Detrimental effects of tiny silt particles on large hydro power stations and some remedies

Abstract

Emergence of silt conscious designs of hydro power plants is an great challenge which calls for pooling the experiences of concerned. It also under lines the desirability of silt consciousness during investigations, design, operation, maintenance, refurbishment and upgrading.
Due to inherent weak geology, rock instability, population explosions and deforestation, all rivers emanating from Himalayas carry enormous quantity of silt during heavy runoff of monsoon from June to September.
Hydro Power stations located in Himalayan region face heavy silt problems during high inflow periods. Siul River carries heavy silt concentration of the order of 30,000 PPM (Part Per Million) (4) affecting generation, eroding turbines and cooling water system, requiring heavy cost towards maintenance of Baira Siul project.
Similarly Chenab River on which Salal Project is located also carries enormous quantity of silt affecting shut down, damage to glacis to the tune of 15 cm to 20 cm, and severe damages to turbines and cooling water system of the project.
Remedial measures have been taken like replacing the metallurgy of stainless steel for runner, guide vanes by 13 Cr Ni4 and hydro siphoning from the reservoir to maintain the generation. A series of other experiments were also tried on these projects by using modern technology. Some of them are successful to some extent.

Full text

Please
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article
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Darde,
P.N.,
Detrimental
effects
of
tiny
silt
particles
on
large
hydro
power
stations
and
some
remedies.
Perspectives
in
Science
(2016),
http://dx.doi.org/10.1016/j.pisc.2016.04.018
ARTICLE IN PRESS
+Model
PISC-180;
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(2016)
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Detrimental
effects
of
tiny
silt
particles
on
large
hydro
power
stations
and
some
remedies夽
P.N.
Darde
Jaipur
National
University,
Jagatpura
Jaipur,
India
Received
7
January
2016;
accepted
5
April
2016
Available
online
xxx
KEYWORDS
Hydro
Power;
Silt;
Turbines;
Cooling
system;
Under
water
components
Summary
Emergence
of
silt
conscious
designs
of
hydro
power
plants
is
an
great
challenge
which
calls
for
pooling
the
experiences
of
concerned.
It
also
under
lines
the
desirability
of
silt
consciousness
during
investigations,
design,
operation,
maintenance,
refurbishment
and
upgrading.
Due
to
inherent
weak
geology,
rock
instability,
population
explosions
and
deforestation,
all
rivers
emanating
from
Himalayas
carry
enormous
quantity
of
silt
during
heavy
runoff
of
monsoon
from
June
to
September.
Hydro
Power
stations
located
in
Himalayan
region
face
heavy
silt
problems
during
high
inflow
periods.
Siul
River
carries
heavy
silt
concentration
of
the
order
of
30,000
PPM
(Part
Per
Mil-
lion)
(4)
affecting
generation,
eroding
turbines
and
cooling
water
system,
requiring
heavy
cost
towards
maintenance
of
Baira
Siul
project.
Similarly
Chenab
River
on
which
Salal
Project
is
located
also
carries
enormous
quantity
of
silt
affecting
shut
down,
damage
to
glacis
to
the
tune
of
15
cm
to
20
cm,
and
severe
damages
to
turbines
and
cooling
water
system
of
the
project.
Remedial
measures
have
been
taken
like
replacing
the
metallurgy
of
stainless
steel
for
runner,
guide
vanes
by
13
Cr
Ni4
and
hydro
siphoning
from
the
reservoir
to
maintain
the
generation.
A
series
of
other
experiments
were
also
tried
on
these
projects
by
using
modern
technology.
Some
of
them
are
successful
to
some
extent.
©
2016
Published
by
Elsevier
GmbH.
This
is
an
open
access
article
under
the
CC
BY-NC-ND
license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
夽This
article
belongs
to
the
special
issue
on
Engineering
and
Mate-
rial
Sciences.
E-mail
address:
pndarde@rediffmail.com
Review
of
previous
work
Water
Analysis
of
Chenab
on
which
Salal
project
is
located
and
River
Baira
on
which
Baira
Suil
project
is
located,
show
that
they
do
not
contain
any
harmful
chemicals
which
may
http://dx.doi.org/10.1016/j.pisc.2016.04.018
2213-0209/©
2016
Published
by
Elsevier
GmbH.
This
is
an
open
access
article
under
the
CC
BY-NC-ND
license
(http://creativecommons.org/
licenses/by-nc-nd/4.0/).

