HomeMy WebLinkAboutKate Petersburg Overhead Underground Reconnaissance Report 1983=. 2
KAKE-PETERSBURG INTERTIE
OVERHEAD/UNDERGROUND
RECONNAISSANCE REPORT
EBASCO
EBASCO SERVICES INCORPORATED
NOVEMBER 1983
KAKE-PETERSBURG INTERTIE
MIXED OVERHEAD/UNDERGROUND TRANSMISSION LINE
RECONNAISSANCE REPORT
SUBMITTED TO
ALASKA POWER AUTHORITY
BY
EBASCO SERVICES INCORPORATED
NOVEMBER 1983
TABLE OF CONTENTS
Page
1. INTRODUCTION. 2... ee ee ee 1-1
1.1 ISSUES TO RESOLVE . 2... 2.2... eee ee eee 1-1 1.2 APPROACH. 2... ee ee ee 1-3
2. MAJOR FINDINGS... . 2... 2. ee ee ee eee |
2.1 PREFERRED CORRIDOR... .... 2... 22 eee eee 2-1
2.2 CONSTRUCTABILITY/COST PREFERENCE... ...... - + 2-2
2.3. CABLE SELECTION . . 2... . eee eee ee eee 2-5
2.4 ROUTE SELECTION ... 1... 2... 2 eee ee eee 2-8
2.5 COST OF PROPOSED SYSTEM ..... 2... 2. ee eee 2-8
3. TECHNICAL STUDIES ... 2... 2. ee eee ee ee eee - 3-7
3.1 ROUTING STUDIES . 2... 2... ee ee ee ee eee 3-1
3.2 GEOTECHNICAL CONSIDERATIONS .... 2... 2.2.2 eee 3-12
3.3 ELECTRICAL... 2... 2 2 eee ee ee ee ee 3-16
3.4 COST ESTIMATES AND INSTALLATION TECHNIQUES... ... 3-36
4. ENVIRONMENTAL CONSIDERATIONS... 2... 2.222 ee eee 4-1
5. CONCLUSIONS AND RECOMMENDATIONS .... 2... 2... ee. 5-1
APPENDIX A — SUMMARY OF UNDERGROUND CABLE INSTALLATION EXPERIENCE
ON THE ILLIAMNA PROJECT
APPENDIX B — CONTACT REPORT WITH ALASKA DEPARTMENT OF TRANSPORTATION
AND PUBLIC FACILITIES
APPENDIX C — MIXED OVERHEAD/UNDERGROUND TRANSMISSION LINE ROUTE DATA
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3-1
3-3
3-4
LIST OF TABLES
UNDERGROUND TRANSMISSION LINE PRE-FEASIBILITY LEVEL COST ESTIMATE
CAPACITIES OF NON-RETURNABLE CABLE REELS
CABLE DATA (2/0 COPPER CABLE)
CABLE DATA (4/0 COPPER CABLE)
LOSSES AND VOLTAGE DROPS
LIST OF FIGURES
EXISTING AND PLANNED ROADS
TRANSMISSION LINE STUDY CORRIDORS
TRANSMISSION LINE ROUTE
TYPICAL SIDEHILL SECTION
LOAD FLOW DIAGRAMS
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2-10
3-18
3-31
3-32
3-35
3-6
3-1
3-15
3-20
through
3-29
1 INTRODUCTION
A preliminary report submitted to the Alaska Power Authority in late
July, 1983 concluded that the underground alternative for the Kake-
Petersburg project was technically viable and offered the potential to
be less costly than the overhead route. In mid-August, 1983 the Power
Authority authorized a reconnaissance level study of the underground
alternative intended to assess the viability of constructing an
entirely underground or mixed overhead/underground transmission line
from Petersburg to Kake. Specifically, the requested study was to
recommend whether to proceed with the feasibility level study of the
Kake-Petersburg alternative and, if so, to identify whether the north
or south corridor should be the subject of detailed study. This report
presents the results of Ebasco Services Incorporated's (Ebasco)
reconnaissance level study of the underground alternative.
1.1. ISSUES TO RESOLVE
Several issues emerged as being important in determining whether to
proceed with the feasibility level analysis of the underground option.
The two most important factors in reconnaissance level evaluation are
cost and constructability. The cost factor is of obvious importance in
the analysis of the underground alternative, because the merit of
further study of the underground option will largely be dependent on
the facilities' projected cost. The cost analysis on the underground
option takes on particular importance because there is virtually no
experience with the installation of underground cables of the length
contemplated in remote areas experiencing conditions similar to those
in the Kake-Petersburg area. These factors require that special effort
be devoted to the establishment of a reasonable cost estimate for this
reconnaissance level investigation. An accurate analysis of the cost
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of the underground option is also important because the optimal mixed
overhead and underground system needs to be identified in this
reconnaissance level study. Therefore, estimates of underground
options must draw on cost estimates in the feasibility report for the
overhead alternative in order to determine the optimal alternative in
the present analysis.
The second factor, constructibility, is closely related to cost
considerations but is appropriately considered as a second factor
because the construction question has three components. First, the
basic question of whether an underground line can be economically
constructed in the Kake-Petersburg area must be assessed. This
fundamental question requires analysis of conditions in the
Kake-Petersburg area as well as the technology available for installing
cables in remote areas. The second factor involves determining the
best location for an underground cable. On the Kake-Petersburg
project, this question must be considered in determining which corridor
should be recommended as well as where within the selected corridor the
route should be located. For example, if the south corridor is
determined to be the preferred one, it remains to be determined whether
it is better to construct in unroaded muskeg areas or unroaded forested
areas within the south corridor. Finally, the constructibility
question has a great influence on the overall cost of the project. The
constructibility analysis should enable a meaningful cost estimate to
be developed, as well as a characterization of the relative confidence
of such an estimate.
The issues identified above are resolved in subsequent sections of this
report. Following this introduction, the general approach employed in
this reconnaissance level investigation is described in Section 1. The
major findings, as they affect the decision about whether to conduct
further studies of the underground option, are highlighted ina
separate section, Section 2. Section 3 presents the technical studies
which support the major findings and recommendations. Technical
studies for geotechnical, electrical, environmental, and cost
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estimating are described in Section 3 and support the conclusion and
recommendation in Section 4. In summary, this report addresses whether
an underground or mixed overhead and underground system should be
studied further and whether such a facility should be located in the
north, south, or other potential corridors linking Kake and Petersburg.
1.2 APPROACH
In order to achieve the study objectives and resolve the issues
identified above, Ebasco employed a nine-step process. These steps
include:
review new and existing information
field analysis
preliminary cable selection
select corridor
identify preliminary route
select optimal overhead/underground system
final cable selection and power system analysis
finalize cost estimate oocmUCchOUCchOUCOOUCOUCOUCUCOUCUCO submit report including recommendation on whether to proceed
with further studies
Review new and existing information: The previously submitted Draft
Feasibility, Routing and Environmental, and Cost and Engineering
Reports contain information used in the assessment of the underground
alternative. In addition, during the review of the previous reports,
information was provided regarding several factors which could affect
the analysis of the underground option. Forest Service information on
construction practices and the proposed additions to the road system in
the Kake area as well as experiences on the Iliamna project (see the
appendix to the Preliminary Report which appears as Appendix A of this
report) are examples of the type of information requiring review.
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Field analysis: Field analysis by Ebasco construction personnel was
undertaken to assess the constructibility of the project and provide
information to the corridor and route selection process. Also during
the field analysis, agencies were contacted regarding the underground
alternative and maps and drawings containing information on local
conditions, as well as planning and design activities, were obtained
during such consultation activity.
Preliminary cable selection: Relatively early in the reconnaissance
level investigation, a preliminary evaluation was made of the type of
cable most appropriate for the project. Such a selection was needed in
order to evaluate what type of equipment would be needed for
construction and to determine what areas are best suited for the
particular cable proposed for use on this project. This preliminary
evaluation was then reexamined as a part of this study as described in
Section 3.3.
Select corridor: In the previous feasibility studies, two corridors, a
north and south corridor, were identified. Subsequent information
provided the impetus to look at modifications or additions to the two
corridors. Modifications would be needed in the Kake area so that an
alternative following the north corridor could take full advantage of
the existing and proposed roads near Kake. New corridors considered
included the Petersburg and Duncan Creek corridors, which were
identified as possibilities during the review of the feasibility study,
and new corridors combining portions of the north and south corridors
linked by routes paralleling Duncan Canal.
Identify preliminary route: Once the corridor was selected, a route
was identified within that corridor. Such route information was
developed in order to prepare a cost estimate for the underground or
mixed overhead/underground alternative.
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Select optimal overhead/underground system: Previous studies assessed
the cost of an overhead transmission line between Petersburg and Kake.
This reconnaissance level study considered these earlier findings along
with information on the cost of the underground option in formulating
its recommendation on the optimal overhead/underground system.
Final cable selection and power system analysis: Power system studies
are needed to finalize the cable selection process and verify that the
proposed system will be functional. System studies were used to modify
earlier conclusions regarding cable selection and routing of the
proposed line. The optimized system developed as a result of the load
flow analysis provided information used in the cost analysis.
Finalize cost estimate: Previous cost information along with extensive
contacts with vendors and operators knowledgeable in the installation
of underground cable were required to accurately develop reconnaissance
level costs for the Kake Petersburg project. Therefore, considerable
attention was focused on the cost estimating question and developing
enough information to estimate costs with confidence.
Submit report: The final activity in the reconnaissance analysis is to
prepare this report which summarizes findings and recommends whether to
proceed with feasibility level studies.
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2 MAJOR FINDINGS
Ebasco engineers conducted field investigations, contacted cable
suppliers and cable installation contractors, and completed independent
analyses of the viability of constructing an underground transmission
line from Petersburg to Kake. These investigations largely focused on
resolving issues identified in Section 1 of this report. The major
findings resulting from these investigations are reported in this
section. The technical studies which led to these findings, are
described in Section 3, Technical Studies.
2.1 PREFERRED CORRIDOR
Two corridors had been identified in the early stages of the
feasibility report for a proposed overhead transmission line from
Petersburg to Kake. The two corridors, known as the north and south
corridors, were re-analyzed in order to determine their relative
suitability for an underground cable. The corridors considered were
reevaluated in light of information provided by the Forest Service
concerning plans for roads to be constructed in 1984. Other
alternatives, including routes through Duncan Portage and along
Petersburg Creek, were also evaluated as were combinations of north and
south corridor routes linked by segments paralleling Duncan Canal.
The results of these investigations of potential underground routings
led to the finding that the south corridor was preferred for an
underground or mixed overhead/underground transmission line. The south
corridor is preferred because installation of an underground cable
would be easier and less costly in the south corridor than within other
corridors considered. The south corridor was also preferred for the
overhead line as described in the previously prepared feasibility
report. When the proposed Forest Service road extending to within two
miles of the pass between Kake and Duncan Canal is completed, the
majority of a routing within the south corridor would be along existing
roads.
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The main advantage of the other primary corridor considered, the north
corridor, would be that it would eliminate the need for a submarine
crossing of Duncan Canal. This potential advantage is more than offset
by the presence of existing roads within the south corridor and the
fact that the slopes along Frederick Sound within the north corridor
‘are rocky and poorly suited for construction activities.
