STEEL TOWERS.
Steel towers are rapidly coming into use for the support of electric
transmission lines that deliver large units of energy at high voltages
to long distances from water-powers.
One case of this sort is the seventy-five-mile transmission of 24,000
horse-power at 60,000 volts from Niagara Falls to Toronto. Another
example may be seen in the seventy-five-mile line of steel towers which
carries transmission circuits of 60,000 volts to Winnipeg. Guanajuato,
Mexico, which is said to have produced more silver than any other city
in the world, receives some 3,300 electric horse-power over a
60,000-volt transmission line one hundred miles long on steel towers.
Between Niagara Falls and Lockport the electric circuits now being
erected are supported on steel towers. On a transmission line eighty
miles long in northern New York, for which plans are now being made,
steel towers are to support electric conductors that carry current at
60,000 volts.
For the elevations above ground at which it is common to support the
conductors of transmission lines--that is, from twenty-five to fifty
feet--a steel tower will cost from five to twenty times as much as a
wooden pole in various parts of the United States and Canada. It follows
at once from this fact that there must be cogent reasons, apart from the
matter of first cost, if the general substitution of steel towers for
wooden poles on transmission lines is to be justified on economic
grounds. During fifteen years the electric transmission of energy from
distant water-powers to important centres of population has grown from
the most humble beginnings to the delivery of hundreds of thousands of
horse-power in the service of millions of people, and the lines for this
work are supported, with very few exceptions, on wooden poles. Among the
transmissions of large powers over long distances at very high voltages
that have been in successful operation during at least several years
with wooden pole lines are the following: the 60,000-volt circuit that
transmits some 13,000 horse-power from Electra station across the State
of California to San Francisco, a distance of 147 miles, is supported
by wooden poles. In the same State, the transmission line 142 miles
long between Colgate power-house and Oakland, at 60,000 volts, and with
a capacity of about 15,000 horse-power, hangs on wooden poles, save at
the span nearly a mile long over the Straits of Carquinez. Wood is used
to carry the two 55,000-volt circuits that run sixty-five miles from the
10,000-horse-power station at Cañon Ferry on the Missouri River to
Butte. Between Shawinigan Falls and Montreal, a distance of eighty-three
miles, the conductors that operate at about 50,000 volts are carried on
wooden poles. Electrical supply in Buffalo to the amount of 30,000
horse-power depends entirely on circuits from Niagara Falls that operate
at 22,000 volts and are supported on lines of wooden poles.
In the operation of these and many other high-voltage transmissions
during various parts of the past decade some difficulties have been met
with, but they have not been so serious as to prevent satisfactory
service. Nevertheless, it is now being urged that certain impediments
that are met in the operation of transmission systems would be much
reduced by the substitution of steel towers for wooden poles, and it is
even suggested that perhaps the first cost, and probably the last cost,
of a transmission line would be less with steel than with wood for
supports. The argument for steel in the matter of costs is that while a
tower requires a larger investment than a pole, yet the smaller number
of towers as compared with that of poles may reduce the entire outlay
for the former to about that for the latter. More than this, it is said
that the lower depreciation and maintenance charges on steel supports
will make their final cost no greater than that of wooden poles.
In the present state of the market, steel towers can be had at from
three to three and one-half cents per pound, and the cost of a steel
tower or pole will vary nearly as its weight. During the first half of
1904 the quotations on tubular steel poles to the Southside Suburban
Railway Company, of Chicago, were between the limits just stated. That
company ordered some poles built up of steel sections about that time at
a trifle less than three cents per pound. Each of these poles was thirty
feet long and weighed 616 pounds, so that its cost was about eighteen
dollars (xxi, A. I. E. E., 754). For a forty-five-foot steel pole to
carry a pair of 11,000-volt, three-phase circuits along the New York
Central electric road the estimated cost was eighty dollars in the year
last named (xxi, A. I. E. E., 753). On the 100-mile line to Guanajuato,
Mexico, above mentioned, the steel towers were built up of 3″ × 3″ ×
3/16″ angles for legs, and were stayed with smaller angle sections and
rods. Each of these towers has four legs that come together near the
top, is forty feet high, weighs about 1,500 pounds, and carries a
single circuit composed of three No. 1 B. & S. gauge hard-drawn copper
cables. The weight of each of these cables is 1,340 pounds per mile, and
the forty-foot towers are spaced 440 feet apart, or twelve per mile,
over nearly the entire length of line. At three cents per pound, the
lowest figure at which these towers could probably be secured for use in
the United States, the approximate cost of each would be forty-five
dollars. Between Niagara Falls and Lockport each of the steel towers
that is to carry a single three-phase transmission circuit has three
legs built up of tubing that tapers from two and one-half inches to
smaller sizes and is braced at frequent intervals. The height of these
towers is forty-nine feet, and the weight of each is 2,800 pounds. At
three cents per pound the cost of each tower amounts to eighty-four
dollars. For a long transmission line in northern New York bids were
recently had on towers forty-five feet high to carry six wires, and the
resulting prices were $100 to $125 each for a tower weighing about 3,000
pounds. On the line between Niagara Falls and Toronto the standard tower
holds the lowest cables 40 feet above ground at the insulators, has a
weight of 2,360 pounds, and would cost $70.80 at 3 cents per pound.
In January, 1902, four steel towers were purchased to support
transmission circuits for two spans of 132 feet each over the Chambly
Canal, near Chambly Canton, Quebec. Each pair of these towers was
required to support eleven No. 2-0 B. & S. gauge bare copper wires with
the span of 132 feet between them. The vertical height of each of these
four towers is 144 feet above the foundation, and they were designed for
a maximum stress in any member of not more than one-fourth of its
ultimate strength, with wires coated to a diameter of one inch with ice
and under wind pressure. For these four steel towers erected on
foundations supplied by the purchasers the price was $4,670, and the
contract called for a weight in the four towers of not less than 121,000
pounds. On the basis of this weight the cost of the towers erected on
foundations was 3.86 cents per pound.
With these examples of the cost of steel towers a fair idea may be
gotten of the relative cost of wooden poles. For poles of cedar or other
desirable wood thirty-five feet long and with eight-inch tops fitted
with either one or two cross-arms an estimated cost of five dollars each
is ample to cover delivery at railway points over a great part of the
United States and Canada. This size of pole has been much used on the
long, high-voltage transmission systems that involve large power units
and use heavy conductors. Examples of lines where such poles are used
may be seen between Niagara Falls and Buffalo, between Colgate
power-house and Oakland, and between Cañon Ferry and Butte. Of course
some longer poles were used in special locations, like the crossing of
steam railways, but it is also true that on the lines supported by steel
towers such locations make exceptionally high towers necessary. The
thirty-five-foot poles will hold the electric lines about as high above
the ground level as the forty-nine-foot towers on the Niagara Falls and
Toronto transmission, because the former will be set so much closer
together. On the line just named the regular minimum distance of the
electric cables above the ground level at the centres of spans is
twenty-five feet. The standard towers on this line carry the lower
electric cables forty feet above the ground at the insulators, and it
was thought desirable to allow a sag of fifteen feet at the centres of
the regular spans of four hundred feet each. On these towers the
conductors that form each three-phase circuit are six feet apart, and
lines drawn between the three cables form the sides of an equilateral
triangle. With a pin fourteen and three-fourths inches long like that
used on these steel towers, and one conductor at the top of a
thirty-five-foot pole, where the other two are supported by a cross-arm
five feet three inches below, giving six feet between cables, the lower
cables are held by their insulators twenty-six feet above the ground,
when the poles are set five feet deep. Between thirty-five-foot poles
one hundred feet is a very moderate span, and one that is exceeded in a
number of instances. Thus on the 142-mile line from Colgate power-house
to Oakland the thirty-five-foot poles are 132 feet apart, and one line
of these poles carries three conductors of 133,000-circular-mil copper,
while the other pole line has three aluminum cables of 168,000 circular
mils. On the later transmission line from Niagara Falls to Buffalo,
which was designed for three-phase circuits of 500,000-circular-mil
cable, the regular distance between the thirty-five-foot poles is 140
feet.
