Optimized Line Design in a Deregulated World
Fred A. Brown, P.E.
President and CEO
LineSoft Corporation
12310 East Mirabeau Parkway
Spokane, WA 99216
Rodney W. Griffith, P.E.
Reliability Manager
Entergy
9425 Pinecroft Dr
The Woodlands, TX 77380
Abstract
Utilities face the dilemma of how to increase power delivery and power line reliability without corresponding budget increases. Through optimization, they are able to improve reliability by performing more upgrade projects within existing budgets, and they are able to design and build new power lines more cost-effectively. Optimization results in best-cost designs without sacrificing performance and reliability and without violating standards and code compliance. Using automated design and optimization software, engineers can effectively evaluate the impact of the many factors that affect the cost, performance, and reliability of electric lines. They can quickly and precisely investigate numerous options and identify the best combination for each situation. The automation solution becomes a natural extension of the engineer’s design process, stimulating new ideas and enhancing creativity. Implementation of optimization requires a process change that results from a candid evaluation of practices throughout the business, including an objective comparison of traditional engineering “rules of thumb” with new engineering procedures. While utilities are justifiably reluctant to disrupt established, successful processes, they have a real incentive to incorporate new automated optimization tools that transform the process of power line design. Optimized design processes can save millions of dollars each year while also enhancing reliability.
Conflcting Pressures
Utilities face unprecedented pressures from seemingly incompatible forces:
- Expand Power Delivery. The public and public officials are demanding more power and rapid design and construction of new facilities.
- Meet Financial Goals. The realities of the current business climate impose severe cost constraints on utilities. Utilities have more projects to accomplish than they have money to accomplish them. As a result, utilities are examining every option to reduce costs.
- Increase Reliability. Regulatory bodies are focusing more than ever on reliability. They are setting performance and reliability standards and imposing penalties on utilities that fail to meet those standards. This is spurring utilities to be proactive in ensuring that their designs meet stringent safety and availability criteria.
To meet these challenges, utilities are examining every possible approach to hold down costs, improve reliability, and enhance customer satisfaction. They are seeking innovative approaches to major increases in workload without corresponding budget growth. This requires a frank reexamination of processes and procedures throughout the organization. Successful utilities are employing best practices, addressing these problems through a creative combination of tactics: changing to new material, standardizing parts for economy-of-scale purchasing, enhancing crew efficiency, re-training and cross-training personnel, outsourcing labor, employing consultants, or sharing of resources across the enterprise. This paper focuses on one vital aspect of the solution, the use of new automation tools to maintain or reduce costs without jeopardizing reliability.
The Case For Automated Optimization
New design and optimization tools are available to:
- Complete designs more quickly and reduce the cost of the design process
- Produce the most cost-effective designs
- Ensure that designs result in reliable power lines
Many factors affect the cost and performance of a power line. The designer must recognize which factors can be safely manipulated to reduce costs and which factors cannot or should not be changed. The designer then determines the optimal combination of variables that results in the best-cost design within reliability standards.
Historically, utilities have limited the variables available to the designer and applied a series of rules of thumb to the process. Typically, they ensured reliability through expensive overdesigns. These standardized rules may or may not be based on sound engineering judgment. While standardized materials and practices are more important than ever, economic and reliability pressures require flexibility within standards, and sophisticated new computer systems make that flexibility possible.
Designers are called upon to process an ever-greater number of distribution work orders in a more expeditious manner with fewer resources. They are also required to ensure reliability under pressure of penalties. These productivity requirements have often caused technicians and designers to employ extremely conservative design methods that allow them to process work orders more quickly. Designers go with what they know will work, from experience or rules of thumb, rather than taking the time to evaluate alternatives that may result in more cost-effective designs.