Please
cite
this
article
in
press
as:
Darde,
P.N.,
Detrimental
effects
of
tiny
silt
particles
on
large
hydro
power
stations
and
some
remedies.
Perspectives
in
Science
(2016),
http://dx.doi.org/10.1016/j.pisc.2016.04.018
ARTICLE IN PRESS
+Model
PISC-180;
No.
of
Pages
4
2
P.N.
Darde
Table
1
Silt
analysis
(NHPC,
1998).
Average
dimensions
of
silt
particles
in
mm
Percentage
Class
0.62—0.031
3—5
Coarse
silt
0.031—0.016
25
Medium
Silt
0.016—0.008
45
Fine
Silt
0.008—0.004
25
Very
Fine
Silt
0.004
and
below
0.5
Clay
Fraction
have
detrimental
effects
on
the
components
of
turbines
working
under
water
and
cooling
system.
On
the
other
hand
it
indicates
that
there
is
75—98.5%
of
nano
particles
of
quartz
in
total
silt
having
hardness
7—8
on
Mohar
scale.
About
90%
of
the
particles
are
of
0.25
mm
and
less
and
thus
making
de-silting
at
Baira
Suil
hydro
Project
in-effective.
Suil
carries
a
silt
concentration
of
30,000
PPM
(Part
Per
Million)
during
heavy
monsoon.
Similar
is
the
case
of
Chenab
River
on
which
Salal
Project
is
located.
Results
of
silt
analysis
is
shown
below
in
Table
1.
Detrimental
effects
of
nano
silt
particles
on
major
components
Silt
wash
load
and
total
load
Total
silt
load
is
the
sum
of
the
bed
load,
suspended
load
and
wash
load.
Bed
load
is
that
part
of
total
load
sediment
mix
of
which
the
stream
composed.
The
particle
size
finer
than
those
represented
in
bed
load
is
determined
by
characteris-
tics
of
bank
and
available
upslope
rate.
In
American
practice
normally
the
fine
sediment
load
is
finer
than
0.062
mm
for
sand
and
clay
channel.
The
silty
clay
and
sand
could
be
considered
as
coarse
gravel
and
stable
bed
channel.
Detrimental
Effects
of
Silt
Normally
Observed
on
The
Fol-
lowing
Components
of
Hydro
Power
Projects.
A)
Reservoirs
The
accumulation
of
silt
along
with
rock
fragments
and
boul-
ders
reduced
the
capacity
of
the
reservoirs
over
the
life
of
them
during
the
operation
period.
Often
cleaning
is
not
an
easy
task.
Sedimentation
is
a
serious
growing
problem
in
the
country.
Dams
constructed
on
rivers
carrying
heavy
silt
charge
get
silted
with
consequent
reduction
in
useful
life
of
reservoirs.
Data
on
116
large
dams
was
analyzed
to
determine
the
detrimental
effects
of
silt
in
India
and
it
was
revealed
that
by
the
year
2020,
over
20%
of
reservoirs
would
have
lost
about
50%
of
the
capacity
(Prasad
and
Darde,
1996).
B)
Spill
Way
Glacis
Silt
and
rolling
boulders
erode
the
spill
way
glacis.
At
some
places
the
erosion
is
quite
abnormal
and
repair
becomes
a
challenge.
C)
Turbines
High
silt
loads
with
quartz
having
large
hardness
damages
turbines
and
guide
vanes.
The
abrasion
of
guide
vanes,
bushes,
cup
seals
and
rubber
cords
causes
heavy
leakages.
Figure
1
Layout
of
Baira
Dam.
The
shaft
seals
get
damaged
frequently.
If
the
failure
of
shaft
seal
takes
place
with
leakage
from
bearing,
the
sit-
uation
becomes
very
alarming
resulting
in
shut
down
of
the
machine.
D)
Cooling
Water
System
The
cooling
water
system
meant
for
cooling
of
thrust
bear-
ing,
stator
and
generator
transformers
get
fully
or
partially
choked
due
to
silt
present
in
the
water
derived
from
water
conductor
system.
In
case
silt
content
is
very
high
the
strainer
gets
completely
choked.
Cooling
tubes
getting
chocked
causing
rise
in
temperature
of
machines
stator
and
generator
transformer
beyond
permissible
limit.
The
impact
is
such
that
it
requires
additional
dewatering
pumps
and
con-
tinuous
repair
of
one
or
other
machines
throughout
the
year.
Ultimately
heavy
cost
of
repair.
Preventive
measures
taken
on
Baira
Suil
and
Salal
Hydro
projects
A)
Baira
Suil
project
Baira
Suil
Hydro
Power
Located
in
Himachal
State,
utilizes
combined
flow
of
River
Baira
and
River
Bhaled
totalling
88
cumecs
to
generate
750
MU
(Million
Units)
of
energy
annually,
has
an
installed
capacity
of
198
MW
(Mega
Watts)
(Fig.
1).
It
was
commissioned
in
1982.
The
flow
of
Bhaled
is
diverted
to
reservoir
created
by
constructing
a
Rock
Fill
Dam
across
the
river
Baira.
The
combined
flow
of
Bhailed
and
Baira
rivers
is
lead
to
Head
Race
Tunnel
7.7
km
taking
off
from
intake
at
Baira
reservoir.
The
head
race
tunnel
com-
mences
from
Baira
Dam
passes
under
the
river
Suil
enroute.
The
flow
of
river
Suil
is
intercepted
by
a
weir
across
river
Suil
and
fed
in
head
race
tunnel
to
augment
the
flow
of
tun-
nel
through
a
vertical
drop
shaft
of
80
m
length.
The
power
house
located
on
right
bank
of
Suil,
houses
three
Francis
Turbines
of
66
MW
capacity
each.
Damage
to
civil
structures
In
addition
to
de-silting
basins
provided
at
three
loca-
tions
designed
to
remove
particle
size
greater
than
0.5
mm

