UNITED STATES DEPARTMENT OF AGRICULTURE

Rural Utilities Service

**RUS BULLETIN 1724E-203**

**SUBJECT: [Guide for Upgrading RUS Transmission Lines]{.underline}**

**TO:** All Electric Borrowers

**EFFECTIVE DATE:** Date of Approval

**EXPIRATION DATE:** Seven years from effective date

**OFFICE OF PRIMARY INTEREST:** Transmission Branch, Electric Staff

Division

**FILING INSTRUCTIONS:** This bulletin replaces REA Bulletin 62-7,
\"Guide for Upgrading REA Transmission Structures for Higher Operating
Voltages,\" issued January 1981.

**PURPOSE:** This guide bulletin provides engineering personnel with
information for upgrading transmission lines.

Adam Glodner 12-28-94

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
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Administrator Date

**TABLE OF CONTENTS**

> PAGE

**1
INTRODUCTION**\...\...\...\...\...\...\...\...\...\...\...\...\...\.....
3

**2. CONSIDERATIONS TO BE MADE IN LINE UPGRADING**\...\...\...\.... 3

**3. STEPS REQUIRED FOR LINE UPGRADE**\...\...\...\...\...\...\...\....
5

**3.1**
Clearances\...\...\...\...\...\...\...\...\...\...\...\...\...\...\....
5

**3.2** Right-of-Way
Width\...\...\...\...\...\...\...\...\...\...\...\..... 5

**3.3** Right-of-Way
Easements\...\...\...\...\...\...\...\...\...\...\.... 6

**3.4** Analysis of Existing Lines and Structures\...\...\...\...\... 7

**3.5** Methods to Upgrading/Converting Using Existing Structures 9

**3.6** Insulation
Levels\...\...\...\...\...\...\...\...\...\...\...\...\... 11

**3.7** Cost
Factors\...\...\...\...\...\...\...\...\...\...\...\...\...\..... 12

**4. IMPROVE
RELIABILITY**\...\...\...\...\...\...\...\...\...\...\...\.... 14

**4.1** Improve Lightning
Performance\...\...\...\...\...\...\...\...\... 14

**4.2** Improve Galloping
Performance\...\...\...\...\...\...\...\...\... 15

**4.3** Improve Aeolian Vibration Performance\...\...\...\...\...\....
15

**5. DETERMINING THE BEST SOLUTION**\...\...\...\...\...\...\...\...\...
16

**5.1** Tangible
Factors\...\...\...\...\...\...\...\...\...\...\...\...\.... 16

**5.2** Intangible
Factors\...\...\...\...\...\...\...\...\...\...\...\..... 16

**5.3** Comparison of
Alternatives\...\...\...\...\...\...\...\...\...\... 17

**5.4** Selection of
Alternative\...\...\...\...\...\...\...\...\...\..... 17

**5.5**
Example\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\....
17

**ABBREVIATIONS**

AAAC-6201 - All aluminum conductor-6201 Alloy

ANSI - American National Standards Institute

ACSR - Aluminum conductor steel reinforced

BIL - Basic insulation level

EMF - Electric and magnetic fields

IEEE - Institute of Electrical and Electronic Engineers

kcmil - Thousand circular mils

kV - kilovolt

kVLL - Line-to-line voltage in kilovolts

MSL - Mean sea level

NESC - National Electrical Safety Code

ROW - Right-of-way

RUS - Rural Utilities Service

SSAC - Steel supported aluminum conductor

**1. INTRODUCTION:** The increasing demand for power, coupled with the
difficulty in obtaining new rights-of-way, dictates that the feasibility
of upgrading the capacity of an existing line be considered. In
upgrading the capacity of a line, the possible options include
installing a larger conductor on existing structures, increasing the
operating voltage, increasing operating temperature, increasing the
reliability, or a combination of above.

In general, environmental problems will be less in upgrading an existing
line than obtaining right-of-way for a new facility; however, upgrading
is not necessarily the correct or only solution for increasing demand or
improving reliability.

The primary purpose of this guide is to furnish engineering information
for use in upgrading standard RUS wood pole type transmission lines in
the 46 kV to 230 kV range. This publication is not intended to supersede
RUS Bulletin\
1724E-200, \"Design Manual for High Voltage Transmission Lines,\"

or any part thereof, for design of new transmission facilities; however,
it does provide guidance and certain special design criteria for
upgrading existing lines while maintaining RUS-NESC\
Grade B construction for transmission lines. Much of the information in
this guide bulletin is also pertinent when upgrading a steel or concrete
pole transmission line.