Line design and structure spotting are historically laborious, complicated tasks. Designers have not had time to thoroughly consider what-if scenarios. Intuition and experience help, but this has been a trial-and-error process. Only with the availability of new automated optimization tools can designers effectively work through the complicated interrelationship of variables that affect the spot, identifying and tracking the cost of each design decision. Automated optimization enables the designer to determine the factors that limit the design, manipulate those factors and then re-spot the line. By modeling designs and varying the factors described below, the designer is able to determine the optimum combination of price, performance, and reliability.
Overhead Optimization Process Factors
No two power line installations are the same. Differences in terrain, wire size, environmental loading, routing constraints, and other factors require that the designer consider each line as a new challenge. There are a number of factors the designer must consider in optimizing the cost and reliability of any line:
Maximum span length
The maximum allowable span length is the single biggest factor in potential savings during optimization. Rather than take the time to analyze each structure and location, designers have typically opted to stouten up the line. For overhead designs, this means shortening the spans. For underground, it means adding equipment (e.g., reducing the number of services per transformer).
- Excessive galloping motion under ice and wind conditions can bring conductors in contact and cause outages. Instead of the costly approach of shortening span length, the designer might consider a longer crossarm to increase phase wire separation or drop the neutral attachment to limit contact between phase and neutral lines.
- Designers might address iced-to-bare concerns by increasing vertical separation between conductors or using crossarm (instead of vertical) construction with the neutral on an offset bracket or on the crossarm.
- Horizontal and vertical separation required by NESC can limit a utility’s standard framing configurations. Designers can gain significantly longer spans by increasing phase and neutral separation at the structure, by increasing phase spacing with a longer crossarm, or by framing the neutral further down the pole.
- Right-of-way limitations often result in vertical construction to avoid overhanging private property. Sometimes, a few feet of overhang easement can allow the designer to use crossarm construction, increasing span length and reducing the total cost of the line, even with the added cost of the easement.
Conductor Tension
Conductor tension can have an enormous effect on line cost. Design tensions set low can result in large sags, excessive conductor motion, and shorter spans. Alternatively, design tensions set high (particularly in areas where short spans are required for reasons other than ground clearance) can result in expensive guying, oversized dead-end crossarms, or aeolian vibration with no appreciable cost benefit. Optimum design tension is particularly important during reconductoring when the line route contains fixed or existing structures. A loose conductor often results in a more flexible spot of new structures without putting existing structures into uplift. In hilly terrain, a slight reduction in design tension can eliminate dozens of hold-down (dead-end) structures in low areas, with considerable savings in material and labor. Designers often use standard sag and tension charts to calculate conductor loads and ground clearances. Without automation, they seldom considered alternative design tensions because
they lacked the tools to analyze multiple options in a reasonable time.
Strength of Structural Components
Structural component strength often restricts spots. Savings come from balancing structural components and the requirements of the line. Clearly, using insulators rated for 25,000 pounds is a poor material choice on a dead-end crossarm rated for 5,000 pounds. The designer can choose between a strong arm or a weak insulator only by investigating the line in question. All that can be seen at a glance is that the two are mismatched. The alternatives below should always be considered when preparing for optimization.
- Provide a Range of Weight Spans Without Skimping on the High End: An allowable
weight span, or vertical span, is the amount of conductor a structure can support vertically. Inadequate weight span for a structure family can significantly affect reliability and line cost and result in an awkward-looking spot. Weight span should rarely be the limiting factor in line spotting because it is usually inexpensive. The cost of doubling a distribution crossarm is insignificant when compared with the cost of installing two or three structures on every hill along the route. Alternatively, it is not practical to design all structures for a large weight span because few structures along the route will require it. The solution is to provide a range of weight spans with associated wind spans for each type of structure. A wide range of weight spans is obviously critical in hilly terrain, but it is often overlooked in flat areas. Limited weight spans can significantly impact line spotting for something as simple as raising the line for a railroad crossing. We recommend minimum weight spans of at least
one-half the maximum allowable span, and maximum weight spans of at least 1.5 times the maximum allowable span. In hilly terrain, a maximum weight span of two to three times the maximum allowable span is often appropriate.
