用过毕业设计水利水电工程英文文献翻译

2021年1月20日发(作者：超标率)
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外文文献：

hydraulicturbines and hydro-electric power
Abstract
Power may be developed from water by three fundamental processes : by action
of its weight, of its pressure, or of its velocity, or by a combination of any or all three.
In modern practice the Pelton or impulse wheel is the only type which obtains power
by a single process the action of one or more high-velocity jets. This type of wheel is
usually
found
in
high- head
developments.
Faraday
had
shown
that
when
a
coil
is
rotated in a magnetic field electricity is generated. Thus, in order to produce electrical
energy, it is necessary that we should produce mechanical energy, which can be used
to
rotate
the
‘coil’.
The
mechanical
energy
is
produced
by
running
a
prime
mover
(known as turbine ) by the energy of fuels or flowing water. This mechanical power is
converted into electrical power by electric generator which is directly coupled to the
shaft of turbine and is thus run by turbine. The electrical power, which is consequently
obtained at the terminals of the generator, is then transited to the area where it is to be
used for doing plant or machinery which is required to produce electricity (i.e.
prime mover +electric generator) is collectively known as power plant. The building,
in which the entire machinery along with other auxiliary units is installed, is known as
power house.

Keywords


hydraulic turbines

hydro-electric power classification of hydel plants
head scheme

There
has
been
practically
no
increase
in
the
efficiency
of
hydraulic
turbines
since
about
1925,
when
maximum
efficiencies
reached
93%
or
more.
As
far
as
maximum
efficiency
is
concerned,
the
hydraulic
turbine
has
about
reached
the
practicable limit of development. Nevertheless, in recent years, there has been a rapid
and marked increase in the physical size and horsepower capacity of individual units.
In addition, there has been considerable research into the cause and prevention of
cavitation,
which
allows
the
advantages
of
higher
specific
speeds
to
be
obtained
at
higher heads than formerly were considered advisable. The net effect of this progress
with
larger
units,
higher
specific
speed,
and
simplification
and
improvements
in
design has
been to
retain for the hydraulic turbine the important
place
which it has
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long held at one of the most important prime movers.
1. types of hydraulic turbines
Hydraulic
turbines
may
be
grouped
in
two
general
classes:
the
impulse
type
which utilizes the kinetic energy of a high- velocity jet which acts upon only a small
part of the circumference at any instant, and the reaction type which develops power
from the combined action of pressure and velocity of the water that completely fills
the runner and water passages. The reaction group is divided into two general types:
the Francis, sometimes called the reaction type, and the propeller type. The propeller
class
is
also
further
subdivided
into
the
fixed-blade
propeller
type,
and
the
adjustable-blade type of which the Kaplan is representative.
1.1 impulse wheels
With
the
impulse
wheel
the
potential
energy
of
the
water
in
the
penstock
is
transformed into kinetic energy in a jet issuing from the orifice of a nozzle. This jet
discharge freely into the atmosphere inside the wheel housing and strikes against the
bowl-shaped
buckets
of
the
runner.
At
each
revolution
the
bucket
enters,
passes
through, and passes out of the jet, during which time it receives the full impact force
of the jet. This produces a rapid hammer blow upon the bucket. At the same time the
bucket is subjected to the centrifugal force tending to separate the bucket from its disk.
On
account
of
the
stresses
so
produced
and
also
the
scouring
effects
of
the
water
flowing over the working surface of the bowl, material of high quality of resistance
against hydraulic wear and fatigue is required. Only for very low heads can cast iron
be employed. Bronze and annealed cast steel are normally used.
1.2 Francis runners
With the Francis type the water enters from a casing or flume with a relatively
low
velocity,
passes
through
guide
vanes
or
gates
located
around
the
circumstance,
and flows through the runner, from which it discharges into a draft tube sealed below