A maximum sag of twenty-four inches between poles 100 feet apart under
the conditions named above brings the lowest points of the wire
twenty-four feet above the ground. The steel towers on the line to
Guanajuato being only forty feet in length, and spaced 440 feet apart,
it seems that the distance of conductors from the ground at the centres
of spans is probably no greater than that just named. Particular
attention is called to this point because it has been suggested that the
use of steel towers would carry cables so high that wires and sticks
could not be thrown onto them. It thus appears that thirty-five-foot
wooden poles set one hundred feet apart will allow as much distance
between conductors, and still keep their lowest points as far above the
ground, as will forty- to forty-nine-foot towers placed four hundred
feet or more apart. The two lines that have their conductors further
apart perhaps than any others in the world are the one from Cañon Ferry
to Butte, on thirty-five-foot wooden poles, and the one to Guanajuato,
on steel towers. In each of these cases the cables are seventy-eight
inches apart at the corners of an equilateral triangle. With steel
towers four hundred feet or wooden poles one hundred feet apart, four of
the latter must be used to one of the former. At $5 per pole this
requires an investment of $20 in poles as compared with at least $45 for
a tower like those on the Guanajuato line, $84 for a tower like those on
the line from Niagara Falls to Lockport, or $70 for one of the towers on
the Niagara and Toronto line. Each of the towers on the line to Toronto
carries two three-phase circuits, and the least distance between cables
is six feet. To reach the same result as to the distance between
conductors with the two circuits on poles, it would be desirable to have
two pole lines, so that $40 would represent the investment in the poles
to displace one tower for two circuits. The older pole line between
Niagara Falls and Buffalo carries two three-phase circuits on two
cross-arms, and the 350,000-circular-mil copper cables of each circuit
are at the angles of an equilateral triangle whose sides are each three
feet long. In this case, however, the electric pressure is only 22,000
volts.
The costs above named for poles and towers include nothing for erection.
Each tower has at least three legs and more commonly four, and owing to
the heights of towers and to the long spans they support it is the usual
practice to give each leg a footing of cement concrete. It thus seems
that the number of holes to be dug for a line of towers is nearly or
quite as great as that for a line of poles, and considering the concrete
footings the cost of erecting the towers is probably greater than that
for the poles. With wooden poles about four times as many pins and
insulators are required as with steel towers, or say twelve pins and
insulators on poles instead of three on a tower. For circuits of 50,000
to 60,000 volts the approximate cost of each insulator with a steel pin
may be taken at $1.50, so that the saving per tower reaches not more
than $13.50 in this respect. In the labor of erecting circuits there may
be a small advantage in favor of the towers, but the weight of the long
spans probably offsets to a large extent any grain of time due to fewer
points of support.
An approximate conclusion from the above facts seems to be that a line
of steel towers will probably cost from 1.5 to twice as much as a line
or lines of wooden poles to support the same number of conductors the
same distance apart, even when the saving of pins and insulators is
credited to the towers. This conclusion applies to construction over a
large part of the United States and Canada. It is known that wooden
poles of good quality retain enough strength to make them reliable as
supports during ten or fifteen years, and it is doubtful whether steel
towers will show enough longer life to more than offset their greater
first cost. It may be noted here that any saving in the cost of
insulators or other advantage that there may be in spans four hundred
feet or more long can be as readily secured with wooden as with steel
supports. With these long spans the requirements are greater height and
strength in the line supports, and these can readily be obtained in
structures each of which is formed of three or four poles with
cross-braces. Such wooden structures have long been in use at certain
points on transmission lines where special long spans were necessary or
where there were large angular changes of direction. In those special
cases where structures 75 to 150 or more feet in height are necessary to
carry a span across a waterway, as at the Chambly Canal above mentioned,
steel is generally more desirable than wood because poles of such
lengths are not readily obtainable. Neither present proposals nor
practice, however, contemplates the use of steel towers having a length
of more than forty to fifty feet on regular spans.
Much the strongest argument in favor of steel towers for transmission
lines is that these towers give a greater reliability of operation than
do wooden poles. It is said that towers will act as lightning-rods and
thus protect line conductors and station apparatus. As to static and
inductive influences from lightning, it is evident that steel towers can
give no protection. If each tower has an especial ground connection it
will probably protect the line to some extent against direct lightning
strokes, but there is no reason to think that this protection will be
any greater than that given by well-grounded guard wires, or even by a
wire run from a ground plate to the top of each pole or wooden tower. If
a direct lightning stroke passes from the line conductors to a wooden
support it frequently breaks the insulator on that support, and the pole
is often shattered or burned. Such a result does not necessarily
interrupt the transmission service, however, as the near-by poles can
usually carry the additional strain of the line until a new pole can be
set. Quite a different result might be reached if lightning or some
other cause broke an insulator on a steel tower, and thus allowed one of
the electric cables to come into contact with the metal structure, as
the conductor would then probably be burned in two. To repair a heavy
cable thus severed where the spans were as much as 400 feet long would
certainly require some little time. Where a conductor in circuits
operating at 20,000 to 35,000 volts has in many cases dropped onto a
wooden cross-arm, it has often remained there without damage until
discovered by the line inspector, but no such result could be expected
with steel towers and cross-arms (xxi, A. I. E. E., 760). Where steel
towers are employed it would seem to be safer to use wooden cross-arms,
for the reasons just stated. This is, in fact, the practice on the steel
towers before named that support 25,000-volt circuits over the Chambly
Canal, and also on the steel towers that carry the 60,000-volt circuits
from Colgate power-house over the mile-wide Straits of Carquinez.
On the 40,000-volt transmission line between Gromo and Nembro, Italy,
where timber is scarce and steel is cheap, both the poles and cross-arms
are of wood. It is thought that the comparatively small number of
insulators used where a line is supported at points about four hundred
feet apart should contribute to reliability in operation, but insulators
now give no more trouble than other parts of the line, and the leakage
of energy over their surfaces is very small in amount, as was shown in
the Telluride tests. Whatever benefits are to be had from long spans are
as available with wooden as with steel supports, and at less cost.
