EXECUTIVE SUMMARY
INDEPENDENT REVIEW OF PROPOSED DOUBLE-CIRCUITING
Xcel Energy Red Rock-Wilson
115 kV Transmission Line
Prepared For
TRANSMISSION LINE STEERING COMMITTEE
Hon. Charles Mertensotto
Mayor,
Hon. Francis Tiffany
Mayor,
Hon. Kathleen Gaylord
Mayor,
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Prepared by: |
At the Offices of: |
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John Guidinger |
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David Shafer, P.E. |
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David Mooberry, P.E.
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Robert McGonegal,
P.E. |
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Kristopher
Strawmyer, P.E. |
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Joel Schaeffer |
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Mike Conley |
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With Assistance
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Rodger Skare |
Collier Towle, Inc |
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Kathleen Egan-Bruhy,
Ph.D. |
Commonwealth
Cultural Resources Group |
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Peter Valberg, Ph.D.
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TABLE OF CONTENTS
Cost Estimates for
Proposed and Optional Projects
Potential
Environmental Effects
Tables
1. Overall Project Summary
with Effect of the Existing Line
2. Calculated
Electric and Magnetic Fields and Noise Within Right-of-Way
Figures
1. Existing and
Alternative Routes (345 k)
2. Existing
115 kV Single-Circuit Wood H-Frame
3. Proposed
115 kV Double-Circuit Tubular Steel Pole
4. Alternative
115 kV Single-Circuit Wood or Steel Pole Tangent Structure
5. Alternative
115 kV Single-Circuit Steel Pole Light Angle Structure
6. 115
kV Double-Circuit Alternative Underground Transmission Line
7. Overhead/Underground
Structure (Typical) 115 kV Transition
8. Curve
Showing Calculated Electric Field Values
9. Curve
Showing Calculated Magnetic Field Values
10.
Curve Showing Calculated Audible
Noise Values
EXECUTIVE
SUMMARY
Introduction
Commonwealth
Associates, Inc., (CAI) was selected by a Steering Committee composed of the
mayors of South St. Paul, Sunfish Lake, and
Mendota Heights (all in Dakota County, Minnesota) to evaluate the proposed
double-circuiting of the Red Rock-Wilson 115 kV electrical transmission line.
Xcel Energy (Xcel) is proposing to replace the existing Red
Rock-Stockyards-Rogers Lake-Bloomington-Wilson 115 kV line with a
double-circuit 115 kV line on the same right-of-way using new structures. The
existing line (Figure 1) is 14.0 miles long, of which 8.9 miles is in northern
This review looks at various aspects of the proposal including: 1) the need for the second circuit, 2) potential alternative system improvements, which would make the second circuit unnecessary, 3) electrical effects in terms of electric and magnetic fields and audible noise, 4) the appropriateness of the tubular steel structure, 5) the economic cost of the proposed project and alternate options, 6) possible alternative routes for the second circuit, and 7) potential impacts to features of the natural and cultural environment.
Proposed Project and Alternative Options
The
project proposed by Xcel would improve the transmission system along the east-west
corridor between Red Rock and Wilson (Figure 1). The proposal consists of
installing a 0.5-mile-long section of new conductor on the existing structures
between Red Rock and Stockyards and then replacing the remaining 13.4-mile
portion of the line across
CAI developed five optional routes or system modifications as alternatives to double-circuiting the existing route. These are discussed in the following paragraphs.
Option A,
like the proposed project, would improve the east-west transmission system
between Red Rock and Wilson. This option would string new conductor for 0.5
mile between Red Rock and Stockyards and then double-circuit the existing line
for 0.8 mile to the area of
Option B
is the same as Option A except that a new 6.8-mile single-circuit line would
follow the south side of Interstate 494 most of the distance to
Option C
would improve the transmission system starting at
Option D
would improve the transmission system starting at the Inver Hills Generating
Station to the south of
Option E
would reconductor or double-circuit 16.3 miles of transmission lines from both
the north (from High Bridge) and from the south (from Inver Hills) as described
for Option C and Option D. Option E would also include stringing new conductor
for 0.5 mile between Red Rock and Stockyards and double-circuiting 2.2 miles of
the existing line between Bloomington and Wilson. However, the existing line would
not be altered across
Need for Second Circuit
CAI
reviewed power flow data provided by Xcel as a part of information submittals
made to the Federal Energy Commission. By 2004, several outage conditions cause
the loadings on 115 kV lines in the
At the
double-contingency level, loss of the Terminal-Western circuit with a prior
outage of either the Red Rock-Stockyards or Stockyards-Rogers Lake circuit
causes overloading of various 115 kV lines in the St. Paul 115 kV system. Also,
loss of the Terminal-Western circuit with a prior outage of the Terminal-Prior
loads the
To reduce these transmission system deficiencies, Xcel proposes to add a new 115 kV circuit between Red Rock and Wilson by rebuilding the existing line into a double-circuit line. Outage of the existing circuit or other associated lines would no longer be a significant concern with this double circuit established.
