THE LOCATION OF ELECTRIC WATER-POWER STATIONS.
Cost of water-power development depends, in large measure, on the
location of the electric station that is to be operated. The form of
such a station, its cost, and the type of generating apparatus to be
employed are also much influenced by the site selected for it. This site
may be exactly at, or far removed from, the point where water that is to
pass through the wheels is diverted from its natural course.
A unique example of a location of the former kind is to be found near
Burlington, Vt., where the electric station is itself a dam, being built
entirely across the natural bed of one arm of the Winooski River at a
point where an island near its centre divides the stream into two parts.
The river at this point has cut its way down through solid rock, leaving
perpendicular walls on either side. Up from the ledge that forms the bed
of the stream, and into the rocky walls, the power-station, about 110
feet long, is built. The up-stream wall of this station is built after
the fashion of a dam, and is reënforced by the down-stream wall, and the
water flows directly through the power-station by way of the wheels. A
construction of this sort is all that could well be attained in the way
of economy, there being neither canal nor long penstocks, and only one
wall of a power-house apart from the dam. On the other hand, the
location of a station directly across the bed of a river in this way
makes it impossible to protect the machinery if the up-stream wall,
which acts as the dam, should ever give way. The peculiar natural
conditions favorable to the construction just considered are seldom
found.
[Illustration: FIG. 10.--Power-house on the Winooski River, near
Burlington, Vt.]
One of the most common locations for an electric water-power station is
at one side of a river, directly in front of one end of the dam and
close to the foot of the falls. A location of this kind was adopted for
the station at Gregg’s Falls, one of the water-powers included in the
electric system of Manchester, N. H., where the spray of the fall rises
over the roof of the station. Two short steel penstocks, each ten feet
in diameter, convey the water from the forebay section of the dam to
wheels in the station with a head of fifty-one feet.
[Illustration: FIG. 11.--Canal and Power-house on St. Joseph River,
Buchanan, Mich.]
A similar location was selected for the station at Great Falls, on
the Presumpscot River (see cuts), whence electrical energy is
delivered in Portland, Me. Four steel penstocks, a few feet long and
each eight feet in diameter, bring the water in this case from the
forebay section of the dam to the wheel cases in the power-house.
[Illustration: FIG. 12.--Power-house on Hudson River at Mechanicsville.]
Where the power-station is located at the foot of the dam, as just
described, that part which serves as a forebay wall usually carries a
head gate for each penstock. The overfall section of a dam may give way
in cases like the two just noted without necessarily destroying the
power-station, but in times of freshet or very high water the station
may be flooded and its operation stopped. The risk of any such flooding
will vary greatly on different rivers, and in particular cases may be
very slight. Location of the generating station close to the foot of the
dam at one end obviously avoids all expense for a canal and cuts the
cost of penstocks down to a very low figure.
Such locations for stations are not limited to falls of any particular
height, and the short penstocks usually enter the dam nearer its base
than its top and pass to the station at only a slight inclination from
the horizontal. At Great Falls, above mentioned, the head of water is
thirty-seven feet.
A short canal is constructed in some cases from one end of a dam to a
little distance down-stream, terminating at a favorable site for the
electric station. Construction of this sort was adopted at the Birchem
Bend Falls of the Chicopee River, whence energy is supplied to
Springfield, Mass. These falls furnish a head of fourteen feet, and the
water-wheels are located on the floor of the open canal at its end. The
power-station is on the shore side of this canal, and the shafts of the
water-wheels extend through bushings in the canal wall, which forms the
lower part of one side of the station, to connect with the electric
generators inside.
This rather unusual location of water-wheels has at least the obvious
advantage that they require no room inside of the station. Furthermore,
as the canal is between the station and the river, any break in the
canal is not apt to flood the station.
[Illustration: FIG. 13.--York Haven Power-house, on Susquehanna River,
Pennsylvania.]
An illustration of the use of a very short canal to convey water from
one end of a dam to a power-station exists in the 10,000 horse-power
plant at Cañon Ferry, Mont., where the head of water is thirty feet. In
this case the masonry canal is but little longer than the power-house,
and this latter sits squarely between the canal and the river, virtually
at the foot of the falls. Other examples of the location of generating
stations between short canals and the river may be seen at Concord, N.
H., where the head of water is sixteen feet; at Lewiston, Me., where the
head is thirty-two feet; and at Spier Falls, on the Hudson River, New
York, where there is a head of eighty feet.