One advantage of steel towers over wooden poles or structures is that
the former will not burn and are probably not subject to destruction by
lightning. Where a long line passes over a territory where there is much
brush, timber or long grass, the fact that steel towers will not burn
may make their choice desirable. In tropical countries where insects
rapidly destroy wooden poles the use of steel towers may be highly
desirable even at much greater cost, and such a case was perhaps
presented on the line to Guanajuato, Mexico.
Mechanical failures of wooden insulator pins have been far more common
than those of poles, both as a direct result of the line strains and
because such pins are often charred and weakened by the leakage of
energy from the conductors. For these reasons the general use of iron or
steel pins for the insulators of long lines operating at high voltages
seems desirable. Such pins are now used to support the insulators on a
number of lines with wooden poles and cross-arms, among which may be
mentioned the forty-mile, 30,000-volt transmission between Spier Falls
and Albany and the forty-five-mile 28,000-volt line from Bear River to
Ogden, Utah. Iron or steel pins add very little to the cost of a line,
and materially increase its reliability. One of the cheapest and best
forms of steel pins is that swaged from a steel pipe and having a
straight shank and tapering stem with no shoulder. A pin of this sort
for the 400-foot spans of 190,000-circular-mil copper cable on the line
from Niagara Falls to Toronto measures three and one-quarter inches long
in the shank, eleven and one-half inches in the taper, and has diameters
of two and three-eighths inches at the larger and one and one-eighth
inches at the smaller end. On spans under 150 feet between wooden poles
pins of this type but with a much smaller diameter could be used to
advantage.
On long transmission lines where the amount of power involved is very
large the additional reliability to be had with steel towers is probably
great enough to justify their use. For the great majority of power
transmissions, however, it seems probable that wooden poles or
structures will long continue to be much the cheaper and more
practicable form of support.
The line of steel towers on a private right of way seventy-five miles
long, carrying two circuits for the transmission of 24,000 horse-power
at 60,000 volts from Niagara Falls to Toronto, is one of the most
prominent examples of this type of construction.
Eventually there will be two rows of steel towers along the entire
length of the line.
On the straight portions of the line the steel towers are regularly
erected 400 feet apart, but on curves the distances are less between
towers, so that their total number is about 1,400 for each line.
Standard curving along the line requires towers placed 50 feet apart,
and a change in the direction of not more than ten degrees at each
tower, except at the beginning and end of the curve, where the change in
direction is three degrees. When the change in the direction of the line
is not more than six degrees, the corresponding spans allowed with each
change are as follows:
Degrees Feet of
change. span.
1/2 300
1 286
1-1/2 273
2 259
2-1/2 246
3 232
3-1/2 219
4 205
4-1/2 192
5 178
5-1/2 165
6 151
At some points along the line conditions require a span between towers
of more than 400 feet, the regular distance for straight work. One
example of this sort occurs at Twelve-Mile Creek, where the stream has
cut a wide, deep gorge in the Erie plateau. At this point the lines make
a span of 625 feet between towers.
[Illustration: FIG. 94.--Transposition Tower (Second Tower).]
[Illustration: FIG. 95.--Elevations and Plan of Tower.]
The regular steel tower used in this transmission measures 46 feet in
vertical height from its foot to the tops of the lower insulators, and
51 feet 3 inches to the tops of the higher insulators. The lower six
feet of this tower are embedded in the ground, so that the tops of the
insulators measure about 40 feet and 45 feet 3 inches respectively above
the earth. At the ground the tower measures 14 feet at right angles to
the transmission line and 12 feet parallel with it. The width of each
tower at the top is 12 feet at right angles to the line, and the two
sides having this width come together at points about 40 feet above the
ground. Between the two L bars thus brought nearly together, at each
side of a tower a piece of extra heavy 3-inch steel pipe is bolted so as
to stand in a vertical position. Each piece of this pipe is about 3-1/2
feet long and carries a steel insulator pin at its upper end. The two
pieces of pipe thus fixed on opposite sides of the top of a tower carry
the two highest insulators. For the other four insulators of each tower,
pins are fixed on a piece of standard 4-inch pipe that serves as a
cross-arm, and is bolted in a horizontal position between the two
nearly rectangular sides of each tower, at a point two feet below the
bolts that hold the vertical 3-inch pipes, already named, in position.
Save for the two short vertical and one horizontal pipe, and the pins
they support, each tower is made up of L-shaped angle-bars bolted
together. Each of the two nearly rectangular sides of a tower consists
of two L bars at its two edges, three L bars for cross-braces at right
angles to the edges, and four diagonal braces also formed of L bars. The
lower halves of the L bars at the edges of each side of a tower have
sections of 3″ × 3″ × 1/4″, and the upper halves have sections of 3″ ×
3″ × 3/16″. This last-named cross-brace and the other two cross-braces
have a common section of 2″ × 1-1/2″ × 1/8″. For the lower set of
diagonal braces the common section is 2-1/2″ × 2″ × 1/8″, and the upper
set has a section of 2″ × 1-1/2″ × 1/8″ in each member. At the level of
the lowest cross-braces the two rectangular sides of a tower are tied
together by one member of 2″ × 1-1/2″ × 1/8″ of L section and at right
angles to the sides, and by two diagonal braces of 5/8″ round rod
between the corners of the tower. On each of its two triangular sides a
tower has four horizontal braces and three sets of diagonal braces. The
two upper horizontal braces are of 2″ × 1-1/2″ × 1/8″ L section, and the
lowest is the same, but the remaining horizontal brace has a section of
2-1/2″ × 2″ × 1/8″. Bars of 2″ × 1-1/2″ × 1/8″ L section are used for
the two upper sets of diagonal braces, and bars of 2-1/2″ × 2″ × 1/8″
for the lower set. In addition to the cross-braces named, each
triangular side of a tower near the top of the corner bars has two short
cross-pieces with the common L section of 3-1/2″ × 3-1/2″ × 5/8″, one
just above and the other just below the cross-arm of 4-inch pipe to hold
it in place. At the bottom of each of the four corner bars of a tower a
foot is formed by riveting a piece of 3″ × 1/4″ L section and 15 inches
long at right angles to the corner bar. On one corner bar of each tower
there are two rows of steel studs for steps, one row being located in
each flange of the L section. On the same flange these steps are two
feet apart, but taking both flanges they are only one foot apart. Every
part of each steel tower is heavily galvanized.
[Illustration: FIGS. 96, 97, 98.--Raising Towers on Niagara Transmission
Line.]
[Illustration: FIG. 99.--One of the Towers in Position.]
The labor of erecting these steel towers was reduced to a low figure by
the method employed, as shown in the accompanying illustration. Each
tower was brought to the place where it was to stand with its parts
unassembled. For erecting the towers a four-wheel wagon with a timber
body about thirty feet long was used. When it was desired to raise a
tower, two of the wheels, with their axle, were detached from the timber
body of the wagon, and this body was then stood on end to serve as a
sort of derrick. This derrick was guyed at its top on the side away from
the tower, and a set of blocks and tackle was then connected to the top
of the derrick and to the tower at a point about one-fourth of the
distance from its top. A rope from this set of blocks ran through a
single block fixed to the base of the derrick and then to a team of
horses. On driving these horses away from the derrick the steel tower
was gradually raised on the two legs of one of its rectangular sides
until it came to a vertical position. The next operation was to bring
the legs of the tower into contact with the extension pieces that were
fixed in the earth and then bolt them together.