The south corridor is also preferred to other corridor options,
including corridors which would go along Petersburg Creek, along Duncan
Creek, or parallel to Duncan Canal. The Duncan Portage corridor would
cross far more unroaded areas than the south corridor and would not
eliminate the need for an underwater crossing of Duncan Canal unless an
underground line is built northward along Duncan Canal toward Portage
Bay. Such a corridor paralleling Duncan Canal would add over ten miles
of length to the line and would cross portions of the Petersburg
Creek-Duncan Salt Chuck Wilderness Area and is not preferred. A
corridor along Petersburg Creek through the Petersburg Creek-Duncan
Salt Chuck Wilderness Area, although shorter than any of the other
alternatives considered, would involve construction of over 20 miles of
line in unroaded areas. Further, construction conditions in the
wilderness area would be difficult and the regulatory obstacles
associated with attempting to construct a line within this corridor
would be significant. In fact, it would literally take an act of
Congress to approve a route along Petersburg Creek.
2.2 CONSTRUCTABILITY/COST PREFERENCE
In order to select an optimized routing and facility configuration, the
relative cost and constructability of various alternatives were
assessed. Both overhead and underground construction in roaded and
unroaded areas were considered. Typical per mile costs were developed
and used in identifying the optimal route within the south corridor.
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There are six facility configurations (not including underbuilding on
the Tyee Lake line) possible for the portions of the proposed route
between Petersburg and Kake. Each of the types of conditions are
described below, along with an estimate of the cost of the various
alternative designs. In reviewing the cost information, it should be
emphasized that these data have been included primarily to enable a
relative comparison of the available alternatives. The absolute
accuracy of these cost numbers is discussed in more detail in
Section 3.4 and more precise numbers will be developed at the
feasibility level study, if authorized by the Alaska Power Authority.
In the present analysis, all costs are in October, 1983 dollars.
2.2.1. Underground Line Along Road
The least expensive construction option identified is to construct an
underground transmission line along or within an existing logging
road. This option is least expensive because it does not require the
purchase or installation of wood poles and associated hardware or any
clearing. There is considerable experience in the use of vibratory
plows and trenching equipment for installing underground cable along
roads. Production rates along roads are generally good (up to 6,000
feet per day) but there is a large amount of uncertainty regarding the
feasibility of installing cables within the roads in the Kake area
because of the large quantities of shot rock used in those roads.
Nevertheless, it is estimated that construction costs for an
underground cable along existing roads would be approximately $65,000
per mile.
2.2.2 Overhead Line Along Road
Construction of an overhead transmission line along an existing road is
the standard method of constructing transmission lines of the voltage
contemplated for the Kake-Petersburg project. Advances in underground
cables and cable installation equipment has reduced the economic
advantage overhead lines (as compared to underground lines) have in the
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future in many areas and findings suggest that the underground cables
will cost less than an overhead line for the Kake- Petersburg project.
On the Kake-Petersburg project, the overhead line is more costly than
the underground option because of the clearing required and because of
the relatively remote location of the project. Typical per mile costs
of an overhead line along an existing road on the Kake-Petersburg
project are approximately $80,000 per mile.
2.2.3 Underground Lines in Unroaded Muskeg Areas
There has been virtually no cable installation work across extensive
distances of muskeg. Contacts with contractors who have worked in
muskeg areas and cable installation equipment manufacturers have
provided information to indicate that constructing a transmission line
in large expanses of unroaded muskeg areas is both possible and
relatively economical. Experience with the installation of drainage
pipe in peat bogs as well as wide pad equipment in muskeg areas suggest
that approximately 4,000 feet per day of cable can be installed in
muskeg areas. Moreover, there is relatively little clearing required
in muskeg areas, further reducing cost. Consequently, in spite of the
fact that unroaded muskeg areas pose logistical problems, it is
estimated that typical sections of underground cable can be installed
in muskeg areas for approximately $70,000 per mile.
2.2.4 Overhead Lines in Unroaded Muskeg Areas
With proper precautions heavy overhead transmission line installation
equipment can be transported across muskeg areas. In addition,
considerable experience exists regarding the use of special planking
and other materials to secure individual wood pole structures in muskeg
areas. The cost of installing these lines, however, is high because of
the access problems and the need for extra materials to support
structures in these weak soil conditions. There is also relatively
little clearing for an overhead line crossing a muskeg area.
Consequently, the estimated typical per mile cost for an overhead line
crossing a muskeg area is approximately $170,000 per mile.
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2.2.5 Underground Line in Unroaded Forested Areas
Along with eliminating the need to transport and install wood
transmission line poles in remote forested areas, underground
transmission lines offer another significant advantage. Clearing in
unroaded forested areas for an underground line will only require that
amount of clearing necessary to accommodate the operation of cable
installation equipment. It is estimated that only a 10-15 foot wide
right-of-way would be required. Risk associated with the installation
of underground cable in unroaded forested areas is associated with the
uncertainty surrounding geotechnical conditions in these areas.
Installation costs for an underground cable are substantially higher if
hard rock is encountered close to the surface. Recognizing that there
is a high degree of variability depending on the subsurface conditions,
typical per mile costs for an underground cable in unroaded forested
areas would be approximately $95,000 per mile.
2.2.6 Overhead Line in Forested Areas
Along with construction problems encountered in constructing an
overhead line in remote areas, significant additional costs are
incurred in unroaded forested areas due to clearing. The clearing
required varies depending on the line's voltage and type of overhead
facility proposed. Along with the actual right-of-way clearing, there
is a requirement to remove danger trees from the areas adjacent to the
transmission line. The cost of falling and removing these danger trees
can be quite high. Consequently, the average typical cost for overhead
construction in unroaded forested areas is approximately $140,000 per
mile. This cost does not include removing logs from remote areas of
the right-of-way.
2.3 CABLE SELECTION
Single phase cable with cross linked polyethylene (XLP) insulation and
jacketed concentric neutral was selected in these studies for the
following reasons.
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In the past few years cables with extruded insulations have been used
almost exclusively for voltages up to 35 kV. Three kinds of insulation
have been used: cross-linked polyethylene (XLP), high molecular weight
polyethylene (HMWPE), and ethylene propylene rubber (EPR). Experience
indicated that HMWPE has a much higher failure rate than XLP and,
therefore, has been abandoned by utilities. However, in recent years
new developments in HMWPE insulation took place and recent
installations indicate that HMWPE insulation may have a lifetime
comparable to that of the XLP insulated cables. Another insulation
that is also used is ethylene propylene rubber (EPR). This insulation
has very good qualities; however, it is more expensive than either XLP
or HMWPE. As there are very little operational data available with
other than XLP, our studies considered XLP cable data exclusively.
The XLP insulation is directly extruded onto the copper or aluminum
conductor. Extruded on top of this is an insulation shield. Outside
of the insulation are the concentric copper neutral wires, in the sizes
considered for the Kake-Petersburg transmission system around a dozen,
helically placed. Outside of these neutral wires is a tough jacket
extruded which protects the neutral both mechanically and from
corrosion.
Cables are available both in single phase and in three phase
arrangements. However, discussion with contractors and utility
officials revealed that the handling of the three phase cable is so
much more difficult, because of its stiffness, that presently the vast
majority of the installations are of three single phase cables. This
holds particularly on installations where the cable is ploughed into
the ground. Based on these recommendations, the use of 3 (or 4) single
phase XLP insulated cables is recommended.
Once the routing is finalized, and the soil conditions along the route
and geological conditions become known, the cable selection can be
reviewed and reconsidered. However, the results of this study are not
affected by the kind of insulation which would be used.
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In recent years cable manufacturers have added tree retardant compounds
and rodent repellent additives. Introduction of these further enhances
the reliability of the cables.
In the Pacific Northwest the average utility experience is that, with
XLP insulated cables in the 25 kV class, one can expect approximately
10 years between mean failures for every 100 conductor miles.
Translating this to the Kake-Petersburg transmission line, with fully
undergrounding the 50 miles means about 7-1/2 years between failures.
It should be noted that experience indicates that if failure does not
occur during the first 24 hours, failures rarely occur later. As the
preceding figure includes many cables installed over the past 25 years,
it is expected that recently manufactured cables will show longer times
between failures.
There is one more point which has to be stressed. The cable statistics
available are for the Pacific Northwest, where the temperatures can be
quite extreme between summer high and winter low. In addition, many of
those cables carry the peak load during the summer air-conditioning
peak.
Unlike these cables, the Kake-Petersburg transmission system would be
loaded only to a fraction of its current carrying capacity (ampacity).
For example, a 2/0 copper conductor cable with 260 mil XLP insulation
can carry 311 amperes at 90°C conductor temperature at 20° ambient.
This has to be compared to the 41.7 ampere load current which the
1.8 MVA load at Kake at 24.9 kV represents. The latter, which is the
full load current at end of the project life, is only 21% of the 311
ampere ampacity mark. As the heat generated inside the cable is
proportional to the square of the current, the actual heat generated
inside the cable at full load will be (0.21)2 = 0.044 or 4.4%. As
the temperature rise at full ampacity is 70°C, one can expect less than
5°C, more likely only 3°C, temperature rise of the conductor during
peak loading at the end of the project life.
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This low temperature rise means that the insulation will practically be
at constant temperature, i.e., around the mean annual area temperature,
and therefore the expected mean time between failures should be much
longer than that experienced by the utilities in the Pacific Northwest.
2.4 ROUTE SELECTION
In accordance with the factors presented in Section 3.1, the south
corridor is the preferred alignment for the mixed overhead/underground
transmission line corridor. After the south corridor was identified as
the preferred one, routing studies were conducted within that corridor
in order to determine the optimal route for a transmission line. The
determination of the proposed route within the transmission line
corridor considered the typical per mile cost information presented in
Section 2.2. Efforts were made to optimize the mix of overhead and
underground transmission line links so that the overall, least cost
route could be identified. Because the south corridor route generally
follows existing or proposed roads, locating a route within the
preferred south corridor was relatively straight- forward, except for
the portion of the route west of Duncan Canal and east of the end of
the proposed Kake road system. For the portion west of Duncan Canal,
air photo analysis was conducted and an alignment selected which
largely followed muskeg areas. The overall length of the proposed
mixed overhead/ underground transmission line is 52 miles. The
selected route includes 2 miles of submarine and 45 miles of
underground cable. It also includes approximately 5 miles of
underbuild construction on the existing Tyee Lake line.
2.5 COST OF PROPOSED S/STEM
The estimated cost of the proposed mixed overhead/underground system is
$8,100,000. A summary of the estimate is presented in Table 2-1. This
prefeasibility level cost estimate is based on typical conditions as
described in Section 2.2 and 3.4 and on the assumption that the
proposed transmission line will be completed after the road from Kake
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aS toward the pass between Kake and Duncan Canal is completed. For
comparison purposes, the estimated cost of an overhead transmission
line, as reported in the Draft Feasibility Report for the overhead
line, escalated to October 1983 dollars, is approximately $10.4 million.
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TABLE 2-1
UNDERGROUND TRANSMISSION LINE
PRE-FEASIBILITY LEVEL COST ESTIMATE
Unit Quantity Unit Price Amount
Land and Land Rights LS 20,000
Substation (incl. reactors) LS 566,000
Overhead (along road)~/ MI 4.95 $ 64,240 318,000
Submarine cable?’ MI 1.59 824,530 1,311,000
Underground (Muskeg) 2” MI 9.32 70,170 654,000
Underground (Roads) 2/ MI 31.05 65,090 2,021,000
Underground (Glacial Tiny2/ MI 5.22 77,200 403,000
Clearing MI 16.79 16,320 274,000
Labor Camp LS 348,000
Mobilization/Demobilization LS 295,000
Subtotal (1983 dollars) 6,210,000
Contingency (20%) 1,240,000
Professional Services LS 625,000
Total (excluding AFUDC) 8,075,000
Rounded Amount 8,100,000
1/ Underbuild on existing line
2/ Unit of measure of miles is line miles, not cable miles.