- Cover All Line Angle Ranges with Appropriate Framing Types: The design should accommodate all ranges of line angles throughout the route with optimal structure types. For example, don’t use only buckarm corner structures for angles over 30º if a double-angle- pin or back-to-back, dead-end structure will suffice. Utilities often set angle ranges for framing configurations regardless of wire size or design tensions. This is an easy design, but a costly oversimplification. The only time this is appropriate is when there is a wire separation constraint. Allowable line angles should be determined based on the allowable transverse load of the structure, which is a combination of wire tension, wind loading, and line angle. Allowable line angles are intimately tied to conductor design tensions. A proper balance between the two is the recommended course of action.
- Guying: The design software should provide appropriate guy and anchor configurations for the full range of line angles on a project. Designers can make generalizations for spotting, but afterwards, the designer should study each guyed structure to see if guys or anchors could be eliminated. Consider the relationship between guying costs and conductor design tension: Do the benefits of stringing the conductor tighter justify the increased cost of guying?
Routing
Angle point placement along a line route is critical to structure spotting. Subtle changes in alignment can mean the difference of several structures per mile. Many angle locations are fixed, but there may still be room to adjust the route, particularly with small angles. Striving to maximize span lengths between angles is the optimal approach. Designers frequently measure the distance between angle points then divide by the desired number of spans to obtain the span length. This is actually working backwards. The best solution results if the designer manipulates the angle points as closely as possible to multiples of the maximum span length. If a structure family has a maximum span of 350 feet, try to locate the turning locations at multiples of 350 feet (i.e. 350, 700, 1050, etc.). When laying out line routes, designers who think long spans, design long spans. If they think short spans, they design short spans. This is important when spotting around long gradual curves or along winding roads with the line
crossing back and forth.
Consider New Materials and Construction Practices
More alternatives to standard wood pole lines are available every year. Designers and standards departments should constantly seek new techniques and products and evaluate potential savings associated with them. Steel, concrete, or laminated poles often provide a cheaper installation with less maintenance. Alternative pole types often eliminate the need for guying, particularly for small line angles. Use of new pole materials can yield savings in easement costs, maintenance, and public relations (guy wires are never popular with the public). The same is true for crossarms, insulators, guys and anchors.
Underground Optimization Process Factors
Concepts that designers should consider during underground line design include:
- Number of lots to be served per transformer
- Front or rear lot design
- Radial or loop feed design
- Estimated load per customer and the effects of varying this load
- Available source voltage
Transformer Sizing
Optimized underground line design enables the utility to solve problems using analytical methods coupled with sound engineering judgment. The designer can consider key constraints to determine maximum allowable transformer sizing for a specific design type, including:
- Transformer, conductor, and equipment size
- Transformer rating factors
- Diversification of loads
- Primary conductor (sizing)
- Ampacities – thermal and economic loading
- Allowable voltage drop
- Allowable flicker
Routing
The allowable routing of primary and secondary circuits is critical to the design process. Factors that dictate routing are the location of easements for front or rear lot design, the attempt to minimize lengths of circuits and number of road crossings, and the requirement to have the appropriate number of services per transformer.
Consider New Materials and Construction Practices
As with overhead design, designers and standards departments should constantly evaluate new techniques and products and not automatically design using materials and techniques that were the norm in the past. New products and materials often provide increased strength and reliability at competitive prices. Polyethylene or PVC conduit often provides cost advantages when one is compared with the other. Total cost of ownership may be a factor when maintenance and operating concerns are considered in comparison with the costs of a direct buried design. Installation methods vary widely from remote controlled boring by water jet drilling methods to full-blown excavation and trenching methods. Alternative conductor types can often eliminate the need for increasing the size of transformers and other devices. Pedestal sizes and types often can yield savings in costs of easements and maintenance. They can also influence public relations, since impediments are never popular with the public.