[Illustration: FIG. 100.--Steel Tower for Transmission Line.]
The tops of the three pins that carry the insulators for each
three-phase circuit are at the corners of an equilateral triangle (Fig.
100), each of whose sides measures six feet. The six steel insulator
pins used on each tower are exactly alike, and each is swaged from extra
heavy pipe. Each finished pin is 2-3/8 inches in diameter for a length
of 3-1/4 inches, and then tapers uniformly to a diameter of 1-1/8 inch
at the top through a length of 11-1/2 inches. This gives the pin a total
length of 14-3/4 inches. In the larger part there are two 9/16-inch
holes from side to side, and within two inches of the top there are
three circular grooves each 3/16 inch wide and 1/16 inch deep. Forged
steel sockets of two types are employed to attach the steel pins with
the pipes. Each socket is made in halves, and these halves are secured
to both the pipe and the pin by through bolts. Like all other parts of
the towers, these steel pins and sockets are heavily galvanized. On
each of the four corner bars of a tower the lower six feet of its length
is secured to the upper part by bolts or rivets. This lower six feet of
each corner bar is embedded in the earth, and the construction just
named makes it easy to replace the bars in the earth when corrosion
makes it necessary.
Footings for each tower are provided by digging four nearly square holes
with their sides at approximately 45 degrees with the direction of the
transmission line, and the shortest side of each hole at least two feet
long. Centres of these holes are 14 feet 3 inches apart in a direction
at right angles to the line, and 13 feet 9 inches apart parallel with
the line. In hard-pan each one of the holes was filled to within 2 feet
6 inches of the top with stones, after the leg of the tower was in
position, and then the remainder of the hole was filled with cement
grouting mixed four to one.
At the bottom of each hole in marsh land a wooden footing 3 feet × 6
inches × 24 inches was laid flat beneath the leg of the tower, and then
the hole was filled to within 2-1/2 feet of the surface with the
excavated material. Next above this filling comes a galvanized iron
gutter-pipe, four inches in diameter, and filled with cement about the
leg of the tower for a length of two feet. Outside of this pipe the hole
is made rounding full of cement grouting.
[Illustration: FIG. 101.--Transmission Line at Welland Canal.]
At some points along the transmission line exceptionally high towers are
necessary, a notable instance being found at the crossing over the
Welland Canal, where the lowest part of each span must not be less than
150 feet above the water. For this crossing two towers 135 feet high
above ground are used, as seen in Fig. 101. Each of these towers is
designed to carry all four of the three-phase power circuits that are
eventually to be erected between Niagara Falls and Toronto. For this
purpose there was used a special design of tower with a width of about
48 feet at right angles to the direction of the line below the top
truss, and a width of about 68.5 feet at that truss where the two lower
conductors of each circuit are attached.
With all spans longer than 400 feet, a tower of heavier construction
than the standard type is used, and this tower provides three insulators
for the support of each conductor. A tower of this type that supports
the lowest conductors about 40 feet above the ground level has its
corner bars made up of 4″ × 4″ × 3/8″ and 4″ × 4″ × 5/16″ L sections,
has three cross-arms of extra heavy 4-inch pipe, and a 6-inch vertical
standard pipe to support each group of three insulators for the highest
conductor of each circuit. Each of the lower conductors of a circuit on
this tower is supported by an insulator on each of the three parallel
cross-arms. On some of these towers, for long spans, the two outside
insulators for the support of each conductor are set a little lower than
the insulator between them.
[Illustration: FIG. 102.--Heavy Tower at Credit River.]
[Illustration: FIG. 103.--Angle Tower Near Bronte.]
Angle towers, used where the line makes a large change in direction at a
single point, have three legs on each rectangular side, a width of 20
feet on each of these sides for some distance above the ground, and a
width of 27 feet 2 inches at the top. In these towers the two legs on
the triangular side that is in compression are each made up of four 3″ ×
3″ × 1/4″ L sections joined by 1-1/2″ × 1/4″ lattices and rivets. Towers
of this sort are used near the Toronto terminal-station, where the line
changes 35 degrees at a single point, and near the crossing of
Twelve-Mile Creek, where the angular change of the line on a tower is 45
degrees. Close to each terminal-station and division-house the
transmission line is supported by terminal towers. These towers differ
from the others in that each carries insulators for only three
conductors, and these insulators are all at the same level. Each
terminal tower has nine insulators, arranged in three parallel rows of
three each for the conductors of a single circuit, and each conductor
thus has its strain distributed between three pins. All three wires of a
circuit are held 40 feet above the ground by a terminal tower, and pass
to their entries in the wall of a station at the same level. As these
terminal towers must resist the end strain of the line, they are made
extra heavy, the four legs each being made up of 4″ × 4″ × 5/16″ and 4″
× 4″ × 3/8″ L sections. For the three cross-arms on one of these towers
three pieces of 4-inch pipe, each 15 feet 9 inches long, are secured at
its top with their parallel centre lines 30 inches apart in the same
plane. Each of these pipes carries three insulator pins with their
centres 7 feet 4-1/2 inches apart. On the bottom of each leg of a
terminal tower there is a foot, formed by riveting on bent plates, that
measure 15 and 18 inches, respectively, on the two longer sides. Each
foot of this tower is set in a block of concrete 5 feet square that
extends from 3.5 feet to 7.5 feet below the ground level.
Insulators for the transmission line, which are illustrated in Fig. 104,
are of brown, glazed porcelain, made in three parts, and cemented
together. The three parts consist of three petticoats or thimbles, each
of which slips over or into one of the others, so that there are three
outside surfaces and three interior or protected surfaces between the
top of an insulator and its pin.
From top to bottom the height of each insulator is 14 inches, and this
is also the diameter of the highest and largest petticoat. The next or
middle petticoat has a maximum diameter of 10 inches and the lowest
petticoat one of 8 inches. Cement holds the lowest petticoat of the
insulator on one of the steel pins previously described, and in this
position the edge of the lowest petticoat is about 2-1/2 inches from the
steel support. At the top of each insulator the transmission conductor
is secured, and the shortest distance from this conductor to any of the
steel parts through the air is about 17 inches.
From the step-up transformer house at Niagara Falls to the
terminal-station at Toronto, a distance of seventy-five miles, each
three-phase, 60,000-volt, 25-cycle circuit on the steel towers is made
up of three hard-drawn copper cables with a cross section of 190,000
circular mils each, and is designed to deliver 12,000 electric
horse-power with a loss of ten per cent, on a basis of 100 per cent
power factor. Six equal strands of copper make up each cable, and this
wire has been specially drawn with an elastic limit of more than 35,000
pounds and a tensile strength of over 55,000 pounds per square inch.
This cable is made in uniform lengths of 3,000 feet, and these lengths
are joined by twisting their ends together in copper sleeves, and no
solder is used. No insulation is used on these cables.