The borrower and its engineer are responsible to fully investigate the
feasibility of an upgrading project based on system load requirements,
sound design practices, economics of construction, operation, and
environmental considerations.

**2. CONSIDERATIONS TO BE MADE IN LINE UPGRADING:** Practically every
power system has found itself in the position of needing to upgrade a
critical transmission line to a higher power transfer capability or
improved reliability. Once this need has been recognized, one
alternative to be considered is whether or not an existing line can be
modified to meet new system requirements. In many cases, the existing
line can be upgraded; however, a hasty decision may result in an
expensive temporary solution to a system load problem that might require
long-term solutions.

Every transmission line upgrading should be evaluated for adherence to
system reliability and planning criteria. The prime tool in performing
this type of evaluation is a system load-flow study.

In addition, some basic analysis can be done using the RUS bulletin on
\"Electrical Characteristics of RUS Alternating Current Transmission
Line Designs.\" This publication provides a means for hand calculations
of individual transmission line performance parameters and
approximations of power transmission capabilities, line voltage drop,
and power losses.

Conductor ampacity can be determined from various sources, such as
conductor manufacturers, EPRI research, the February 1959, IEEE paper
titled \"Current Carrying Capacity of ACSR\" by H. E. House and P. D.
Tuttle, IEEE Standard 738-1993, IEEE standard for Calculating the
Current Temperature of Bare Overhead Conductors (ISBN 1-55937-338-5) and
the Aluminum Conductor Handbook by the Aluminum Association. Each
utility will have to define its maximum operating limits given ambient
temperatures and wind conditions.

Using one or more of the types of analyses described above, certain
essential parameters of the proposed upgraded or converted transmission
line should be defined, namely:

o Operating voltage.

o Line current.

o Proposed conductor size.

o Maximum operating conductor temperature.

Other parameters may also be established but these four are essential
for the transmission line analysis.

Table 2-1 provides a list of minimum recommended conductor sizes for
various operating voltages.

TABLE 2-1

RUS Recommended Minimum Conductor Sizes(1)

[kV]{.underline}LL [ACSR]{.underline} [AAAC-6201]{.underline}

34.5 1/0 123.3 kcmil

46 2/0 155.4 kcmil

69 3/0 195.7 kcmil

115 266.8 kcmil 312.8 kcmil

138 336.4 kcmil 394.5 kcmil

161 397.5 kcmil 465.4 kcmil

230 795 kcmil 927.2 kcmil

\(1\) The above minimum sizes are based on mechanical, corona and radio
interference considerations. Larger conductors may very often be
required because of the economics of power losses and other factors.

Prior to an upgrade, an environmental review of the project is required
in accordance with 7 CFR Part 1794, RUS\' Environmental Policies and
Procedures. Concerns on Electric and Magnetic Fields (EMF), clearance
limitations due to airport approaches, or increased audible noise in
sensitive neighborhoods will have to be addressed.

The borrower should investigate the existing electrical demand on the
proposed transmission line to be upgraded. Discussions should be held
with the construction and operation personnel on the duration, schedule
conflicts, and limitations of an outage. Outage duration and schedule
could impact the design and construction sequence of the line upgrade.

**3. STEPS REQUIRED FOR LINE UPGRADE**

**3.1 [Clearances]{.underline}:** The analysis of structure upgrading
assumes conformity to the electrical clearances recommended by RUS
Bulletin 1724E-200. Where the bulletin is silent on clearances, the
National Electrical Safety Code (NESC) or local code, if more stringent,
is to be utilized. If the local code is more stringent than RUS Bulletin
1724E-200, then that code should be followed.

The latest edition of the NESC should be referred to for emergency and
standard operating installations. Maximum operating temperature can be
based on long term operating conditions. Rules 230A2a and 230A2b of the
NESC are referred to concerning emergency installations

The engineer should compare original design clearances and operating
temperatures with current NESC requirements and RUS recommendations in
Bulletin 1724E-200. Since NESC and RUS clearances have been redefined
over the years, it may be possible to now operate an existing line at
higher temperatures due to redefined clearance requirements. Also, older
lines may have been designed for ice loadings and may have additional
capacity available at high operating temperatures.

**3.2 [Right-of-Way Width]{.underline}**: One of the most important
electrical clearance requirements is sometimes overlooked in procuring
of right-of-way easements for transmission lines. The width of the
right-of-way depends upon many factors, such as:

a\. Structure configuration (phase spacing).

b\. Conductor size and weight.

c\. Structure span length.

d\. Amount of conductor sag.

e\. Amount of conductor blow out.

f\. Operating voltage.

g\. Elevation (MSL).

