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3. Small Hydropower Planning

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3. Small Hydropower Planning Small-Hydro Visual Guide 3. Power Generation Planning 3. SMALL HYDROPOWER PLANNING Tracing by GPS Location Map Proposed Axis Tunnel Scheme P/H Site (Alt1) Open Channel (Alt 1) P/H Site Open Channel (Alt1) (Alt 2) Waypoints <Intake Site> <Powerhouse site> 036 Ban Sentham 045 Bridge over river where water will be 037, 038 Cross river by foot discharged 039 Original axis 046 Village (Ban Somboun?) 040 Alternative axis 1 (no slope on 050, 051 Farm and paddy along the river R/B) 052 Confluence of small river from L/B 041 Alternative axis 2 (no slope on 053 Existing weir R/B) 054 Paddy area 042 D/S side of paddy that extends 055 Foot of mountain at the valley on L/B 056-057 Climb the valley along footpath (L/B of 043 Paddy approx 100 m U/S of axis valley)(P/H site to be around this area) 044 Bridge over road 058 Top of mountain 059 Flat land after climbing gentle slope from 058 From 059 to 044 is almost jeepable footpath. There are sugarcane farms along this footpath, and slope is generally gentle. JICA M/P Study on Small-Hydro in Northern Laos [ 29 ] December 2005 Small-Hydro Visual Guide 3. Power Generation Planning General Layout of Power Facilities Site Selection • Discharges are stable even in the dry season. • Specific discharge (m3/sec/km2) in the dry season is relatively high. • (L/H) rate is small. • Distance from the demand centre is short. Potential Site-1 Main stream L1 Potential Site-2 L2 H1 Tributary H2 L / H < 40 General outline L / H < 20 Advantageous sheme L / H < 15 Excellent s cheme where L : length of waterway H : head Small/Mini Hydro Utilizing Drops or Falls Nearby demand Head Tank Penstock Cross drain Powerhouse Power Canal at valley Slope protection or box culver De-silting Basin • De-silting basin to be located next to intake • Low velocity to regulate excessive flow & sand • Steep slope enough to wash out sediment to river Intake • Intake to be located in a straight river stretch • Side intake with weir or Tyrolean intake • Sand flushing gate to be provided beside the weir General Layout of Small Hydropower System JICA M/P Study on Small-Hydro in Northern Laos [ 30 ] December 2005 Small-Hydro Visual Guide 3. Power Generation Planning General Layout Weir Intak e De-silting Basin Power Canal Head Tank De-silting basin Trashracks • velocity < 0.3 m/s Trashracks Spillway Intak e Gate • slope steeper than 1/30 Side Spillway Spillway Power canal Sand Drain Gate Slope 1/500 ~ 1/2,000 River Outlet / Sand Flush Gate Sand Drain Gate Typical Profile of Open Waterway System Head Tank Penstock Powerhouse Tailrace Trashracks Head Tank Spillway • to be located on stable ridge • capacity against load change • spillway & sand drain Sand Drain Gate Anchor Block Powerhouse • to be built on firm foundation Penstock • to be located above FWL • to avoid potential land slide area • drainage around • to be located on stable ridge • to be located below hydraulic grade line • slope protection & drain along penstock TWL • penstock directly from de-silting basin may be possible according to topography Typical Profile of Waterway System JICA M/P Study on Small-Hydro in Northern Laos [ 31 ] December 2005 Small-Hydro Visual Guide 3. Power Generation Planning Selection of Waterway Route Features of Waterway Routes Catchment Waterway Route River flow Head Area length A Small Small Large Large B Medium Medium Medium Medium C Large Large Small Small Source: Guide Manual for Development Aid Programs and Studies of Hydro Electric Power Projects / New Energy Foundation Selection of Penstock Route Notice that the channel can be shorted to avoid the risk and expense of construction across a steep slope. Source: JICA Study Team Channel and Penstock Option JICA M/P Study on Small-Hydro in Northern Laos [ 32 ] December 2005 Small-Hydro Visual Guide 3. Power Generation Planning Determination of Design Discharge Relationship between Maximum Discharge and Minimum Discharge Discharge Maximum Power Discharge Minimum Power Discharge 95% Dependability Qmax Qmin 0 50 95 100 Occurrence Probability of Exceedance (%) Relationship between Potential Discharge and Demand ) ) /s 3 W Potential (Q min ) > Demand m k ( ( Q put e g r Out ha c s Di t u l o il Firm Power Output p S Irrigation Demand Q Non - Operation Period min Min. Discharge 1 2 3 4 5 6 7 8 9 10 11 12 ) /s ) Potential (Q min ) < Demand 3 m ( ① 24 hours Supply with Min. PowerMax. Power Output Q e for 24-hour g r or ha Output (kW ② Peak Power Operation Disc ll out i p Max. Power Output S Demand Peak power operation Min. Power Output or Demand Control Irrigation Qmax Qmin Non - Operation Period Min. Discharge 1 2 3 4 5 6 7 8 9 10 11 12 JICA M/P Study on Small-Hydro in Northern