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3 TECHNICAL STUDIES OF THE KAKE-PETERSBURG INTERTIE
RECONNAISSANCE LEVEL REPORT
Technical studies are categorized in four major areas including:
routing
geotechnical
electrical ooo 08 cost estimates and cable installation techniques
Studies within these categories led to the major findings presented in
Section 2. The results of the technical studies are described in the
following subsections, each addressing important considerations in the
four categories identified above.
3.1 ROUTING STUDIES
Routing studies conducted in conjunction with analysis of the mixed
overhead/underground option consisted of alternative corridor
evaluations and subsequent identification of routes within the selected
corridor. Each facet of the routing studies are described separately
below.
3.1.1 Alternative Corridor Evaluating
Two routing corridors for overhead transmission lines were identified
in the Draft Feasibility Report for the Kake-Petersburg Intertie
project. These two corridors known as the north and south corridors
were evaluated as to their suitability for an overhead transmission
line. During the investigation of underground alternatives, new issues
emerged as being important in determining the optimal route for an
underground or mixed overhead/underground transmission line route.
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The most important new routing consideration was to seek areas for the
cable where it could be easily plowed into the ground. Relatively deep
organic soil (greater than 3 feet) or other loosely consolidated material
are most preferred for cable installation. Conversely, installing
underground cables in rocky areas is extremely difficult and costly and
avoiding rocky areas is of far greater importance for an underground
cable than for an overhead transmission line. The underground cable,
which requires less clearing, also has the advantage of having less
environmental impact than an overhead line. Consequently, less
consideration need be given to avoiding environmentally sensitive areas
for an underground cable than for an overhead line.
Another new issue related to the studies described in this report
includes the consideration of road building plans of the U.S. Forest
Service and Alaska Department of Transportation and Public Facilities.
Current road building plans of these organizations were obtained during
contacts in September and October 1983 and were incorporated into the
analysis of routing alternatives. Contact with the Alaska Department of
Transporation and Public Facilities led to the finding that there are no
immediate plans for constructing a road from Petersburg to Kake and it is
unlikely that funding will be available for such a road within the next
five years. Information obtained from the Forest Service, however,
revealed plans to construct several new roads within both the north and
south corridors. These roads are shown on Figure 3-1 with particular
emphasis given to those roads anticipated to be constructed in 1984.
Since the timing of construction on many of these roads is tied to timber
harvesting contracts, the exact date construction will be completed is
difficult to estimate.
Of particular importance to this study are the roads planned in the north
corridor, beginning near Hamilton Creek and the road extending southeast
from the end of the existing Kake road system toward the pass between
Kake and Duncan Canal. The road beginning at Hamilton Creek is currently
under construction while the road extending southeast toward the pass is
to be constructed as a part of the North Irish Timber Sale. The North
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ALASKA POWER AUTHORITY
KAKE-PETERSBURG INTERTIE OVERHEAD/UNDERGROUND eer PROPOSED ROADWAY RECONNAISSANCE REPORT
LEGEND
a rnd EXISTING ROADWAY
mesememe TO BE COMPLETED IN 1984 : ft game (lla 3
EBASCO SERVICES INCORPORATED
Irish Timber Sale was sold several years ago so, consequently, the road
could be constructed at any time. The actual construction date,
however, depends to a certain extent on timber market conditions which
currently are depressed, thereby deferring the likely construction date
past 1984. For the purposes of estimating costs on this project, it is
assumed the underground cable will be installed after the proposed road
is constructed.
Although certain new issues emerged as being important when considering
the new underground transmission line option, several important factors
in locating an overhead transmission line are also important in
determining the best location for an underground or mixed overhead/
underground transmission line. These factors include the high
desirability associated with paralleling existing roads, thereby
reducing cost, environmental impacts and construction difficulties.
Also important in routing both overhead and underground transmission
lines is the high desirability associated with avoiding rugged
terrain. Mobilizing construction activities in such areas is difficult
and can be costly. Finally, although environmental constraints for
locating an underground transmission line are less than those
associated with an overhead transmission line, there is still a need to
avoid environmentally sensitive areas with an underground transmission
line. Soil disturbance associated with an underground transmission
line will be greater than for an overhead transmission line in spite of
the fact that, in general, impacts will be far less for an underhead
line.
In light of the similarities and differences associated with evaluating
the underground transmission line alternative, it was determined that
the first step to be taken in evaluting underground alternatives would
be to review previous studies and site conditions in light of the
requirements for constructing an underground transmission line.
Consequently, a transmission line construction specialist visited the
project area and conferred with Forest Service and other local
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engineers and contractors regarding conditions along the potential
corridors linking Petersburg and Kake. Information gathered on the
constructability site visit together with a review of previous studies
in the project area determined that it was appropriate to consider the
two previous corridors identified (north and south corridors),
incorporating modifications into routings, and to evaluate several
other corridors for possible use by an underground transmission line.
The results of routing studies in the north, south, and other corridors
are presented below while the location of these corridors is shown in
Figure 3-2.
3.1.1.1 North Corridor
Two major issues concerning the north corridor transmission line option
have arisen since completion of the Draft Feasibility Report. First,
the scheduled construction of a major portion of a road potentially
linking Petersburg and Kake (see Figure 3-1) in 1984, suggested that
the north corridor might be better suited for an overhead or
underground transmission line than previously concluded. Use of the
north corridor would also reduce the need for one submarine cable
crossing, aS compared to the south corridor, because it would not
involve a crossing of Duncan Canal. The second major finding concerned
the constructability of the north corridor, particularly as it relates
to the section along Frederick Sound. The field review of this area,
as well as discussions with personnal familiar with the shore along
Frederick Sound, concluded that construction of either an overhead or
underground transmission line in this area would be extremely costly.
Underground construction would be prohibitively expensive because of
shallow bedrock and steep slopes. An overhead line would also be
difficult to construct in the area because of similar factors.
Further, environmental considerations make construction of either an
overhead or underground transmission line in the portion of the north
corridor along Frederick Sound difficult.
3-5
4973B
VE
LEGEND
gee ges OTHER CORRIDORS CONSIDERED
KAKE-PETERSBURG INTERTIE OVERHEAD/UNDERGROUND RECONNAISSANCE REPORT
TRANSMISSON LINE STUDY
CORRIDORS FIG 3-2
EBASCO SERVICES INCORPORATED
Although construction of a transmission line along Frederick Sound
would be difficult and expensive, it is recognized that if a road were
constructed in this area, transmission line costs associated with
either the overhead or underground option would be substantially
reduced. Therefore, the Alaska Department of Transportation and Public
Facilities was contacted to determine the likelihood of development of
a road in this area. As a result of this contact (see Appendix B), it
was concluded that a road would not likely be constructed along
Frederick Sound for at least the next five to ten years. In light of
these concerns, as well as the concerns described in the Draft
Feasibility Report, it was concluded that the north corridor routing
contained significant disadvantages for the proposed transmission line
linking Petersburg and Kake.
3.1.1.2 South Corridor
The south corridor was identified as the preferred one for an overhead
transmission line from Petersburg to Kake in the Draft Feasibility
Report. The primary reason for its selection was the fact that, of the
alternatives considered, it offered the greatest opportunity to
parallel the existing roads; the cost of an overhead line along
existing roads is substantially less than for overhead lines in
unroaded areas. The primary disadvantage of the south corridor is the
fact that two submarine cable crossings are required; one at Wrangell
Narrows and the other at Duncan Canal. Another drawback of locating a
route within the south corridor is the need to cross a pass between
Duncan Canal and Kake. The elevation of this pass, 700 feet above sea
level, is the highest point of any of the alternatives under
consideration. There are, however, several features of this route
which make it better suited for an underground line.
The relatively large expanse of muskeg on the west side of Duncan Canal
provides a considerable area with relatively high suitability for use
of underground cable. Further, information obtained from the Forest
Service also indicates that there are plans to construct a road
3-7
4973B
southeast from the existing road end near Big John Creek toward the
pass between Duncan Canal and Wrangell Narrows crossed by the south
corridor (see Figure 3-1). Extension of this road would reduce
construction costs and the overall length of unroaded area which would
be transversed by the transmission line. Extension of this logging
road would reduce the costs associated with constructing either an
overhead or underground transmission line from Petersburg to Kake. In
general, the south corridor is favorable for constructing an
underground or mixed overhead/underground transmission line.
3.1.1.3 Other Corridors
Figure 3-2 identifies four other general corridors which were evaluated
for use by an underground cable linking Petersburg and Kake. The first
one involves paralleling Petersburg Creek across the Duncan Canal-
Petersburg Salt Chuck Wilderness Area and offers the apparent advantage
of having the shortest overall distance from Petersburg to Kake. It,
like the north corridor, would also only require one submarine cable
crossing. This alternative, although offering apparent advantages, has
a significant disadvantage in that there are large segments of unroaded
areas to which access would be difficult and in which construction
would be costly. Of its estimated total length of 44 miles,
approximately 17 would be in an area which is unroaded. Moreover, the
area is unroaded in part because it is within the National Wilderness
Preservation System and requires special presidential and congressional
action if any portion of it is to be used for a transmission line
corridor. Because of the problems of obtaining the necessary approval
for use of this corridor, it is doubtful whether approval could be
obtained in an expeditious manner, if at all. The fact that
alternatives exist which are comparable in cost suggest that it would
be ill-advised to seriously pursue a routing through the Petersburg
Creek-Duncan Salt Chuck Wilderness Area.
The second corridor considered involves crossing Wrangell Narrows
adjacent to the town of Petersburg and then heading west and north to
Kake. This corridor would follow Duncan Creek west toward Duncan Canal
4973B
and then proceed north through a portion of the Petersburg Creek-Duncan
Salt Chuck Wilderness Area. This route has the disadvantage of
crossing primarily unroaded, forested areas. Construction of a line
within it would be more costly than constructing a line in the south
corridor. Because the Duncan Portage route also crosses the Petersburg
Creek-Duncan Salt Chuck Wilderness Area all the ensuing environmental
and regulatory problems would also be anticipated.
The final two routing alternatives considered, combine portions of the
north and south corridors. The first of these would follow the south
corridor to Duncan Canal and then proceed north along the east shore of
Duncan Canal to a point where it would rejoin the north corridor. This
route would take advantage of the existing road system on the
Lindenberg Peninsula and would follow the proposed road system into
Kake from the area near Portage Bay. This corridor was considered and
not recommended because of the relatively large unroaded area which
would be crossed by the underground cable. From the end of the road on
the Lindenberg Peninsula north to the proposed road near Portage Bay is
approximately 20 miles. Moreover, there is considerable clearing
required to provide access for underground cable installation
equipment. Consequently, the cost of this alternative would be higher
than that along the south corridor. Another alternative corridor
considered followed the south corridor through the crossing of Duncan
Canal and the proceeded north following muskeg areas toward the
Proposed extended Kake road system. This alternative, which avoids the
pass between Duncan Canal and Kake crossed by the south corridor, has
several distinct disadvantages. First, its total length is
approximately 65 miles of which approximately 15 are in unroaded
areas. Second, it contains two submarine cable crossings. Finally,
the corridor crosses relatively inaccessible areas where construction
would be difficult. In general, this corridor offers no advantages
over the south corridor alternative described in the Draft Feasibility
Report and includes several disadvantages as compared to that
corridor.
3-9
4973B
3.1.1.4 Routing Recommendations
After reviewing the north, south, and other alternatives described
above, it was concluded that the south corridor was preferred. It was
preferred because it avoids the steep, environmentally sensitive area
along Frederick Sound, has the lowest overall construction cost, and
affords the greatest opportunity to parallel existing and proposed
roads.