[Illustration: FIG. 104.--Insulators.]
Instead of a tie-wire, a novel clamp is employed to secure the copper
cable on each insulator. This complete clamp is made up of two separate
clamps that grasp the cable at opposite sides of each insulator and of
two half-circles of hard-drawn copper wire of 0.187 inch diameter. Each
half-circle of this wire joins one-half of each of the opposite clamps,
and fits about the neck of the insulator just below its head. Two bronze
castings, one of which has a bolt extension that passes through the
other, and a nut, make up each separate clamp. When the combined clamp
is to be applied, the sides are separated by removing the nut that holds
them together, the half-circles are brought around the neck of the
insulator, and each of the side clamps is then tightened on to the cable
by turning the nut that draws its halves together. This complete clamp
can be applied as quickly as a tie-wire, is very strong, and does not
cut into the cable.
Each of the regular steel towers is designed to withstand safely a side
strain of 10,000 pounds at the insulators, or an average of 1,666 pounds
per cable. With the 190,000-mil cable coated to a depth of 1/2 inch with
ice and exposed to a wind blowing 100 miles per hour, the estimated
strains on each steel pin for different spans and angular changes in the
direction of the line are given in the accompanying table:
POUNDS STRAIN ON PINS, 1/2-INCH SLEET, 100 MILES WIND.
=====+=========================================
| Degrees and Minutes.
Span,+-----+-----+-----+-----+-----+-----+-----
feet.| 0 | 0.30| 1 | 1.30| 2 | 2.30| 3
-----+-----+-----+-----+-----+-----+-----+-----
0| 0| 35| 69 | 104| 138| 173| 207
100| 256| 291| 325| 360| 394| 429| 463
200| 512| 547| 581| 616| 650| 685| 719
300| 768| 803| 837| 872| 906| 941| 975
400|1,024|1,059|1,093|1,128|1,162|1,197|1,231
500|1,280|1,315|1,349|1,384|1,418|1,453|1,487
600|1,536|1,571|1,605|1,640|1,674|1,709|1,743
700|1,792|1,827|1,861|1,896|1,930|1,965|1,999
800|2,048|2,083|2,117|2,152|2,186|2,221|2,255
900|2,304|2,339|2,373|2,408|2,442|2,477|2,511
1,000|2,560|2,595|2,629|2,664|2,698|2,733|2,767
-----+-----+-----+-----+-----+-----+-----+-----
=====+===================================
| Degrees and Minutes.
Span,+-----+-----+-----+-----+-----+-----
feet.| 3.30| 4 | 4.30| 5 | 5.30| 6
-----+-----+-----+-----+-----+-----+-----
0| 242| 276| 311| 345| 380| 414
100| 498| 532| 567| 601| 636| 670
200| 754| 788| 823| 857| 892| 926
300|1,010|1,044|1,079|1,113|1,148|1,182
400|1,266|1,300|1,335|1,369|1,404|1,438
500|1,522|1,556|1,591|1,625|1,660|1,694
600|1,778|1,812|1,847|1,881|1,916|1,950
700|2,034|2,068|2,103|2,137|2,172|2,206
800|2,290|2,324|2,359|2,393|2,428|2,462
900|2,546|2,580|2,615|2,649|2,684|2,718
1,000|2,802|2,836|2,871|2,905|2,940|2,974
-----+-----+-----+-----+-----+-----+-----
The copper cables were so strung as to have a minimum distance from the
ground of 25 feet at the lowest points of the spans. In order to do this
the standard steel towers that hold the lower cables 40 feet above the
ground level at the insulators are spaced at varying distances apart,
according to the nature of the ground between them. At each tower the
upper cable of each circuit is 5 feet 3 inches higher than the two lower
cables, and this distance between the elevations of the upper and the
lower cables is maintained whatever the amount of sag at the centre of
each span. If there is a depression between two standard towers on a
straight portion of the line, the sag in the centre of a span 400 feet
long may be as much as 18 feet. Where a rise and fall in the ground
between towers make it necessary to limit the sag to 14 feet in order to
keep the lowest cables 25 feet above the highest point of earth, the
length of span is limited to 350 feet. If the rise and fall of ground
level between towers allow a sag of only 11 feet with the lowest cable
25 feet above the earth, the length of span with 40-foot towers is
reduced to 300 feet; and if for a like reason the sag is limited to 8
feet, the span may only be 250 feet.
[Illustration: FIG. 105.--Take-up Arrangement on Terminal Tower.]
At each terminal tower, where the cables are secured before they pass
into a terminal-station, the three insulators for each cable are in a
straight line with their centres, 30 inches apart. When a line cable
reaches the first insulator of the three to which it is to be attached
on one of these towers, it is passed around the neck of this insulator
and then secured on itself by means of two clamps that are tightened
with bolts and nuts. See Fig. 105. The cable thus secured turns up and
back over the tops of the three insulators and goes to the
terminal-station. Around the neck of the insulator to which the line
cable has been secured in the way just outlined a short detached length
of the regular copper cable with the parts of a turnbuckle at each end
is passed, and this same piece of cable also passes around the neck of
the next insulator in the series of three. By joining the ends of the
turnbuckle and tightening it, a part of the strain of the line cable in
question is transferred from the first to the second insulator of the
series. In the same way a part of the strain of this same line cable is
transferred from the second insulator of the series to the third, or one
nearest to the terminal-station.
INDEX.
