General Overview – In SRHP, Sikidiri two nos. of Hydel units having capacity 65 MW each and both the units are in series (water discharged from 1st Unit is utilized for power generation by 2nd Unit).

Name of project – Subernarekha Hydel Project, Sikidiri

Scope of project – Following is the scope of project :-

1. I. To supply 75 cusecs firm water to industrial belt of Ranchi including Ranchi city.
2. II. To generate hydro electric power to the extent of 130 MW at 14% load factor for peaking Purposes for 3.4 hrs.
3. III. To supply water to Tata and other industrial lower down.

Power Channel 1 –

• Shape – Trapezoidal
• Design Discharge – 2,000 cusecs
• Length of channel – 24,100 ft. (7348 meters or 7.348 km)
• Bed width – 15 ft.

Power Channel 2 –

• Shape – Trapezoidal
• Design Discharge – 2,000 cusecs
• Length of channel – 12,380 ft. (3,777 meters or 3.777 km)
• Bed width – 08 ft.

Penstock No. 1 –

• Type – High Tensile Steel Pipe
• Diameter – 3.912 meters
• Length – 481.291 meters

Penstock No. 2 –

• Type – High Tensile Steel Pipe
• Diameter – 3.912 meters
• Length – 307.660 meters

Tunnel 1 –

• Type – D shape
• Length of tunnel – 1140 meters
• Depth – 18.37 ft. (D shape section)

Tunnel 2 –

• Type – D shape
• Length of tunnel – 366 meters
• Depth – 18.37 ft. (D shape section)

Hydro Turbine –

• Type of turbine – Francis with vertical shaft. (RA-170/638 –BVM-2800)
• Runner diameter – 2800 mm
• Speed of rotation – 300 r.p.m.
• Normal output – 65 MW + 10% overload
• No. of guide vanes – 24
• No. of stay vanes – 12
• No. of runner blades -16

Governing system of turbine –

• Type of governor – EHG-40
• Operating duty of Governor – Peak Load / Frequently Control
• Diameter of Main guide valve – 100 mm
• Diameter of Main guide valve – 100 mm
• Normal operating of oil pressure – 40 Kg/cm2

Disc Valve –

• Diameter of valve – 2600 mm
• Static head – 140 m
• Max. Discharge – 61 M3/Sec.

Hydro Generator –

• Type of product – S.V. 570/170 – 20
• Type of generator – Suspension
• Rated output – 72000 KVA, 65 MW + 10% overhead
• Rated voltage – 11 KV
• Rated current – 3780 Amps.
• Rated power factor (Lagging) – 0.9

Machine Specifications

Machine Excitation – Conventional

• Main Exciter:
  • Type: SE-139/22 – BP
  • Rated Capacity: 240 kW / 620 kW
  • Rated Voltage: 210 V / 340 V
• Pilot Exciter:
  • Type: SE-72/10 – 10 P
  • Rated Capacity: 8 kW
  • Rated R.P.M.: 300

Stator

• Height: 3150 mm
• Diameter of Air Gap: 4900 mm
• Outside Diameter of Frame: 7100 mm
• Weight of Wound Stator: 121 T
• Number of Sectors: 3
• Class of Insulation: B
• Total Generator Weight: 415 T
• Weight of Rotor: 193 T

Cooling Systems

• Lower Guide Bearing Oil Cooler:
  • Cooling water flow: 3.75 m³/hr
  • Max. Temp. of cooling water at inlet: 35°C
• Upper Guide Bearing Oil Cooler:
  • Cooling water flow: 11.35 m³/hr
  • Allowable working pressure: 2.5 kg/cm²
  • Testing water pressure during 1 hr: 3.5 kg/cm²
• Thrust Bearing Oil Cooler:
  • Cooling water flow: 43 m³/hr
  • Allowable working pressure: 3 kg/cm²
  • Testing water pressure during 30 minutes: 4 kg/cm²
• Turbine Guide Bearing:
  • Cooling water flow: 2.00 m³/hr
  • Max. Temp. of cooling water at inlet: 35°C
• Air Cooler:
  • Air flow: 4 m³/sec
  • Cooling water flow: 37 m³/hr
  • Allowable working water pressure: 3 kg/cm²

Brief

• Installed capacity: 65 MW each
• Year of commissioning:
  • Unit No. 1: 1977
  • Unit No. 2: 1980
• Discharge: 2000 cusec for full load
• Plant Load Factor: 14% — plant should run daily for 03h 21m 36s (1225 hrs/year as per water availability)
• Turbine: Francis with vertical shaft
• Peak draft (Discharge): 2000 cusec
• Firm draft (No load discharge): 300 cusec
• Gross head: 133 m
• RPM: 300
• Rated output: 72,000 kVA
• Rated voltage: 11 KV
• Type of governor: EHG 40
• Type of generator: Suspension
• Generation (2023–24):
  • Unit No. 1: 49.408 MU
  • Unit No. 2: 47.425 MU
  • Total: 96.833 MU
• Present status: Both units available for generation