3.1.2 Routing Within South Corridor
Once the south corridor was selected as the preferred corridor, a route
was selected within that corridor. The selected route follows existing
roads wherever posible becasue the cost of a line along the road has
the lowest overall cost. Because roads exist over most of the route's
length, only the portion of the route between Duncan Canal and the end
of the road system in Kake required detailed investigation. In the
area requiring more detailed routing studies the location was optimized
considering the typical per mile costs presented in Section 2.4. The
location of the recommended mixed overhead/underground transmission
line route, including the reroute area, is shown in Figure 3-3. In
general, the line would go south from Petersburg Substation to the
point where the south corridor crosses Wrangell Narrows. From that
point northwest to Kake, the recommended route would consist of
submarine or underground cable, generally following existing roads, all
the way to Kake. In unroaded sections of the route, the cable would be
located in muskeg areas wherever possible.
Once the new route was located, the entire route was reinventoried and
a table developed describing conditions along the route. The tabular
information developed is presented in Appendix C while a summary of the
Major parameters appears below.
3-10
4973B
LEGEND
MIXED OVERHEAD / UNDERGROUND TRANSMISSION LINE ROUTE!
HXX OVERHEAD TRANSMISSION LINE ROUTE NOT USED BY
MIXED OVERHEAD / UNDERGROUND LINE Say ; SS et NO ‘ KAKE-PETERSBURG INTERTIE ce Yee TaN SS EX OVERHEAD/UNDERGROUND RECONNAISSANCE REPORT
ee AND MIX N | : —_—— OVERHEAD D ED OVERHEAD / UNDERGROUND : f See ; S TRANSMISSION LINE ROUTE
TRANSMISSION LINE ROUTE { uth Wet. Af oo ‘ ‘ ig FIG 3-3
I ANTS /c TR J a: CMS EBASCO SERVICES INCORPORATED
MIXED OVERHEAD/UNDERGROUND TRANSMISSION LINE (miles)
Roadside Unroaded Submarine Underbuild Total
Cable Cable Cable on Tyee Line Length
31.05 14.55 1.59 4.95 52.14
3.2 GEOTECHNICAL CONSIDERATIONS
The reconnaissance level geotechnical studies of the underground option
focused on identifying the factors which differentiate routing
alternatives and facilitate an estimate of project costs. The existing
subsurface conditions, as well as the likelihood of avalanches, rock
falls, or other events which could jeopardize the reliable operation of
the line, are analyzed in the discussion which follows.
3.2.1 Underground Conditions
For the purpose of evaluating the installation of underground cable,
three general categories of subsurface conditions need to be
considered; these are rock, soil, and roads. The characteristics
associated with each of these categories are presented below.
3.2.1.1 Rock
Schist, graywacke, and greenstone are the three types of rock generally
encountered. On occasion a granite will "mix" with the types listed.
All of the rock present exhibits similar qualities as related to
excavation and cable installation.
All surface rock will be weathered with little of it being considered
"rippable." Only the surface layers (top +3 feet) of the schist could
be ripped by a Caterpillar D-8 Bulldozer or Caterpillar 225 excavator.
A Caterpillar 235 excavator with carbon teeth may be able to penetrate
deeper. However, the production rate of a caterpillar excavator would
not approach trenchers or plowing equipment. In addition, excavators
(backhoes) would require separate cable feed equipment.
3-12
4973B
Generally speaking, one must count on drilling and "shooting" all
rock. If it is determined to be acceptable to place cable 12 inches
below surface and then encase in ducting or other type of protective
conduit, no drilling and shooting should be required.
3.2.1.2 Muskeg
Depths will vary from 2 to 60 feet. The surficial organic material
will be extremely fiberous with moisture contents ranging from 50 to
300 percent (dry weight basis).
Wide pad track equipment could generally traverse the muskeg areas two
to five times before a "bog" would be generated. The organic material
will "stand open" in cuts, whether such cuts are made by an excavation
or by a ditch witch. The cuts, however, will fill with water in an
extremely short period of time.
3.2.1.3 Soil
Soils are generally thin and organic. Organics will yield to
stratified silty sands of marine or lacustrine sedimentary origin.
Glacial soils (drift or tills) will generally overlay bedrock.
The glacial drifts and/or tills are exceptionally dense. In most
instances they cannot be ripped or dug except for the top two (+)
feet. Usually glacial soils are drilled and shot (as in rock). Once
the material is disturbed and subjected to moisture, it will flow,
making the tills and/or drifts difficult to manage for major earthwork
operations.
3.2.1.4 Roadbeds
The vast majority of all roadways in the project area are constructed
using large quantities of shot rock. The rock will be angular (100%
fracture) and vary in size from +3 inches to +2 feet. In many
3-13
4973B
instances the roads are constructed on stumps and "layed" logs and
brush, allowing the shot rock to "float" over the weaker, wet sublying
soils. In the past several years the Forest Service has been
encouraging the use of fiber fabrics to "float" the roadways; however,
many loggers prefer the native logs. Construction specifications
generally call for at least 24 inches of cover material over the
organic (wood) materials, although at times less cover material is
encountered. A typical cross section for a Forest Service road is
shown in Figure 3-4.
Excavation of shot rock roads is relatively easy with such equipment as
a Caterpillar 225 or235 excavator. Backfilling is typically
accomplished by a bulldozer which, considering the angular rock, could
damage electrical cable, if proper care and cable selection are not
taken. Stream drainage pipe conduits are found frequent along roads
and are buried at shallow depths. In areas of culvert pipe conduits,
consideration should be given to reducing the burial depth of
electrical cable because if the cable must be buried deeper than 24
inches, replacement of the culvert may be required. However, staying
in the downhill section of the road, hand excavating and substantial
cable slack should preclude this. Generally, streams or creeks will
cross the roadway and require culverts every 400 feet.
3.2.2 Avalanches, Rockfalls, and Other Surface Conditions
Avoiding the north corridor greatly reduces the possibility of entering
avalanche or rockfall areas. Beach access along the west side of
Duncan Canal will be steep but manageable for track equipment. This
statement also holds true for the Pass between Duncan Canal and Kake at
approximately milepost 30 in the south corridor. In general,
geotechnical hazards which could affect the line are minimal, except
for the steep rockfall and avalanche prone slopes along Frederick Sound
in the north corridor.
3-14
4973B
EXCAVATION
VARIABLE
SLOPE AS DESIGNED 1’ DITCH & VARIABLE _VARIABLE ” MIN. : =|
SUBGRADE 24"’ MIN. DEPTH
ROCK MATERIAL MIN. B
ORIGINAL GROUND
TYPICAL SIDEHILL SECTION
FOREST SERVICE ROAD
NO SCALE
ALASKA POWER AUTHORITY
KAKE-PETERSBURG INTERTIE OVERHEAD/UNDERGROUND RECONNAISSANCE REPORT
TYPICAL SIDEHILL SECTION
FIG. 3-4
EBASCO SERVICES INCORPORATED
3.3. ELECTRICAL CONSIDERATIONS
3.3.1 Conductor Selection
At present most utilities use cross-linked polyethylene insulated
cables for 25 kV underground applications. Heavy molecular weight
polyethylene have not been used in recent years, because of the
problems with failures due to aging. However, it should be noted that
the problem seems to be overcome and the new high molecular weight
polymer insulations may become as good as those with cross-linked
polyethylene. For the purpose of this study, cross-linked polythelyne
insulation was selected.
For 25 kV cable, the usual insulation thickness is 260 mils. The cable
insulation and semi-conducting shield are extruded. Solid, coated
copper wires, uniformly spaced around the insulation form the
concentric neutral. The cross-section area of the neutral is 1/3 of
the copper equivalent of the central conductor. Because the Petersburg
to Kake transmission system will carry balanced load, and the
transformer at Kake will be delta connected on the 24.9 kV side, the
only major purpose of the neutral is to supply sufficient current to
the relays, and trip them, in case of a ground fault. Despite the
fact that the neutral will not carry current, it cannot be eliminated,
because of relaying problems.
Investigation into present market conditions revealed that cables with
copper conductors are comparable in price to their aluminum
counterparts having the same ampacity. The reason for this is that,
for the first time in recent times, the price of copper per pound is
less than that of aluminum. As mentioned earlier, copper conductors
have certain advantages as can be discerned from a comparative
analysis.
3-16
4973B
A comparison is presented below. The comparison will be made based on
equal resistance, which means that an aluminum conductor cable will be
considered equivalent to a copper conductor cable if the two have
approximately the same resistance over the same length.-/ This
translates into the following equivalents:
1/0 copper conductor cable is approximately equivalent to a 3/0
aluminum cable
2/0 copper conductor cable is approximately equivalent to a 4/0
aluminum cable
3/0 copper conductor cable is approximately equivalent to 250 kCM
aluminum cable
4/0 copper conductor cable is approximately equivalent to 350 kCM
aluminum cable
Directly comparing these conductor cable equivalents leads to several
findings. First, and most important, because of its smaller diameter, a
copper conductor cable will be much more flexible than its equivalent
sized aluminum conductor cable. Being more flexible, it is easier to
handle a copper cable than the equivalent aluminum conductor cable, and
therefore installation costs are considerably lower for a copper cable
than for an equivalent aluminum cable. This is a very important
feature, particularly in remote areas where working conditions are not
very favorable.
Capacities of various size cable reels are shown in Table 3-1. As the
table indicates, more copper conductor cable can be shipped in a single
length, on the same size reel, than an equivalent amount of aluminum
conductor cable. This is a very important aspect because the most
V Within the range of conductor sizes involved, equivalency with
respect to resistance also means equivalency in ampacities.
3-17
4973B
TABLE 3-11/
CAPACITIES OF NON-RETURNABLE CABLE REELS
Capacity in Feet2/
Reel Code 6636 71848
2/0 copper 4700 9300
3/0 copper 4000 8100
430-KeM aluminum 3600 7500
250 kCM aluminum 3300 6300
1/ The Okanite Company, Bulletin 721.1
2/ 260 mil XLP insulation, 1/3 jacketed neutral
3-18
4973B
vulnerable place in a cable system is the splicing. Any reduction in
the number of splices will increase reliability of the system. Also,
splicing is an expensive operation; therefore, fewer splices mean lower
installation costs.
The next aspect which favors copper conductor cables is the fact that
the splicings (or weldings) are much more reliable for copper than for
aluminum. Copper is less apt to corrode, and particularly under
adverse weather condition, splicing can be accomplished with higher
reliability.
The fact that copper corrodes very little, when compared to aluminum,
is a further advantage in case of cable failure. Should a cable fail,
moisture can penetrate through the damaged insulation, which leaves the
conductor exposed to the environment. Considering that in the
Kake-Petersburg transmission system a cable may lay underground
unrepaired for several months, an aluminum cable can be considered more
vulnerable. As the moisture penetrates into the cable, long sections
of the cable can become damaged.
All of the preceding favor copper conductor versus aluminum. In the
past, when copper prices were high compared to aluminum prices, it made
good economic sense to use aluminum. With today's shift in prices
copper conductor cables become just as economical in many applications
as aluminum conductor cables.
Based on the calculations made in earlier studies, L/ preliminary
calcuations indicated that 2/0 copper conductor with 1/3 neutral is the
most promising conductor size. Therefore, detailed investigations were
made with this conductor, and the results indicated that the
preliminary estimate was correct. Eight cases of load flow studies
1/ Kake-Petersburg Intertie Underground Transmission Line
Alternative, Phase I - Preliminary Technical Analysis Report;
Ebasco Services Incorporated; July 29, 1983.