CAI System Study Methods
CAI’s
study was conducted using the TRANSMISSION 2000 Power Flow computer program
package developed by CAI and used for many years for transmission modeling
projects for utilities throughout the
Electrical loading on the Twin Cities 115 kV system is influenced primarily by local load and generation levels and the summer peaks in the Twin Cities area. Since the thermal ratings of the overhead circuits are substantially higher during the lower load winter season, the summer loading conditions were used for the study. Both the 80 and 100 percent peak system load levels were studied. Under certain conditions the 80 percent off-peak loads can produce higher loadings on certain facilities than the 100 percent peak loads.
Xcel
currently imports substantial hydroelectric capacity and energy from
Tn order to keep the amount of power imported from Manitoba Hydro constant under all conditions, generation output was appropriately adjusted in the study at various Xcel generators in the base cases with different system load levels. The generation adjustment was accomplished using an Economic Dispatch Order ($/MWh Comparison List) of all Xcel units. Tn general, oil-fired generation was removed in the study first, then the gas-fired generation, coal-fired generation, and finally nuclear and hydroelectric units.
Results
CAI’s studies of Xcel’s proposed improvements to the Red Rock-Wilson line and five alternate options indicate that none of the plans satisfies all of the identified transmission system needs. However, Xcel’s proposed plan comes the closest to meeting the needs, taking into account the economic cost of the improvements.
Options A and B are electrically almost identical to the proposed plan. These two options would place the second circuit on one of two potential alternative routes.
With
Option C at the 80 percent load level, the Rogers Lake-Stockyards circuit loads
to 116 percent of its normal rating for the double-contingency outage of the
Terminal-Western and Terminal-Prior 115 kV circuits. This level of loading is
essentially the same magnitude experienced without any system improvements (117
percent) for the same outage. Therefore, Option C does not solve one of the
most significant overload conditions in the
Option D would result in maximum contingency loading on the High Bridge-Rogers Lake circuit of approximately 120 percent of normal line ratings. Option D does not eliminate, but does reduce, the overload on this circuit, but not as well as Xcel’s proposed plan. Option D reduces many other overloads at a reasonable economic cost.
Option E appears to satisfy more transmission needs than Option C and about the same level as Option D. The higher cost of Option E compared to Option D or Xcel’s preferred plan would be a disadvantage.
Separate
from comparing the options identified above, CAI’s study indicated a need for
reconductoring or double-circuiting the
CAT calculated anticipated levels of electric and magnetic fields (EMF) and audible noise for the existing line on H-frame structures (Figure 2) and the proposed double-circuit line using steel pole structures (Figure 3). For the alternative route portions of Options A and B, calculations were made for a single-circuit tangent (Figure 4) and light-angle structure configuration (Figure 5). For the reconductored lines put forward under Options C, D, and E, the expected EMF and audible noise values would be similar to the values calculated for the existing line. Calculations were also made for a double-circuit underground line (Figures 6 and 7).
Calculated electric and magnetic field values are shown in Table 2 (and plotted in Figures 8 through 10). Double-circuiting the existing line on the existing right-of-way will reduce the electric and magnetic fields. Maximum electric fields measured 3 feet above the ground at the edge of the right-of-way will be reduced from 1.0 to 0.6 kilovolt per meter (kV/m). Assuming a load of 800 amps for the existing circuit and 400 amps per circuit after double-circuiting, magnetic field strengths will be reduced from 86.7 to 21.0 milligauss (mG) at the edge of the 50-foot right-of-way assuming that the conductor phases are arranged on the new structures as shown in Figure 3.
Noise may be produced when the energized conductors are wet, such as during rainy periods. Compared to the existing line, CAT’s calculations (Figure 10) indicate that audible noise will be slightly increased from 20.4 to 24.5 decibels (dB(A)) to a listener standing at the edge of the 50-foot right-of-way. The increase is accounted for in part by the increased number of conductors in the double-circuit line. However, this noise level is still very low and should be rarely heard in an outdoor setting. Conditions most likely to cause these noise levels to be noticed would be when other background noise is absent, the wind is still, and the conductors are wet from fog, rain, or snow.
