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Tashiding HEP
Salient Features

PROJECT LOCATION

State Sikkim
District West
Stream Rathang Chu River
Location of Power House (nearest village) Tashiding
Latitude 270 20’28” N
Longitude 880 13’59” E

HYDROLOGY

Catchment area at Barrage Site 553 sq. km
Average Annual precipitation in snow fed catchment 1250 mm
Average Annual precipitation in rain fed catchment 2500 mm
Average Annual Inflow        2578 mm
Flood Discharge for River Diversion (~Q25) Non-Monsoon  175 Cumec
Flood Discharge with return Period T=100 years 1650 Cumec
Standard Project Flood Discharge (SPF) (~Q 500) 2000 Cumec
Probable Maximum Flood Discharge (PMF) 2690 Cumec

RESERVOIR

Pond Level (FRL) El. 910.00 m
Minimum Draw down Level El.905.00 m
Maximum Water Level El.914.00 m
Pondage above MDDL (Diurnal storage) 0.051 M cum
Submergence area at FRL 1.33 ha
Stretch of Reservoir 0.27 km

DIVERSION TUNNEL

Shape & Size Horse- shoe shaped, 4.5 m
Length 167 m
Flow Velocity 10.42  m/sec
Diversion  Flood        175 cumec
Lining Thickness (PCC) 150 mm
DIVERSION STRUCTURE
Type  Barrage
Top elevation of barrage El.917.0 m    
Height of barrage above crest level 12 m
Length of barrage between abutments 42.50 m
River bed level (deepest) 896.50 m
Design flood  1650 cumec

BARRAGE BAY

Crest elevation El. 898.00 m
Number 4
Width of each bay 6.5 m
Total floor length 138 m
Gates  
Type Fixed wheel type Vertical Lift
No. & Size Four, 6.5 m (W) x 9.0 m (H)   

Under sluice Gates

Crest elevation El.896.50 m
Number 1
Width of each bay 6.5 m
Total floor length 138 m
Gate  
Type Fixed wheel type Vertical Lift
No & Size One, 6.5 m(W) x 9.0 m (H)

Intake

Location

On right bank, 7.3 m upstream of barrage axis

Total width between abutments

24m

Trash Rack Structure

Inclined

Size of opening for trash rack

5 Nos.  4m (W)

Crest Level of Trash rack EL.900.40 m
Size of Intake opening 4.3 m(W) x 4.5 m(H)
Invert level of Intake at entry EL.896.85 m
Design Discharge 50.76 Cumec
Velocity of flow through Trashracks 0.75 m/sec
No., Type & Dimension of Gates One, Vertical lift gate, 4.3 m(W) x 4.5 m (H)

HEADRACE TUNNEL-HRT

Shape & Size Horse- shoe shaped, 4.5 m
Length 5.437 km
Flow Velocity at Design Discharge 3.02  m/sec
Design Discharge 50.76 cumec
Lining Thickness (PCC) 200-300 mm

Adit To HRT

Location  About 1.59 km d/s of Barrage axis
Shape  & Size D-shaped, 4.5m
Length   236 m
Level El. 875.00m

SURGE SHAFT

Vertical Shaft Restricted Orifice Type
Internal Diameter 8.5 m
Height of shaft 61.05 m
Concrete lining thickness Varying from 300 mm to 600 mm
Lining Type RCC Lining
Vertical Lift Gate size 3.5 m (W) x 4.5 m (H)
Top of Surge shaft El. 936.00 m
Bottom of Surge shaft El. 877.00 m
Max. Surge level El. 933.20 m
Min. Surge level El. 879.35 m
Orifice dia. 2.00 m

Adit to HRT & Surge Shaft Bottom

Shape & Size
D-Shaped, 4.5m
Entry Sill Level EL.869.00 m
Length 89 m

PRESSURE TUNNEL/PENSTOCK

Total Length upto Bifurcation 441.53 m
Internal Diameter 3.5 m
Horizontal length from Surge Shaft to portal 63.28 m
Inclined Penstock Length from portal to Bifurcation point 378.25 m
Number of anchor blocks 5

Bifurcation Point

20 m upstream of PH

No. of Branch after Bifurcation 2
Diameter after Bifurcation 2.5 m
Branch penstock length 25 m & 33 m
Steel liner thickness 16 mm to 32 mm
Grade of Steel lining ASTM 537 Class-II

POWERHOUSE

Type

Surface Powerhouse

Size 50.5 m(L) x 33.5 m(W) x 44.1 m(H)
Number of units Two (2)
Rated Discharge per unit 25.38 Cumec
Turbine Speed 428.57 rpm
Min. Tail Water Level EL.686.6 m
Normal Tail Water Level EL. 688.5 m
Gross Head (monsoon period) EL. 221.5 m
Net Rated Head 208.33 m
Installed Capacity 2x 48.5 MW
Inlet Valve Type Spherical Valve
Number 2
Turbine Axis Elevation EL. 681.60 m
Generator type Suspended
Nominal Speed 428.57 rpm
Voltage / Frequency 11 KV /50 Hz
Power Factor 0.9
No. & Size of Draft Tube Gates Two nos., 5.14 m (W) x 4.03 (H)

TRANSFORMER

Type and capacity Three phase,11KV/220KV, 60 MVA, OFWF
Location  Outdoor on right bank of the river
Number 2

TRAILRACE CHANNEL

Type Open Channel
Length (Including tail pool) 78.5 m
Bed Slope (Tail Pool)     1:4
Nominal Discharge   50.76 Cumec
River Bed Elevation EL.686.00 m

SWITCHYARD

Type

Outdoor

Size 42 m x 53 m
Location of Switchyard Upstream of  PH on right bank at El. 710 m
Bus bar Voltage    220KV

TRANSMISSION LINE

Type Switch yard to Melling pooling station, 220 KV single circuit
Length      About 27 km

ESTIMATED COST

Civil Works (Including gates & hoists)

Rs  204.21 Crore

E&M Works (Including cost of Transmission line to pooling station) Rs. 156.83 Crore
Total Basic Cost Rs. 361.04 Crore
Escalation during construction Rs. 34.79 Crore
Interest during Construction Rs. 70.12 Crore
Total (Generation Works) Rs. 465.95 Crore
Cost per MW installed Rs. 4.80 Crore

POWER BENEFITS

Annual Energy Generation including 10% overloading utilizing high inflow (90% Dependable Year) 450.04GWh
Annual Energy Generation in Average Year including 10% overloading utilizing high inflow (50% Dependable Year)   480.35 GWh
Design Energy Generation including 10% overloading utilizing high inflow (90% Dependable Year with 95% machine availability)
435.22 GWh
Annual Plant Load Factor 51.22 %

FINANCIAL ASPECTS

Levelized Tariff (35 years) for Design Energy at 90% Dependable Year

Rs 2.02 /kWh

FIRR at Rs.2.09/kWh tariff    9.85 %
FIRR at Rs.2.25/kWh tariff 11.23 %

CONSTRUCTION  PERIOD

Construction Period in months (excluding pre-construction works) 33 months