Combining Optimization Factors
The practices discussed above directly impact the cost and reliability of a design. The optimal combination of these factors may not be obvious without considering each individually and determining its importance to the overall balance of the system. For example, increasing vertical conductor separation invariably requires a taller pole to maintain the same ground clearance. However, the cost/benefit of longer spans makes the cost of the extra pole height insignificant. For underground design, the number of services divided by the number of transformers provides an indicator of necessary equipment. The right-of-way issues associated with the optimal equipment placement may complicate the trenching and construction process. This may lead to costly construction techniques that negate the cost/benefit of optimal equipment placement. However, the developer may determine that the cost scenario improves when a new trenching method is applied (e.g., horizontal drilling across developed right of ways).
Viewing the line as a system increases the potential for the greatest cost savings and reliability improvements. All variables within the designer’s control, including construction materials and methods, allowable span length, conductor type, and conductor tension, should be synchronized with the terrain and with constraints outside the designer’s control. While this may seem obvious, it is often overlooked in day-to-day line design. For example, if span lengths are limited to 200 feet for other reasons, ten-foot crossarms that allow 400-foot spans under galloping conditions are unnecessary, costly, and of no benefit to the system.
Conclusion
The winning utility will successfully optimize line design. Even with ever-rising costs, it is possible to hold down the total installed cost of transmission and distribution lines while maintaining or even increasing the performance and reliability of the line. This requires a rethinking of the entire design and construction process. However, with the urgent need to expand productivity without budget increases, the benefit is evident.
It is time to bring the old rules of thumb under close scrutiny and start embracing new engineering practices. The technology is available and the payoff significant. The return in the first year alone can easily make the cost of implementing the technology insignificant. All it takes are the tools, the skills, and a focus on optimized, sound engineering approaches to power line design.
Pilot Studies
Because rethinking the design process is only one way to extract value and provide improvement, this paper has focused on the big picture of optimization, suggesting that an iterative design process is needed for optimal designs. In the following tables, we demonstrate real-world results of the optimization process.
The tables summarize the results of distribution and transmission pilot projects conducted at large U.S. utilities to demonstrate hard-dollar savings in construction, labor, and material. The utilities also realized less quantifiable benefits of the optimization process, such as savings in design time, design consistency, code compliance, and process improvement.
The studies randomly selected previously constructed work orders. LineSoft personnel worked alongside the original utility designers to redesign and optimize each work order. All constraints faced by the original designers were discussed and included in the optimized design. Constraints included fixed pole locations (for taps, customer agreements, access, etc.), prohibitive zones where structures could not be placed (roadways, driveways, railroads, etc.), transmission crossings, and joint use considerations.
All costs are based on the standard labor and material costs. Costs shown include all material and labor costs associated with the work order in its entirety. Transfer and removal of existing poles, conductor, and equipment are included as well as installation of new structures and conductor.
Table 1 Overhead Distribution Pilot Study Results
| Job | Description/Tactics | | Material | Labor | Total |
| Large Jobs | 1 | New construction, three-phase 1/0ACSR primary service to commercial development. The line runs along a moderately developed suburban/rural road. Six of the 28 structures were fixed |
Original | $33,100 | $31,200 | $64,300 |
| Optimized | $26,500 | $25,800 | $52,300 |
| Eliminated 10 poles, 12 guys, 6 anchors. Shorter poles at many locations.
| $ Savings | $6,600 | $5,400 | $12,000 |
| % Savings | 19.9% | 17.3% | 18.7% |
| 2 | Highway relocation and reconductor from 1/0 ACSR conductor to 336 ACSR conductor. Approximately one-half of the line is double circuit 25kV/15kV. Eleven of the 18 structure locations were fixed |
Original | $32,000 | $42,700 | $74,700 |
| Optimized | $28,400 | $39,000 | $67,400 |
| Eliminated 5 poles, 1 guy. Installed several shorter poles. | $ Savings | $3,600 | $3,700 | $7,300 |
| % Savings | 11.3% | 8.7% | 9.8% |
| 3 | Rebuild and reconductor of an existing 3-phase #4 copper line to 336 ACSR conductor. The reconductored line will serve as an extension to a main feeder. Fourteen of the 30 structure locations were fixed. |
Original | $24,100 | $52,400 | $76,500 |
| Optimized | $22,600 | $47,800 | $70,400 |
| Eliminated 6 poles. |
$ Savings | $1,500 | $4,600 | $6,100 |
| % Savings | 6.2% | 8.8% | 8.0% |
| 4 | New construction of a 336 ACSR feeder parallel to two existing feeders in a congested, urban area. All 14 structure locations were fixed.