If the second circuit is placed on an alternative single-circuit route, the electric and magnetic field values would also be lower along both the new line and along the existing line than along the existing line at present. At 3 feet above the ground, calculated electric field values at the edge of the right-of-way for the new single-circuit line are 0.3 to 0.6 kV/m and (at 400 amps) calculated maximum magnetic field values are 15.9 to 27.2 mG. Audible noise is calculated to be 21.8 to 23.2 dB(A) at the edge of the 50-foot right-of-way.
Placing the two circuits underground would eliminate the electric field at grade and reduce the maximum magnetic field to 1.0 to 1.2 mG at the edge of the 50-foot right-of-way. The underground line would not produce noise.
These values would be slightly higher for the narrower 40-foot-wide right-of-way as shown in Table 2.
Generally, when adding circuits in urban areas where right-of-way space is limited, utilities use tubular steel poles instead of wood and lattice steel designs for the 115 kV class of transmission line. Vertical double-circuit tubular structures are compact, strong and lightweight, and can be assembled and erected with a minimum of effort at the work site. Tubular steel poles are also used for all sorts of other applications, such as antenna masts, light poles, and flagpoles.
The design
work for the line will develop specifications so that the line can be properly
constructed to withstand the static, construction, wind, and ice loads expected
during the service life of the line. Many hundreds of miles of transmission
lines across the
Cost Estimates for Proposed and Optional
Projects
To assist
in comparing the project proposed by Xcel to the options developed by CM, a
series of conceptual cost estimates were prepared by CAT. These cost estimates
attempt to compare whole project costs, including the costs of terminal and
transmission system modifications outside
CAT cost estimates for the options are:
Double-circuiting project proposed by Xcel - $16.1 million
Option A: Single-circuit segment on Alternative Route A — $16.8 million
Option B: Single-circuit segment on Alternative Route B — $17.3 million
Option C: Rebuild line between High Bridge, Rogers Lake and Wilson — $21.6 million
Option D: Rebuild line between Inver Hills, Rogers Lake and Wilson — $16.1 million
Option F: Rebuild line between High Bridge, Rogers Lake, and Inver Hills — $19.2 million
Underground costs were also developed by CAT for three underground segments. The cost to underground a 3,000-foot double-circuit line on the existing right-of-way through the residential area in South St. Paul is estimated to be $4.6 million. The cost of an underground segment extending 7,000 feet cross the city of Sunfish Lake on the existing right-of-way is estimated to be $9.8 million. The cost for a 9,700-foot segment on a realigned route following the south side of Highway 110 and the east side of Delaware Road in Sunfish Lake is estimated to be $14.1 million. These estimates account for the savings in overhead transmission line costs.
Alternative Routes
Many people living near the existing line have expressed their opinion that the second circuit should be placed on another route instead of double-circuiting on the existing right-of-way. CM assembled a routing team and conducted a routing study to develop alternative routes for the second circuit.
Since no concern has been expressed with double-circuiting portions of the existing route, the CAT routing team did not study alternative routes in these areas. Areas where alternative routes were not considered are between Red Rock and Concord Street in South St. Paul and the area west of the Minnesota River in Bloomington in Hennepin County. In the remaining 7.6-mile corridor in Dakota County, members of the routing team visited the project area on various dates
and studied aerial photographs and maps to identify and evaluate potential alternative routes that minimized impacts to features of the natural and cultural environment. Segments of the existing route were designated as links so that alternative routes could be compared to the existing route. Because of the intensively developed land uses in many areas, alternative routes were placed almost entirely along existing road rights-of-way or combined as a second circuit on other existing transmission lines in the area.
Five routes from the link-node network were assembled for review as shown in Table 1.
Comparison of Routes A and B
Alternative Route A appears to be somewhat superior to Alternative Route B, primarily in terms of fewer residences within 250 feet of the route centerline. Route B would also require doublecircuiting an existing line (link 18) through 2,300 feet of residential land uses and across 1,650 feet of the Visitation Monastery and School south of the Rogers Lake Substation. Route A, which enters the Rogers Lake Substation from the north, would double-circuit an existing line for 2,400 feet to reach the substation across the Mendota Country Club’s golf course. Both routes would degrade the visual appearance to motorists of scenes along Interstate 494 and Minnesota Highway 110. Both of these relatively new roads are not currently cluttered by power lines or other developments.
