PEPPARA GENERATING STATION THIRUVANANTHAPURAM

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PEPPARA GENERATING STATION THIRUVANANTHAPURAM
IV report

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PEPPARA GENERATING STATION


IMPORTANT COMPONENTS OF GENERATION
1. Kaplan Turbine
2. Alternator
3. Gear arrangement
4. Penstock
5. Draft tube
6. AGC

KAPLAN TURBINE
If the water flows parallel to the axis of the rotation of the shaft, the turbine is known as axial flow turbine. And if the head at the inlet of the turbine is the sum of pressure energy and kinetic energy and during the flow of water through runner, a part of pressure energy is converted into kinetic energy, the turbine is known as reaction turbine.
For the axial flow reaction turbine, the shaft of the turbine is vertical. The lower end of the shaft is made larger which is known as hub or boss. The vanes are fixed to the hub and hence hub acts as a runner for axial flow reaction turbine.
If the vanes on the hub are adjustable, the turbine is known as a Kaplan Turbine. This turbine is suitable where a large quantity of water at low heads is available. The main parts of a Kaplan turbine are:
1. Scroll casing
2. Guide vanes mechanism
3. Hub with vanes or runner of the turbine
4. Draft tube
The water from the penstock enters the scroll casing and then moves to the guide
vanes. From the guide vanes, the water turns through 90 and flows axially through the runner.

Details:
Type : Horizontal
Low Head : 20m
Discharge : 18 m3/s
Rated Speed : 375 rpm
Run away speed : 1100 rpm
Output : 3.3 MW
PENSTOCK
Penstocks are pipes of large diameter which carry water under pressure from the storage reservoir to the turbines. These pipes are made of reinforced concrete. When water is flowing from head race to the turbine, a loss of head due to friction between the water and penstock occurs. There are other losses also such as loss due to bend, pipe fittings, loss at the entrance of penstock etc.

DRAFT TUBE
The pressure at the exit of the runner of a turbine is generally less than atmospheric pressure. Thus the water at the exit of the runer cannot be directly discharged to the tail race. A pipe of gradually increasing area is used for discharging water from the exit of the turbine to the tail race. This pipe of gradually increasing area is called a draft tube. One end of the draft tube is connected to the outlet of the runner while the other end is submerged below the level of water in the tail race.
TECHNICAL DATA Maximum head : 32m
Minimum head : 11m
Maximum output : 3560 kW
Minimum output : 1005 kW
Efficiency : 90.4%

Generator Data
Type : SA, Brushes
Nominal output : 3530 KVA
Power factor : 0.85
Nominal voltage : 11000V, Amp - 185
Nominal speed : 750 rpm
Runaway speed : 2200 rpm
Connection type : Star
Excitation (ac exciter) : 45V (dc)
Ampere : 6A (dc)
Rotating facing driven end : clockwise
Rating : continuous
Weight of stator : 8600 kg
Weight of rotor : 10200 kg
Weight of base plate : 3000 kg
Weight of alternator :24000 kg
GD2 of alternator : 5100 kgm2

Stopping
1. Bring down the load current using the opening limiter
2. When the current reaches almost zero, switch off the VCB
3. Switch off AVR main switch and auxiliary supply. Put back the pot to zero
4. Put the BFV selector switch in HAND, press 'Close' button
5. Close Bypass valve of BFV
6. Close cooling water line, stop GB oil pump
7. Switch off AC, DC supply, to TGCP, AVR panel, R & A panel
8. Release the hydraulic pressure using either of the 2 knobs
9. Tighten the knob when pressure comes to zero.