Air-blast cooled transformers, 129
Air-gap data, 183
Air gaps, number in series to stand given voltage, 183
Albany-Hudson Ry. Plant, 121
Alternating currents, 227
Alternator voltage, 118
Alternators, 103
data, 118
for high voltage, 120
inductor, 112
types of, 111
Aluminum as a conductor, 200, 209
cables in use, 213
conductor joints, 206
conductors, 27, 28
corrosion of, 211
properties of, 212
soldered joints, 206
_vs._ copper, 209
wire, cost of, 29
Amoskeag Mfg. Co. plant, 51, 52
Amsterdam (N. Y.) plant, 121
Anchor ice, 59
Anderson (S. C.) plant, 121
Apple River (Minn.) plant, 1, 26, 27, 28, 71, 97, 98, 99, 102, 118,
119, 124, 126, 127, 134, 174, 187, 190, 192, 208, 245, 264, 294
Arc lighting, 167
Arcing, 46
Automatic regulators, 162
Barbed wire, 169, 175
Belt drive, 83, 107
Bienne plant (Switzerland), 42
Birchem Bend, 57, 67, 79, 95, 97, 98, 102
Blower capacity necessary to cool transformers, 130
Boosters, 133
Boston-Worcester Ry. plants, 121
Braces for cross-arms, 259
Bronze conductors, 200
Brush discharge, 281
Buchanan (Mich.) plant, 88
Building materials, 95
Bulls Bridge plant, 63
Burrard Inlet (B. C.) plant, 111, 112
Bus-bars, 142, 147
dummy, 145
Cable insulation, 195
sheaths, 194
ways, 140
Cables, aluminum, 212
aluminum, in use, 213
charging current, 197
cost of, 188, 196
for alternating current, 194
high-voltage, 191
paper insulated, 196
protection against electrolysis, 195
rubber-covered, 195
submarine, 192
temperature of, 198
voltage in, 190, 196
Canadian-Niagara Falls Power Co., 121
Canals, 51, 53
long, 68
Cañon City plant, 26, 27, 28, 117, 118, 127, 208
Cañon Ferry plant, 1, 3, 26, 27, 28, 46, 49, 53, 62, 68, 69, 83, 89,
94, 95, 97, 102, 105, 112, 113, 118, 119, 124, 125, 126, 127, 130,
132, 134, 174, 208, 233, 234, 245, 246, 249, 254, 257, 259, 268, 272,
280, 282, 294, 295, 302
Cedar Lake plant, 90
Chambly plant, 96, 110, 149, 156, 172, 189, 249, 255, 256, 257, 267,
272, 287, 294, 295, 311, 312
Charging current for cable, 197
Charring of pins, 276, 278
Chaudière Falls plant, 118
Choke-coil used with lightning arresters, 180
Circuit breakers, 135, 150
breakers, time limit, 152
Circuits, selection of, 233
Coal, price of, in Salt Lake City, 8
Colgate plant, 1, 3, 26, 27, 28, 74, 82, 83, 90, 94, 97, 98, 99, 101,
102, 108, 112, 113, 118, 127, 130, 132, 134, 187, 190, 201, 206, 208,
213, 245, 246, 250, 254, 257, 272, 277, 280, 282, 294, 295, 304, 309
Columbus (Ga.) plant, 83, 115
Compounding, 160
Compressive strength of woods, 302
Conductivity of the conductor metals, 201
Conductors, 200
aluminum, 27, 28, 206
aluminum, properties of, 212
coefficients of expansion, 200
corrosion of, 211
cost of, 22, 29, 203, 204, 205
cost of aluminum, 29
cost of per k. w., 28
cost of copper, 29
data, 204
data from representative transmission plants, 208
expansion of aluminum and copper, 211
melting points, 200
minimum size for transmission line, 202
properties of ideal, 200
relative conductivity, 201
relative cost of, 20
relative properties for equal lengths and resistances, 204
relative strengths for given area, 203
relative weight for given conductivity, 202
relative weight of, 202
relative weights of three-phase, two-phase, and single-phase lines,
220
resistance of, 225
skin effect, 206, 233
weight per k. w., 27
Conduits, 195
radiation loss in, 198
temperature rise in, 198
Constant current regulator, 167
transformer, 167
Control equipment for d. c. and a. c. plants, 35
Copper conductors, 200
cost of, 22
_vs._ aluminum, 209
wire, cost of, 29
Corrosion of conductors, 211
Cross-arm braces, 258
iron, 284
location of, 257
material, 258
Cross-arms, 49, 256
Crossings, 187
Dales plant (White River), 26, 27, 28, 71, 134, 208
Dams, 62
Delta connection, 131
Depreciation, 11
Design of power-plant, 83
Dike, 60
Direct connection, 84
Discharge, static, 170
Distribution system, 158
Draught tubes, 79
Dummy bus-bars, 145
Easton (Pa.) plant, 121
Edison Co. (Los Angeles) plant, 118
Efficiency constant-current transmission, 216
curves, motor-generator set, 117
of constant-voltage transmission, 217
of transformers, 133
relative, of a. c. and d. c. transmission, 35
Electra plant, 1, 3, 74, 82, 83, 92, 94, 97, 98, 101, 102, 108, 112,
113, 118, 127, 174, 206, 208, 212, 213, 233, 235, 236, 245, 248, 253,
254, 256, 259, 272, 275, 277, 280, 281, 282, 294, 295
Electric power, market for, 7
Electrical Development Co., Niagara plant, 120
Electricity _vs._ gas, 6
Electrolysis, 195
Energy curves of hydro-electric stations, 13
electrical, cost of at switchboard, 23
Entrance end strain, 261, 325
insulating discs, 262
into buildings, 179
of lines, 179, 261, 265
through roof, 269
wall openings, 262
Entries for transmission lines, 261
Expansion, coefficient of, for copper and aluminum, 211
coefficients of, for various conductor metals, 200
Farmington River (Conn.) plant, 26, 27, 28, 58, 118, 125, 134, 208,
212, 213,
245
Feeders, 143
Ferranti cables, 192
Fire-proofing, 95
Floor, distance from roof to, 95
location of, 79
space, 12, 101, 102
space per k. w. of generators, 12
Floors, 95
Fog, 46, 277
Fore-bay, 59, 60
Foundations, 95
Frequency, 113, 127
effect on transformer cost, 116
Fuel, price of, in Salt Lake City, 8
Fuses, 135, 150
Garvins Falls plant, 56, 60, 79, 80, 94, 96, 97, 102, 113, 145, 240,
294
Gas _vs._ electricity, 6
Gears, 84, 108
Generators (a. c.), 103
d. c. _vs._ a. c., 31
Generators, belt-driven, 107
capacity of, 32
compounding of, 160
cost of, 40
(a. c.) cost, 32
(a. c.) data, 118
direct-connected to horizontal turbines, 89
to impulse wheels, 90
connection to vertical shafts, 84
(d. c.) field excitation of, 41
floor space, 101
per k. w., 12
gear-driven, 108
(a. c.) high-voltage, 120
(d. c.) in series, 31
(d. c.) installation of, 41
insulation of, 39, 45
lightning protection, 34
limiting voltage of, 44
(a. c.) limiting voltage of, 32
(d. c.) limiting voltage of, 31
overload capacity, 103
relation between voltage and capacity, 127
revolving armatures, 112
fields, 112
series-wound, 41
speed regulation, 38
Glass _vs._ porcelain insulators, 288
Great Falls plant, 54, 60, 61, 64, 67, 78, 92, 93, 102, 114, 118
Greggs Falls plant, 54, 56, 64, 240
Ground connections, 178
for guard wires, 171, 172
Grounded guard wires, 168
Guard wires, 168
installation of, 175
Guying of poles, 255
Hagneck (Switzerland) plant, 86
Hooksett Falls plant, 56, 131
Hydro-electric plants, 1
built at the dam, 64-67
canals, long, 68-73
long and short, 58
short, 53-56
capacity and weight of conductors per k. w. for various plants, 27
(800 k. w.) cost of, 10