All of these factors should be considered before a transmission line is
upgraded or converted. In the case of item \"e\" above, RUS Bulletin
1724E-200 discusses conductor blow out and ROW widths based on blow out
calculations.

The following nominal right-of-way widths have been generally proven to
be satisfactory and, in most instances, provide sufficient clearance for
a fallen structure to remain within the right-of-way.

Nominal Line ROW Width ROW Width

[(kV)]{.underline} [(Meters)]{.underline} [(Feet)]{.underline}

69 23-30 75-100

115 23-38 75-125

138 30-46 100-150

161 30-46 100-150

230 46-61 150-200

**3.3 [Right-of-Way Easements]{.underline}:** Easements and permits
should be reviewed to determine any language that prohibits increased
sag or ampacity across the described land. For example, a river crossing
may require revision of an existing Army Corps of Engineers crossing
permit. Easements may have language that greatly restrict the use of the
right-of-way. It should be noted that a borrower may have owned and
operated a 69 kV transmission line within a 30.5m (100 ft.) easement for
the past several years and yet this same 30.5m (100 ft.) easement will
not be sufficient for operating at a higher voltage. The following list
is provided to assist the borrower and engineer in foreseeing some of
the common problems of reusing existing right-of-way.

a\. Some easements may have restricted structure locations and/or line
configuration. Thus in some localities, any change in the configuration
or relocation of individual structures may require renegotiating the
easement.

b\. The centerline of construction does not always correspond to the
centerline of the easement.

c\. Some easements do not specify the right-of-way width. In these
instances, legal counsel will be required to determine the right-of-way
status for upgrading the line.

d\. \"Permanent easements\" should not be confused with \"easements for
construction.\"

e\. Some easements limit the wire size and line voltage.

f\. Encroachments may conflict with a line upgrading.

> o Buildings constructed on or near the right-of-way of the line may be
> located such that horizontal and vertical clearances for an upgraded
> line cannot be met. In many instances, once the permanent facility is
> built within the easement or ROW and \"Code Clearance\" to the line is
> complied with, the borrower cannot force the owner to move the
> facility.
>
> o Ponds or lakes may have been created or expanded.
>
> o New roads and/or driveways may have been built.
>
> o In some areas a change in land use should be considered an
> encroachment. For example, undeveloped rural areas may have been
> converted to producing farmland. This may cause problems in providing
> adequate vertical clearance for the expected use of large harvesting
> combines and/or heavy farming equipment.
>
> o Irrigation systems may have been added.
>
> o Utility or communication facilities may have been constructed since
> the transmission line was built.
>
> o Commercial signs may have been installed.

g\. Easements may contain limitations on tree clearing and/or line
accessibility.

h\. \"Blanket Easements\" should be reviewed by legal counsel.

i\. Line modification might be limited due to the construction of
airstrip facilities or a radio/TV transmitter built nearby since the
original line was constructed.

j\. Public Utility Commission or Public Service Commission approval may
have to be obtained.

k\. Elevation or voltage changes for railroad crossings, highway
crossings, aircraft approaches, or any other crossing may require a
permit.

**3.4 [Analysis of Existing Lines and Structures]{.underline}:** Before
an existing structure or line becomes a feasible candidate for voltage
conversion or improving the current rating, a thorough records search
must be made, detailed field information obtained, and comprehensive
engineering calculations made.

An in-depth review of the design parameters and construction methods
used for the existing transmission line must be conducted at the
beginning of any proposed line conversion or upgrading project. The
purpose of such a thorough study is to clearly define the starting point
and configuration before becoming committed to an expensive,
time-consuming line modification.

**3.4.1** Several essential facts about the existing facilities must be
ascertained:

a\. What basic design criteria was used? Is the original design data
book available? What specific overload factors were used? Which version
of codes or design manuals were used?

b\. What basic electrical clearances (horizontal and vertical) were used
in the original design? Are original construction drawings/contract
documents available? Are existing plan-and-profile drawings up to date?
Has a foot patrol been made to detect right-of-way encroachments,
heights and locations of all utility crossings, and changes in ground
elevations (cuts/fills)? Are pole heights, classes, and locations
correct as shown on plan-and-profile drawings? Are all highways,
streets, and railroads accurately shown? Have any airports or radio/TV
stations been built in the general area since the original line
construction?

c\. Was the existing line designed for greater loads than necessary?
Will the existing foundation and soil conditions sustain increased loads
on the upgraded structure? What standard was used in selecting pole
embedment depths? Do the existing structures have any surplus strength
capabilities? What does the survey of the wood poles indicate concerning
the condition of the existing poles? Is the groundline circumference in
excess of the minimum dimension for the ANSI wood pole class? Is the
wind span for the individual structure less than the maximum allowed for
pole strength capabilities or uplift limitations? Does the existing line
meet current NESC \"when installed\" criteria? What is the condition of
the insulators, conductors, overhead groundwire, and conductor and pole
hardware?

