Power Plant Development and Electrical Transmission and Distribution Systems
EA-I. (G
^
eorge^
W. Rathjens)
POWER PLANT DEVELOPMENT AND ELECTRICAL TRANSMISSION AND DISTRIBUTION SYSTEMS
CONTENTS
|
|
Page
|
|
Hydroelectric Power
|
1
|
|
Transmission Lines
|
3
|
|
Electrical Distribution
|
4
|
|
Electrical Grounds
|
5
|
|
Bibliography
|
6
|
EA-I. Rathjens: Power Plant Development
LIST OF FIGURES
|
|
|
Page
|
|
Fig. 1
|
Precipitation, Fairbanks, Alaska 1904-1946.
From records Fairbanks Station U.S. Weather Bureau
|
2-a
|
|
Fig. 2
|
Temperature, Fairbanks, Alaska 1904-1946.
From records Fairbanks Station, U.S. Weather Bureau.
|
2-b
|
|
Fig. 4
|
Lifting forces from swelling of ground because of
freezing
|
3-a
|
|
Fig. 5
|
Collars or muffs around pole to assist in preventing
lifting of pole
|
4-a
|
|
Fig. 6
|
Lifting of pole because of freezing water at foot
of pole
|
4-b
|
|
Fig. 7
|
Pole anchor in permafrost
|
4-c
|
EA-I. Rathjens: Power Plant Development
PHOTOGRAPHIC ILLUSTRATIONS
With the manuscript of this article, the author submitted 4
photographs (Figs. 3, 8, 9 & 10) for possible use as illustrations.
because of the high cost of reproducing them as halftones in the printed
volume, only a small proportion of the photographs submitted by con–
tributors to Volume I,
Encyclopedia Arctica
, can be used, at most one or
two with each paper; in some cases none. The number and selection must
be determined later by the publisher and editors of
Encyclopedia
Arctica
. Meantime all photographs are being held at The Stefansson
Library.
EA-I. (G. W. Rathjens) ^✓^
POWER PLANT DEVELOPMENT AND ELECTRICAL TRANSMISSION AND DISTRIBUTION SYSTEMS
Since the problems of power development and electrical transmission and
distribution systems in the Arctic and Subarctic have much in common with
those in more temperate zones, no attempt will be made here to give a full
treatment to the problem, but rather only those phases peculiar to the
arctic and subarctic regions will be discussed.
It is first of all to be emphasized that, in these regions, solutions to
problems will vary with local conditions to a much greater extent than is
general in more temperate zones. Much of the discussion in the article
“Construction for Placer-Mining Operations” is applicable to power plant
development and electrical transmission and distribution systems. Power plant
development as used in this article contemplates the generation of electrical
energy by one or more of the following methods: (
1
) hydraulic turbines and
the development of water power; (
2
) internal-combustion engines; and (
3
)
steam turbines or steam engines (this is discussed in article “Analysis of
Design Factors for Power, Heating, Ventilating, and Refrigeration Systems
for Alaska”).
Hydroelectric Power
In the development of hydroelectric power, the extent of stream flow
which it is practical to develop requires careful and special study in each
EA-I. Rathjens: Power Plant Development
locality. The exposure of an arctic river and storage or pondage area
are extremely important. Much water will have to be stored as ice and the
exposure of such masses of ice will largely determine whether or not the
water so stored will be available when required. The writer has in many
instances seen flowers blooming on one hillside of a valley while ice was
still present in relatively large quantities on the other side of the same
valley, or over the crest of a small hill.
The amount of water stored in the moss and tundra and above the permafrost
area will not only depend upon the rainfall, character and details of the
surface and its ability to retain moisture, but also upon the timing of the
fall rains with respect to the freeze-up of the surface of the ground, moss,
or tundra, and depth of seasonal thaw with respect to the upper limits of
permafrost; also whether or not the water available in thawed lenses or
pockets of gravel in the permafrost can be used at critical seasons of the
year.
From a study of Figures 1 and 2 and Table I, it will be apparent that
storage or pondage and deep seepage present quite a different problem than in
a temperate zone, requiring careful detailed study of each individual area.
In most cases such studies will indicate that the capacity of development is
considerably less than for like stream flows and precipitation in milder
climates and that relatively large installations of supplementary or auxiliary
power will, in many cases, have to be given consideration.
In areas where permafrost and frozen much are present, any change in the
thermal equilibrium of the materials may result in releasing from confinement
large volumes of much which, because of the particle size of the solids, are
readily carried in suspension in moving water. When the water with such solids
reaches storage areas serious silting problems may result.
Fig.
25^1.^ - Precipitation, Fairbanks, Alaska 1904-1946.
From records Fairbanks Station, U. S. Weather Bureau.
Fig.
26^2.^ - Temperature, Fairbanks, Alaska 1904-1946.
From records Fairbanks Station, U. S. Weather Bureau.