| Original | $13,000 | $24,200 | $37,200 |
| Optimized | $11,400 | $21,200 | $32,600 |
| Installed several shorter, lower-class poles. Eliminated 11 guys, 4 anchors. | $ Savings | $1,600 | $3,000 | $4,600 |
| % Savings | 12.3% | 12.4% | 12.4% |
| 5 | New construction of three-phase service to an industrial pump location in a rural area.
| Original | $39,100 | $40,500 | $79,600 |
| Optimized | $32,000 | $34,300 | $66,300 |
| Eliminated 10 poles. Installed mostly 40’ poles instead of 45’ poles. | $ Savings | $7,100 | $6,200 | $13,300 |
| % Savings | 18.2% | 15.3% | 16.7% |
| 6 | Reconductor of an existing three-phase 336 ACSR feeder to 954 AAC in a congested, urban area. Seven of the 14 structure locations were fixed.
| Original | $20,900 | $58,400 | $79,300 |
| Optimized | $19,800 | $51,300 | $71,100 |
| Eliminated 2 poles; removed 2 poles instead of reframing. | $ Savings | $1,100 | $7,100 | $8,200 |
| % Savings | 5.3% | 12.2% | 10.3% |
| Small Jobs | 7 | Two-pole, single-phase line extension to a new residence. Both pole locations were fixed.
| Original | $2,190 | $1,590 | $3,780 |
| Optimized | $1,590 | $1,470 | $3,050 |
| Used 50kVA transformer instead of 100kVA. Installed two 40’ poles instead of one 40’ and one 45’ pole.
| $ Savings | $600 | $120 | $730 |
| % Savings | 27.4% | 7.6% | 19.3% |
| 8 | Two-pole, three-phase line extension to a commercial building and future sewer lift station. Both pole locations were fixed.
| Original | $6,300 | $3,010 | $9,310 |
| Optimized | $4,450 | $2,880 | $7,330 |
| Used 150kVA 3-phase bank instead of 300kVA bank. Installed two 40’ poles instead of two 45’ poles. |
$ Savings | $1,850 | $150 | $1,980 |
| % Savings | 29.4% | 4.3% | 21.3% |
TABLE 2 Overhead Transmission Pilot Study Results
| Job | Description/Tactics | | Original | Optimized | Savings |
| 1 | Approximately 5.1 miles of 230kV single circuit, wood H-frame line through rugged terrain. The phase conductors are 556.5 kcmil ACSR Dove with two 7 #8 Alumoweld static wires.
| Average span length | 1,173 | 1,227 | |
| Structures per mile | 4.7 | 4.5 | |
| Average cost per structure | $15,019 | $12,572 | |
| Total cost per mile | $70,680 | $56,700 | $13,980 |
| 19.8% |
| Cost of 5.1 mile line | $360,500 | $289,150 | $71,350 |
| 19.8% |
| 2 |
Approximately 3.3 miles of single circuit, single pole 138kV line. The design uses Thomas & Betts Light Duty (LD) series tubular steel poles with steel davit arms and suspension insulators. The line traverses hilly terrain with some steep sections. The conductors are 556.5 kcmil ACSR Dove with a single 7 #8 Alumoweld static wire.