There is some gain in security in many cases by locating the
power-station several hundred feet from the dam and a little to one side
of the main river channel. For such cases a canal may be cheaper than
steel penstocks when the items of depreciation and repairs are taken
into account. Aside from the question of greater security for the
station in the event of a break in the dam, it is necessary in many
cases to convey the water a large fraction of a mile, or even a number
of miles, from the point where it leaves its natural course to that
where the power-station should be located. An example in point exists at
Springfield, Mass., where one of the electric water-power stations is
located about 1,400 feet down-stream from a fall of thirty-six feet in
the Chicopee River, because land close to the falls was all occupied at
the time the electric station was built.
[Illustration: FIG. 14.--Power-house at Cañon Ferry on the Missouri
River.]
[Illustration: FIG. 15.--Shawinigan Falls Power-plant.]
The Shawinigan Falls of the St. Maurice River in Canada occur at two
points a short distance apart, the fall at one point being about 50 and
at the other 100 feet high. A canal 1,000 feet long takes water from the
river above the upper of these falls and delivers it near to the
electric power-house on the river bank below the lower falls. In this
way a head of 125 feet is obtained at the power-house. The canal in this
case ends on high ground 130 feet from the power-house, and the water
passes down to the wheels through steel penstocks 9 feet in diameter.
[Illustration: FIG. 16.--Power-house on White River, Oregon.]
Another interesting example of conditions that require a power-house to
be located some distance from the point where water is diverted from its
natural course may be seen at the falls on the Apple River, whence
energy is transmitted to St. Paul, Minn. By means of a natural fall of
30 feet, a dam 47 feet high some distance up-stream, and some rapids in
the river, it was there possible to obtain a total fall of 82 feet. To
utilize this entire fall a timber flume, 1,550 feet in length, was built
from the dam to a point near the power-house on the river bank and below
the falls and rapids. The flume was connected with the wheels, 82 feet
below, by a steel penstock 313 feet long and 12 feet in diameter.
As the St. Mary’s River leaves Lake Superior it passes over a series of
rapids about half a mile in length, falling twenty feet in that
distance. To make the power of this great volume of water available, a
canal 13,000 feet long was excavated from the lake to a point on the
river bank below the rapids. Between the end of the canal and the river
sits the power-station, acting as a dam, and the water passes down
through it and the wheels under a head of twenty feet.
[Illustration: FIG. 17.--Power-house Across Canal at Sault Ste. Marie,
Mich.]
By means of a canal 16,200 feet long from the St. Lawrence River a head
of water amounting to fifty feet has been made available at a point on
the bank of Grass River near Massena, N. Y. There again the
power-station acts as a dam, and the canal water passes down through it
to reach the river.
[Illustration: FIG. 18.--Canal and Station on Payette River, Idaho.]
From these illustrations it may be seen that in many cases, in
comparatively level country, a water-power can be fully developed only
by means of canals or pipe lines, and the generating stations cannot be
located at the points where the water is diverted.
Thus far the cases considered have been only those with moderate heads
and rather large volumes of water. In mountainous country, where rivers
are comparatively small and their courses are marked by numerous falls
and rapids, it is generally necessary to utilize the fall of a stream
through some miles of its length in order to effect a satisfactory
development of power. To reach this result, rather long canals, flumes,
or pipe lines must be utilized to convey the water to power-stations and
deliver it at high pressures.
In cases of this kind the cost of the canal or pipe line may be the
largest item in the power development, and it may be an important
question whether this cost should be reduced or avoided by the erection
of several small generating plants instead of one large one. California
offers numerous examples of electric-power development with water that
has been carried several miles through artificial channels. An
illustration of this class of work exists at the Electra power-house on
the bank of the Mokelumne River, in the Sierra Nevada Mountains. Water
is supplied to the wheels in this station under a head of 1,450 feet
through pipes 3,600 feet long leading to the top of a near-by hill. To
reach this hill the water, after its diversion from the Mokelumne River
at the dam, flows twenty miles through a canal or ditch and then through
3,000 feet of wooden stave pipe.
Another example of the same sort may be seen in the power-house at
Colgate, on the North Yuba River, in the chain of mountains above named.
Water taken from this river passes through a wooden flume nearly eight
miles long to the side of a hill 700 feet above the power-house, and
thence down to the wheels through steel and cast-iron pipes, five in
number and thirty inches each in diameter.