**3.4.2** A survey will be required to spot check clearances and verify
the profile. The field effort begins with determining the physical and
mechanical condition of the existing line. This is in addition to or in
conjunction with a survey of the existing centerline. A quick spot check
of elevations will reveal if a full survey will be required. An
inventory of any changes to the physical features along the centerline
should be recorded with corresponding elevations. Measurements should
also include conductor attachment heights, obstructions, right-of-way
encroachments, and check of span lengths. All wire crossing heights
should be measured during the field survey.

Aerial photography may be used to prepare new plan-and-profile sheets.
The cost will increase with the level of accuracy desired for the aerial
survey. A detailed cost comparison between aerial photography services
and a ground patrol survey should be analyzed.

**3.4.3** Finally, the data should be analyzed to determine the optimal
plan for improvement. Any changes made to the existing line must, as a
minimum, comply with the latest edition of the NESC. Sag and tension
parameters of the existing conductor will have to be determined. Design
tensions may not be very accurate if actual span lengths are not the
intended design lengths or if the field sagging of the wire was not
accurate. Raising structures, moving structures, etc., will change sag
and tension characteristics. Raising a structure may gain clearance in
one span but lose clearance in an adjacent span. Raising a line usually
results in increased tension in the conductor and can put unwanted
longitudinal forces in the new system. If a structure needs to be
raised, the engineer should review the designed cold curve on the
profile to check for a potential uplift problem.

If the existing pole has adequate strength, conductors may be raised to
permit greater sag or to increase clearances. The lower crossarm may
have room to be raised a foot or two depending on the original vertical
spacing or line posts may be added to existing crossarms to increase
clearances. Caution should be exercised, however, that the solution to
one problem does not create another. If the line has experienced
galloping, changing the vertical spacing may introduce phase-to-phase
contact.

If the field survey reveals a distribution line crossing is restricting
the clearance underneath the transmission line, the owner of the
conflicting line should be contacted to remove the conflict. This
approach may be less expensive than changing the transmission
facilities.

**3.5 [Methods to Upgrading/Converting Using Existing
Structures]{.underline}:**

When upgrading a line, the engineer should take advantage of local
environmental experience concerning temperature, ice and wind loadings.
For example, if a transmission line exists in a medium loading zone, but
was designed for heavy loading conditions, the structures may have
strength in excess of what the NESC required and which can be used in
upgrading.

In the previous section, some items of review were suggested to help
determine whether the existing structure configurations have any
significant strength or electrical clearance parameters in excess of
that required by the NESC or recommended by RUS Bulletin 1724E-200. If
the existing structures are found to have certain strength or height
advantages, an upgrading or conversion may be possible with a minimum of
expense involved in material and construction. Some of the methods of
line modification that would fall into this category are:

o Reconductor.

o Bundle conductors.

o Retension existing conductors.

o Increase line voltage using existing conductors.

o Increase operating temperature using existing conductors.

These methods of line modification may be used individually or may be
used in combination with one other. Each method has unique problems
which need to be considered in upgrading.

**3.5.1** [Reconductor]{.underline}: Removing existing conductors and
installing a single larger conductor may be a valid line modification
technique, provided the existing structures have adequate pole strength
and ground clearance to accommodate the increase in vertical and
transverse loads and increased conductor sag.

A larger conductor usually results in considerably higher line tension.
Therefore, all conductor fittings, angle attachments, and deadend
attachments will need to be reviewed for the new strength requirement.
Utilizing new or different conductor configurations will result in
different galloping conductor ellipses. The revised configuration should
be analyzed in the maximum, minimum, and ruling spans to determine
whether the conductors will come in contact during galloping conditions.

Another method of line upgrading/conversion utilizes the installation of
a conductor which has certain vibration damping characteristics such as
Steel Supported Aluminum Conductor (SSAC), Trapezoidal, or Twisted Two
Conductor (T2) type of conductors. Each specialty conductor has unique
installation and handling concerns.

The following items need to be considered for a reconductor project:
clearances, insulator strength, foundation capacity, conductor hardware,
guy strength, pole and structure strength, anchor capacity, vibration,
and galloping concerns.

**3.5.2** [Bundle Conductors]{.underline}: The bundling of conductors to
achieve voltage upgrading may be a valid technique. This method of line
modification lends itself to structures that have excessive pole
strength in their present configuration. Sufficient ground clearance
will be required to offset any increase in insulator string length and
voltage clearance requirements.