3-19
4973B
TOTAL LOSSES:
LINE: 100kW
REACTORS : -
TOTAL: 100kW
TOTAL CABLE CHARGING: 2.81 MVAR
PARAMETERS :
CONDUCTOR: 2/0
COMPENSATION: none
1.023/-3.1° Loan AT KAKE: none
ALASKA POWER AUTHORITY
KAKE-PETERSBURG INTERTIE
OVERHEAD/UNDERGROUND RECONNAISSANCE REPORT
LOAD FLOW FIG. 3-5
EBASCO SERVICES INCORPORATED
TOTAL LOSSES:
LINE: 140kW
REACTORS: -
TOTAL: 140kW
TOTAL CABLE CHARGING: 2.57 MVAR
PARAMETERS:
CONDUCTOR: 2/0
COMPENSATION: none
0.94/-2.7° LoaD AT KAKE: 1.6MM, 0.9 p.f.
ALASKA POWER AUTHORITY
KAKE-PETERSBURG INTERTIE
OVERHEAD/UNDERGROUND RECONNAISSANCE REPORT
LOAD FLOW FIG. 3-6
EBASCO SERVICES INCORPORATED
TOTAL LOSSES:
LINE: 20kW
REACTORS: 15kW
TOTAL: 35kW
TOTAL CABLE CHARGING: 2.79 MVAR
PARAMETERS :
CONDUCTOR: 2/0
COMPENSATION: 1 x 1.5 MVAR
1.0/-1.1° LOAD AT KAKE: none
ALASKA POWER AUTHORITY
KAKE-PETERSBURG INTERTIE
OVERHEAD/UNDERGROUND
RECONNAISSANCE REPORT
LOAD FLOW FIG. 3-7
EBASCO SERVICES INCORPORATED
TOTAL LOSSES:
LINE: 130kW
REACTORS : 15kW
TOTAL: 145kW
TOTAL CABLE CHARGING: 2.52 MVAR
PARAMETERS :
CONDUCTOR: 2/0
COMPENSATION: 1 x 1.5 MVAR
0.93/-0.8° LoaD AT KAKE: 1.6MW, 0.9 p.f.
ALASKA POWER AUTHORITY
KAKE-PETERSBURG INTERTIE
OVERHEAD/UNDERGROUND RECONNAISSANCE REPORT
LOAD FLOW FIG. 3-8
EBASCO SERVICES INCORPORATED
TOTAL LOSSES:
LINE: 10kW
REACTORS : 30kW
TOTAL: 40kW
TOTAL CABLE CHARGING: 2.76 MVAR
PARAMETERS : CONDUCTOR: 2/0
COMPENSATION: 2 x 1.5 MVAR
1.0/0.2° — LoaD AT KAKE: none
ALASKA POWER AUTHORITY
KAKE-PETERSBURG INTERTIE
OVERHEAD/UNDERGROUND RECONNAISSANCE REPORT
LOAD FLOW FIG. 3-9
EBASCO SERVICES INCORPORATED
TOTAL LOSSES:
LINE: 160kW
REACTORS: 30kW
TOTAL: 190kW
TOTAL CABLE CHARGING: 2.47 MVAR
PARAMETERS :
CONDUCTOR: 2/0
COMPENSATION: 2 x 1.5 MVAR
0.92/0.5° LOAD AT KAKE: 1.6MW, 0.9p.f.
ALASKA POWER AUTHORITY
KAKE-PETERSBURG INTERTIE
OVERHEAD/UNDERGROUND RECONNAISSANCE REPORT
LOAD FLOW FIG. 3-10
EBASCO SERVICES INCORPORATED
TOTAL LOSSES:
LINE: < 6kW
REACTORS : 36kW
TOTAL: <42kW
TOTAL CABLE CHARGING: 2.77 MVAR
PARAMETERS :
CONDUCTOR: 2/0
COMPENSATION: 4 x 0.6 MVAR
1.0/-0.4° Loan AT KAKE: none
ALASKA POWER AUTHORITY
KAKE-PETERSBURG INTERTIE
OVERHEAD/UNDERGROUND RECONNAISSANCE REPORT
LOAD FLOW FIG. 8-11
EBASCO SERVICES INCORPORATED
TOTAL LOSSES:
LINE: 140kl!
REACTORS : 36kW
TOTAL: 176kW
TOTAL CABLE CHARGING: 2.49 MVAR
PARAMETERS :
CONDUCTOR: 2/0
COMPENSATION: 4 x 0.6 MVAR
0.92/-0.1° LOAD AT KAKE: 1.6MW, 0.9p.f.
ALASKA POWER AUTHORITY
KAKE-PETERSBURG INTERTIE
OVERHEAD/UNDERGROUND RECONNAISSANCE REPORT
LOAD FLOW FIG, 3-12
EBASCO SERVICES INCORPORATED
TOTAL LOSSES:
LINE: 20kW
REACTORS : 15kW
TOTAL: 35kW
TOTAL CABLE CHARGING: 2.97 MVAR
PAPAMETERS :
CONDUCTOR: 3/0
COMPENSATION: 1 x1.5 MVAR
1.0/-1.0° Loa AT KAKE: none
ALASKA POWER AUTHORITY
KAKE-PETERSBURG INTERTIE
OVERHEAD/UNDERGROUND RECONNAISSANCE REPORT
LOAD FLOW FIG. 3-13
EBASCO SERVICES INCORPORATED
TOTAL LOSSES:
LINE: 100kW
REACTORS : 15kW
TOTAL: 115kW
TOTAL CABLE CHARGING: 2.75 MVAR
PARAMETERS :
CONDUCTOR: 3/0
COMPENSATION: 1 x 1.5 MYAR
0.94/-0.7° LoaD AT KAKE: 1.6MM, 0.9p.f.
ALASKA POWER AUTHORITY
KAKE-PETERSBURG INTERTIE
OVERHEAD/UNDERGROUND RECONNAISSANCE REPORT
LOAD FLOW
FIG. 3-14
EBASCO SERVICES INCORPORATED
were made with the 2/0 copper conductor cable. In addition,
calculations were made using 3/0 copper conductor cables. However,
preliminary calculations indicated that 1/0 copper conductor would not
be a good selection in this case.
The main parameters for 2/0 and 3/0 copper cables are presented in
Tables 3-2 and 3-3, respectively. The calculations were based on
methods developed by Dr. W.A. Lewis, as published in the Cyprus—Rome
Book, referenced in the tables.
Also based on the earlier studies performed by Ebasco, it was decided
that a five section system, each 10 miles long, should be used to
evaluate the usefulness of a certain conductor. In addition, the
studies involved various methods of compensation. The results are
shown in Figures 3-5 through 3-14.
The underground transmission system with no compensation was
investigated first. The case with no load at Kake is shown in
Figure 3-5. The voltage rise at Kake is only 2.3 percent, which is
very moderate. Having no compensation, the maximum charging current
occurs at the Petersburg bus. The reactive power at this location is
2.81 MVAR, and proves to be the largest charging current observed
during all the studies.
The 2.81 MVAR corresponds to 65.2 ampere charging current at
Petersburg, which is only 21 percent of the 311 ampere current carrying
capacity ampacity (ampacity) of the cable. Considering that 0.212
equals 0.044, or 4.4 percent, it becomes clear that the thermal stress
on the insulation would be minimal, indeed, because the temperature
rise of the conductor over the soil would be less than 5°C. This means
that even under this most unfavorable condition, the conductor would
practically not heat up at all during its entire life.
3-30
4973B
TABLE 3-2
V CABLE DATA~
Conductor:
Insulation:
Neutral:
Arrangement:
2/0 copper, 19 strand
260 mil XLP, 25 kV nominal
11x #14 AWG copper ("1/3 neutral")
3 single phase cables tightly trenched,
1/4" average gap assumed between cables
R conductor
R neutral
Conductor diameter
Neutral wire diameter
Number of neutral wires
Insulation OD
Geometric mean distance
Conductor geometric mean radius
Neutral wire geometric mean radius
Ampacity
Pos. sequence resistance
Pos. sequence reactance
Capicitance
Capacitive reactance
0.0815 ohm/1000', at 15° C. 59° F
0.243 ohm/1000', at 15° C. 59° F
0.42 inch
0.0641 inch
in
1.0 inch
0.108 feet
0.0125 feet
0.00104 feet
311 ampere
0.0907 ohm/1000', at 15° C
0.0402 ohm/1000', at 15° C
0.0105 microfarad/1000'
59.1 kohm per 1000'
Cyprus (formerly Rome) UD Technical Manual, 5th edition, pp. 45-48
and p. 79.
Westinghouse Transmission and Distribution Reference Book,
4th edition, p. 49.
Northern Electric, Electrical Conductors Handbook, 10th edition,
p. 45.
3-31
4973B
TABLE 3- 3
CABLE DATAL/
Conductor:
Insulation:
Neutral:
Arrangement:
3/0 copper, 19 strand
260 mil XLP, 25 kV nominal
14x #14 AWG copper ("1/3 neutral")
3 single phase cables tightly trenched,
1/4" average gap assumed between cables
R conductor
R neutral
Conductor diameter
Neutral wire diameter
Number of neutral wires
Insulation OD
Geometric mean distance
Conductor geometric mean radius
Neutral wire geometric mean radius
Ampacity
Pos. sequence resistance
Pos. sequence reactance
Capicitance
Capacitive reactance
0.0646 ohm/1000', at 15° C. 59° F
0.191 ohm/1000', at 15° C. 59° F
0.47 inch
0.0641 inch
14
1.06 inch
0.117 feet
0.016 feet
0.00104 feet
346 ampere
0.073 ohm/1000', at 15° C
0.0316 ohm/1000', at 15° C
0.0478 microfarad/1000'
55.5 kohm per 1000'
Cyprus (formerly Rome) UD Technical Manual, 5th edition, pp. 45-48
and p. 79.
Westinghouse Transmission and Distribution Reference Book,
4th edition, p. 49.
Northern Electric, Electrical Conductors Handbook, 10th edition,
p. 45.
3-32
4973B
The total losses caused by the charging currents are 100 kw.2/ These
losses represent no load losses and, therefore, are on the system 24
hours a day, 365 days a year. However, under certain loading conditions,
the losses may be less than the losses at full load.
The load flow on Figure 3-6 shows the no compensation case at 1.6 MW,
0.82 MVAR at Kake; this corresponds to 1.8 MVA at 0.9 p.f. The losses in
this case are 140 kW, or 8.6% of the load at Kake.
Figure 3-7 shows the load flow conditions with only one 1.5 MVAR reactor
on the line. This reactor is a low loss reactor, having approximately 1%
loss of its MVA rating. There is a remarkable drop in no load losses, to
35 kW, when compared to the 100 kW case without compensation. More
drastic is the reduction in line losses, which drops to one fifth of its
uncompensated value, to 20 kW; however, 15 kW reactor losses have to be
added to this amount, resulting in the 35 KW total no load losses.
The voltage on the 24.9 kV bus in Kake is 1.0 per unit, the same as it is
to Petersburg. It should be noted that all intermediate bus voltages are
at unity.
When the same system is loaded with 1.6 MW at 0.9 power factor at Kake,
the voltage drops by 7.4%. This voltage drop is acceptable. The results
of the load flow calculations can be seen in Figure 3-8. The voltage at
Kake is at 0.926 per unit and the total losses of the transmission system
are 145 kW, or 9.1%, of the load at Kake.
An attempt was made to improve the system by placing two 1.5 MVAR
reactors onto the system. Buses 2 and 5 were selected for their
locations. With no load at Kake the results are shown in Figure 3-9.
