BUNAKHA H.E. PROJECT

  • The Bunakha Hydro Electric Project is located near village Bunakha, in Chukha Dzong (District) in the Western Bhutan. The site is located 3.25Km u/s of existing Chukha dam approachable by 2.5 Km long foot tact connecting Puentsholing -Thimphu National Highway at 102 Km Milestone. Phuentsholing is 105  Km From project site.
     
    The nearest rail head is New Alidwarpur (West Bengal) which is situated at a distance of 175 Km from Project site and the nearest road head in India is Hasimara (West Bengal) on NH - 31C, connecting Siliguri and Guwahati.
     
    THDC India Limited (THDCIL) and National Institute of Rock Mechanics (NIRM) signed a Memorandum of Understanding (MoU) in October 2010 for carrying out the Engineering Geological Investigations by NIRM for the Detail Project Report (DPR) of Bunakha Hydro Electric Project (BHEP). This phase of investigation was in continuation to the investigations carried out by WAPCOS Limited in January 1995. The updated DPR has been submitted to Ministry in  Aug, 2011. Bunakha HEP is posed for implementation through Joint Venture of THDCIL and Bhutanese PSU. Signing of implementation agreement is under progress.
  • GENERAL:
    1 LOCATION  
      Country Bhutan
      River Wangchu
      Dam Site Near Buankha village (3.25 km u/s of Chukha H.E. Project)
      Latitude           27°08’00’’N
      Longitude 89°32’33’’E
      Nearest Airport            Paro
     
    2 HYDROLOGY  
      Catchment area 3540 Sq.Km
      Mean annual runoff 2619 Mcum
      Probable Maximum flood 10028 Cumecs
      Sedimentation rate 1.00mm /year
     
    3 RESERVOIR  
      Maximum Water level (MWL) EL 2008 m
      Full reservoir level (FRL)        EL 2006 m
      Min. Draw down level             (MDDL) El 1950 m
      Gross Storage 329.16 Mcum
      Live Storage 250.62 Mcum
      Area under Submergence at FRL 6.82 Sq. Km
      Length of the reservoir 17.25 Km at FRL of EL 2006 m
     
    4 DIVERSION ARRANGEMENT  
      DIVERSION SLUICES  
      Number 2 Nos
      Size Width 6.0m by height 8.0m
      Shape Rectangular
      Diversion sluice bulkhead gates Vertical lift bulkhead gates
      Size of gate Width 6.0m by height 8.0m
      Gate operation platform EL 1863.0m
      Inlet Invert Level EL 1846.0m
      Outlet Invert Level EL 1842.0m
      COFFERDAMS  
      Upstream Cofferdam Rockfill dam with inclined clay core and grouted cutoff
      Crest level of u/s cofferdam EL 1863.0m
      Height of u/s cofferdam 20m (approx)
      Downstream Cofferdam Rockfill dam with clay core
      Crest level of d/s cofferdam EL 1851.0m
      Height of d/s cofferdam 8.0m (approx)
      DIVERSION CAPACITY  
      Water at 1.0 m below crest of upstream coffer dam  Capacity 1013.4 cumecs corresponding to EL 1862.0m
      DIVERSION FLOODS  
      25 year non monsoon flood 566 cumecs
      25 year monsoon flood 2,020 cumecs
     
    5 DAM  
      Type Roller Compacted Concrete
      Top width 12m
      Top elevation of Dam EL 2010.0 m + 1m wave protection wall
      Deepest foundation level EL 1813.0 m
      Height of Dam above deepest foundation level 197 m
      Length of Dam at the top 429.5 m
      Bottom width at Max. Section 196m
     
    6 SPILLWAY  
      PMF 10028 Cumecs
      Routed PMF 8756.61 cumecs
     
    6A LOW LEVEL SPILLWAY  
      Capacity 8756.61 cumecs through 5 gates and 1 auxiliary spillway open with water level at EL2008.
      Number of bays 6
      Size of Bays 6m wide by 9m high
      Crest Level EL 1915 m
      Energy Dissipation Flip Bucket
      Gate arrangement Radial gates of vertical opening 9m high by 6m wide
      Guard gate arrangement Vertical lift wheel gates of 9m high by 6m wide, one for each opening
     
    6B GATED AUXILARY SPILLWAY  
      Capacity 118.57 cumecs at water level EL 2008m
      Number of bays 1
      Size of bay 4m high by 4.5m width in block 14 & 15
      Crest Level EL 2002.0m
      Energy Dissipation Flip bucket
     
     
    7 INTAKE  
      Invert Level EI 1940 m
      Number 3
      Trash rack Inclined screens of width 5m by inclined length of  9.0m with 2 screens per penstock
      Service Gate arrangement Single vertical lift wheel gate with hydraulic hoist per penstock
      Service Gate size 3.5 m (W) X  3.5 m (H)
      Guard Gate arrangement Single vertical lift slide gate with winch hoist per penstock
      Guard Gate size 3.5 m (W) X 3.5 m (H)
     