However, in CAI’s opinion, neither alternative route offers any strong advantage to double-circuiting the existing line as proposed by Xcel. Although there are now fewer existing residences along the alternative routes, it is likely that residences will soon be built along these routes given the extensive and rapid urban development underway in the project area. Review of aerial photography of recently developed land indicates that residential development will cover most of the land in the area.
In proposing a double-circuit line, Xcel has given up some electrical reliability to reduce environmental impact. Utility system planners, including those at Xcel with whom CAI talked, will almost always prefer single-circuit lines because they provide greater electrical reliability from outages caused by storms and other events. Storms of sufficient strength to cause an outage of a 115 kV transmission line will generally outage both circuits on a double-circuit line. If the two circuits are on separate single-circuit lines some distance apart from each other, there should be much less chance that both circuits will be lost to a single storm. Perhaps Xcel understands the difficulties of obtaining a new right-of-way in the project area and has not really given up much. However, for whatever reasons that double-circuiting was proposed, the result should be reduced environmental impact compared to placing the second circuit on a new transmission line.
Comparison of Routes C, D, and F
Table 1 also provides comparative environmental data for Routes C, D and F. These “routes” are existing 115 kV lines that would be upgraded under Options C, D, and F, respectively, by double-circuiting or reconductoring the lines as an alternative to double-circuiting much of the existing Red Rock-Wilson line. No new line would be constructed for these three options.
Although the most suitable option will be determined first by system considerations, the environmental inventory in Table 1 shows the settings of these lines in response to questions from the public.
These existing lines are in place and, as such, have existing impacts. Double-circuiting or reconductoring the lines would add somewhat to the existing impacts by, for example, increasing the impact to visual resources from larger structures and more numerous conductors for double-circuiting or from larger conductors and perhaps some larger replacement structures for reconductoring. Short-term construction impacts would also occur. In CAI’s experience, both double-circuiting and reconductoring of an existing line result in less impact to the surrounding environment than development of a new line. Table 1 does not attempt to account for the different intensity of impact to environmental resources from activities that would range from constructing a new line to double-circuiting or reconductoring.
Use of Highway Right-of-Way
Like other states, Minnesota highway regulations do not allow parallel utility lines on “freeway” type rights-of-way, although short crossings of and overhanging interstate highway right-of-way are usually allowed when no other alternatives are available. Some utility lines may be allowed on peripheral interstate-owned parcels that are outside the highway boundary fence and beyond any vehicular highway access ramps. However, access to the utility line for construction and maintenance must be from off-highway routes.
On other Minnesota state highways that are not “freeways,” utility lines may be placed on highway rights-of-way with the approval of the Minnesota Department of Transportation. However, if the highway is to be widened or otherwise moved, the utility must pay to move the transmission line at its own expense. Like most utilities, where transmission lines parallel a road right-of-way, Xcel’s policy is to locate the structures a minimum of 2 feet outside the road right-of-way to avoid possible moving costs.
Crossing the Minnesota River
Due to potential ecological impacts to the sensitive and unique wetlands on the Minnesota River bottoms, CAT did not establish a link along Interstate 494 west of Dodd Road. In a meeting on August 23, 2000, in St. Paul to discuss this specific subject, the Minnesota Department of Natural Resources (DNR) indicated that it did not want to see a proliferation of new right-of-way in the Minnesota River bottoms because of the extreme sensitivity of the area to ecological impact. Wetland permits would be difficult to obtain because a new route along Interstate 494 would certainly be viewed by the Minnesota DNR as more damaging to wetland resources than double-circuiting the existing line.
Potential Environmental Effects
Count of Residences Within 50 Feet of the Existing Line
A count was made of the residences within 250 feet of the centerline of the existing transmission line. The following residences were counted:
Distance Number
0-25 feet 24
26 to 50 feet 21 (Includes 4 apartment buildings)
51 to 100 feet 40 (Includes 1 apartment building)
100 to 250 feet 140 (Includes 7 apartment or condominium buildings)
Three houses encroach on the existing Xcel transmission line right-of-way. These are:
815 3 rd Avenue South, South St. Paul
2166 Charlton Road, Sunfish Lake
2196 Dodd Road, Mendota Heights
Effect on Residential Property Values
A major concern of local residential property owners adjacent to a high-voltage transmission line is that the line will reduce the value of their property. These fears are based primarily on visual concerns, possible interference with the development of their property, and the potential for EMF concerns to repel potential buyers.