The voltage at Kake is almost unity and the total no load losses are
50 kW. The load flow for full load is shown in Figure 3-10; the voltage
dropped to 0.915 pu and the total losses are 190 kW.
1/_ The expected accuracy of loss calculations in this report is +5 kW.
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Finally, a system with 4 small reactors at each of the intermediate
buses was also investigated. In this case, the smallest commercially
available reactor size was utilized; a bank of three reactors each
rated 0.2 MVAR or a total of 0.6 MVAR per bank. The reactors are of
the low loss variety. Their losses are 1.5% of their rated MVAR.
Figures 3-11 and 3-12 show the load flows at Kake in case of no load
and of full load, respectively. The voltage at Kake at no load is
unity, and drops to 0.92 pu at full load.
It is interesting to note that with no load at Kake the total losses
are less than 42 kW. The line losses themselves are less than 6 kw,
because the computer printout gave 0.00 MW, indicating that no rounding
occurred. However, the reactors represent 36 kW losses, giving a total
of not exceeding 42 kW, making this arrangement less favorable than the
one reactor version which has losses of only 35 kW. The total losses
at full load are 176 kW or 11% of Kake's load.
The losses and the voltage drops are tabulated in Table 3-4. From the
table it can be seen that the best arrangement for the cable
transmission system with 2/0 copper conductor is one 1.5 MVAR reactor
at bus no. 4. This version has the lowest no load losses by far, and
its losses at full load are only 5 kW more than the lowest case, which
is the uncompensated line. The voltage conditions of all four
calculated versions would be acceptable.
Based on the above results, calculations were made using 3/0 copper
conductor cable and one 1.5 MVAR reactor at bus no. 4. The results of
the load flows are shown on Figures 3-13 and 3-14; the former shows
conditions at no load and the latter at full load at Kake. The no load
case indicates that the losses are about the same for 3/0 copper
conductor than for 2/0 conductor. However, the losses are somewhat
less, by 30 kW, at full load. Only detailed engineering design and
analyses can tell whether this 30 kW reduction in loss is worth the
additional cable cost.
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TABLE 3-4
LOSSES AND VOLTAGE DROPS
2/0 Copper conductor
No compensation
1x1.5 MVAR at bus 4
2x1.5 MVAR at buses 2 and 5
4x0.6 MVAR at intermediate buses
3/0 Copper conductor
1x1.5 MVAR at bus 4
4973B
No Load
3-35
Losses in kW
100
35
50
<42
35
Full Load
140
145
190
176
115.
P.U. Voltage
in Kake
At Full Load
0.942
0.926
0.915
0.92
0.943
No attempt was made to calculate load flows for 1/0 copper conductor
cable. After doing some preliminary calculations, it was concluded that
such cable would increase the voltage drop, at least close to 10%.
Whereas 7.4% voltage drop is a comfortable value, decreasing the
conductor size would increase the voltage drop to levels which may be
less desirable. It should be noted that the 7.4% voltage drop neither
includes the drop across the transformer at Kake nor considers the
voltage variations at the Petersburg bus.
The short circuit duty at Kake was calculated for the 2/0 copper
conductor alternative and was found to be 17.9 MVAR.
Finally, it should be kept in mind that the analyses presented in this
section were based on an all underground system and therefore represents
the "worst case" situation. Any further fine tuning of these
computations would require detailed engineering design.
3.4 COST ESTIMATING AND CABLE INSTALLATION TECHNIQUES
The construction technique which would be used to install an
underground cable varies, depending on conditions where the cable is to
be installed. In general, loosely consolidated material is favored
because faster and less expensive installation techniques involving
vibratory or static plows can be used. In more consolidated material
and rock, trenching techniques involving trenchers, backhoes, or rock
saws are used. These techniques are slower and more costly. A general
description of information obtained on plowing and trenching practices
is provided below. More detailed back-up information on cable
installation and cost estimates was submitted to the Power Authority
under separate cover.
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/ 3.4.1 Installation Techniques
Plowing
Vibratory and static plowing were analyzed for possible use on the
Kake-Petersburg project. Static plowing equipment is available from
several manufacturers. Such equipment is typically attached to the
back of bulldozers in association with cable reel equipment. Little
attention was focused on static plowing in this study because vibratory
plows are felt to be faster and otherwise more cost-effective for use
on the Kake-Petersburg project.
A variety of vibratory plowing equipment is also currently on the
market. An example of a typical equipment set-up involves use of a
Vibra-King plow, attached onto the back of a bulldozer. Vermeer also
manufactures a vibratory plow unit which is completely self-contained.
Vibratory plows can be obtained in rubber-tired or tracked equipment.
Vibratory plowing needs approximately one-half the horsepower required
for normal static plowing and is therefore less costly. Vibratory
Plowing has been successfully employed in shot rock roads with boulders
up to two feet in diameter; the boulders are often brought to the top
by the vibratory plowing. If boulders larger than two feet in diameter
are encountered, slight deviations in the cable's alignments may be
required. The actual cable installing process on the Kake-Petersburg
project would likely involve installing the cable into the road itself
or into the side of the road. Installing the cable in the side of the
road can be accomplished by offset plowing, which enables the operators
to stay on the road while the cable is plowed into the side of the road
or the ditch.
Vibratory plowing has been successfully used throughout the United
States. The project engineer and contractor of one successful cable
project near Iliamna were contacted regarding their experiences with
vibratory plows. The vibratory plowing production rate on the Iliamna
project averaged approximately one mile per day. Production rates have
reached a maximum of 2,000 feet of plowing per hour when the machine
was working effectively.
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For the estimate on the Kake-Petersburg project it has been assumed
that the production rate of vibratory plowing will be approximately
1,750 feet of plowing per day. Certain difficulties in vibratory
plowing in roads are expected because of the presence of stumps which
may be encountered less than two feet below the road surface and
because of culverts which cross under the roads. The problem with
depth of cover is somewhat minimized by installing the cable on the
downhill side of the road where the fills are deeper. Potential
installation problems caused by culverts under the road can also be
minimized by locating the cable on the downhill side of the road or by
hand-excavating under the culvert. Potential problems related to
angular rock cutting the cable could also be reduced by selecting a
cable which has the proper jacket. A bulldozer following the vibratory
plow can handle any backfilling operation as well as any preripping of
the road where required in difficult sections. During installation,
all three cables can be fed at the same time using 3 individual cable
reel carriers attached to a bulldozer at least the size of a
Caterpiller D-7, but would be more easily handled by a D-8 or D-9.
Regarding the depth of burial, the National Electric Safety Code
recommends cable installed with at least 30" of cover; however, it is
believed that 24" of cover in the road will be sufficient with
selection of the proper jacketed cable. Away from the roads in
selected areas where excavation is difficult, ground coverage may be
enhanced by constructing a small berm above the cable trench. This
procedure, which will be used in localized areas typified by bedrock
close to grade, will help reduce construction costs.
Trenching.
Many manufacturers currently make trenching machines including Vermeer,
DitchWitch, Barber-Greene, Midmark, Pengo-Jetco, Cleveland, Koehring,
and Burkeen. Studies conducted by Ebasco focused on Vermeer trenchers
for trenching ahead of the cable laying operation in muskeg. These
trenchers can also be used in the roads; however, the production rates
in roads would probably not be as good as the vibratory plowing system
and therefore did not receive serious consideration for use on roads.
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A tracked trencher would be required on muskeg since it would give
higher flotation than rubber-tired equipment. Should additional
flotation be required in sensitive muskegs, wider pads can be welded
onto the tracks. The sawing action of a trencher would be better than
static plowing in muskegs. According to Merlin Nation and Sons, a
contractor who installs drainage pipe in sensitive peat bogs in
Washington State, such a trencher can saw through stumps and even
occasionally bring stumps up to the surface.
Based on an analysis of conditions in the Kake area, it doesn't appear
that three cables can be supported off cable reels on the trenchers;
instead it appears that there would have to be additional equipment
following behind the trencher. Because rubber-tired equipment would
have difficulty maneuvering in the muskegs, an all-terrain type of
vehicle such as a Bombadier, Terraflex, or Nodwell would probably be
required. Bombadier specifically markets a muskeg carrier; however,
given the weight of three cable reels, a larger size Bombadier would
probably be required; something similar to the Model TF-360. Even with
proper precautions, a trencher can occasionally get bogged down or
partially sunk. A winch attachment on the front of the trencher, with
an additional bulldozer, can pull the partially sunk trencher out of
the muskeg. Sound construction practices will also be required to keep
scarring of the muskeg by construction equipment transversing it to a
minimum.
Merlin Nation & Sons has cut 6,000-8,000 feet of trenching in one day
in peat without many logs, and up to 9,500 feet a day in ideal peat
with low moisture content. However, Nation and Sons estimate their
average production at 4,000-5,000 feet per day. The more times peat is
traversed, the less weight it can support. For the Kake-Petersburg
project, a production rate of 2,500 feet per day in muskeg is
estimated. Production in muskeg is dependent upon the water content of
the muskeg, the amount of stumps encountered, and the density of the
peat. Trenching with a chain trencher in frozen muskeg would probably
be easier than in normal muskeg in that less scarring to the muskeg
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would be encountered. There would also be less of a problem with
getting bogged down in the muskeg. However, an early snowfall, which
would tend to insulate the ground, could keep the muskeg from freezing
during any given year.
In rock areas a rock saw may be required. Many manufacturers make rock
saws both as self-contained saws and for attachments onto bulldozers or
trenchers. Production rates, however, of self-contained or attached
unit rock saws are slow. Vermeer noted actual production rates of
one-half foot per minute in basalt with an approximate cost of $5.00
per linear foot for teeth. Vermeer also has experienced actual
production rates of 4 feet per minute in softer rock such as limestone,
with less than $1.00 per foot for teeth. Production rates in rock are
determined by the hardness of the rock, which in turn governs how often
the teeth need to be changed. Most rock saw teeth are not capable of
being sharpened and are replaced routinely during operations. Given
the extremely slow production rates in rock, it is advisable to avoid
rock wherever possible. Not avoiding large sections of rock makes the
underground option prohibitively expensive. It is assumed that through
careful design and location work and by the use of small] earth berms to
obtain the necessary cover where rock is close to the surface, it is
possible to avoid virtually all sections of rock by proper routing
around the rock. Drilling and blasting would be more expensive and
ripping would be less expensive than rock sawing.
Trenchers may be required in glacial till soils. The production rate
of the trencher in glacial till has been assumed to be 1,000 feet per
day in the present analysis. Preripping may be required in difficult
areas. It is questionable whether the rock encountered in the
Kake-Petersburg area would be rippable and indications from past
construction in this area are that drilling and blasting may be
required; therefore, avoiding rock areas as previously metioned is
mandatory to economic feasibility.
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General Considerations
An extensive effort has been made to research contractor experience
with the various types of soils which will be encountered by the
Kake-Petersburg Underground Transmission Line option. However, it
should be realized that any cross-country underground cable operation
would be a pioneering type operation and, as such, could result in high
bids due to the contractors' assumed risks. A substantial contingency
of 20% has been included for protection against these risks. In
addition to information included in this report, Ebasco has presented
all estimating assumptions and manufacturers' literature to the Alaska
Power Authority. Escalation and Allowance for Funds Used During
Construction have not been included in the estimate. Production rates
and equipment spreads are also based on information solicited from
representatives of the U. S. Forest Service during a site visit and
supplemented by subsequent discussions. Contractors, magazine
articles, independent consultants, equipment manufacturers and
distributers, and in-house Ebasco construction personnel also provided
input for this cost and constructibility analysis.