Horizontal conductor bundles usually consist of two conductors per
bundle at voltages less than or equal to 345 kV. The horizontal bundle
minimizes the amount of additional ground clearance required for voltage
upgrading because the same wire size and resulting conductor sag may be
utilized. One disadvantage to this technique is that a new conductor
cannot be added to form a horizontal bundle with an existing conductor
(even if they are the same size) because of the difference in initial
and final conductor sag and tension values.

Vertical conductor bundles may be utilized in most of the same
situations as the horizontal bundle. The vertical bundle arrangement
requires about 305 mm (12\") to 356 mm (14\") more height at the
conductor attachment point than the horizontal bundle, due to the length
of the conductor hanger. There are some advantages to the vertical
bundle technique. One advantage is that a new conductor can be installed
in the top position of a vertical bundle and the existing conductor
installed in the lower position. Another advantage is that vertically
bundled conductors may be installed on certain single-pole structures
(e.g., horizontal line post construction).

**3.5.3** [Retension]{.underline}: If conductors are resagged to higher
line tensions, vibration dampers may be required. Guyed structure
strength, guy strength, insulator strength, conductor hardware strength,
foundation capacity, anchor capacity, and uplift capacity also need to
be considered.

**3.5.4** [Increase Line Voltage]{.underline}: Some structures may be
upgraded/converted to higher voltage levels by raising the shield wire
on a type of bayonet and installing new or modified crossarms or
conductor attachment points to higher positions. Structures that may be
modified in this manner must have a considerable amount of excess pole
strength in their present configuration. Raising the shield wire and
conductor locations will increase the ground line moment and other
structure loadings. Increasing line voltage may require increasing line
insulation by adding additional porcelain bells or by changing out
suspension or posts to longer units of porcelain or polymers. If the
existing conductor is to be utilized at a higher operating voltage, it
must be capable of conveying greater electrical loadings. Conductor
separation, insulator swing, corona, insulation level, and ground
clearance must be considered.

**3.5.5** [Increase Operating Temperature]{.underline}: Prior to the
release of the 1977 NESC, utilities generally were designing their
transmission and distribution facilities to meet operating temperatures
of 120°F. At high ambient temperatures with low wind speeds, this
criteria does not provide for a high power transfer. With increasing
electrical demand, many utilities are focusing on increasing the
operation limits of existing transmission facilities. The utility should
contact and/or follow conductor manufacturer\'s recommendations for
maximum operating temperatures. Ampacity is limited by ground-t-
conductor clearance and thermal properties of the conductor. Each
utility should calculate its own conductor ampacity based on local
ambient and operating conditions. The ground clearance for most lines
with small conductor (4/0 ACSR and smaller) in the Heavy Loading
District is controlled by the sag of the iced conductor, not the 120°F
hot sag. During summer peak, the transmission line should have
additional capacity in those cases. A preliminary spot check can be
performed by drawing the higher operating temperature curve over the
existing profile. Generally, old transmission lines do not have reliable
records due to inaccuracies of elevation measurements, addition of
roadways, and new developments that have regraded the ground beneath the
transmission line. Other utilities may have crossings that have not been
documented on the utility\'s permanent records.

**3.6 [Insulation Levels]{.underline}:** In general, the shield angle
for lightning protection should be 30 degrees. However, the shield angle
may be increased to 40 degrees based on the line\'s loading,
reliability, and the system integrity required by the individual line
being upgraded.

For a more detailed analysis on lightning performance, the engineer is
referred to an April 1985, IEEE paper, \"A Simplified Method for
Estimating Lightning Performance of Transmission Lines,\" pages 919-932.

For horizontal post insulators, it is recommended that a BIL be
approximately 20 percent above NESC dry flashover. For suspension
insulators, it is recommended that insulator strings conform to the
recommended insulation levels in RUS Bulletin 1724E-200, \"Design Manual
for High Voltage Transmission Lines.\" However, one bell less than
standard may be used if the following criteria are met:

o The line has an overhead ground wire.

o The pole ground resistance is less than 10 ohms.

o The line is located in an area of moderate isokeraunic\
levels\*.

o The line has no contamination problems.

A polymer insulator should have electrical ratings equivalent to its
porcelain counterpart. Usually the polymer insulator will have an
increased length, reduced weight, and increased leakage distance. The
reduced weight will affect the insulator swing clearances. Each
manufacturer will have different levels of creepage, leakage, flashover
characteristics, BIL levels, and strength ratings.