(1500 k. w.) cost of, 11
cost of labor, 12
cost of operation, 12, 77
design of, 83
floor, 79
space per k. w., 101
interest and depreciation, 11
linked together, 56-58
load factors, 14, 15
location of, 64
model design, 12
operation, 59
_vs._ steam plant, 5, 12
with pipe-lines, 73-77
with steam auxiliary, 84
Ice, 59
Impulse wheel speed, 108
wheels, 82, 90
location of, 99
Indian Orchard plant, 57, 84
Inductance, 206, 230
Induction, electro-magnetic, electrostatic, 168
on lines, 206
regulator, 162
Inductor alternators, 112
Insulation, as affected by ozone, 197
cost of paper _vs._ rubber, 196
of a. c. and d. c. lines, 34
of apparatus, 142
of cables, 195
of electrical machines, 45
of generators, 39
protection against ozone, 198
Insulator arc-over test, 291
-pins, 270 (see Pins)
Insulators, 277, 282, 287, 322
and pins, data from various plants, 280
defective, 288
glass _vs._ porcelain, 288
in snow, 293
method of fastening to iron pins, 271
novel clamp, 323
on various transmission lines, 294
petticoats, 294
testing of, 288
tests, 290
test voltage, 289
with oil, 287
Iron conductors, 200
Kelley’s Falls plant, 56
Kelvin’s law, 219
Labor, cost of, 12
in hydro-electric stations, 12
Leakage, 275, 287
line, 207, 214
Lewiston (Me.) plant, 118, 120, 122, 167, 213
Lighting, incandescent, minimum frequency, 116
series distribution, 167
Lightning arrester, effect of series resistance, 185
arresters, 168, 176
ground connection, 178
multiple air-gap, 176, 183
non-arcing metals in, 184
series connection of, 180
shunted air-gaps, 185
with choke coil, 180
protection, 34
Line calculations, 221-232
charging current, 197
conductors, 200
conductors, cost of, 22
weight of, 21
construction, 222
cost, 310
cross-arms, 49
spacing of wires, 46
(a. c.) transmission, 34
(d. c.) transmission, 33
end strain, 325
leakage, 47
loss, 39
losses due to grounded guard wires, 176
Lines, sag, 309
transposition of, 314
Line voltages, 45
Load factors, 14, 15
lighting, 61
maximum, 60
motor, 160
railway, 164
Loss in conduits, 198
relation to weight of conductors, 215
Losses due to grounded guard wire, 176
on transmission lines, 215
Ludlow Mills plant, 26, 27, 28, 57, 79, 100, 121, 208, 213
Madrid (N. M.) plant, 26, 27, 28, 118, 208
Manchester (N. H.) plants, 120
Market for electric power, 7
Materials, building, 95
for line-conductors, 200
Mechanicsville plant, 58, 67, 109, 121, 174
Melting points of conductor metals, 200
Montmorency Falls plant, 26, 27, 28, 240
Motor load, 160
Motor-generator set efficiency curve, 117
Motors, series-wound, 41
(d. c.) speed regulation, 38
synchronous, 241
Multiple air-gap arrester, 176
Needle-point spark-gap for measuring pressure, 290
Neversink River plant, 75, 179
Niagara Falls Power Co., 3, 59, 81, 86, 87, 93, 94, 95, 97, 101, 102,
105, 106, 107, 108, 112, 113, 117, 118, 119, 127, 133, 137, 140, 143,
145, 151, 153, 161, 165, 170, 181, 188, 194, 195, 208, 211, 240, 245,
246, 257, 272, 273, 275, 280, 287, 289, 294, 295, 297
Nitric acid from air, 281
Non-arcing metals, 184
North Gorham (Me.) plant, 120
Ogden (Utah) plant, 26, 27, 28, 118, 120, 132, 134, 208, 245
Ohm’s law, 223
Oil switches, 136
Ontario Power Co., 121
Operating expenses, 59
Operation, cost of, 12, 77
Operations, reliability of, 311
Ouray (Col.) plant, 121
Overhead line connection to underground, 197
Overload capacity of generators, 103
Ozone, 197
Painting of poles, 255
Paper insulated cables, 196
_vs._ rubber insulation, 196
Payette River (Idaho) plant, 73, 101
Penstocks, 59, 98
Phase, 113
Pike’s Peak plant, 77
Pilot wires, 161
Pins, 259, 270
and insulators, data from various plants, 280
burning of, 270, 276, 278
charring of, 276, 278
composite, 281
compressive strength of woods, 302
design of, 298
dimensions of, 301
formula for diameter of, 299
iron, 275, 285, 286
expansion of, 290
method of fastening insulators, 271
method of fastening to cross-arms, 271
metal, 271, 275, 282, 285, 286
of uniform strength, 300, 302
proportions, 301
relative cost of metal and wooden, 284
shank, 274
shoulder, 275, 299, 305
softening of threads, 280
steel, 275, 312
strain with 1/2-inch sleet and 100-mile wind for different spans,
324
strains on, 270, 298
strength of, 303
table of standard, 301
treatment of, 259, 275
weakest point, 298
wooden, data from various plants, 272
dimensions of, 272
dimensions of standard, 273
Pipe-lines, 73
Pittsfield (Mass.) plant, 121
Pole line, cost of, 21
lightning arresters, 179
relative cost of, 20
lines, 246
Poles, cost, 310
depth in ground, 254
diameter of, 254
dimensions of, 254
guying of, 255
iron, 284
length of, 253, 309
life of, 255
setting of, 252
spacing of, 249
steel, cost of, 307
treatment of, 255
woods for, 252
Porcelain _vs._ glass insulators, 288
Portland (Me.) plant, 120, 166, 239
Portsmouth, N. H. plant (steam), 102, 118, 119, 120, 121, 144, 194,
264, 294
Power plant, relative cost of a. c. and d. c., 36
transmitted, total cost of, 24
Radiation loss in conduits, 198
Railway crossing, 187, 252
service, 164
Red Bridge plant, 53, 60, 79, 93, 94, 96, 97, 99, 101, 102
Regulation, 155, 239
as effected by synchronous motors, 165
at receiving end, 162
hand, 161
Regulator, automatic, 162
constant-current, 167
induction, 162
Relay-switches, 145
Resistance, 225
in series with lightning arrester, 185
Revolving armature alternators, 112
field alternator, 112
River crossings, 187, 190, 249
Roof, distance from floor, 95
Roofs, 95
Rope-drive, 83
Rotaries, cost of, 117
suitable frequency for, 115
Rubber-covered cables, 195
maximum temperature, 198
protection against ozone, 198
Sag in lines, 309
St. Hyacinthe (Que.) plant, 118
St. Joseph plant, 66
St. Maurice plant (Switzerland), 31
Salem (N. C.) plant, 121, 122
San Gabriel Cañon plant, 26, 27, 28, 208
Santa Ana plant, 1, 26, 27, 28, 74, 76, 82, 83, 92, 94, 95, 96, 97,
98, 99, 101, 102, 208, 245, 263, 280, 281, 294, 295, 296
Sault Ste. Marie plant, 72, 83, 85, 89, 97, 102, 104, 105, 112, 113,
117, 118, 120, 127
Scott system, 132
Series distribution, 167
machines, 41
Sewall’s Falls plant, 26, 27, 28, 155
Shawinigan Falls plant, 1, 70, 71, 107, 116, 117, 163, 164, 166, 209,
212, 213, 235, 236, 242, 245, 267, 272, 273, 280, 282, 294, 295, 296
Sheaths for cables, 194
Shunted air-gaps, 185
Skin effect, 206, 232
Snoqualmie Falls plant, 3, 4
map of transmission lines, 4
Snow, 293
Soldered joints, 206
Spacing of poles, 249
of wire, 234
Spans, long, 190, 250
strains for different lengths, 324
Sparking distances, 182
voltages, 182
Speed, peripheral, of impulse wheels, 108
