UNITED STATES DEPARTMENT OF AGRICULTURE 

Rural Utilities Service 

BULLETIN 1724D-105

RD-GD-2009-59

SUBJECT: Rural Distribution System Voltage Conversion Considerations

TO: Rural Utilities Service Electric Borrowers and Rural Utilities Service Electric Staff 

EFFECTIVE DATE: Date of Approval. 

OFFICE OF PRIMARY INTEREST: Electric Staff Division 

INSTRUCTIONS: This is a new bulletin. 

AVAILABILITY: This bulletin can be accessed via the Internet at 

http://www.usda.gov/rus/electric/bulletins.htm

PURPOSE: This bulletin recommends that, during initial development and periodic updating 

of system Long-Range Plans (LRPs), system planners include an evaluation of whether it would 

be beneficial to convert some system circuits to a different voltage energization level. To assist 

planners, the bulletin provides engineering guidance on the economic and other factors that 

should be considered in voltage conversion evaluations. This bulletin was prepared with the

intent that planners also refer to Rural Utilities Service Bulletin 1724D-101A, “Electric System 

Long-Range Planning Guide.” 

 May 22, 2009 

_____________________________________ ____________________

James R. Newby Date 

Assistant Administrator 

Electric Program 

Disclaimer: The contents of this guidance document does not have the force and effect of law and is not 

meant to bind the public in any way. This document is intended only to provide clarity to the public 

regarding existing requirements under the law or agency policies.
Bulletin 1724D-105 

Page 2 

ACKNOWLEDGMENTS 

This new bulletin was developed through a cooperative effort of the Rural Utilities Service and 

the System Planning Subcommittee of the National Rural Electric Cooperative Association’s 

Transmission and Distribution Engineering Committee. At the time of publication, System 

Planning Subcommittee members included: 

Robin Blanton, Piedmont EMC, NC - Chairman 

David Garrison, Allgeier Martin & Assoc, OK - Secretary 

Steve Atkinson, Northern Virginia EC, VA 

Mark Barbee, Kansas Electric Power Co-op, KS 

Bob Dew, PowerTech Engineering, GA 

Joe Dorough, Jackson EMC, GA 

Ronnie Frizzell, Arkansas Electric Co-op Corp., AR 

Dee Fultz, Chugach EA, AK 

Wayne Henson, East Mississippi EPS, MS 

Donald Junta, Rural Utilities Service, DC 

Joe Perry, Patterson & Dewar Engineers, Inc., GA 

Georg Shultz, Rural Utilities Service, DC 

Ryan Smoak, McCall-Thomas Engineering Co., Inc., SC 

Harold Taylor, Georgia Transmission Corporation, GA 

Chris Tuttle, Rural Utilities Service, DC 

Kenneth Winder, Moon Lake EA, UT 

Brian Tomlinson, CoServ Electric, TX 

The System Planning Subcommittee and Rural Utilities Service wish to dedicate this publication 

to the memory of David Obenshain, past Subcommittee Chair and Engineering Manager at 

Piedmont Electric Membership Corporation, Hillsborough, NC. His hard work, leadership, and 

character will be missed. 
Bulletin 1724D-105 

Page 3 

TABLE OF CONTENTS 

1 INTRODUCTION ...............................................................................................................4 

2 PRINCIPLES .......................................................................................................................4 

3 ECONOMIC ANAYSIS FACTORS...................................................................................6 

4 QUALITATIVE CONSIDERATIONS.............................................................................11 

5 ANALYSIS........................................................................................................................13 

ABBREVIATIONS 

BIL – Basic impulse insulation level; a reference value of electrical insulating capability 

expressed in terms of the crest value of withstand voltage of a standard full-impulse voltage 

wave. 

CFR – Code of Federal Regulations. 

DV – Dual voltage; applicable to transformers that have multiple taps allowing the user to select 

optional voltage excitation levels. 

FCR – Fixed charge rate; an estimate of the percentage carrying costs of an investment, usually 

taking into consideration the cost of capital, operations and maintenance, taxes, and depreciation. 

GrdY – Grounded wye; most common three-phase distribution system phase and grounding 

conductor connection scheme where one end of each of three transformer windings (comprising 

the individual phases of a three-phase system) is solidly connected to one another and effectively 

grounded to earth via a grounding conductor. 

IEEE – Institute of Electrical and Electronics Engineers. 

kV – Kilovolts, or 1000 volts. 

kVA – Kilovolt-amperes; measure of apparent power on electrical systems. 