Please
cite
this
article
in
press
as:
Darde,
P.N.,
Detrimental
effects
of
tiny
silt
particles
on
large
hydro
power
stations
and
some
remedies.
Perspectives
in
Science
(2016),
http://dx.doi.org/10.1016/j.pisc.2016.04.018
ARTICLE IN PRESS
+Model
PISC-180;
No.
of
Pages
4
Detrimental
effects
of
tiny
silt
particles
3
Photo
1
Damage
to
turbine
blades.
Photo
2
Erosion
of
lower
ring.
(NHPC,
1998),
the
reservoir
acts
as
a
siltation
tank
and
the
diversion
tunnel
is
now
used
to
flush
the
reservoir
once
every
year.
Complete
flushing
of
reservoir
is
carried
out
once
every
year
for
about
24
h
during
which
the
turbines
remained
shut
down.
During
monsoon
silt
is
flushed
for
15
min
through
diversion
tunnel.
Pirongar
nalla
joining
Suil
weir
upstream
has
a
startling
characteristic
that
during
rainy
season
silt
concentration
increases
from
300
PPM
to
30,000
PPM,
in
a
matter
of
hours.
As
soon
as
silt
concentration
increases
beyond
3000
PPM,
the
discharge
from
Suil
is
taken
off
from
the
turbines
affecting
generation
of
power.
Effect
of
silt
on
turbines
The
quartz
content
of
silt
of
size
0.8
mm
in
water
are
75—98%
mostly
in
angular
form
causing
sever
damages
to
all
under
water
components.
To
reduce
the
damage
due
to
silt,
runners
were
replaced
by
modified
designs.
The
metallurgical
components
of
stain-
less
steel
for
runner
and
guide
vanes
were
changed
to
13
Cr
Ni4.
A
series
of
other
experiments
were
also
tried
(damages
are
shown
in
Photos
1
and
2).
Due
to
silt,
choking
of
cooling
tubes
and
frequent
failure
of
cooling
water
system
has
been
encountered.
As
a
first
Figure
2
Layout
of
Salal
Project.
step
all
the
cooling
water
tubes
of
brass
have
been
replaced
by
Copper
Nickel
which
are
more
resistance
to
silt.
B)
Salal
Hydro
Power
project
Salal
Hydro
Power
Project
located
in
the
state
of
Jammu
and
Kashmir
across
river
Chenab
(Layout
is
located
in
Fig.
2),
utilizes
the
head
of
94.5
m
to
generate
28
MU
(Million
Units)
of
energy
annually.
It
comprises
of
a
118
m
high
Rock
Fill
Dam,
113
m
high
Concrete
Dam,
six
penstock
leading
to
the
power
house,
with
six
number
of
Francis
Turbines.
The
capacity
of
spill
way
is
22,427
cumecs.
The
spill
way
has
been
provided
with
12
radial
gates
of
size
1254
m
×
9.14
m.
It
has
a
capacity
of
690
MW
(Megawatt).
First
stage
was
com-
missioned
in
the
year
1987
and
second
stage
in
1996.
As
per
provision
of
agreement
between
India
and
Pakistan,
the
water
level
in
the
reservoir
has
been
main-
tained
at
FRL
(Full
Reservoir
Level)
487.68
m.
The
six
under
sluices
provided
during
construction
had
to
be
plugged
and
crest
level
has
to
be
provided
not
more
than
9.14
m
below
FRL
with
spill
way
crest
at
478.68
m.
The
effective
depth
of
live
storage
is
9.0
m.
The
intake
has
been
provided
at
the
level
of
476.685
m.
Therefore
civil
structures
play
an
impor-
tant
role
so
far
silt
problem
is
concerned.
Bottom
removal
is
not
possible.
The
entire
rotor
has
to
be
taken
out
at
the
time
of
repairs.
Severity
of
silt
on
civil
structures
There
is
no
silt
removal
arrangement
at
Salal
Project.
Rock
Fill
Dam
and
Concrete
dams
have
to
act
as
an
siltation
tanks.
From
the
first
year
of
filling
of
reservoir,
it
started
silting
up.
In
addition
project
has
suffered
two
severe
floods,
one
in
1988
and
second
in
1992
which
aggravated
the
siltation
and
reservoir
got
silted
up
to
crest
level
just
after
five
years
of
operation.
It
received
about
32
Million
Cubic
Metres
of
silt
annually
which
passes
through
spill
way
glacis
and
spill
way
buckets.
The
bed
of
the
river
got
elevated
than
it
was
expected.
Levels
vary
from
477
m
to
484
m.
The
capacity
has
been
reduced
from
285
Million
Cubic
Metres
to
9
Mil-
lion
Cubic
Metres.
Fig.
3
depicts
the
increase
of
bed
level
during
various
years.
In
the
deepest
of
the
bucket
the
sur-
face
was
eroded
exposing
reinforcement
causing
pot
holes
of