| Average span length | 527 | 644 | |
| Structures per mile | 10.3 | 8.5 | |
| Average cost per structure | $7,183 | $7,130 | |
| Total cost per mile | $74,000 | $60,500 | $13,500 |
| 18.2% |
| Cost of 3.3 mile line | $224,250 | $199,650 | $44,600 |
| 18.2% |
| 3 | Approximately 0.9 miles of 138kV single circuit wood pole line with 12.5kV distribution underbuild. The transmission conductor and distribution phases are 556.5 kcmil AAC Dahlia with a 159 kcmil ACSR Guinea shield wire and 4/0 AWG AAC Oxlip neutral. The terrain is flat, but the constraints of the distribution underbuild require one-half of the structure locations be fixed due to taps, line angles, and utility crossings.
| Average span length | 239 | 281 | |
| Structures per mile | 23 | 20 | |
| Average cost per structure | $4,355 | $4,612 | |
| Total cost per mile | $101,600 | $92,250 | $9,350 |
| 9.2% |
| Cost of 0.9 mile line | $91,450 | $83,000 | $8,450 |
| 9.2% |
| | | | Total | Savings | Structures |
| 4 | Approximately 10.3 miles of 230kV, single circuit transmission line through hilly terrain. The design uses Thomas & Betts Light Duty (LD) series tubular steel poles with polymer-braced post insulators and 795 kcmil ACSR Tern conductor with one 7 #7 Alumoweld shield wire. Several design tensions and maximum span lengths were considered to determine their impact on the total installed cost of the line.
| Original Design | $660,148 | | 72 |
| 1,000 Ft. Max span | 7,000 lbs MTW | $584,283 | $75,865 | 68 |
| 11.5% |
| 8,000 lbs MTW | $596,600 | $90,548 | 68 |
| 13.7% |
| 1,200 Ft. Max span | 7,000 lbs MTW | $567,833 | $92,315 | 66 |
| 14.0% |
| 8,000 lbs MTW | $557,181 | $102,967 | 66 |
| 15.6% |
| 1,500 Ft Max span | 7,000 lbs MTW | $557,391 | $102,757 | 63 |
| 15.6% |
| 8,000 lbs MTW | $553,068 | $107,080 | 63 |
| 16.2% |
TABLE 2 Overhead Transmission Pilot Study Results (Continued)
| | Description/Tactics | | Wood Poles | Steel Poles |
| 5 | Approximately 23 miles of 69kV, single circuit, single wood pole transmission line with polymer line post insulators. The conductor is 477 kcmil ACSR Hawk with one 3/8” EHS static wire. The terrain is hilly with few spotting restrictions. Two options were considered: 1) Thomas & Betts Light Duty (LD) series tubular steel poles with polymer line post insulators and a maximum allowable span of 600 feet. 2) Slightly greater vertical insulator separation and polymer braced post insulators and a maximum allowable span of 1,000 feet. | | | 600’ Spans | 1,000’ Spans |
| Average Span Length | 296 | 519 | 743 |
| Structures per Mile | 18 | 11 | 8 |
| Average Cost per Structure | $2,571 | $3,950 | $4,902 |
| Total Cost per Mile | $190,992 | $165,935 | $151,977 |
| Total Cost for 23 Miles | $1,090,029 | $947,024 | $867,363 |
| Savings per Mile | | $6,218 | $9,682 |
| Savings per 23 Miles | | $143,005 | $222,660 |
| 13.1% | 20.4% |
| | Description/Tactics | | Original Design | Optimized Design |
| 6 | Wood, single pole line designed for 100kV, but initially energized at 44kV. The design uses polymer line post insulators. |
Number of Structures | 25 | 19 |
| Material Cost | $97,092 | $75,635 |
| Labor Cost | $65,614 | $57,574 |
| Total Cost | $162,706 | $133,209 |
| Savings | | $29,497 |
| 18.0% |
Table 3 Underground Distribution Pilot Study Results
| Job | Description | Tactics | | Material | Labor | Total |
| 1 | 71-lot subdivision with primary, secondary, and service conductors direct buried with trencher type excavation. The services are assumed to be 45 feet in length after they enter the lot they are to serve. The load per lot is 8kVA @ PF=0.95 with air conditioner starting current of 77.3 amps @ PF=0.85.