peripheral of turbines, 85, 103
regulation, 38, 42
d. c. motors, 38
Spier Falls plant, 1, 2, 3, 54, 58, 61, 62, 68, 91, 94, 98, 124, 126,
127, 130, 141, 142, 146, 161, 174, 236, 237, 243, 244, 245, 250, 253,
266, 280, 285, 287, 289, 291, 294, 295, 296, 312
Star connection, 131
Static discharges, 170
Steam and water-power station combined, 84
electric plant, cost of labor, 12
cost of operation, 12
floor area per k. w., 102
_vs._ water-power, 5
Steel towers, 306
Storage capacity, 15
Strains on insulation as affected by resistance in series with
arrester, 185
Stray currents, protection against, 195
Submarine cables, 187, 192, 194
Sub-station, arrangement of apparatus, 128
Sub-stations, 157, 237
Surges, 136
Switchboard, 156
wiring, 146, 148, 149
Switches, 135, 244
arcing of, 135
electrically operated, 140
long break, 135
oil, 136
open-air, 136
pneumatically operated, 140
power operated, 138
relay, 145
Switch-houses, 141, 142, 238, 244
Switching, 146
high-tension, 147
Synchronous converters, 115
cost, 117
motors, 165, 241
Tail-race, 96
Telephone, 161
Telluride plant, 47, 160, 169, 181
Temperature of cables, 198
rise in conduits, 198
Tensile strength of conductor metals, 201
Time-limit circuit-breaker, 152
Time relays, 152, 153
Towers, 250, 306
angle, 320
cost, 310
dimensions, 314
erection of, 316-319
heavy, 320
reliability of operation, 311
spans, 313
steel, cost, 307, 308
steel pins, 312
strain on, 324
Transformers, 122
air-blast _vs._ water-cooled, 129
artificially cooled, 129
at sub-stations, 125
blower capacity necessary to cool, 130
constant-current, 167
cooling, quantity of water necessary, 129
cost, 21, 116, 124, 134
cost of operation, 129
cost of, relative, 20
delta and star connections, 131
efficiency, 133
frequency, effect of, 116
insulation, 45
in transmission systems, 134
limiting voltage for, 32
location of, 97
polyphase, 124
regulation, 125
reserve, 149
secondary, in series, 131
single-phase, 124
two- to three-phase, 132
used to compensate drop, 133
used to regulate voltage, 162
voltages, 45
when to use, 122
Transmission, constant-current, 38, 216
constant-voltage, 40, 217
continuous-current, 31, 32
control equipment, 35
cost of, 19, 40, 222
(d. c.) cost of, 40
efficiency, 35, 41
first long line, 37
frequency, 113
generator end, 103
lightning protection, 34
limiting voltage, 44
lines, arcing, 46
calculation of, 221-232
charging current, 197
construction, 222
cost, 310
cross-arms, 49, 256
crossings, 187, 190
data from various plants, 245
effect of length on cost, 20
effect of length on cost of power, 24
efficiency, 22, 24
end strain at entries, 325
entrance to buildings, 179, 261
inductance, 206
induction, 168
insulation, 34
insulators (see Insulators), 287
insulator-pins (see Pins), 270
interest, maintenance and depreciation, 22
leakage, 47, 207, 214
length of, capacity of, population supplied, 8
lightning arresters (see Lightning Arresters), 179
lightning protection, 118
long spans, 190
loss, 22, 39
losses, 215
maximum investment in, 220
method of fastening conductors to insulators, 323
operation, 311
pole spacing, 249
regulation with synchronous motors, 241
relative weights of three-phase, two-phase, and single-phase, 228
right-of-way, 246
sag in, 309
spacing of wire, 234
steel towers (see Towers), 306
switch-houses, 238
switches, fuses, and circuit-breakers, 135
take up, arrangement for, 325
total cost of, 22
total cost of operation, 23
transposition of wires, 206, 314
voltage, 21, 215
in cables, 190
regulation, 130
wind pressure, 210
long line, 221
minimum-sized wire, 202
physical limits of, 44
a. c. pole line construction, 34
d. c. pole line construction, 33
pole lines, 246
problems, 19
regulation, 155, 239
selection of circuits, 233
single _vs._ parallel circuits, 241
spacing of conductors, 46
submarine, 187
three-phase, 113
three-phase and two-phase, 228
two-phase, 113
underground, 187
without step-up transformers, 120
Transposition of wires, 206
Turbines, high-speed, 107
horizontal, 79, 83, 89, 97
impulse, 82, 90, 99
speed of, 108
low-head good speed, 105
peripheral, speed of, 85, 103
pressure, 79
several on same shaft, 85, 105
vertical, 79, 84, 85, 86, 97
Underground cable connected to overhead line, 197
cables, 187
Victor (Colo.) plant, 26, 27, 28, 208
Virginia City plant, 118
Voltage drop compensation, 133
fluctuations, 218
high, alternators, 120
measurements, 290
in cables, 190, 196
limiting, 44
for a. c. machines, 32
for d. c. machines, 31
of transmission lines, 21, 215
regulation, 130, 155
sparking, 182
test for insulators, 289
Volts per mile, 26
Wages paid attendants, 12
Walls, 95
Washington & Baltimore Ry., 121
Washouts, 81
Water-cooled transformers, 129
Water-power, development of, 51
high head, 74-77
low head, 51-74
per cent. of energy available, 16
pure hydraulic development, 51
stations (see Hydro-electric Stations)
storage capacity, 15, 61
utilization of, 10
_vs._ steam, 5
Water, storage of, 15, 61
Weight of the conductor metals, 202
Welland Canal plant, 1, 26, 27, 28, 208, 245, 248
Westbrook (Me.) plant, 120
White River to Dales plant, 26, 27, 28, 71, 134
Wind, 324
pressure on lines, 210
Winooski River plant, 64
Wire room, 139
Wood, compressive strength of, 302
Woods for poles, 252
Yadkin River (N. C.) plant, 26, 27, 28, 118, 208
Transcriber’s Notes
This transcription uses the text of the original work.
Inconsistencies (e.g., per cent. and per cent; Chambly and Chamblay;
Garvin’s and Garvins Falls; 1-0 and 1/0 B. & S. gauge; hyphenation;
capitalisation; use of italics, etc.) have been retained, except as
mentioned below. Some of the calculations in the book give different
results to the ones provided; these have not been corrected.
In this book, “cm.” stands for circular mils, not for centimeters.
Page 76, Fig. 16: the text in the centre of the illustration
probably reads 1200 feet Pipe Line.
Page 111: between figures 44 and 46 the original book has figure
51_a_; the numbering has not been changed.
Changes made:
Obvious minor typographical and punctuation errors have been
corrected silently.
Fractions have been standardised to x/y; all occurrences of _vs._
have been italicised.
In-line multi-line formulas have been changed to single-line
formulas.
Table of Contents: the Index has been added.
page 15: table header changed to small caps as others
page 31: Electrical transmission changed to Electrical transmissions
page 56: Canon changed to Cañon
page 77: Tlaluepantla changed to Tlalnepantla
page 312: Teluride changed to Telluride
page 332: Canon changed to Cañon.