the tail-water level. All
the runner passages are completely filled with water, which
acts
upon
the
whole
circumference
of
the
runner.
Only
a
portion
of
the
power
is
derived from the dynamic action due to the velocity of the water, a large part of the
power being obtained from the difference in pressure acting on the front and back of
the runner buckets. The draft tube allows maximum utilization of the available head,
both because of the suction created below the runner by the vertical column of water
and because the outlet of he draft tube is larger than the throat just below the runner,
thus utilizing a part of the kinetic energy of the water leaving the runner blades.
1.3 propeller runners
nherently
suitable
for
low-head
developments,
the
propeller-type
unit
has
effected marked economics within the range of head to which it is adapted. The higher
speed of this type of turbine results in a lower-cost generator and somewhat smaller
powerhouse substructure and superstructure. Propeller-type runners for low heads and
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.
small outputs are sometimes constructed of cast iron. For heads above 20 ft, they are
made
of
cast
steel,
a
much
more
reliable
material.
Large-diameter
propellers
may
have individual blades fastened to the hub.
1.4 adjustable-blade runners
The
adjustable-blade
propeller
type
is
a
development
from
the
fixed- blade
propeller wheel. One of the best-known units of this type is the Kaplan unit, in which
the
blades
may
be
rotated
to
the
most
efficient
angle
by
a
hydraulic
servomotor.
A
cam on the governor is used to cause the blade angle to change with the gate position
so that high efficiency is always obtained at almost any percentage of full load.
By
reason
of
its
high
efficiency
at
all
gate
openings,
the
adjustable- blade
propeller-type
unit
is
particularly
applicable
to
low- head
developments
where
conditions are such that the units must be operated at varying load and varying head.
Capital cost and maintenance for such units are necessarily higher than for fixed-blade
propeller-type units operated at the point of maximum efficiency.
2. thermal and hydropower
As stated earlier, the turbine blades can be made to run by the energy of fuels or
flowing water. When fuel is used to produce steam for running the steam turbine, then
the
power
generated
is
known
as
thermal
power.
The
fuel
which
is
to
be
used
for
generating steam may either be an ordinary fuel such as coal, fuel oil, etc., or atomic
fuel
or
nuclear
fuel.
Coal
is
simply
burnt
to
produce
steam
from
water
and
is
the
simplest
and
oldest
type
of
fuel.
Diesel
oil,
etc.
may
also
be
used
as
fuels
for
producing
steam.
Atomic
fuels
such
as
uranium
or
thorium
may
also
be
used
to
produce steam. When conventional type of fuels such s coal, oil, etc. (called fossils )
is used to produce steam for running the turbines, the power house is generally called
an Ordinary thermal power station or Thermal power station. But when atomic fuel is
used to produce steam, the power station, which is essentially a thermal power station,
is
called
an
atomic
power
station
or
nuclear
power
station.
In
an
ordinary
thermal
power station, steam is produced in a water boiler, while in the atomic power station;
the boiler is replaced y a nuclear reactor and steam generator for raising steam. The
electric
power
generated
in
both
these
cases
is
known
as
thermal
power
and
the
scheme is called thermal power scheme.
But, when the energy of the flowing water is used to run the turbines, then the
electricity
generated
is
called
hydroelectric
power.
This
scheme
is
known
as
hydro
scheme, and the power house is known as hydel power station or hydroelectric power
station.
In a hydro scheme, a certain quantity of water at
a certain potential head is
essentially made to flow through the turbines. The head causing flow runs the turbine
blades,
and thus
producing electricity from the generator coupled to
turbine.
In this
chapter, we are concerned with hydel scheme only.
fication of hydel plants
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.
Hydro-plants may be classified on the basis of hydraulic characteristics as follow:
①

run-off river plants .
②
storage plants.
③
pumped storage plants.
④
tidal plants. they
are described below.
(1)