| 1a: Utility layout: 14 lots/ transformer—Conductors and transformers automatically sized and optimized. Transformer, secondary conductor, and size of service conductors reduced. |
Original | $21,369 | $27,135 | $48,504 |
| Optimized | $17,708 | $27,135 | $44,843 |
| $ Savings | $3,661 | $0 | $3,661 |
| % Savings | 17.1% | 0% | 7.6% |
| 1b: Utility layout: 14 lots/transformer—Additional secondary and service conductors made available for optimization. LineSoft coincidence factors used.
| Original | $21,369 | $27,135 | $48,504 |
| Optimized | $15,791 | $27,135 | $42,926 |
| $ Savings | $5,578 | $0 | $5,578 |
| % Savings | 26.1% | 0% | 11.5% |
| Total includes the cost of the transformers but not the service cost. |
| 2 | 88-lot subdivision with primary and secondary in conduit with trencher type excavation. The services are in conduit in the right-of-way and direct buried after they enter the lot they are to serve and assumed to be 75 feet in length. The load profile for each lot was a 2,000 square foot home with air conditioning.
| 2a: Utility layout: 9 lots/transformer—Conductors automatically sized. Transformer, secondary conductor, and service conductors reduced | Original | $44,735 | $68,435 | $113,170 |
| Optimized | $37,035 | $67,667 | $104,702 |
| $ Savings | $7,699 | $768 | $8,467 |
| % Savings | 17.2% | 1.1% | 7.5% |
| 2b: Utility layout: 6 lots/transformer—Equipment and conductors automatically sized. Only original conductor sizes were used in optimization.
| Original | $44,735 | $68,435 | $113,170 |
| Optimized | $37,732 | $61,623 | $99,355 |
| $ Savings | $7,002 | $6,813 | $13,815 |
| % Savings | 15.7% | 10.0% | 12.2% |
| Total includes the cost of the transformers but not the service cost. |
| 3 | 115-lot subdivision with primary and secondary direct buried with backhoe type excavation. The services are direct buried with trencher type excavations and assumed to be 100 feet in length after they enter the lot they are to serve. The load profile for each lot was for a 2,100 square foot home with air conditioning.
| 3a: 6 lots/transformer—Conductors automatically sized. Transformer, secondary conductor, and service conductors reduced using established criteria for coincidence and transformer rating factors.
| Original | $60,728 | $81,481 | $142,209 |
| Optimized | $51,244 | $81,481 | $132,725 |
| $ Savings | $9,484 | $0 | $9,484 |
| % Savings | 15.6% | 0% | 12.2% |
| 3b: 8 lots/transformer—Equipment and conductors automatically sized. Only utility standard conductor sizes were used in optimization.
| Original | $60,728 | $81,481 | $142,209 |
| Optimized | $49,931 | $82,133 | $132,064 |
| $ Savings | $10,797 | ($651) | $10,146 |
| % Savings | 17.8% | -0.8% | 7.1% |
| 4 | 109-lot subdivision with primary and secondary direct buried with backhoe type excavation. The services are direct buried with trencher type excavations and assumed to be 100 feet in length after they enter the lot they are to serve. The load profile for each lot was for a 2,100 square foot home with air conditioning.
| 4a: 6 lots/transformer—Conductors automatically sized. Transformer, secondary conductor, and service conductors reduced using established criteria for coincidence and transformer rating factors.
| Original | $48,965 | $67,859 | $116,824 |
| Optimized | $40,631 | $67,859 | $108,490 |
| $ Savings | $8,333 | $0 | $8,333 |
| % Savings | 17.0% | 0% | 7.1% |
| 4b: 4 lots/transformer—Equipment and conductors automatically sized. Only utility standard conductor sizes were used in optimization.
| Original | $48,965 | $67,859 | $116,824 |
| Optimized | $43,693 | $64,363 | $108,056 |
| $ Savings | $5,271 | $3,496 | $8,767 |
| % Savings | 10.8% | 5.2% | 7.5% |
|