The Kotmale Power Plant is a major hydroelectric power station in Sri Lanka's Mahaweli Complex. It has an installed capacity of 3 * 67 MW generated from three underground power stations and contributes around 445 GWh annually. Water is collected from a rock fill dam with a spill level of 704m and fed through long penstocks and surge chambers to maintain constant pressure. The plant uses Francis vertical turbines connected to generators to produce electricity, which is stepped up and sent to the grid via a switchyard consisting of components like circuit breakers and transformers.

1. HYDRO POWER GENERATION
KOTMALE POWER PLANT
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2. MAHAWELI COMPLEX
 Mahaweli Hydro power complex consists of seven major power station which has an installed
capacity of 836 MWs.
 It contribute around 13% electrical energy to the country annually.
 The major power stations coming under Mahaweli complex are, Kotmale, Victoria,
Randenigala, Rantambe, Ukuwela, Bowatenna and Nilambe and Upper Kotmale.
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3.  Kothmale (67 x 3 MW)
 Victoria (70 x 3 MW )
 Randenigala ( 61 x 2 MW)
 Rantambe ( 24.5 x 2 MW)
 Ukuwela ( 20 x 2 MW)
 Bowatenna ( 40 x 1 MW)
 Nilambe ( 1.66 x 2 MW)
 Upper Kotmale (75 x 2 MW)
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4. KOTMALE POWER PLANT
Introduction
 A main hydro power plant in Sri Lanka that produces 3*67 MW
 Water head is 229m
 Underground power station
 Annual energy generation is 445 GWh
 Use for frequency control
 Can also be used as the initial supplier, in case of a blackout
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5. DAM AND IT’S COMPONENTS
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Dam
• Water spill level – 704m
• Rock fill with concrete membrane
• Minimum operation level – 665m

6. PENSTOCK
• Low pressure tunnel length – 6954m
High pressure tunnel length – 142m
• Surge chamber- Release the water pressure in case of a sudden
stoppage.(water hammer)
• Maintains constant pressure during operation.
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7. SPILL GATES
Spillway type – radial gated chute type
Three gates
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8. 8
Adit
• A supplementary opening to remove excess water and for maintenance activities.

9. POWER HOUSE
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• This is the first underground
power house in Sri Lanka
• Consist of 3 units each with
67MW maximum capacity

10. TURBINE
 Francis type vertical axis turbine (Used in medium head
power stations )
 Wicket gates – 24
 Spiral water supply with decreasing diameter to maintain
constant pressure
 Governor controls active power by controlling wicket
gates through 2 servo motors (hydraulic operation)
 Electrical, electronic and mechanical protection systems
are used.
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11. GENERATOR
 Stator windings – star connected
 Number of stator poles – 16 (to reduce operational speed)
 Maximum Speed – 375 rpm
 90 MVA with a power factor 0.85
Rotor
 Previous method was developed to brushless excitation because of low maintenance
 Field current is low in brushless excitation method
 Automatic voltage regulator (AVR) controls the reactive power by controlling the field current
 At initial operation rotor is lifted above about 2mm by the thrust bearing
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12. SWITCH YARD
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13. SWITCH YARD COMPONENTS
 Isolators
 Circuit breakers – Oil Circuit breakers
- SF6 breakers
 Surge arresters
 Capacitive voltage transformers
 Current transformers
 Wave traps
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14. SWITCH YARD COMPONENTS
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Isolators
• Used to provide visible
mechanical disconnection for
safety
• Mainly used in maintenance
• Can be operated only after
opening the circuit breaker

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Oil Circuit breakers
• Earliest breaker type in Kotmale switch yard
• Spring mechanism(millisecond operation)
• Auto reclose operation
• Use oil as the medium to absorb the spark

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SF6 Circuit breakers
• Excellent insulating, arc extinguishing
• constant physical and chemical properties of SF6 gas
• The gas is non-inflammable and chemically stable. The decomposition
products are non-explosive
• Can be used for higher voltage breaking
• Low maintenance
Disadvantages
• Imperfect joints leading to leakage of the SF6 gas. Continuous monitoring
devices are required
• Arched SF6 can be poisonous

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Capacitive Voltage transformers
• Used to step down high voltage signals and provide a low voltage
signal, for metering and for protection relays
• Capacitors are used as voltage dividers to drop down voltage so that it
can be further stepped down by a VT for measuring.

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• CT is used in current measurement and signaling for
protective relays
• Surge arresters are used to protect components from
surges like lightning
• Wave trap is used to block the high frequency signals
in power line communication

19. TRANSFORMER BAY
 9 single phase transformers are used
 3 for each generator unit
 3 Zig-zag transformers are used to create an earth and to get the supply for the
auxiliaries.
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20. NILLAMBE POWER STATION
Introduction
 Mini hydro power plant
 Priority is power generation
 Maximum capacity is 2x 1.6 MW
 Total head is 110m
 Total annual energy generation is 14.7 GWh
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21. COMPONENTS
 Forebay
 Open Canal
 Penstock(278m)
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22. POWER HOUSE
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• Salient Pole rotor generator with 6
poles (1000 rpm)
• Generated terminal voltage 6.3kV
• Permanent magnet excitation (direct
excitation)
• Fly wheel to absorb vibrations
• Three phase transformer
• Francis type horizontal turbine

23. OTHER COMPONENTS
 Indoor switch station feeds 33kV voltage to the grid
 Battery supply
 Water cooling
 Fairly large oil circuit breakers
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24. THANK YOU
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