Laos [ 33 ] December 2005 Small-Hydro Visual Guide 3. Power Generation Planning Calculating Head Loss and Effective Head FSWL 2 v1 /2 h1 v1 h2 Intake Head Tank Hg : gross head (m) He : effective head (m) Penstock h1 : head loss between Intake & head tank He h2 : head loss between head tank & tailrace Hg H e = H g − h1 − h2 − h3 h3 : head between mean pitch level and TWL Tailrace h3 Powerhouse TWL Source: JICA Study Team Effective Head for Impulse Turbines FSWL 2 v1 /2 h1 v1 h2 Intake Head Tank Hg : gross head (m) He : effective head (m) Penstock h1 : head loss between Intake & head tank He h2 : head loss between head tank & tailrace Hg v 2 h3 : head between draft tube WL and TWL H = H − h − h − 2 − h e g 1 2 2g 3 Tailrace 2 v2 /2 v2 Powerhouse TWL h3 Source: JICA Study Team Effective Head for Reaction Turbines JICA M/P Study on Small-Hydro in Northern Laos [ 34 ] December 2005 Small-Hydro Visual Guide 4. Design of Civil Structures 4. DESIGN OF CIVIL STRUCTURES Major Civil Structures Headrace Intake Headtank Channel Intake Weir Penstock Powerhouse Tailrace Intake and Desilting Basin JICA M/P Study on Small-Hydro in Northern Laos [ 35 ] December 2005 Small-Hydro Visual Guide 4. Design of Civil Structures Design of Intake and Desilting Basin N Intake Headrace Desilting Basin Channel B Side Spillway A Rip Rap Weir Skimmer Wall Trashrack Intake Gate Desilting Basin Side Spillway Headrace Channel Location of Intake Outside of meander Erosion and damage by flood Inside of meander Entrance of sediments to the waterway Straight section Good for intake site JICA M/P Study on Small-Hydro in Northern Laos [ 36 ] December 2005 Small-Hydro Visual Guide 4. Design of Civil Structures Intake Design Considerations Apron and riprap: to protect against Submerged weir: 1/20-1/50 slope: scouring to avoid sedimentation to flush sediment Skimmer wall: Avoid floating debris to enter Intake sill 1 m above riverbed: Avoid sediment to enter Trashrack: avoid entrance of floating objects Weir - Functions & Considerations Functions • To secure depth for intake • To store water Considerations • Weir axis perpendicular to river • structure to reach rock foundation • Stability (Overturning, Sliding, Bearing) • Backwater effect upstream • Weir protected against erosion • Apron to avoid scouring JICA M/P Study on Small-Hydro in Northern Laos [ 37 ] December 2005 Small-Hydro Visual Guide 4. Design of Civil Structures SWHeirAP E- T yp¥* esMERGE FORMAT - Structured on rock foundation Concrete - Most common Weir - Durable - High cost Floating - Structured on gravel foundation - Need seepage path Concrete - Durable Weir - High cost Concrete - Structured on gravel foundation faced - Surface protected with concrete - Relatively durable Gabion Weir - Low cost - Structured on gravel foundation Gabion - Sediment between rock forms strong structure - Low cost Stone - Structured on gravel foundation Masonry - Low cost Design of Desilting Basin N Functions Intake Desilting Basin • To remove sediments B • To spill excess water A Consideration • Appropriate length of basin • Appropriate length of side spillway JICA M/P Study on Small-Hydro in Northern Laos [ 38 ] December 2005 Small-Hydro Visual Guide 4. Design of Civil Structures Desilting Basin - Required Length Actually Required Length L = L0 x (2 ~ 3) Required Minimum Length L0 H V V < 0.3 m/s u = 0.1 m/s u Desilting Basin - Side Spillway Side Spillway JICA M/P Study on Small-Hydro in Northern Laos [ 39 ] December 2005 Small-Hydro Visual Guide 4. Design of Civil Structures Headrace Channel Structures Functions • To convey water until head tank where there is enough head Considerations • Avoid steep channel slope so not to waste head • Avoid passing channel through steep mountain side • Slow velocity to avoid abrasion of canal • Attention when crossing valleys Open Channel Types Construction Cost CHEAP Expensive Weak Stone Strong Earth Masonry Concrete Canal Canal Canal Durability JICA M/P Study on Small-Hydro in Northern Laos [ 40 ] December 2005 Small-Hydro Visual Guide 4. Design of Civil Structures Channel Slope (S) Channel section can be smaller, but head will be 1/500~1/1,000 lost Good for high head schemes where loss of head is not critical 1/1,000~1/1,500 General application Head loss can be reduced, but channel section will be bigger 1/1,500~1/2,000 Good for low head schemes where loss of head is critical 1/500~1/1,000 1/1,000~1/1,500 1/1,500~1/2,000 Uniform Flow and Channel Section Uniform Depth (h0) = Water finds its own depth h0 depends on: -Channel Slope (S) -Roughness Coefficient (n) -Channel Section h0 1 h0 Roughness Coefficient m Concrete: 0.013~0.016 Masonry: 0.016~0.020 B Earth: 0.020~0.025 JICA M/P Study on Small-Hydro in Northern Laos [ 41 ] December 2005 Small-Hydro Visual Guide 4.
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