Run-off river plants.
These
plants
are
those
which
utilize
the
minimum
flow
in
a
river
having
no
appreciable
pondage
on
its
upstream
side.
A
weir
or
a
barrage
is
sometimes
constructed
across
a
river
simply
to
raise
and
maintain
the
water
level
at
a
pre-determined level within narrow limits of fluctuations, either solely for the power
plants
or
for
some
other
purpose
where
the
power
plant
may
be
incidental.
Such
a
scheme is essentially a low head scheme and may be suitable only on a perennial river
having sufficient dry weather flow of such a magnitude as to make the development
worthwhile.
Run-off river plants generally have a very limited storage capacity, and can use
water
only
when
it
comes.
This
small
storage
capacity
is
provided
for
meeting
the
hourly
fluctuations
of
load.
When
the
available
discharge
at
site
is
more
than
the
demand (during off-peak hours ) the excess water is temporarily stored in the pond on
the upstream side of the barrage, which is then utilized during the peak hours.
he
various
examples
of
run-off
the
river
pant
are:
Ganguwal
and
Kolta
power
houses located on Nangal Hydel Channel, Mohammad Pur and Pathri power houses
on Ganga Canal and Sarda power house on Sarda Canal.
The various stations constructed on irrigation channels at the sites of falls, also
fall under this category of plants.
(2) Storage plants
A storage plant is essentially having an upstream storage reservoir of sufficient
size so as to permit, sufficient carryover storage from the monsoon season to the dry
summer
season,
and
thus
to
develop
a
firm
flow
substantially
more
than
minimum
natural
flow.
In
this
scheme,
a
dam
is
constructed
across
the
river
and
the
power
house
may
be
located
at
the
foot
of
the
dam
such
as
in
Bhakra,
Hirakud,
Rihand
projects etc. the power house may sometimes be located much away from the dam (on
the downstream side). In such a case, the power house is located at the end of tunnels
which carry water from the reservoir. The tunnels are connected to the power house
machines by means of pressure pen-stocks which may either be underground (as in
Mainthon and Koyna projects) or may be kept exposed (as in Kundah project).
When the power house is located near the dam, as is generally done in the low
head
installations
;
it
is
known
as
concentrated
fall
hydroelectric
development.
But
when the water is carried to the power house at a considerable distance from the dam
through a canal, tunnel, or pen-stock; it is known as a divided fall development.
(3) Pumped storage plants.
A
pumped
storage
plant
generates
power
during
peak
hours,
but
during
the
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.
off-peak hours, water is pumped back from the tail water pool to the headwater pool
for future use. The pumps are run by some secondary power from some other plant in
the system. The plant is thus primarily meant for assisting an existing thermal plant or
some other hydel plant.
During
peak
hours,
the
water
flows
from
the
reservoir
to
the
turbine
and
electricity
is
generated.
During
off-peak
hours,
the
excess
power
is
available
from
some other plant, and is utilized for pumping water from the tail pool to the head pool,
this minor plant thus supplements the power of another major plant. In such a scheme,
the same water is utilized again and again and no water is wasted.
For
heads
varying
between
15m
to
90m,
reservoir
pump
turbines
have
been
devised,
which
can
function
both
as
a
turbine
as
well
as
a
pump.
Such
reversible
turbines can work at relatively high efficiencies and can help in reducing the cost of
such a plant. Similarly, the same electrical machine can be used both as a generator as
well
as
a
motor
by
reversing
the
poles.
The
provision
of
such
a
scheme
helps
considerably in improving the load factor of the power system.
(4) Tidal plants
Tidal
plants
for
generation
of
electric
power
are
the
recent
and
modern
advancements,
and essentially work on the principle that
there is
a rise in
seawater
during high tide period and a fall during the low ebb period. The water rises and falls
twice a day; each fall cycle occupying about 12 hours and 25 minutes. The advantage
of this rise and fall of water is taken in a tidal plant. In other words, the tidal range, i.e.
the difference between high and low tide levels is utilized to generate power. This is
accomplished by constructing a basin separated from the ocean by a partition wall and
installing turbines in opening through this wall.
Water passes from the ocean to the basin during high tides, and thus running the
turbines and generating electric power. During low tide
，
the water from the basin runs
back to ocean, which can also be utilized to generate electric power, provided special
turbines
which
can
generate
power
for
either
direction
of
flow
are
installed.
Such
plants are useful at places where tidal range is high. Rance power station in France is
an example of this type of power station. The tidal range at this place is of the order of
11 meters. This power house contains 9 units of 38,000 kW.
-plants
or
hydroelectric
schemes
may
be
classified
on
the
basis
of
operating head on turbines as follows:
①

low head scheme (head<15m),
②
medium
head scheme (head varies between 15m to 60 m) ,
③
high head scheme (head>60m).
They are described below:
(1) Low head scheme.
A low head scheme is one which uses water head of less than 15 meters or so. A
run off river plant is essentially a low head scheme, a weir or a barrage is constructed
to raise the water level, and the power house is constructed either in continuation with
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