 +
<br/>
 +
 
 +
[[Category:Hydro]]
 +
 
 +
= References =
 +
 
 +
<references />
  
 
[[Category:Hydro]]
 
[[Category:Hydro]]

Latest revision as of 20:58, 10 November 2015

► Back to Hydro Portal


Weir and Intake

A (overflow) weir maintains a constant water level in the river at this point. This allows to divert a constant amount of water from the river into canal, penstock and turbine. If there is substantial silt in the water (muddy or sandy grounds) it requires a flush gate. Such gate can be opened to clear out silt which is usually transported with waters downstream but settles before a weir.

Intake is the structure between river an canal. It consists of a gate to open/close the water feed. A rake prevents major debris to enter the system. The intake is located preferably on an outside of a river bend in a way that silt and debris is not “automatically” streamed in. Due to it’s location in/on the river it is to be designed to withstand floods.

Weir construction.jpg



Canal

The canal transports the water towards the point where it drops steeply. To gain much height difference possible it is aligned with as little slope as possible. Canals usually lay on valley slopes. It is to be secured that no waters cross the canal uncontrolled (flushing above or under) from its side.. 1 - ½ meter path between hillside and canal allows its comfortable maintainance and prevents slides blocking the flow.


Sandtrap

The sandtrap separates silt and debris from the water before it enters penstock and turbine. It can be placed on the beginning or the end of the canal. The forebay is wider than the canal so the water goes slower. Therefore fine materials such as sand and mud settle at the bottom. A flush gate or a flush pipe at smaller installations is used to clean the sandtrap during maintainance intervals. A spillway ensures controlled overflow in case of flooding of canal.

Sand trap forebay.jpg

Forebay and Trash Rack

In the forebay tank the connection towards the penstock must not be the lowest point. The lowest point is towards a flush pipe. At such sand and mud can be flushed out during maintenance intervals. The forebay is closed by a trash rack. It's preventing any debris entering the penstock!
Trash rack Features: As wide as possible to prevent quick blocking by debris. Grid should be cleanable by a rake from the top. Easy access and comfortable handling make regular cleaning more probable.

Ererti I forbay , trash rack and flush gate.JPG
Penstock.jpg

Pipeline (Penstock)

Within the penstock pipeline the height difference creates pressure on the water. The pressurized water feeds the turbine. On top of the penstock a breather pipe prevents negative vacuum effects within the pipe during sudden shutting of the shutter valve. This valve is mounted directly before the turbine. It allows to close the water flow during maintenance or in emergency. This is to be done carefully to prevent a water hammer (strong pressure impulses). A pressure gauge mounted on the pipe before entering the turbine indicates the “net-head”. It also allows to monitor eventual irregularities within penstock or turbine.

The penstock is to be rested on supports in a way that they can slide on top due to heat/cold expansion/shrinking. Expansion joints are required to avoid changes in length to damage the structure. No forces from penstock must act on neither forebay nor turbine. Avoid steep angles (>135º) in pipe conduction. It reduces net-head and degrades much quicker than straight pipe (strengthening required on outer bend of an elbow).


Powerhouse

Powerhouse 3.jpg

The turbine, generator, and electrical control have to be protected from: rain, theft and unauthorized access. Moving parts and electrical current can be dangerous for untrained people. The turbine should be nicely accessible, placed min. 1 ½ m from the walls. The location has to be dry even during floods. Rainwater from the hill is to be drained away from the house.

Tail Race (water outlet)

below the powerhouse is the tail race where the turbine spills its water. Strong forces easily wash out such canal if its not prepared accordingly. The tail race usually feeds back the water to the river.



Poles (wood pole protection)

The previously used Boucherie system has not proven successful in the tropics because it was not effective against termites. Experience with this system were made by GTZ in Burundi during the 70th. (one manufacturer of the chemical is/was:Wolmanit). The necessary 'Boucherie system' pole caps have long been out of industry production.


The only effective means (of wood protection) in the tropic is Creosote because it is also effective against termites.

The poles can be dipped - but this is not very effectively because only the outer sides of the mast is covered. After a short time the agent runs down the mast. What remains is the bare wood. The only advantage is that thickens the protection is thickend in the earth transition zone.
The only effective wood pole protection is the industrial pressure/vacuum process with creosote.

Cylindrical steel poles are more durable but more expensive than wood poles.
Several European manufacturer produce galvanized, octagonal steel poles that can be used.

Alternatively and dependend from actual design,
you may keep powerlines short, use local available materials and ensure mechanisms for regular maintenance.


Alternative low cost solutions may be concrete filled bamboo posts. If applicable and resources are available, a locally implemented maintainance system which replaces the posts if necessarymay be a solution too.



Further Information


References