3.4.2 Joint Road and Transmission Line Construction
Analysis of the cost of installing either an overhead or underground
transmission line between Petersburg and Kake led to the finding that
construction of a transmission line would be substantially less if it
would follow an existing road, rather than cross an unroaded area.
Both clearing and mobilization costs would be substantially reduced if
an existing road is followed. Because of the potential cost savings
associated with following existing roads and the fact that both the
Forest Service and Department of Transportation and Public Facilities
have plans to construct roads between Petersburg and Kake, analysis was
undertaken to determine if there were significant cost advantages
associated with the joint construction of a transmission line and road.
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4973B
The primary finding of the analysis of joint road and transmission line
construction is that only minimal cost reductions can be achieved by
undertaking these activities simultaneously. Transmission line
construction proceeds much more rapidly than highway construction and
occurs in several distinct stages. For example, overhead construction
involves clearing, pole setting, stringing, and tensioning activities,
which occur sequentially. Underground cable construction also proceeds
rapidly and sequentially because it requires relatively little
excavation due to the fact that only enough excavation to install 3 or
4 cables of less than 2 inches in diameter in the same trench is
required. Therefore, although roads greatly facilitate the
installation of overhead or underground transmission lines, the actual
transmission line construction process proceeds much more rapidly than
does road construction. Furthermore, if cable were to be laid in
conjunction with highway construction activities, there would be a
greater chance that the cable would be damaged during installation
activities. The use of shot rock in road construction is common in the
Kake-Petersburg area and filling and other operations involving moving
such material in the vicinity of cables, which would occur during the
joint construction of roads and installation of an underground cable,
would likely cause more damage to the underground cable than if the
cable were installed after the road is completed. Thus, although the
presence of road is highly desirable for the construction of a
transmission line from Petersburg to Kake, there are relatively few
advantages associated with pursuing these activities simultaneously.
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4973B
4 ENVIRONMENTAL CONSIDERATIONS
Environmental studies of the mixed overhead/underground transmission
line option focused on evaluating major concerns which would favor one
corridor or one design option over another. Major environmental
permitting issues which would effectively prevent successful completion
of the project were identified as were issues requiring consideration
in the subsequent feasibility level analysis.
The major environmental consideration related to any of the
alternatives under study relates to the potential crossing of the
Petersburg Creek-Duncan Salt Chuck Wilderness Area. Obtaining approval
to locate a transmission line across the wilderness area, either an
overhead or underground transmission line, would be difficult. This
assessment is based on a review of Section 1107 of the Alaska National
Interest Lands Conservation Act (ANILCA). An analysis of this act,
which expressly established a procedure for locating a utility corridor
within designated wilderness areas, revealed that it would take a
presidential recommendation approved by Congress to enable such a
corridor to be established. Such a presidential recommendation would
need to be accompanied by an analysis comparing a range of alternatives
available to cross the wilderness. Obtaining such residential and
congressional approval for a transmission line would be time consuming,
difficult, and there would be no certainty that such an approval could
be obtained. This realization makes alternatives within the Petersburg
Creek-Duncan Salt Chuck Wilderness Area undesirable from a regulatory
and environmental perspective.
In addition to the Wilderness Area, the other environmentally sensitive
area is the shoreline along Frederick Sound north from Petersburg
toward Twelvemile Creek. This area constitutes an important visual
resource as well as provides a wildlife habitat for bald eagles located
in the area. Constructing an overhead or underground line in this
rugged area would be difficult and would arouse environmental concern.
Such concern would not necessarily prohibit construction in this area,
but would make it more difficult.
4977B
4-1
The net result of the issues identified above is to indicate that the
south corridor is preferred from an environmental viewpoint. Moreover,
the most sensitive area of the south corridor is the muskeg flat west
of Duncan Canal where concerns related to potential waterfowl impacts
were raised as_a-concern during the feasibility study of the overhead
option. An underground line would avoid such potential impacts. As a
result of these general considerations, the south corridor was found to
be the environmentally preferred one.
Once the preferred corridor was identified, environmental analysis
efforts turned toward identifying potential concerns within the south
corridor. Such environmental concerns do not appear to be significant,
but will require analysis in the feasibility level studies, if
authorized. Specifically, there are potential environmental effects
associated with crossing a muskeg area with cable laying equipment, if
proper precautions are not taken. Therefore, environmental studies
during the feasibility level analysis should focus on measures which
could be taken to minimize potential disturbance to muskeg areas.
Development of low pressure vehicles for use in crossing the muskegs
and refinement of plowing techniques used in the actual cable laying
installation activities need to be analyzed from an environmental
perspective. In addition, in other areas envirommental concerns
related to the establishment of small berms above certain portions of
the installed underground cables should be considered. Such berms,
which could develop in small areas as a result of cable installation,
may affect drainage patterns and efforts will be required to identify
Measures to limit the effect of such construction practices.
49778 4-2
5 CONCLUSIONS AND RECOMMENDATIONS
Investigations summarized in this report suggest that there is a high
likelohood that a mixed overhead/underground transmission line would
cost considerably less than an overhead line. The optimal transmission
line for the Kake-Petersburg project consists of approximately five
miles of underbuild construction on the existing Tyee Lake line, two
miles of submarine cable, and 45 miles of underground cable.
Reconnaissance level investigations indicate that the reduction in
capital cost for such an alternative, as compared to an overhead line,
would be approximately 2.3 million dollars, or approximately 20% of the
total project costs. The 2.3 million dollar cost reduction assumes
that the transmission line would be constructed after the proposed road
from the existing Kake road system toward the pass between Kake and
Duncan Canal is constructed.
Calculations indicate that 260 mil XLP insulated 210 copper conductor
cable with 1/3 jacketed neutral is probably the best choice, though
detailed engineering design may swing the scale for a one size larger
or one size smaller conductor. The 2/0 conductor cable would be able
to transmit the 1.6 MW power from Petersburg to Kake even in case of an
all cable transmission line with only one 1.5 MVAR reactor bank. The
final choice of conductor size and degree of compensation will depend
on the final mix of overhead and underground line sections.
Although projected cost savings associated with the mixed
overhead/underground transmission line compare favorably to the
overhead transmission line alternative, there are certain
considerations which should be considered in evaluating whether to
proceed with feasibility level studies.
First, it should be emphasized that the lack of experience with long
distance underground cable installations makes it difficult to
accurately estimate the cost of an undergound cable in the
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Kake-Petersburg area. Consequently, the total cost estimate might be
considerably higher or lower than what is estimated in this report.
Second, although the mixed overhead/underground line compares favorably
with the overhead option, no formal evaluation has been made of the
mixed overhead/underground option's merit in comparison to the existing
base-case diesel system. Draft feasibility level studies for the
overhead line conducted earlier concluded that the overhead alternative
was feasible only under certain conditions, namely, if the Kake Cold
Storage load were connected into the local transmission system and if
load growth were to occur at a level associated with Ebasco's high
growth scenario.
Because the mixed overhead/underground option costs less than the
overhead alternative, it can not necessarily be assumed that the
project will change from being one which should be developed.
Nevertheless, it is recognized that the reduction in capital cost
associated with the underground option improves the project's overall
economics. A preliminary economic analysis of the mixed overhead/
underground option suggests that the benefit/cost ratio will be on the
order of 1.1 to 1. This preliminary analysis assumes that the general
assumptions used in the State economic analysis methodology (i.e., fuel
escalation rate, discount rate, etc.) currently under consideration by
the Power Authority staff will not be substantially revised. The
finding also assumes that forecast information used in the Draft
Feasibility Report has not changed and that the economic value of line
losses will not be significant.
In light of the potentially favorable economics of the mixed overhead/
underground transmission line, it is recommended that feasibility level
studies of the mixed overhead/underground alternative be authorized.
Initially, however, feasibility studies should focus on updating the
Kake forecast and the effect any changes in economic assumptions would
have on the project's economic feasibility. If such a preliminary
economic evaluation suggests that the project will compare favorably
with the base case, then the more detailed engineering evaluation of
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the mixed overhead/underground alternative should proceed. It is also
recommended that the economic evaluations consider line losses
associated with the proposed transmission facility under two scenarios:
1) full utilization of Tyee Lake power and 2) low utilization of Tyee
Lake power. Sensitivity analysis of the value of line losses and other
important economic variables should also be conducted.
Another task which should be included in the feasibility level studies
is to investigate and plan the establishment of a test section of
underground cable. Ideally, such a test section could be undertaken in
conjunction with planned transmission or distribution line
installations in the immediate area of the project. However, other
areas in Southeast Alaska could also be considered. The feasibility
level study should outline a program for providing better information
which can improve the accuracy of the cost estimates for the
underground cable installation.
Finally, because the potential feasibility of the project is closely
linked to the amount of completed road between Petersburg and Kake, it
is recommended that the methods be explored for expediting construction
of the Forest Service road from the existing Kake road system toward
the Pass between Duncan Canal and Kake. It may be possible to work
with the timber purchaser responsible for constructing the road or to
seek other funds such as those available to the Forest Service through
sources established by ANILCA. Constructing this road as soon as
possible would shorten the time until the transmission line could pass
the state's economic feasibility tests.
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4972B
APPENDIX A
ILIAMNA UNDERGROUND PROJECT
BACKGROUND INFORMATION
KAKE-PETERSBURG INTERTIE PROJECT
Meeting Summary - March 3, 1983
Additional Studies Related to Underground and
North Corridor Options for the Proposed Kake-Petersburg Project
Attendees
Miles Yerkes, Alaska Power Authority
Patty DeJong, Alaska Power Authority
Remy Williams, Alaska Power Authority
William Kitto, Ebasco Services Inc.
John Szablya, Ebasco Services Inc.
Malcolm Menzies, R & M Consultants, Inc.
Robert Dryden, Dryden and LaRue Consulting Engineers
Meeting Summary
On March 3, 1983, a meeting was hela to review the advisability of
conducting additional studies to analyze new alternatives for
constructing the proposed Kake-Petersburg transmission line. New
alternatives discussed included a line in either the north corridor or
a line using an underground cable for most of its length. The meeting
began with Bill Kitto reviewing the status of project activities. He
described that a Feasibility Report had been submitted during November,
1982, and that the report had dismissed the possibility of constructing
the line underground because of technical and reliability
considerations. The report also failed to evaluate the north route in
detail because of environmental considerations and because of the fact
that it was well removed from any existing access corridors. Following
the release of the Draft Feasibility Report, public meetings were hela
in Kake and in Petersburg and comments were obtained. Bill Kitto
explained that the primary opinion expressed at the Kake meeting was
A-1
that residents of that community felt that interconnection to the Tyee
System would bring them cheap hydroelectric power. This view by the
residents of Kake prevailed, although it was repeatedly explained by
Remy Williams and Bill Kitto that the Tyee power which would be
transmitted to Kake by the Intertie would not be low cost power.
Despite these explanations, residents of Kake continued to state the
opinion that interconnection with the Tyee System would enable their
community to prosper because of low electricity rates and enable them
to install electric heat and other large electricity-consuming
devices. Bill Kitto also explained that comments were received from
the public regarding the load forecast stating that that forecast was
too low and did not properly reflect the growth in Kake. Bill Kitto
explained that subsequent to that meeting, David Reaume, author of the
load forecast, considered these comments and concluded that the initial
forecast was indeed accurate and that the most recent growth in
electricity consumption was related primarily to new purchases as a
result of the permanent fund checks received by residents of the
community of Kake.
Bill Kitto also explained that two important comments were received on
the Draft Feasibility Report. The first comment came from the U.S.