LRP – Long-Range Plan; see RUS Bulletin 1724D-101A. 

Mil – Unit of length equal to 1/1000 of an inch (25.4 micrometers) used especially for 

dimensioning the diameter of wire and the thickness of conductor insulation on underground 

power cables. 

OSHA – Occupational Safety and Health Administration. 

RUS – Rural Utilities Service – An Agency of the USDA. 
Bulletin 1724D-105 

Page 4 

1 INTRODUCTION 

a Electric distribution system planning engineers should routinely include, as part 

of their Long-Range Plan (LRP) and LRP update process, the study and 

evaluation of possible conversion of system circuits to a higher utilization voltage. 

Voltage conversion can provide an effective means to economically improve 

service and reliability when implemented at the correct time and when thoroughly 

and meticulously coordinated. Conversions, however, can negatively impact the 

budget when prematurely implemented or poorly planned and coordinated. 

b Before implementing a voltage conversion, conversion plans and projections need 

to show that a conversion will provide significant benefits to the organization. 

Thus, planning engineers’ recommendations to go forward with conversions have 

to be based on comprehensive justification studies that show that the projected 

benefits outweigh the projected costs of the conversion. 

c Planning engineers will find it helpful to review papers that document the voltage 

conversion experiences of other utilities, as well as discuss experiences directly 

with utility personnel. For Cooperatives considering 34.5 kV as a distribution 

voltage, one paper of interest is “Case Study of Radial Overhead Feeder 

Performance at 12.5 kV and 34.5 kV” by Roger E. Clayton and John M. Undrill 

of Electrical Power Consultants, Inc., and Eugene L. Shlatz of Green Mountain 

Power Company (document available from IEEE). 

d This non-codified bulletin presents some of the many considerations that need to 

be included in voltage conversion studies. This bulletin should not be considered 

a complete guide for preparing voltage conversion studies. No matter how many 

points the bulletin discusses, there will always be additional points that the 

planning engineer should consider for a particular system. 

e It should also be stated that, when economically justified, there are many benefits 

to Cooperatives that convert portions of their systems to higher voltages. While 

recognizing and acknowledging these benefits, this document focuses more on the 

cautions and considerations prior to making a voltage upgrade. Cooperatives 

considering conversions to a new system voltage are also encouraged to talk with 

other Cooperatives in their area who have experience with the higher voltage. 

2 PRINCIPLES 

a A decision to commit to convert the voltage on a circuit or circuits or the entire 

distribution system is a consequential decision in the life of a distribution power 

system. The decision to leave circuits on a system at their present voltage is just 

as crucial. It is crucial to the long-term welfare of the system to examine whether 

voltage conversion is in the best interests of system operation and the ratepayers. 
Bulletin 1724D-105 

Page 5 

b Anyone involved in a voltage conversion study (and an LRP) should be concerned 

with the basic question of overall costs to the ratepayers, which, for electric 

cooperatives, are the system member-owners. Although conversion costs to a 

distribution system may appear to be low under some scenarios, be careful to 

view the entire picture. 

c In some voltage conversion scenarios, costs and obligations could be transferred 

to and obligate the distribution system’s power supplier and/or other distribution 

systems. A “one utility” cost comparison should be developed and the least cost 

option, with an acceptable expectation of reliability should be utilized. 

d This bulletin does not recommend retaining the present system voltage any more 

than a conversion to a higher voltage. The bulletin simply recommends the 

voltage conversion question be studied thoroughly and objectively. 

e Most RUS electric borrower distribution line conversions involve upgrading 

12.47GrdY/7.2 kV lines to 24.9GrdY/14.4 kV lines, but the principles provided in 

this bulletin apply to any conversion under study. 

f Theoretically, if a system voltage conversion results in the voltage being doubled, 

load currents of the converted lines should be one-half their previous level, and 

the losses should be cut to one-quarter their former amounts. The overall effects 

of losses on lines and connected equipment, such as transformer core (iron) and 

copper (winding) losses, should be considered in studies. For voltage conversion 

projects that involve long time periods to completion, the use of step transformers, 

dual-voltage distribution transformers, and other equipment with appreciable iron 

losses should also be factored into your analysis. 

g Distribution line voltage conversion may become necessary for reasons other than 

sound engineering economics. For example, an electric system may be faced with 

the need for transmission construction that is not practical, requiring an alternative 

solution such as voltage conversion. Other similar situations, which may make 

voltage conversion a likely solution, include state or local government regulations 

on the placement of electrical facilities, and difficult geographic considerations. 

h Some LRP strategies involve employing an estimated growth rate greater than 

that actually expected for the purpose of “stressing” the system’s key components. 