Even with long flumes, canals, and pipe lines, it may be necessary to
locate a number of generating stations along a single river of the class
now under consideration in order to utilize its entire power. Thus on
the Kern River, which rises in the Sierra Nevada Mountains and empties
into Tulare Lake, two electric power-stations are under construction,
and surveys are being made for three more. Of these stations, the one at
the lowest level will operate under an 872-foot head of water, and this
water, after its diversion from the river, will pass through twenty-one
tunnels, with an aggregate length of about ten miles, and through six
flumes mounted on trestles and having a total length of 1,703 feet.
Next up-stream is a station near the point where water is diverted for
the plant just named. This second station will work under a head of 317
feet, and water for it will come from a point farther up-stream by
canals, tunnels, and flumes, with an aggregate length of eleven and
one-half miles. At three points still higher up on this river it is the
intention to locate three other power-stations by conducting the water
in artificial channels, about twelve and one-half, fifteen, and twenty
miles in length respectively.
Farther south in California, on the Santa Ana River and Mill Creek,
extensive power developments on the lines just indicated have been
carried out. On Mill Creek, about six miles from the city of Redlands,
is an electric station operating under a head of 530 feet, with water in
part diverted from the stream a little less than two miles above and
brought down through a steel pipe 10,250 feet long and thirty inches
in diameter. This pipe line also takes water from the tail race of
another generating plant at its upper end. With some additions and
modifications, the station just described is the famous Redlands plant,
built in 1893, and believed to be the first for three-phase transmission
in the United States.
[Illustration: FIG. 19.--Canal and Power-station on Neversink River, New
York.]
At the upper end of the pipe line just named the second station
operates, in part, with water drawn from Mill Creek through a
combination of tunnels, flumes, and cement and steel pipes, with a
combined length of about three miles, and delivered to some of the
wheels with a head of 627 feet. The other wheels at this plant receive
water drawn from the same creek by a pipe line about six miles long. A
large part of this line is composed of 31-inch cement pipe, laid in
trenches and tunnels. The water in the 8,000 feet of pipe next to the
power-house has a fall of 1,960 feet, and this pipe is of steel and 24
and 26 inches in diameter. The head of 1,960 feet, minus friction losses
in the steel pipes, is delivered at the wheels.
From the foregoing it appears that in a space of eight miles along Mill
Creek there is a fall of more than 2,490 feet. To utilize this fall,
water is diverted from the creek at three points within a distance of
six miles and delivered in two power-stations under three different
heads. As the stream gathers in volume between the upper and the lower
intakes, an equal amount of power could have been developed in a single
station only by taking the three separate conduits or pipe lines to it
and delivering their water there at three heads.
Whether the expense of extending conduits and pipe lines to a single
generating station will more than offset the advantages to be gained
thereby is a question that should be decided on a number of factors
varying with each case. In general, it may be said that the smaller the
volume of water to be handled and the greater its head, the more
advantageous is it to concentrate the generating machinery in the
smallest practicable number of stations.
On the Santa Ana River, into which Mill Creek flows, the Santa Ana
plant, whence energy is transmitted to Los Angeles, is located. Water
reaches this plant through a conduit of tunnels, flumes, and pipes, with
a total length of about three miles from the point where the flow of the
river is diverted. The 2,210 feet of this conduit nearest the
power-plant are composed of 30-inch steel pipe, with a fall of 728 feet.
Within fifteen miles of Mexico City are five water-power stations that
supply energy for its electrical system. Two of these stations are on
the Monte Alto and three are on the Tlalnepantla River, the two former
stations being about three miles, and the more distant of the three
latter stations five miles, apart. At a distance of several miles above
the highest station on each river the water is diverted by a canal, and
the water of each of these canals, after passing through the wheels of
the highest station, goes on to the remaining station, or stations, on
the same river by a continuation of the canal.
[Illustration: FIG. 20.--Wood Pipe Line to Pike’s Peak Power-house.]
By placing the stations so short a distance apart the head of water at
each station is reduced. On one stream these heads are 492 and 594 feet
respectively, and at two of the stations on the other stream they are
547 and 295 feet respectively. This division of the total head of water
afforded by each river results in a rather small capacity for each
station, the total at the five plants being only 4,225 kilowatts.