Many studies have been made of the effect of transmission lines on residential property values. Most of the studies are performed using one of two methods. The first method is to conduct an opinion survey of persons owning homes along transmission lines, other home owners, and real estate professionals. The second method is to compare the sale prices of homes along transmission lines to similar homes not along transmission lines. Opinion surveys generally show that people believe homes near a transmission line would sell for about 4 to 10 percent less than a similar house not near a transmission line. Most of the sale price comparisons show that actual sales prices for houses along transmission lines are either very similar to other comparable houses or that the price is generally no more than about 2 to 4 percent lower. The studies often show that houses adjacent to transmission lines take slightly longer to sell than a similar house not adjacent to a transmission line.
Minneapolis-based Colliers Towle, Inc., was requested to perform a survey of sale prices for the Steering Committee. The firm compared the recent sale prices of 12 subject houses along the existing Xcel transmission line by. pairing each subject house with three comparable similar houses in the same neighborhood. Colliers Towle also selected 10 other subject houses along a double-circuit transmission line in the Twin Cities area having the same type of tubular steel structures proposed for the Red Rock-Wilson line. The 10 houses along this line were paired with a total of 13 comparable houses in their neighborhoods. Colliers Towle appraisers adjusted the sales price of the comparable houses to equalize differences in house characteristics with the subject house.
The study found that houses adjacent to transmission lines sold for an average of 0.5 percent less than houses not near transmission lines. The houses near the line took an average of 5.5 days longer to sell. Although the scope of the study is limited, the results are very similar to other studies that compare sales prices.
Color of Structures
Steel-pole transmission structures may be painted or left in the natural galvanized finish, which is a light gray color. Generally, painted structures are not galvanized and therefore are more prone to rust discoloration, even if painted. Light pastel hues of blue, brown, blue, and red are commonly used. Painting becomes a maintenance item for the utility, and the structures may exhibit paint flecking or peeling and rusting in the last few years of the painting cycle.
Wetlands
A wetland permit to double-circuit the existing route or build a single circuit on either Route A or B will be required from the Minnesota DNR. The existing route crosses approximately 7,100 feet of wetland soils. Alternative Routes A and B cross 8,400 and 8,100 feet of wetland soils, respectively. Most of the wetlands are in the Dodge Nature Center or along the Minnesota River.
Some wetland tree clearing will be needed to construct the single-circuit line on Alternative Routes A and B in wetlands. One or two replacement structures will have to be located in wetlands on the existing route where it crosses the Dodge Nature Center, and on all routes several replacement structures will have to be located in the Minnesota River bottoms. Other wetlands should be narrow enough to be spanned between structures.
All
activities within the wetland will be in accordance with any conditions
contained in any state or local permits required under applicable wetland
protection acts or ordinances. Wetland impacts will be temporary and will
consist of soil compaction on the right-of-way, damage to low-growing
vegetation, and disturbance to streams from the installation of temporary
culverts to cross stream channels. Wetland impacts can be minimized by the use
of mats for temporary construction access roads or by scheduling construction
during the winter when the soils are frozen in winter. Once the line is placed
in service, the construction road will be removed from wetland areas, and in
upland areas the roadway will be allowed to revegetate. Usually, wetland
right-of-way areas rapidly return to a condition similar to their
pre-disturbance condition, although some weedy species may persist for a few
years. Soil compaction and vegetation disturbance should be dissipated after a
growing season.
Dodge Nature Center
Short-term impacts will be associated with the construction activities of rebuilding the existing line or Alternative Route A across the Dodge Nature Center. The existing right-of-way crosses approximately 2,950 feet of the nature center along its southern property line, and Alternative Route A crosses about 2,700 feet of the nature center on its northern boundary. Existing or potential right-of-way for the two routes would encompass about 3.4 acres and 3.1 acres, respectively. Route A crosses approximately 1,600 feet of wetland soils; Route B crosses about 650 feet of wetland soils.
Some trimming of trees and tall shrubs may be needed, and a few specific danger trees (tall trees near the right-of-way) may have to be removed. A temporary culvert may be installed in the large ditch on the western side of the Dodge Nature Center and possibly at other locations to allow the passage of equipment along the right-of-way. As previously discussed for wetlands, construction equipment will compress soils and low-growing vegetation on the right-of-way, especially at structure construction sites.
Double-circuiting the existing line will somewhat increase visual aesthetic impacts to nature center visitors due to the increased height of the double-circuit replacement structures. The more natural appearance of the existing wood-pole H-frame structures would be lost to steel structures. Alternative Route A would increase overall visual impacts by adding a second circuit across the nature center on its northern boundary while leaving the existing single-circuit line in place. Alternative Route B would avoid any change to the visual resources at the nature center.