This strategy is not recommended for voltage conversions, where the use of a 

realistic system growth rate should be employed. Overestimating the growth rate 

may result in premature initiation of a voltage conversion project that is not 

economically nor technically justified. 

i A meaningful voltage conversion study looks at the long-term costs of two or 

more technically feasible alternatives. Proposed alternatives should be capable of 

handling projected system loads at all times throughout the entire period covered 

by the LRP, and each alternative should address and eliminate the voltage 
Bulletin 1724D-105 

Page 6 

problems found within the LRP study period. Since voltage conversion is a 

process that takes quite a few years to accomplish on many systems, the LRP 

provides a recommended way to evaluate the merits and timing of voltage 

conversion possibilities. Via the LRP, system components can be “stressed” for 

both the existing system voltage and the proposed converted voltage and rational 

decisions can be made on whether and when to initiate any conversions. If 

stressing scenarios applied for the last few years of the LRP indicate that the 

system does not yet need to be fully converted to a higher voltage, there could be 

concern that it is not economical to convert the system at all during the LRP 

planning period. 

j It is typical to study conversion of an entire system, but partial system conversion 

may be more practical and economical for some systems. If different portions of 

a system have load characteristics that vary considerably, it may be best to 

concentrate the study on conversion of a portion of the system. However, it needs 

to be noted that a decision to convert a portion of a system might reduce the 

ability to shift load to alleviate losses, or to restore or backfeed circuits in case of 

outages. Because of these reduced abilities, for effective analysis, voltage 

conversion studies that focus on converting a portion of a system need to include 

more scenarios or alternatives than studies that concentrate on full system 

conversion. 

k All factors that can be studied using engineering economics need to be evaluated 

thoroughly using expected load for each year or each “load block” (i.e., 5 years, 

10 years, and 20 years) of the plan. Many of these economic considerations are 

discussed in Section 3 of this bulletin. However, many voltage conversion 

considerations are difficult or impossible to study quantitatively. A number of 

these factors are presented in Section 4 of this bulletin. 

l Voltage conversion to a higher voltage can typically result in fewer new 

substations and thus fewer new transmission taps or transmission line extensions 

than a 7.2/12.47 kV system. Alternative voltages may be carefully evaluated as a 

means to mitigate the ever increasing cost and difficulty in obtaining transmission 

right-of-way.

3 ECONOMIC ANALYSIS FACTORS 

a A study of economic alternatives is readily performed and detailed by using a 

specifically designed spreadsheet or other computer software application, 

hereinafter in this bulletin to be referred to as a spreadsheet. Planning engineers 

should examine available spreadsheets before making a decision as to which tool 

they wish to use or before developing their own spreadsheet. Some consultants 

have developed spreadsheets that may be good for a certain area’s wholesale rates 

or for certain delivery point policies. The Agency has developed an economics 

analysis spreadsheet that may be useful. The Agency spreadsheet is described in 

RUS Bulletin 1724D-104, “Engineering Economics Computer Workbook 
Bulletin 1724D-105 

Page 7 

Procedure.” An electronic copy of the spreadsheet is available on the Agency 

Web site at http://www.usda.gov/rus/electric/bulletins.htm. Statewide 

associations may also have appropriate spreadsheets available. Spreadsheets can 

be linked so transmission costs may be separated from distribution costs, and 

power suppliers’ costs can be separated from and/or combined with distributors’ 

costs. 

b Spreadsheets should be designed to display and summarize the engineer’s cost 

estimates for the various alternatives by time period. Spreadsheets should contain 

all quantifiable factors including the following: 

(1) Evaluation of the costs associated with ordinary system improvements that 

will be needed under each scenario. It will generally be necessary to 

modify existing plans for ordinary system improvements if the voltage 

conversion process is undertaken. 

(2) Evaluation of the cost associated with losses under each scenario. 

(3) Evaluation of the costs associated with member service extensions should 

be evaluated. These costs, on a per unit length basis, usually will be 

higher at the higher converted voltage. 

(4) Evaluation and planning for distribution transformer replacement. For 

instance, planning engineers need to decide whether to use dual-voltage 

(DV) transformers or two transformers on a pole in preparation for the 

actual conversion day. Planning should include consideration of the longterm use of DV transformers and what to do with them after a section is 

converted. 