**3.7 [Cost Factors]{.underline}:** Up to this point, the considerations
to be made in transmission line upgrading have dealt mainly with system
operational requirements, electrical clearance requirements, and
structural performance capabilities. Information presented in this
section will direct attention to expenditures of resources involved in
line conversion and upgrading. These expenditures include finances,
time, manpower, environmental, and material, to note only a few.

**3.7.1** [Additional Right-of-Way Costs]{.underline}: Perhaps the most
important questions to be resolved in any proposal for line upgrading or
conversion concern the right-of-way affected by the line changes. The
method of calculating the minimum required right-of-way width for the
proposed structure was described in section 3.2, page 5.

Another critical question concerning right-of-way is whether or not
additional and adjacent right-of-way can be obtained. If the existing
line route crosses predominantly rural countryside, the chances are good
that additional/adjacent right-of-way can be obtained. If, however, the
existing line route crosses a developing residential area or is
restricted by other existing rights-of-way or geographical features, it
may be virtually

impossible to obtain additional/adjacent right-of-way. In that

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

\*Isokeraunic level - The average annual number of thunderstorm days
used for lightning statistics.

case, alternate methods of line construction must be considered, e.g.,
tear down and rebuild on existing right-of-way width.

If the utility concludes that the additional/adjacent right-of-way width
can be obtained, the next question is the cost of the additional
right-of-way in terms of time and money. Experience has proven that
right-of-way negotiations, settlements, and condemnation actions require
considerably more time and money to acquire than first anticipated.

It is suggested that an assessment of real estate values and properties
affected by the line conversion be made by a private real estate broker
or registered land appraiser. It is further suggested that neighboring
cooperatives and public utilities be contacted to gain information
concerning their recent experience in time and expense involved in
right-of-way procurement or condemnation proceedings.

A firm commitment to proceed with line upgrading or conversion should be
withheld until the utility is satisfied with the accuracy and adequacy
of answers to the questions concerning additional right-of-way.

**3.7.2** [Material Costs]{.underline}: The cost of material involved in
the proposed line conversion or upgrading should be studied. There are
at least three significant items that must have value assessments made
or derived. The first is the \"book\" value of the existing structure,
items, or wires that will be affected by the line modification or
retirement. (This may be obtained from the property accounting records.)
Secondly, the salvage value of the removed materials must be estimated
or otherwise defined. (This value should be entered as a deduct item
when estimating the total project cost.) Thirdly, the cost of the
material to be installed must be defined in order to establish new
structure costs for property accounting records.

Another item that should be considered is the availability of the types
of material being considered for use in the proposed conversion or
upgrading. Material lead time varies in an unpredictable manner;
therefore, the designer should check the supply or availability of
materials needed in the time frame planned for line conversion. Items
such as horizontal line post insulators, long-assembled crossarms, and
cushioned suspension units are usually long lead time items, and their
acquisition may have a bearing on project planning.

**3.7.3** [Labor Costs]{.underline}: The labor cost to convert or
upgrade the proposed transmission line will probably be the most
significant expense item in the project. The amount of time and labor
activities required in a line conversion will be substantial. Labor
costs may be several times as great as material costs.

The categories of labor costs that must be identified and tabulated are
the labor to remove specified items of existing line materials and
dispose of as directed; modify/revise existing structures; install new
line materials; clear additional\
right-of-way.

If the proposed upgrade is a radial line, additional cost for \"hot line
work\" should be considered if unable to take an outage.

**3.7.4** [Technical Analyses]{.underline}: A complete analysis of the
existing transmission line must be performed. An upgrading or conversion
project will have preliminary engineering expenses that must be
considered. The costs should include the time and expenses for the
activities listed below.

> o Record Search - A complete search of design records, drawings, and
> property records to determine the criteria used in design and
> construction of the existing line.
>
> o Field Inspection - A complete and detailed inspection of the
> existing transmission line must be performed, including foot patrol,
> pole inspection, plan-and-profile verification, right-of-way
> encroachment inspection, pole height verifi- cation, pole ground line
> circumference measurements, etc.
>
> o Engineering Analysis - Design analyses of the existing line and the
> upgraded structure must be performed including structure strength and
> hardware analysis, conductor galloping, electrical clearances,
> computation of overload factors, verification of the accuracy of
> engineering drawings, etc.

**4. IMPROVE RELIABILITY:** There are several methods to upgrade a line
and improve its reliability. The following methods may be used in
combination with each other to decrease the number of outages to a line.