    8 PRESSURE SHAFT  
      Number 3 Nos.
      Diameter 3.5 m, Circular
      Length 200m
     
    9 POWER HOUSE  
      Type Dam Toe Surface
      Design Discharge 46.89 cumecs
      Rated Head 141.62m (net)
      Size Machine hall: 54m(l) x 20m(w) x 52.5m(h)
    Service bay: 30 m(l) x 20m (w) x 18.5m(h)
    Control room: 56m(l) x 15m(w) x 6m(h)
      Type of Turbine and no. of units Vertical Francis, 3 units of 60MW each
      Installed Capacity 180 MW
      Turbine Centre Line Level El. 1837.0 m
      Service Bay Level El. 1860 m
      Normal Tail Water Level El. 1844.5 m
      Minimum Tail Water Level El. 1842.1 m
      Max. TWL (PMF=10028) El. 1859.3 m
     
    10 TAILRACE  
      Number 3 Nos.
      Type Open trough from draft tube to river
      Design Discharge 46.89 Cumec (Each bay)
     
    HYDRO-MECHANICAL WORKS:
    11 BULKHEAD GATES FOR DIVERSION SLUICES
      Type of Gate Fixed wheel with downstream skin plate and downstream seals.
      No. of bays 2 (Two)
      No. of gates required 2 (Two)
      Size of opening 6.00 m (wide) x 8.00 m (high)
      Sill level EL. 1845.00 m
      Design head corresponding to top of opening of sluice bay 79.0 m
      Operation Gate will be operated by Rope drum hoist of adequate capacity (120 MT tentative)
     
    12 SLUICE BAY RADIAL GATES
      Type of Gate Radial gate
      No. of openings 6 (Six)
      No. of Gates 6 (Six)
      Size of opening 6.00 m (wide) x 9.00 m (high)
      Sill Elevation EL.1915.00 m
      Level of Centre of Trunnion EL.1926.00 m
      Radius to outside of skin plate 13000 mm
      Design head (corresponding to FRL) 91.0 m
      Operation Lowering / raising under unbalanced head conditions by double cylinder hydraulic hoist ( 2 x 175 MT)
     
    13 EMERGENCY GATE FOR SLUICE BAY RADIAL GATES
      Type of Gate Fixed wheel with upstream skin plate and upstream seals.
      No. of bays 6 (Six)
      No. of gates required 6 (Six)
      Size of opening 6.00 m (wide) x 9.00 m (high)
      Sill level EL.1915.00 m
      Design head 91.0 m
      Operation Double acting Hydraulic hoist of adequate capacity (160 T tentative)
     
    14 SPILLWAY STOPLOG
      Type of gate Vertical lift Slide type with upstream skin plate and seals
      No. of openings 6 (Six)
      No. of sets of stoplog 1 (One)
      Size width of opening 6.00 m (wide) x 9.00 m (high)
      Number of stoplog elements 4 Nos. (3 Interchangeable and one top unit)
      Sill Elevation EL.1915.00 m
      Design head (corresponding to FRL) 91.0 m
      Operation The Stoplog units will be operated by electrically operated Gantry Crane of adequate capacity (tentative 20 MT) through lifting beam.
    15 AUXILIARY SPILLWAY GATE
      Type of gate Vertical lift Fixed Wheel type with upstream skin plate and seals
      No. of openings 1 (One)
      No. of gates 1 (One)
      Clear width of opening 4.50 m
      Total height of gate 4000 mm + 500 mm freeboard
      Sill Elevation EL.2002.00 m
      Design head (corresponding to FRL) 4.0 m
      Operation The gate will be operated by electrically operated rope drum hoist of adequate capacity (tentative 15 MT).
     
    16 TRASHRACKS
      Type of trashrack Inclined
      No. of bays 6 (Three tunnels having two bays each)
      No. of sets of trashracks required 8 including two spare sets
      Clear width 5.75 m
      Total vertical height of trashrack 9.20 m
      Sill level EL.1939.00 m
      Differential head for design 6.0 m
      Operation Trashracks will be operated by Auxiliary Hoist attached with Trashracks cleaning M/c of approx 7.5 MT capacity
     
    17 INTAKE GATES
      Type of Gate Fixed wheel with downstream skin plate and downstream seals.
      No. of bays 3 (Three)
      No. of gates required 3 (Three)
      Size of opening 3.50 m (wide) x 3.50 m (high)
      Sill level EL.1940.00 m
      Design head 66.0 m
      Operation Gate will be operated by Hydraulic Hoist of adequate capacity (approx 60 MT) mounted on a Bonnet cover.
     
    18 INTAKE STOPLOG GATES
      Type of gate Vertical lift Slide type with downstream skin plate and seals
      No. of openings 3 (Three)
      No. of sets of stoplog 1 (One)
      Size of opening 3.50 m (wide) x 3.50 m (high)
      Number and size of stoplog elements 2 Nos. of equal height
      Sill Elevation EL.1940.00 m
      Design head (corresponding to FRL) 66.0 m
      Operation The Intake and Spillway Stoplog units will be operated by electrically operated common Gantry Crane of adequate capacity through lifting beam.
     