(5) Evaluation of the use of two-winding transformers or autotransformers 

when a step bank is required. Overvoltage as well as overcurrent 

protection schemes need to be developed and appropriately included in the 

spreadsheet for evaluation. Standardization of kVA sizes should be 

studied, and appropriate evaluation factors should be included in the 

spreadsheet. 

(6) Evaluation and replacement of underground primary cable with higher 

voltage circuits or maintaining existing lower voltage cables and feeding 

them with step-down transformers. 

(7) Evaluation and use of capacitors under each scenario. 

(8) Evaluation and planning with regard to sectionalizing. There are many 

decisions to be made while the conversion process is under way. Some 

systems have reported that smaller fuse sizes at higher voltages tend to 

nuisance-fail from lightning surges. Effective preparation for voltage 
Bulletin 1724D-105 

Page 8 

conversion includes proper consideration and application of protective 

devices. Such higher voltage devices may be purchased and installed for 

application long before the conversion actually takes place. However, be 

careful to ensure that these devices will work properly at the lower 

operating voltage. For example, reclosers may be purchased for the higher 

operating voltage, but they will require the proper closing coil ratings for 

the lower operating voltage while used at the lower voltage energization 

levels. Later, reclosers will require appropriate different closing coil 

ratings for their higher operating voltage at the time of conversion. If the 

voltage conversion impacts areas with DG or other energy sources, the 

Cooperative will need to ensure that any associated protective systems are 

not negatively impacted by the voltage change. 

(9) Evaluation and planning for new substations or changes to existing 

substations that might be necessary during the LRP. This should also 

include any changes to inventory of spare major substation equipment. 

(10) Evaluation and planning related to new transmission. New transmission 

should be considered even for systems that have no current transmission 

facilities. The solution that is economical for the distribution system and 

the distribution system's power supplier usually is the soundest solution. 

(11) Evaluation and planning for right-of-way maintenance. There may be 

differences in methods and cost associated with maintenance of higher 

voltage overhead lines with respect to tree limbs, etc. 

(12) Evaluation and planning to avoid ferroresonance problems. Systems 

operating at higher voltage levels are more susceptible to the flow of 

objectionably high currents related to ferroresonance conditions. 

Attention to proper use and protection of three-phase reclosers and 

three-phase switching equipment becomes extremely important. The 

system’s three-phase distribution transformer bank connection schemes 

need to be studied, and all costs for protection and additional provisions 

need to be included in the spreadsheet. 

(13) The effect of voltage conversion on large-load consumers. Special 

utility-owned electrical equipment and the spares to be maintained need to 

be included in the spreadsheet. Planning engineers need to also consider 

whether large-load consumers may be required to change their own 

equipment as a result of voltage conversion. 

(14) Evaluation of and planning for lower voltage surplus equipment. 

Depending on how rapidly the conversion process proceeds, there may be 

a surplus of electrical equipment used on the old lower voltage system. 

This equipment may have a low salvage value but may be used on other 

parts of the system depending upon the conversion timeframe. 
Bulletin 1724D-105 

Page 9 

(15) The implementation, extent, and timing of the voltage conversion. Many 

line construction activities are undertaken to prepare for a voltage 

conversion. Included are replacing lower voltage insulators with higher 

voltage insulators, hanging dual-voltage transformers (or a second 

transformer), installing step transformers, removing pole ground wires 

above the system neutral (see RUS Bulletin 1728F-803, “Specifications 

and Drawings for 24.9/14.4kV Line Construction”), and changing out 

underground cable and associated riser installations on poles. There also 

may be a need to change out a number of poles. With so many activities 

and items to complete, there may be a desire to do more to “make the 

system as good as it can be” in the first years of operation at the higher 

voltage. If considerable resources were to be expended in pursuit of such 

a desire in excess of a need, a system might not follow the most 

economical path. There is a certain amount of benefit to be derived, 

however, from replacement of aged equipment incidental to voltage 

conversion. For appropriate, effective evaluation, studies need to involve 

methodical inclusion of the various activities and installations during the 

time period when they are actually needed. 