**4.1 [Improve Lightning Performance]{.underline}:** There are a number
of ways to reduce the number of outages due to lightning strikes to the
phase conductors. One of the most effective ways is to attach an
overhead ground wire to the structure such that the shield angle to the
conductors is 30 degrees or less. If structure strength permits, a
bayonet may be added to the structure to either add an overhead ground
wire or to raise the existing shield wire and decrease the shielding
angle.

Lightning arrestors with proper grounding may be used to decrease
flashovers due to lightning. Design data and earth resistivity data
should be provided to the manufacturer so that quantities and location
of arrestors are properly determined. The benefit of lightning
arrestors, as compared to the overhead ground wire, is that they will
not greatly increase the loadings on the structure.

Improving grounding on a transmission line will decrease the number of
outages on a shielded transmission line. Additional ground rods may need
to be driven to reach lower resistivity soil layers. In high resistivity
soil, counterpoise may be the best solution. Chemically treated ground
rod systems may be necessary in high resistivity soils.

Insulation should be considered to improve the BIL level of the line. In
contaminated areas, higher silicone rubber composition polymer
insulators may also be considered. The silicone material provides a
hydrophobic surface (water beading) reducing the deposits of
contaminants.

The final method of reducing outages due to lightning involves lightning
dissipation devices. The basis of these devices is that they lower the
voltage differential between the ground surface and the cloud charge
below flashover levels. Sharp points of these devices ionize the
surrounding air, allowing safe transfer of electrical charge to a
grounding system. Since grounding is a key element in the performance of
these devices, grounding techniques mentioned above may have to be used
in highly resistive soils. Lightning experts disagree on the
effectiveness of these devices.

**4.2 [Improve Galloping Performance]{.underline}:** Outages may occur
from phase-to-phase contact of galloping conductors. Outages from
galloping conductors can be reduced several ways:

a\. Increase conductor separation by raising or lowering crossarms.

b\. Add air flow spoilers to break up the uniformity of ice buildup on
the conductor.

c\. Reduce span lengths by adding additional structures.

d\. Reconductor with T2 type conductors. (Structure strength, guying,
and other mechanical factors must be evaluated.)

e\. Add mid-span spacers to eliminate conductor slap. (Conductor
hardware should be reviewed closely to prevent conductor damage due to
aeolian vibration or dynamic stress.)

f\. Add detuning pendulums to dissipate the low frequency energy.

**4.3 [Improve Aeolian Vibration Performance]{.underline}:** Aeolian
vibration may cause conductor fatigue and eventually conductor breaks
creating outages. Several measures may be taken in order to reduce
aeolian vibration:

a\. Install spiral vibration dampers to conductor sizes not exceeding 19
mm (3/4\") diameter. For larger conductor, a pendulum type damper should
be used.

b\. Use cushioned suspension or support hardware in place of
conventional support clamps.

c\. Monitor vibration frequency and amplitude through current recording
devices.

d\. Initiate a visual inspection program to review the conductor, armor
rod, or tie wire damage. Check cotter key or hardware wear and look for
the presence of black aluminum oxide.

e\. Add detuning pendulums to dissipate the mechanical energy.

**5. DETERMINING THE BEST SOLUTION**

**5.1 [Tangible Factors]{.underline}:** The primary factor in a line
conversion or upgrading is the total estimated cost of the proposed
project. As described earlier, the estimated cost for each alternative
method of line conversion should be carefully prepared. The estimated
cost of a totally new transmission line and right-of-way should also be
prepared for comparison of cost and public interest.

A second tangible factor is the time element available to provide the
needed system modifications. If increased power requirements or system
service is required and the time available to construct these system
improvements is very limited, then the modification of existing power
lines on existing rights-of-way can be a very tangible asset.

A third tangible factor is the electrical system capability. If
additional service is needed, or requested, in a part of the system
which has marginal or limited capabilities, the necessity for system
improvement becomes a tangible factor.

**5.2 [Intangible Factors]{.underline}:** In developing any system
improvement, there are a multitude of factors to evaluate. Some of these
are intangible items and thus cannot be meaningfully evaluated in
monetary terms. Two such factors are consumers\' interests and public
relations. Reliability of service and consumer interests are obviously
related. When system analyses conclude that a line conversion or
upgrading is necessary to provide the desired reliability of service,
the consumers\' interests are being supported, and the project warrants
careful consideration.

Maintaining good public relations is a desirable posture for any
organization. A proposal to utilize existing transmission line
rights-of-way for needed system improvements certainly is an attempt to
develop good public and consumer relations. Therefore, the upgrading or
conversion of existing transmission lines within existing rights-of-way
or minimal increases in rights-of-way width is in the best interests of
the general public where possible.