Forest Service who indicated that they were currently planning to let
contracts on a road system from the Hamilton Creek area east toward
Portage Bay. This would reauce the total length of the line between
Kake and Petersburg within the north corridor substantially. The
second important comment related to the Alaska Uepartment of
Transportation and Public Facilities who indicated that they would be
interested in participating in a joint effort to construct a
transmission line/road corridor to Kake. Based on these two agency
comments and the Power Authority's request to look at the underground
option in more detail, Ebasco Services was recommending that the Power
Authority prepare a brief report to look into the option of
constructing an overhead-underground line within either the north or
south corridors linking Kake and Petersburg. Bill Kitto explained that
A-2
it was the main purpose of this meeting to initiate these studies and
to discuss risks and tradeoffs involved in underground construction in
such an area.
Following Bill Kitto’s remarks, Bob Dryden described the work he haa
been involved in in Iliamna. He explained that this project involved
Constructing approximately 35 miles of 24.9 kV underground cable. He
explained that they had investigated construction of an overhead line
in this area, but had discarded it because of economic reasons and
because of potential impacts. A particular concern in the Iliamna area
was the potential impact an overhead line would have on aircraft. They
also considered an underground system because they believed use of a
vibratory plow would enable them to install an underground cable
economically in the area. Bob explained that there were three types of
vibratory plows which they had considered, and that they were very
happy with the installation approach they ultimately selected. He
suggested that the contractor, Dodge Electric of wasilla, Alaska, be
contacted for specific information about the approach they used.
Bob then described several of the important considerations related to
their experience in lliamna. In reviewing some of the drawbacks, Bob
explained that the installation approacn they had used required three
operators. He said two cats, a D450 and a D6, were needed, as well as
a vehicle to properly hanale and transport the cable. The cats had
larger size motors to handle the hydraulics. The cat with the
vibratory plow had one cable drum, the other had two drums.
The following specific points were made by Bob Dryden and others:
1. Installation costs ran about $3/ft on the Iliamna pruject.
2. Geotechnical conditions were different at Iliamna than in
Southeast Alaska. He said that in particular, the soils in
A-3
the Iliamna area were largely composed of alluvial material
and were relatively easy to work when compared with some of
the hardpan found in Southeast Alaska.
Bob cautioned that not as much concern needs to be given to
the depth of seasonal frost in the Kake area. While
discussing this point, Malcolm Menzies pointed out that in
some years, the ground dia not freeze in Southeast Alaska,
depending on when the first heavy snowfall occurred.
The cable was buried to a depth of approximately 42 to 48
inches on the Iliamna project, although it probably would have
been possible to bury it at a shallower cepth.
When areas of bedrock were encountered on the Iliamna project,
Bob Dryden indicated that they rerouted the underground cable
to avoid such areas.
The cable used at Iliamna was 25 kV, single phase, URD type,
with cross linked polyethelene insulation, 1/0 aluminum
conductor and concentric neutral. It had a diameter of 1.45
inches overall.
Use of 15 kV cable instead of 25 kV would reduce costs by 1%
to 2%, however, the 25 kV is stronger and can take much more
of a beating.
In describing the Iliamna project, Bob Lryden stated that the
length of the cable installed was approximately 35 miles, and
that a portion of it had been energized since October, 198z
without any failure.
It was explained that the cable installation equipment
installed approximately 2,000 feet of cable per hour when
A-4
10.
11.
12.
13.
working effectively. In general, because of the vibratory
nature of the equipment, it was difficult to work more than
2-1/2 to 3 hours per day. As a general rule, workers worked
approximately two hours per day and repaired the equipment
approximately ten hours per day. On the average they laid 1/2
mile in the morning and 1/2 mile in the afternoon. The line
was constructed between August 1 and September 15, 1982.
There were approximately 30 phase breaks on the Iliamna
project; the cable snapped when the pull was too much. In
spite of the number of breaks, a break never went undetected
and there was no marginal damage to the cable.
In general, Bob Dryden stated that the vibratory Plow cannot
deal with overburden material even as thin as 2 inches,
because it would clog the equipment and keep it from
functioning properly.
Bob Dryden also recommended that because of the unique
operating conditions of the vibratory plow and other cable
installation equipment, it would be advisable for the
contractor who installed the line at Iliamna to be sent to
Southeast Alaska to judge the problems that coula be expected
from installing such a line in that area. He said that such
an on-the-ground inspection would be well worth the money
prior to proceeding with the construction of such a line.
Bob reviewed a number of ways that his firm had tried to
eliminate problems related to the organic layer of the soil
which had made their machine inoperable. He explained that
using a ripping technique to cut the vegetation prior to
installation of the cable was less than satisfactory. He
suggested that removal of the material prior to installation
of the cable was the most prudent approach, by driving a
rolling hoe ahead of the vibratory (or other) cable plow.
A-5
14.
15.
16.
7.
Electrical charging problems were also identified as a concern
and various solutions for such problems were discussed.
Although the Iliamna line was not compensated, Bob said he
would compensate similar future lines. The use of lightning
arrestors was tried initially by Dryden and LaRue, but were
found to be unacceptable, instead Ohio Brass MOV type surge
arresters were used.
Discussions of installation techniques led to the finding that
it might be worthwhile to consider use of a frostwheel on the
project and to install the line during winter months. Bob
Dryden felt that such an approach would make sense, given the
anticipatea problems of using a vibratory plow in the
forested, densely vegetated area of Southeast Alaska.
Mike Yerkes provided his comments on the feasibility of an
underground line and suggested that Ebasco look into various
types of wheel operators which could be contacted to determine
the costs and practicality of using such an approach in
Southeast Alaska. Mike also suggested that future studies
determine the parameters affecting the results of the study by
considering the length of the cable, size of the cable,
reliability of the cable and what happens under faulting.
Bob Dryden reported that two faults were experienced on the
Iliamna project. One fault remains unexplained, while the
other occurred on a cable section routed across a lake where
the cable sat on a sandbar and was under the pressure of ice
which finally damaged the cable. They used compression-type
splices with slip back sleeves and found the ones GE made to
be the best. For fault location it is necessary to have
trained people and suitable equipment available. Bob
explained that it was very necessary to sectionalize the line
frequently over its entire length. He suggested using a pad
A-6
APPENDIX B
CONTACT REPORT - ALASKA DEPARTMENT
OF TRANSPORTATION AND PUBLIC FACILITIES
eC Interoffice Correspondence
pate October 20, 1983 FILEREF
TO File OFFICE LOCATION
a 7 Ww FROM W. Kitto OFFICE LOCATION (ENVIROSPHERE)
KAKE-PETERSBURG INTERTIE STUDY
supsect CONTACT WITH ALASKA DEPARTMENT OF TRANSPORTATION
AND PUBLIC FACILITY PLANNING
On October 13, 1983, I contacted Norton Cook of the Alaska Department of Transportation
and Public Facilities Planning to discuss the Department's plans regarding a road
between Petersburg and Kake. Mr. Cook, who is in the Planning Division, indicated
that the Department is committed to a route in the North Corridor for the proposed
road between Petersburg and Kake. Mr. Cook indicated, however, that a road between
Petersburg and Kake was in the long-term plan. He further indicated that it was
very unlikely that the construction of the road from Petersburg to Kake would be
accelerated. He stated that recent concerns related to funding had deferred many
projects and that the high cost of the road between Petersburg and Kake would be
a significant detriment to such a road being constructed. Mr. Cook indicated
that such a road could be funded through the Forest Highway Program or other
state and federal projects. The major difficulty with using such funds is that
such funds are in high demand and the Kake-Petersburg project would need to
compete with other projects in southeast Alaska to obtain the limited funding.
The limited availability of funds suggests that the road from Petersburg to
Kake will not be completed for some time, according to Mr. Cook.
In response to my question about when such a road would be completed, Mr. Cook
indicated that it was very difficult to estimate when funds would become available,
but he thought that the Kake-Petersburg road would be constructed within the five
to fifteen year time frame, although he indicated that this estimate was highly
speculative. He also said that the project could quite easily be pushed even
further into the future.
WDK:p1
APPENDIX C
Data presented in Table C-1 were developed using the basic information
assembled during routing studies for the mixed overhead/underground
transmission line as well as data from the Draft Feasibility Report for
the overhead line. Consequently, some segments shown in Table C-1 are
not included in the recommended route.
4975B
C-1
TABLE C-1
‘ KAKE-PETERSBURG TRANSMISSION LINE DATA SHEET (MIXED OVERHEAD/UNDERGROUND OPTION)
SEGMENT LENGTH ROADWAY UNROADED GROUND SLOPE SOILS VEGETATION
NO. MI. POST MI. AC. MI. AC, 0-15% 15-303 30-55% 55% PEAT ROCK SILTY-SAND 0 0-60' +60' DANGER TREES
1, 0-4.95 4.95 4.95 2.0 2.95 -- -- 0.2 1.5 3.25 0.8 4,15
2, 4,95-5.04 0,09 -- -- 0.09 0.09 0.05 0.04 0.03 0.06
3. 5.04-5.55 0.51 N/A N/A N/A N/A N/A N/A N/A N/A -- = 0.51 N/A N/A OW/A N/A
4. 5,55-14,10 8.55 8.55 25.91 4.00 3.72 0,83 1.0 4.55 3.0 0 0.5 8.05 855
5. 14,1-15.70 1.6X N/A N/A 1.6 3.88 1.60 -- -- -- 0.4 0.2 1.0 0.2 #04 1.6 320
5A.* 14,1-15.85 1.75" N/A N/A 1.75 52 Mi.(20')=1.26 1.70 0.05 = N/A N/A 1.23 0.52 N/A 1,23 0.52
6. 15.70-16.78 1.08 X N/A N/A N/A N/A N/A N/A N/A N/A - - 1.08 N/A N/A ON/A
6A.* 15.85-17.45 1.60" N/A N/A N/A N/A N/A N/A N/A. N/A = -- 1.60 N/A N/A OW/A
6B.* 15, 7-16.3/15.85 0.6 N/A N/A 0.6 0. 6(10)=0, 73AC 0.6 N/A N/A N/A -- -- 0.6 0.5 5.6 3.4 2694
7, 16,78-30.25 13.47X 0 -- - 13.47 32.65 7.00 5.07 1.30 0,10 2.0 1.0 10.97 422
TA.* 17,45-26.15EQ 8.70" N/A N/A 8.70 8.70(.20)20'=4.22 6.04 1.51 1.15 N/A 6.04 215 1.51 WA 1.4 (30 220
78.* 27.0EQ-31.4 4.4" N/A N/A 4.4 4.4(.8)20'=8.55 1.5 2.5 0.4 N/A 2.0 0.1 2.3 N/A 4,0 5,95 1680
8. 30.25-40.20 9.95X 3.10 9.39 6.85 16.60 6.75 3.00 0.20 N/A 1.5 3.0 5.45 OA 1.0 4.3
BA.* 31.4-37.1 5.7* 5.7(?) 5.7(10")=6.91 N/A N/A 5.5 0.2 N/A N/A v4 1.0 4.3 N/A N/A 6,29 629
8B. * 37,1-40,2 3.1* 3.1 3.1(10)=3.76 N/A N/A 3.1 N/A N/A N/A 0.1 0.3 27 N/A N/A 741 ™
9. 40,20-46.49 6.29 6.29 19.06 4.29 2.0 N/A N/A 0.20 1.0 5.09 WA 0.30 2.8 31
10. 46,49-53.90 7.41 7.41 22.45 -- -- 6.41 1.00 N/A N/A 0.2 0.9 6.31 0.6 --
53.05 -- Includes 5A route
X Section of overhead line being replaced.
(53.65) -- Use old cable X-ing and run above beach storm line
49758