    19 DRAFT TUBE GATES
      Type of gate Vertical lift, slide type downstream (Turbine side) skin plate and downstream sealing
      No. of bays 3 (Three)
      No. of gates required 3 (Three)
      Size of opening 7.80 m (wide) x 3.00 m (high)
      Sill level EL.1830.60 m
      Max. TWL EL.1842.108 m
      PMF EL.1859.26 m
      Design head 11.508 m (Check for design head corresponding to PMF with increase in permissible stresses)
      Operation The gate will be operated by electrically operated Gantry Crane of adequate capacity (tentative 40 MT) through lifting beam.
     
    ELECTRO-MECHANICAL WORKS:
    20 INSTALLATION  
      1.     Capacity (Nominal) 180 MW
      2.     No. of units x unit Rating x head x type 3 x 60 MW x 141.62 m x VF
      5.     Generation Type Peaking duty
      6.     Type of Development Storage
      7.     Power Plant Location At toe-of-dam; left bank, Wangchu river.
     
    21 TURBINE  
      1.     Type x Nos x Rating VF x 3 x 61224.49 kW
      2.     Rated/(Head Range) 141.62 m (161.0 - 103.0)
      3.     Normal Turbine discharge 46.89 m3/sec.
      4.     Speed 250 rpm
      5.     Runner Dimensions
    (D3- Discharge dia, mm)
    2.6 m
      6.    Turbine Setting level El 1837.0 m 5.11 m below  min. TWL (El 1842.11 m)
      7.    Max. Static Pressure at inlet level 170.0 m (approx)
      8.    Max. dynamic pressure (water Hammer) at inlet 247.0 m (approx)
     
    22 GOVERNOR  
      1. Type Digital-Electro-Hydraulic
      2. Oil Pressure 60 kg/cm2
      3. Governor Closing & Opening time for turbine regulation & transients limits 5 to 7 seconds
     
     
     
    23 TURBINE INLET VALVE Provided
     
    24 EMERGENCY CLOSING DEVICE FOR TURBINE
      (Governor failure, turbine racing to runaway speed) – Intake gate made quick closing type (in 2 min.) by hydraulic hoist provision  
     
     
     
     
    25 GENERATOR AND EXCITATION SYSTEM
      1.    Type x Nos x rating Vertical x 3 x 66.67 MVA
      2.    Overload Rating Continuous 73.33 MVA
      3.    Other basic parameters 11 KV, 3850 A, 3 phase,
        0.90 PF,  50 Hz.
      4.    Excitation system SEE
     
     
    26 GENERATOR-TRANSFORMERS (STEP-UP)
      1. Type x Nos of Banks Three phase
      2. Rating Each Bank 75 MVA, 11kV / 220 kV
      3. Type of cooling ODWF                                                                                              ODWF
      4.  Location Downstream side of PH
     
    27 POWERHOUSE
      1. Machine Hall (LxWxH) 91 m x 21 m x 49 m
      2. Overall Plan (LxW)
    including u/s & d/s bays
    91 m x 58.4 m
      SERVICE BAY  
      3. Service bay level El. 1860.0m
      4. Unloading Bay level &
    Transformer Bay (Approach)
    El. 1860.0 m
      5. Turbine Setting level El. 1837.0m
      6. Setting depth 5.11m below min TWL of  El 1842.11 m
      7. Max TWL (10,000 yr Flood) El 1859.26 m
     
    28 INTERCONNECTION GEN-TRANSFORMERS TO SWITCHYARD (220 kV)
      1.       Nos of ICs x type Transformer desk
      2.       Span 200 m each
      3.       Intermediate supports 1 D/C tower + 1 S/C tower
      4.       Reqd. Continuous Rating of each 1C 75 MVA at 220 KV
     
     
    29 220 KV SWITCHING SCHEME & STATION
      1.     Type of Scheme Double bus, single breaker,
      2.     Nos. of Bays 6 nos (3 in coming from Generator-transformers, 3 outgoing transmission lines)
      3.      Location downhill on outlet side of power house, about  500m distance
      4.      El & Area El 1990.0 m to 1960.0 m
    120 m L x 135 m (W)
    30 TRANSMISSION LINES
      1.      Total nos. 3
      2.      Loop-in & Loop out with Existing Chukha - Simtokha line 2 nos out of 3
      3.      To Switching station of Tala HEP (400 kV & 220 kV) downstream of Chukha 1, route length about 40 km
      4.      Continuous rating of each line Entire plant capacity of 222 MVA inclusive of over load.
     
    31 DAM & STORAGE PARAMETERS
      1.      FRL El 2006.0 m;
      2.      MDDL El 1950.0 m
     
    32 TAIL WATER LEVELS
      1.      Min TWL. El 1842.11 m
      2.      Nor. TWL El 1844.518m
     
    33 GROSS HEADS
      1.      Maximum 164.0 m
      2.      Minimum normal 106.0 m




Updated on : 18/02/2018