Please
cite
this
article
in
press
as:
Darde,
P.N.,
Detrimental
effects
of
tiny
silt
particles
on
large
hydro
power
stations
and
some
remedies.
Perspectives
in
Science
(2016),
http://dx.doi.org/10.1016/j.pisc.2016.04.018
ARTICLE IN PRESS
+Model
PISC-180;
No.
of
Pages
4
4
P.N.
Darde
Figure
3
Silt
deposit
in
Salal
Reservoir.
Photo
3
Damage
to
lower
ring.
250
to
500
mm
depth.
The
concrete
portion
of
sill
of
spill
way
got
damaged
exposing
the
embedded
angles
and
plates.
The
retaining
wall
got
damaged
up
to
a
depth
of
2
m.
The
glacis
and
flip
bucket
have
been
treated
with
rein-
forcement
concrete
and
silika
fumes.
Whenever
it
is
less
than
15
mm
epoxy
is
applied
on
the
surface.
The
flushing
is
done
by
operating
spill
way
gates
whenever
the
discharge
is
4250
cumecs
during
monsoon
from
May
to
September.
This
way
the
capacity
could
be
retrieved.
Forestation
and
catchment
area
treatment
was
also
resorted
to.
To
keep
the
area
near
the
intake
and
to
maintain
the
head,
the
area
is
kept
free
of
silt
by
adopting
sipho-
ning
techniques
and
disposing
the
silt
quite
away
from
the
dam.
Damages
to
turbine
components
Due
to
invert
level
of
intake
being
lower
than
spill
way
crest,
silt
gets
entry
in
to
penstock.
The
impact
of
the
silt
on
turbine
has
been
so
sever
that,
besides
deep
pits
on
trailing
edges
and
skirt
of
turbines,
almost
all
turbine
blades
have
cracked.
There
was
knife
edging
of
outer
edge
of
turbines
to
the
extent
of
50
to
70%.
The
thickness
has
been
reduced
drastically.
Lower
ring
top
cover
lines,
upper
and
lower
guide
vanes
and
labyrinth
are
the
mostly
affected
components.
The
lower
liner
of
the
lower
ring
of
the
order
of
12
mm
was
washed
out.
Photo
3
depicts
the
damage.
Cooling
system
Silt
choked
the
tubes
of
water
cooling
system.
Due
to
sprin-
kling
of
water
on
the
stator
winding,
two
stator
faults
were
encountered
in
1996
and
1997.
To
tide
over
such
problems
cyclone
separators
were
installed.
Conclusions
The
area
near
the
intake
was
kept
silt
free
to
maintain
the
head
by
adopting
siphoning
techniques.
The
metallurgical
components
of
stainless
steel
for
run-
ner
and
guide
vanes
were
replaced
by
13Cr
Ni4.
To
tide
over
the
problems
of
silt
on
the
cooling
systems
cyclone
separators
were
installed.
Many
experiments
on
various
components
of
Baira
Suil
and
Salal
Projects
proved
successful
to
some
extent.
It
needs
further
research
work
and
experimentation
on
metallurgy,
catchment
area
treatment
and
flushing
of
silt
arrangement.
References
NHPC,
1998
April.
Ware
Power.
House
Magazine.
Prasad,
Y. ,
Darde,
P.N.,
1996.
Management
of
Silt
Problems
in
Baira
Suil
Project
located
in
Himalayan
Region.
In:
International
Con-
ference
on
Hydro
1996,
China.