(16) Evaluation and planning for the purchasing, warehousing, and handling of 

extra amounts of materials during the entire conversion process. The most 

notable material items will include underground cable and arresters and 

distribution transformers with three different primary voltage schemes (the 

existing voltage, dual voltage, and the final conversion voltage). When 

converting to a higher voltage for the first time, the planning engineer 

needs to study whether it is better, for example, at 25kV to be conservative 

and use 345-mil primary underground cable or to use 260-mil cable. Plans 

should be made as to whether all new construction will follow the 

specifications for the new voltage level, keeping in mind the length of 

time until conversion is planned. Materials for the lower voltage level 

could continue to be handled by the warehouse for years. Of course, a 

system with new equipment using existing performance specifications 

may experience a measurable benefit regarding losses, maintenance costs, 

and/or reliability. 

(17) Evaluation and planning decisions need to be made about the order of 

conversion. Such decisions may be handled, if necessary, by modeling 

them year-by-year in the worksheet. Many questions need to be answered. 

A few examples are the following: 

• Is it best to build a temporary substation adjacent to an existing one? 

If so, is the temporary substation built for the new voltage or the 

existing voltage? 

• Does an existing substation need to be relieved of load? 
Bulletin 1724D-105 

Page 10 

• Is it better to use step transformers in a substation to step the voltage 

 up, or step it down? 

• Is it better to convert starting from the ends of the distribution system 

 or from the substation? 

(18) Evaluation and planning for deteriorated system components. How will 

deteriorated components be handled? When converting to a higher 

voltage, the replacement of existing equipment with new equipment rated 

for the higher voltage is classified as betterment, and is eligible for both 

financing and capitalizing. Replacing existing equipment with like 

equipment (when not converting the voltage) may not be financeable. 

(19) Evaluation and planning for the means and cost of training employees in 

staking, construction, materials, mapping and services to design and apply 

specifications and safe work practices for higher voltage. 

 

(a) System maps, especially those used in the field, should clearly 

indicate the different voltages and should be kept up-to-date 

throughout a conversion process. Mapping should detail where 

two dead-ends are installed between the line energized at one 

voltage and the line energized at another voltage with a dead span 

in between. 

(b) Training and safety-related cost may also result from changes in 

purchasing and testing specifications for rubber goods and other 

safety-related products for proper performance at the higher, 

converted, voltages. In most cases, costs for training and safety 

considerations can be estimated for planning purposes. 

c Engineering economics studies should be prepared that easily detail the plan’s 

parameters and are of such presentation quality that plan alternatives are well 

contrasted for understanding by non-engineers. Usually, economic studies 

involve the use of spreadsheets for ease of development and “what if” scenarios 

for understandable presentation to decision makers. The Agency recommends 

that the template used for presentation of the study results show the investment by 

LRP steps and by major construction and material factors, such as new 

distribution lines, distribution line conversions, new substations, major substation 

changes, step transformers, distribution transformers, meters, service upgrades, 

sectionalizing equipment, security lights, ordinary replacements, conductor 

replacements, capacitors, and regulators. Transmission factors include new line, 

line changes, and new substations. 

(1) The substation presentation spreadsheet could detail each substation’s 

conditions at the various steps of the LRP. This would show high-side 
Bulletin 1724D-105 

Page 11 

voltage, distribution voltage, load, transformer size, and regulator size. 

Temporary substations would also be shown. 

(2) A spreadsheet would be needed to show operating cost. The rows of the 

spreadsheet might be each year of the LRP, and the columns could be 

present investment cost, future (inflated) investment cost, fixed charges 

(determined by applying the fixed charge rate), the difference in losses, 

total annual operating cost, the present worth of the particular year’s costs, 

and the cumulative present worth cost. 

(3) Detailed spreadsheets will include a listing of improvements, their unit 

costs year by year, and a sum of all those items. There may be separate 

spreadsheets for a power supplier’s costs. 

(4) Spreadsheets should show actual costs in the year incurred as well as the 

present worth of costs for all years studied. 

4 QUALITATIVE CONSIDERATIONS 

Many factors need to be considered when undertaking voltage conversion that may be 

difficult to quantify and evaluate on an economic basis. RUS borrowers should make 

every attempt to evaluate, as far as practical, alternatives on an economic basis. Factors 

difficult to quantify may be included in the narrative portion of the conversion study. 