Water Availability

• Reservoir level: 1924.20 ft as on 10-04-2024
• Radial gates open at: 1934.00 ft
• Water requirement per hour: 2000 cusec (165 Acre-ft/hr)

Short Term Planning / Annual Maintenance

Mechanical Works

• Unit No. 1:
  • Centering, leveling, alignment of turbine
  • Testing/rectification of defects in turbine bearings
  • Testing/rectification of defects in all coolers, air, water & oil pipelines and valves
  • Ultrasound testing of penstock
  • Scheduled repair and maintenance of mechanical parts/equipment as required
• Unit No. 2:
  • Scheduled repair and maintenance of mechanical parts/equipment as required
  • Replacement of spider pipes, overhauling of brake and jack system
  • Testing/rectification of defects in all coolers, air, water & oil pipelines and valves
  • Ultrasound testing of penstock

Civil Works

• Total area: ~485 Acres (includes power canal, power house I & II, switchyard, store, road, residential colony, I.B.)
• Residential quarters: ~200
• Repair/maintenance of power canal, switchyard building, power houses 1 & 2, office building, residential quarters, etc.
• Comprehensive repair of canal structures (PC-I to IV) after severe damage observed during complete dry out; urgent to prevent accidents and leakage

Renovation and Modernisation

Units are operational after ~45 years since commissioning (total generation: 7486 MU). However, equipment and technology are obsolete, requiring R&M to address frequent glitches.

Mechanical

• Upgradation of old runner, labyrinth, pivot ring, stay ring
• New guide vanes with self-lubricating bushings
• Dynamic oil cooling for guide and thrust bearings
• Upgrade brake and jacking system
• Upgraded cooling system for bearing coolers and stator winding coolers
• Upgrade MIV sealing and operating system
• Modernize water intake/outlet gates and operation system
• Upgrade OPU arrangement with automation
• Automate all important valves
• Collapsible gate in tail race in place of permanent barrier
• Upgrade governing system with servo system
• Rehabilitate penstock and associated systems

Electrical

• Static excitation system
• Rehabilitate with class F insulation (replace class B) for stator winding
• Replace static relay system with Micom or equivalent
• Auxiliary power from 11 KV generation output
• Auto synchronization system
• Replace old 80 MVA GT transformer with new (updated protection & cooling)

Note: Above works are based on current site engineer assessment; expert consultancy may be required for detailed DPR preparation.

Operational Statistics (as on 31-03-2024)

Progressive Running Hours (since commissioning)

• PH-I: 63,577:10 hrs
• PH-II: 70,658:33 hrs

Cumulative Generation (since commissioning)

• PH-I: 3748 MU
• PH-II: 3738 MU
• Total: 7486 MU

Main Heads / Points – RLA Study

Hydro Turbine

• The current turbine has been in continuous operation since commissioning.
• Assessment of aging effects on turbine materials is required to determine residual life expectancy and suggest alternatives.
• Possible upgrades: old runner, guide vanes, related brake and jacking system, draft tube, etc.

Hydro Generator

• Includes stator winding, stator core, rotor & other components, and excitation system.
• Currently using Class ‘B’ insulation for stator winding; should be upgraded to Class ‘F’ insulation for:
  • Higher allowable working temperature
  • Better thermal conductivity
  • Improved dielectric properties

Generator Transformer

• Replace existing old 80 MVA GT transformer with a higher rating and updated protection & cooling arrangement.
• Assessment to be made regarding uprating this system.

Governor

• Currently installed: G-40 series electro-hydraulic governor (EHG) [BHEL make].
• Issues: unable to operate units in auto mode; system is obsolete (since commissioning).
• RLA should assess requirement for an upgraded governor compatible with the latest technology, SCADA system, or alternatives.

Pipelines and Waterways

Penstock

• In service since commissioning; visible wear and tear.
• Frequent welding required due to occurrence of holes.
• Rusted iron chips found during annual maintenance (suggesting thickness reduction).
• Ultrasonic testing required to assess remaining life.

Canals / Bye-pass / Tunnels

• Condition is poor; only makeshift R&M work being done (pot-hole filling, parapet wall repairs, panel repairs).
• Complete assessment desired from Getalsud dam to PH-II, including:
  • Power Canals I to IV
  • Cross drains of Power Canal I & II
  • Escape channels I & II (velocity breakers damaged, water leakage)
  • Bye-pass
  • Tunnels I & II (damaged ceiling portions)
  • Tail race