Electrical Power development by using Tidal Energy.

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2. Tides and Tidal Power stations:
 Gravitational and rotational forces exerted
on the sea water gives rise to tides with
varying heights during a day
 In roughly 25 hours there are two high
tides and two low tides.
 Tidal power development uses high tide
periods to fill a reservoir behind an
embankment or barrage.
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3.  During low-tide periods this stored water
is made to flow through turbines coupled
to electric generators.
 Tides at any particular location are caused
by gravitational pull exerted by the Sun
and the moon.
 The highest amplitude for the high tide
occurs during full moon and new moon
days, these are known as “spring tides”.
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4.  The height decreases as the days
progress towards the quarters. The low
amplitudes for the high tides are known as
“neap tides”.
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6.  The high tides do not occur at the same
time by the clock on all days.
 As a result there is a change in phase
between generation of power at a tidal
power station.
 Due to intermittent nature of power
generation from a tidal scheme, there
must exist a way of storing the power and
use it when necessary.
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7.  If several hydro-electric power stations
exist on the system, the power generated
by a tidal power station can be used to run
pumps to store more water in the
reservoir, in addition to the water stored
naturally in the river.
 Other way is synchronizing tidal power
station with an existing power system
when its generators are generating power.
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8.  All such schemes require starting,
synchronizing and shutting down twice a
day.
 With the use of main computers in the
overall control scheme at the control room
and mini-computers at the power station,
these operations can be programmed and
the desired operational procedures can be
automated in the schedule.
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9. Modes Of Operation:
 During one tidal cycle of about 12 hours
25 mins, commencing with a high tide
when the tidal level is maximum, the level
goes through a decrease in height called
the ebb tide reaching its min height after
about 6 hrs 12.5 mins and then tide rises
once again to reach maximum height after
about 6 hrs 12.5 mins.
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11. Generating modes:
a) Ebb generation: when the tide is falling
on the seaward side of the embankments,
stored water in the basin is allowed to flow
through the turbine, after closing the
sluices through which the basin was filled
during the rising portion of tidal activity.
b) flood generation: When the tide is rising,
water can be sent through the turbine
chute. This is opposite to ebb generation
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12. c) Two-way generation: The generation can
be both during ebb and flood tides.
d) Pumping and Turbining: water can be
pumped in addition to natural rise of tide
from seaward to basin to obtain an
increase in head. Then during the ebb tide
turbine functions as the prime mover to the
generator which acted as a motor during
the pumping operation earlier.
Of these only first and last are used.
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13. Ebb generation:
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14. Ebb generation:
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15.  For ebb generation, a barrage built across
the bay is equipped with sluice gates to
permit water to fill the basin and one way
turbine generators which operate when the
tide decreases.
 Turbine generators operate until the
operating head becomes too low in the
basin. This occurs sometime later than low
water.
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16.  For two-way or double effect generation, both
ebb and flood tides are utilized.
 Advantages:
 power can be produced over a longer period than
only ebb generation.
 More nearly match the load requirement connected
on the system
 Disadvantages:
 Turbine must be designed for two-way flow, resulting
in reduction in turbine efficiency.
 Operational head is much lower than ebb generation.
 Estimated Output is 10-15% less than one-way ebb
generation
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18.  The pump – turbine operation can
increase energy production over both ebb
generation only and two-way generation
types.
 An example of single effect and double
effect generation is given in table for a
proposed tidal power scheme which will
have 140 turbine generators at 60MW
each.
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19. Tidal
range
in mts
No. of hrs of
power gen
Avg turbine
head, mt
Max power
output, Mw
S.E D.E S.E D.E S.E D.E
6.5 3.5 10.3 4.5 2.7 4500 2100
8.5 4.7 10.8 5.4 3.4 6100 3500
11.5 5.7 11.5 6.8 4.4 8400 3750
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20.  Max power generated during single effect
generation and ebb generation is nearly
double that for double effect operation.
 The no. of hours of operation for double
effect is nearly twice that for single effect
operation so that energy produced is
nearly the same for both types.
 on account of lower heads for double
effect operation design of turbines poses
problems and high expense than for single
effect ebb generation.
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21.  Fig given below shows energy output
during one tide of about 6 hrs when ebb
generation or flood generation is used.
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22.  The same effect as two-way generation
can also be achieved with two-basin
schemes.
 In this, some of the machines operate as
pump-motors to fill a second basin by
using part of the power developed during
ebb generation of the main turbine-
generators from the first basin.
 The stored water in the 2nd basin is then
used for power generation during the
period in which the main power station is
idle.
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23. This scheme prolongs the duration of
power supply to the connected power
system based on solar-day cycle.
But most of the tidal power schemes
prefer the single ebb generation with
or without additional pumping.
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24.  Operation of such schemes is pictorially
represented in fig below:
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