**5.3 [Comparison of Alternatives]{.underline}:** The purpose of
information presented in this document is to provide various concepts
for structure and line modifications. Each of the available methods of
line conversion or upgrading will involve differing expenditures for
materials, labor, rights-of-way, engineering analyses, etc. It is
important, therefore, to prepare comprehensive cost estimates for each
of the configurations to be considered for the upgrading project.

**5.4 [Selection of Alternatives]{.underline}:** After comparing the
various factors described above, the best overall solution can be
determined. Although minimizing construction costs is important, the
need for system improvements may be so critical that an emergency
situation exists, and costs become less important.

Each situation must be evaluated independently and conscientiously. When
this is done, the owner can objectively determine the best solution for
its system\'s needs and be confident that the interests of the consumers
and the general public are also being served.

**5.5 [Example]{.underline}:** A borrower has operated and maintained
20.92 kilometers (13 miles) of 69 kV transmission line, radial feed,
that serves a 69/12.5 kV substation with six distribution feeders. The
transmission line utilizes H-frame TH-1G structures with 266.8 (26/7)
ACSR conductors and (2)-3/8\" H.S. steel shield wires constructed within
a 30.48m (100 ft.) wide easement. The \"Long-Range Plan\" specifies the
need to convert the distribution feeders to 14.4 kV and the
transmission/substation facilities to 138 kV with 795 (26/7) ACSR
conductors and relocate the source substation.

The initial investigation reveals the following facts:

a\. It is currently the month of July with present peak loads already at
the system\'s maximum capability with only a small unbalanced condition,
thus, in-service for the 138 kV operation will be required within 11
months.

b\. Alternative sources for the distribution loads are not available or
they are impractical for long-term operation.

c\. The weak link in the transmission/substation system is the 266.8
conductor. The 69/12.5 kV transformer has additional capacity for the
distribution loads and space was provided for two additional 12.5 kV
feeders.

d\. The right-of-way contains numerous new crossings and encroachments,
(utility, public, and private).

e\. Part of the easements have been purchased by structure location and
with limited right of access.

f\. A metal plating company and railroad spur have since been located
along .75km (1/2 mile) of this line.

g\. The extremely harsh winters with unusually heavy ice have made
construction impractical from November through January for the past 4
years.

h\. The original line was designed with 198m (650 feet) ruling span,
274m (900 feet) maximum span, a conductor operating temperature of
48.90°C (120°F) hot and -17.8°C (0°F) cold, a basic structure of 60 feet
Class 2 poles, one crossarm with some structures being X-braced, and the
conductors were attached with cushioned suspension units. Dampers were
not required as the 266.8 ACSR conductor was installed at a moderate
tension. It was placed in service 9 years earlier.

i\. The profile drawings are incomplete and all other design data has
been lost.

j\. Operations records show a high outage rate due to lightning, trees,
and galloping conductors.

k\. The 69 kV line can be taken out of service only during periods of
low demand.

The following preliminary options must first be reviewed before the
actual upgrading is to be considered.

a\. Determine all other feasible routes on both public and private
properties. These routes shall include right-of-way widths of 15.24m (50
feet), 22.86m (75 feet), and 30.48m (100 feet) and a cost/mile for each.

b\. Determine the relative cost of \"new\" single pole and H-frame
construction with 795 (26/7) ACSR conductors.

c\. Determine the feasibility of expanding the 69/12.5 kV substation by
adding a second 69 kV line, possible loop feed.

d\. Determine the cost of removing the existing line and building a new
line in its place.

e\. Determine if another conductor, 477 (26/7) ACSR or 636 (26/7) ACSR,
can be used at 100°C (212°F) operation and calculate the losses.

All indications resulted in a common proposal, namely, that the existing
line will have to be converted to 138 kV on the existing right-of-way,
with a minimum available outage time, using the same structure locations
and reconductoring with 636 MCM 26/7 ACSR conductor to be operated at
100°C (212°F).

In summary, the TH-1G to TH-VS (69 kV to 138 kV) conversion structure is
recommended for the detailed design considerations. Throughout the
detailed design, the engineer must be aware of specific individual
structure locations that cannot be converted by the use of this
structure. Those unique locations will require special design
considerations and/or replacement with standard RUS 138 kV transmission
structures.

In general, the specific structure for this conversion is chosen for the
following reasons:

a\. It is compatible with hot-line work.

b\. It provides substantial increase in ground clearance to permit
reconductoring to 636 conductor and operating at 100°C (212°F). If the
ground clearance becomes a governing factor as the design progresses,
consideration will have to be made as to the use of self damping
conductors and/or installing dampers on a tightly strung 636 (26/7)
ACSR.