In contrast with this figure the already mentioned Electra plant has
generators of 10,000, the Santa Ana plant generators of 3,000, and the
larger of the two Mill Creek plants generators of 3,500 kilowatts
capacity. It should be noted that the cost of operation, as well as that
of original construction, will vary materially between one large and
several smaller stations of equal total capacity, the advantage as to
operative cost being obviously with the one large plant.
[Illustration: FIG. 21.--Power-house at Great Falls, Presumpscot
River.]
All of the power-stations here considered have been equipped with
water-wheels and generators operating on horizontal shafts, and this is
the general practice. This arrangement brings the generators and the
floor of the power-station within a few feet of the level of the
tail-water. By the general use of draught tubes with turbine wheels the
floors of stations are often kept twenty feet or more above the
tail-water level.
Where the total available head of water is quite small, as is often the
case with rivers where the volume of water is great, it is generally
necessary to bring the level of the station floor down to within a few
feet of the tail-water. The Birchem Bend station of the Springfield,
Mass., electric system affords a good example of this sort, the floor of
this station being only 2.6 feet above the ordinary level of the
tail-water. At this station the difference of level between the head-
and tail-water is only fourteen feet, and even with the low floor level
named the top sides of the horizontal turbine wheels are covered only by
4.5 feet of water.
At the Garvin’s Falls station of the Manchester, N. H., electric system
the level of the floor of the generator room is thirteen feet above the
ordinary level of the Merrimac River, on the bank of which this station
is located; but in this case the total head of water is about
twenty-eight feet. The high water of the Merrimac in 1896, before the
Garvin’s Falls station was built, reached a point 5.24 feet above its
present floor level, and 18.24 feet above the ordinary level of the
river at the point where the station is located.
Under the Red Bridge electric station of the Ludlow Manufacturing
Company, on the Chicopee River, in Massachusetts, the tail-water is
twenty feet below the level of the floor and twenty-four feet below the
centres of the water-wheel and generator shafts. The difference between
wheel-shaft and tail-water levels at this station is near the maximum
that can be attained with horizontal pressure turbines, because a
draught tube much longer than twenty-five feet does not give good
results.
In a pressure turbine the guides and wheel must be completely filled
with water, as must also the draught tube, for efficient operation. If
draught tubes are much more than twenty-five feet long, it is hard to
keep a solid column of water from turbine to tail-water in each, and if
this is not done a part of the head of water becomes ineffective. As
pressure turbines are employed almost exclusively at electric stations
with low heads of water, it is frequently impossible to locate such
stations above the possible level of tail-water in times of flood if
horizontal wheels direct-connected to generators are employed.
[Illustration: FIG. 22.--Power-house at Garvin’s Falls on the Merrimac
River.]
If turbines with vertical shafts are to be used, a power-station may
be so located or constructed that all the electrical equipment will be
above the highest known water-mark. With vertical shafts, connecting
wheels, and generators, the main floor of an electric station may be
located above the crest of the falls where the power is developed
instead of at or near their base.
[Illustration: FIG. 23.--Power-house No. 2 at Niagara Falls.]
By far the most important examples of electric stations laid out on this
plan are those at Niagara Falls, where there are four such plants. Two
of these generating plants, with an aggregate capacity of 105,000
horse-power, stand a mile above the falls, and are supplied with water
through a short canal from Niagara River. Beneath each of these two
stations a long, narrow wheel pit has been excavated through rock to a
depth of 172 feet below the level of water in the canal. Both wheel pits
terminate in a tunnel 7,000 feet long that opens into the river below
the falls.
In this wheel pit the tail-water level is 161 feet below that of the
water in the canal, and 166 feet below the floor of the power-station.
Water passes from the canal down the wheel pits to the wheels near the
bottom through steel penstocks, each seven feet in diameter, and a
vertical shaft extends from each wheel case to a generator in the
station above.
Locations like that at Niagara give great security against high water
and washouts, but are seldom adopted because of the large first cost of
plant construction. With heads of water from several hundred to 2,000
feet the loss of a few feet of head reduces the available power to only
a very slight extent, and impulse wheels are usually employed. Draught
tubes are not available to increase the heads at such wheels, and any
fall of the water after it leaves the wheels does no useful work.
[Illustration: FIG. 24.--Colgate Power-house.]
Electric stations driven by impulse wheels under great heads, like those
at Colgate, Electra, Kern River, Santa Ana River, and Mill Creek, may be
located far enough above the beds of their water-courses to avoid
dangers from freshets, without serious loss of available power.