^Table I^
EA-I. Rathjens: Power Plant Development
Anchor ice and ice forming on permafrost must be considered when design–
ing intakes. Such ice is frequently released in large blocks, carrying with
it sand and gravel.
^
[:
3 we be hold is used.
]^
It must be borne in mind that the capacity of pipes and other similar
hydraulic structures may be materially reduced by the formation of ice on
the interior walls. Figure 3 illustrates a 60-inchs pipe which collapsed
during cold weather. An ice plug had formed at the intake and when one of
the lower valves was opened to drain the pipe, portions of the pipe collapsed
because the provisions for admitting air into the pipe failed to work.
Transmission Lines
In designing transmission lines (pole or tower) for the distribution of
electrical energy in areas where permafrost is present, especially if the
permafrost extends upward so it makes contact or nearly a contact with the
lower limit of seasonal thaw, additional factors other than those usually
evaluated in the development and design of transmission lines should be given
consideration.
The reconnaisance survey for a line should include an investigation of
(
1
) the character of the cover which acts as an insulator to the permafrost
immediately below such cover, (
2
) the depth of seasonal thaw, (
3
) the character
and packing of the materials in place, immediately above the upper limit of the
permafrost, (
4
) the relationship between freeze-up and rainfall, and (
5
) the
general characteristics of the terrain, giving special attention to the possible
movement of water on the surface in the zone of seasonal thaw and the zone
between the seasonal thaw and permafrost.
The freezing and swelling of the materials in the “frost zone” may develop
forces which tend to lift a pole as illustrated in Figure 4. The effect of
Fig.
29^4.^ - Lifting forces from swelling of ground because of freezing.
EA-I. Rathjens: Power Plant Distribution
^
[:
]^
such lifting forces can be materially reduced by placing collars or muffs
^
Fig. 5^
around the pole as illustrated in Figure 5 or by providing a weak or slip
plane around the pole.
In the setting of poles, consideration must be given to the surface
water as indicated by arrows in Figure 6, and the groundwater from
b
which
may seep along the contact between the pole and the ground until it reaches
the foot of the pole where it freezes, lifting the pole. Successive layers
of ice at the foot of the pole results in successive lifting of the pole.
Adhesion between a pole and permafrost may be assisted, to overcome the
^
Fig. 6, 7^
lifting force
a
(Fig. 6), by fastening an anchor near the base of the pole
in the permafrost as illustrated in Figure 7. Where this construction is
used, care must be taken when back-filling the excavation to avoid the
development of a contact surface at
a
(Fig. 6), which may permit the migration
of groundwater. Wherever practical, the writer recommends that this type of
anchorage be avoided.
In the Arctic, tripod construction over the tundra has been effectively
used for temporary and semipermanent telephone lines where first cost and
time are the governing factors. This construction is especially applicable
in areas where small native timber is available.
In using tripod construction at angle points, it may be advisable to
suspend a rock or basket of rocks from the tripod or from the legs of the
tripod in order to assist in the prevention of overturning. The tripods are
usually
set on the tundra
during cold weather when the surface is frozen.
Electrical Distribution
Consideration must be given to the large range of temperatures in the
Arctic in the calculation of sags and spacing of wire when designing electrical
Fig.
30^5.^ - Collars or muffs around pole to assist in
preventing lifting of pole.
Fig.
31^6.^ - Lifting of pole because of
freezing of water at foot of pole.
Fig.
32^7.^ - Pole anchor in permafrost.
EA-I. Rathjens: Power Plant Distribution
distribution lines. Because of the high cost of properly preparing foundations
and maintaining them, long spans are indicated. Large temperature ranges re–
sulting in relatively great sags require careful consideration of resulting
tensions (1; 2; 3; 4).
Careful study of local weather conditions in any particular area is
recommended because wind and ice conditions vary greatly in different section.
The writer has experienced local winds in Greenland which were greater than
any winds of which he has knowledge in either the temperate zone or Alaska.
When investigating the corona limit of high-tension lines in the Arctic, the
investigation should not be limited to the fair-weather value. Local and
seasonal conditions at which it will operate should be considered.
Electrical Grounds
In permafrost areas the grounding of electrical equipment is not as
readily accomplished as in a temperate zone. It has been the writer’s prac–
tice, wherever practical, to carry the grounds to a zone of assured and
continuous groundwater movement; otherwise, the system was treated as
ungrounded.
EA-I. Rathjens: Power Plant Development
BIBLIOGRAPHY
1. Copperweld Steel Company, Glassport, Pa.
Sags and Tension Charts for
Conductors in Overhead Lines
.
2. General Electric Company. “Performance charts for 60 cycle transmission
lines,”
Gen.Elect.Rev
. Oct., 1932.
3. Graybar Electric Company.
Calculations by Direct Use of the Catenary
Curve
.
4. Pender, Harold, and DelMar, William.
Handbook for Electrical Engineers
.
N.Y., Wiley, 1922.
G
.
^
eorge^
W. Rathjens