The following are some items that may not be easy to quantify: 

a The margin of protection will not rise as much as the voltage increases. The 

industry standard basic impulse insulation level for equipment and apparatus used 

on a 12.47/7.2 kV system is 95 kV BIL. The same standard for a 29.9/14.4 kV 

system increases only to 110 kV BIL. As a result, the susceptibility of the higher 

voltage system to lightning flashovers needs to be studied. Will lightning cause 

more cable and/or transformer failures at the higher voltage? 

b Distribution circuits maintained at higher voltages have a lower associated voltage 

drop. This can allow system planners to extend the length of distribution circuits 

and serve a greater number of customers. However, longer distribution circuits 

incur more exposure to outages, accompanied by greater numbers of customers 

affected by an outage. A sectionalizing study and additional equipment may be 

required to address the economic considerations of extended circuits. 

c In sectionalizing 12.47/7.2 kV systems, there may be situations where it becomes 

difficult for the planning engineer to apply simple, inexpensive protection 

solutions. An example is a situation in which actual minimum fault currents may 

not readily be sensed by typical protective devices. Because of the higher 

magnitude minimum fault currents associated with operating at a higher voltage, 

these types of protection problems may be less troublesome. 
Bulletin 1724D-105 

Page 12 

d Backfeed opportunities (or the lack thereof) need to be examined and 

appropriately included in the design and implementation of a voltage conversion 

project, especially if a lengthy voltage conversion process is expected. 

e System design and implementation courses of action have to be well thought out 

and carried out to ensure there will not be objectionable numbers of outages to 

consumers during preparations for voltage conversion and on conversion day. 

f Special care is necessary to make certain that adequate, problem-free, 

sectionalizing measures are designed and applied where step transformers are 

used to feed underground construction serving larger distribution transformers. 

g For systems converting to a higher voltage for the first time, higher voltage cable 

is not as pliable as lower voltage cable. Cooperative personnel should acquire 

conductor samples to help evaluate the new cable to gain installation and 

operational experience. 

h The LRP should include two alternative evaluations of load growth on the system. 

One alternative would detail accommodating the growth with the existing, lower 

voltage system, while the other alternative assesses accommodation of the load 

growth by converting one or more substation areas to a higher voltage. The 

economic development climate or load growth characteristics within a system’s 

service area should be considered as an influence on conversion plans. 

i The use of the proposed voltage by other distribution cooperatives and statewide 

purchasing organizations should be considered in terms of access to properly 

equipped and trained storm restoration line workers and emergency supplies of 

materials. 

j Since more customers may be served from each circuit, respectively, with higher 

as opposed to lower primary voltages, more customers are likely to see power 

quality problems if they arise on the circuit. It should be stated that a higher 

voltage system will be stiffer and should see fewer voltage dips, all things equal. 

k Radio interference has been reported to be a greater problem on systems operating 

at higher voltage levels. This is one reason why Agency specifications for “pole 

protection” do not show use of a grounding conductor above the neutral at 

voltages higher than 12.47/7.2 kV, except for a crossarm mounted arrester. Some 

experts recommend keeping the clearance between hardware (such as pins or 

bolts) and grounds at greater than 10 inches (25.4 centimeters). However, 

maintaining this separation can be a design problem when there is a need to install 

a ground wire up to a crossarm-mounted arrester. 

l Aesthetics, population, congestion of facilities, or contaminated areas could affect 

a decision. 
Bulletin 1724D-105 

Page 13 

m A decision may be required to consider the application of step-up or step-down 

transformer banks for a variety of reasons. Either autotransformers or 

two-winding transformers may be purchased for these applications. Many 

utilities report that two-winding transformers are more reliable, especially at or 

near substations. Experience has shown that autotransformers work better when 

applied on feeders away from substations, and they last longer when their 

impedance is more than 4 percent (on their own rating base). Reactance inserted 

in the delta tertiary winding may help autotransformers better withstand lightning 

and through faults. For any application of either type of transformer, good 

grounding and adequate lightning arrestors are a primary consideration. 

5 ANALYSIS 

Once all the estimates and facts have been gathered and the analyses of the base system 

with the alternatives have been evaluated, the total present worth dollars for each 

economic factor under each option studied have to be developed. The appropriate 

economic factors have to be summed to determine the grand total. If the economics show 

two alternatives are close in evaluated cost, then the system planner should perform 

sensitivity analyses to see if a change in one or more assumptions will clarify the system 

planning decision. Examples of sensitivity variables would be growth rates, interest 

rates, and/or real estate costs (for substations and transmission lines). Another sensitivity 

variable might be the longevity of a plan beyond the time range studied. A system 

planner might also evaluate two alternatives for their load-carrying capability in the 

intermediate conversion steps. In the absence of a clear economic recommendation to 

change the system voltage, many planners believe that the present system voltage should 

be retained because of what is known about the existing system in comparison to the 

unknown situations to be faced with the alternatives.