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Recommended Procedure for Conductor OptimizationGreg Parent, P.E., S.E., Senior Engineer, Greg.Parent@ulteig.com

James Thomas, PhD, Lead Studies Engineer, James.Thomas@ulteig.comJosh Potts, P.E., Technical Manager, Josh.Potts@ulteig.com

Stacey Page, P.E., Engineer, Stacey.Page@ulteig.com

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Conductor Optimization Procedure

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1. Transmission Planning and/or Renewable Integration2. Minimum Required Conductor Size3. Initial Conductor Set Selection

4. Transmission Line Capital Investment Costs5. Electrical Loss Calculations

6. Financial Modeling – Iteration 1

7. Financial Modeling – Iteration 2

Procedure DescriptionDetermine the requirements of the new transmission line:

• Length• Voltage• Rating

Determine the smallest conductor that can meet the

required Thermal Ratings, Corona, EMF and Audible

Noise requirements.

Select an initial set of conductor sizes to analyze for construction costs and

electrical losses.

Determine the specific costs for different structure types and the specific costs within

each structure type for supporting different

conductor sizes.

Calculate the Electrical losses for each of the

different conductor sizes

Create a Financial model to determine which conductor of the initial conductor set yields the lowest total life

cycle cost.

From the results of the first iteration financial model,

determine if another conductor size could yield an

even lower total life cycle cost.

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1. Transmission Planning & Renewable Integration

http://www.news.gatech.edu/features/building-power-grid-future

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https://www.eia.gov/state/maps.php

1. Transmission Planning & Renewable Integration

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Financial Impact• Minimizing up front cost while maximizing total

life cycle value from the following advantages– Lower system losses– Lower market prices– Lower cost of interconnection (access to better points

of interconnection)– More energy

1. Transmission Planning & Renewable Integration

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Example Design Inputs• Each phase consisting of bundled (2) sub-conductors 18 inches apart.• Elevation assumed as 7600 ft• Line must support 1200 MW nameplate capacity• Right-of-Way of 150 ft width• Voltage of 362 kV at 1.05 per unit• Transmission line conductor family specified to be ACSR• Structure Type Specified to be Steel Monopole

2. Minimum Required Conductor Size

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Thermal Rating• Follow IEEE 738 to calculate the thermal rating of the conductor, or maximum operating temperature.• PLS-CADD can perform IEEE 738 calculations.• SWRate can also perform these IEEE 738 calculations.

2. Minimum Required Conductor Size

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• EMF is dependent on voltage, current and distance to edge of ROW. These are more expensive to adjust as they require structure, loading and right of way changes.

Corona, EMF & Audible Noise Calculations

• Typical guidelines: AN=55 dBA at edge of ROW based on EPA guidelines, Electric Field=12 kV/m occupational exposure and Magnetic Field=1.2 Tesla (12E6 mG) occupational exposure according to International Commission on Non-Ionizing Radiation Protection (ICNIRP).

• Different states have different guidelines for AN and EMF. Some individual counties have their own guidelines. Verify for your location.

• AN is dependent on the conductor size as the larger the conductor the less the gradient on the surface so the farther from corona inception voltage.

2. Minimum Required Conductor Size

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Conductor

Sub -Conductor

Overall Diameter (in.)

Conductor Max

Operating Temp (deg C)

Maximum AN at ROW (dBA)

Electric Field at

ROW (kV/m)

Maximum Electric

Field (kV/m)

Magnetic Field at

ROW (mGauss)

Maximum Magnetic

Field (mGauss)

Design Limit -- 100 55.0 12.0 12.0 12E6 12E6

(2) 795kcmil ACSR “Drake” 1.107 97.8 54.0 0.84 1.40 37.1 73.2

2. Minimum Required Conductor Size

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• After determining minimum acceptable conductor size select a preliminary set of three or four more conductors that each that each increase in ampacity by 10-15%.

3. Initial Conductor Set Selection

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• Conductor Types– Fairly wide range of ampacity– Similar/same aluminum/steel ratios– Min (2) 795kcmil ACSR “Drake”– Max (2) 1590kcmil ACSR “Falcon”– Yours will differ based on needs

4. Transmission Line Capital Investment Costs

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Structure Types, ROW’s and Associated Costs• Considerations:

– Structure Type• Steel (monopole/H-frame), Wood H-frame, Lattice• (Structure Type can usually be narrowed down quickly based upon client preferences and standards)

– ROW required• Depends on span length, conductor type and structure type

– Construction installation costs– Conductor type and size– Geotechnical considerations– Other Misc. Costs– The bigger the project, the more time you should invest on this exercise.

• Our Hypothetical Line:– 345kV Single Circuit– 50 miles– 1200 MW Nameplate Load– Steel Monopole

4. Transmission Line Capital Investment Costs

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• Results:

• Other items to consider

4. Transmission Line Capital Investment Costs

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Conductor Inputs• Conductor Size• Low and High Temp AC

Resistance• Thermal Coefficients

• Absorptivity • Emissivity

Location• Altitude of Conductors• Latitude• Line Azimuth (Orientation of

the line relative to Due North)• Solar Day and Time

5. Electrical Loss Calculations

T-Line Inputs• Voltage of Line• Length of Line• Design Electrical Load for loss

calculations (ILOSS)• Traditional Generation Vs.

Renewable Generation

Local Conditions – Climate• Design Wind Speed and

Wind Angle blowing on conductor.

• Ambient temperature• Atmosphere

Required input information

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• Total Losses are determined from the following:

– Length of Line– Conductor Resistance– Operating Temperature of the line

• Absorption and Emissivity values of the conductor

• Determine Conductor Temperature Under the Electrical Load for Loss Calculations (ILOSS) using IEEE 738.

– PLS-CADD can perform these IEEE 738 calculations for your different conductor sizes.

– Southwire created an IEEE 738 calculator program, SWRate for their conductors.

5. Electrical Loss Calculations

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• Model the different conductor sizes in PSSE or EasyPower to determine losses over the length of the line.

• Make sure to model the transmission line with the specific conductor temperatures associated with each conductor size.

5. Electrical Loss Calculations

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Minimizing Total Lifecycle CostThese input variables are critical to determine the optimal conductor size for the transmission line. Some can be calculated but others must come from the client. Specifically:• Price of Power

• Annual Increase in Cost of Power

• Cost of Capital

6. Financial Modeling – Iteration 1

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6. Financial Modeling – Iteration 1

+

+

=

There might be another conductor size that could yield a lower total cost.

795kcmil 1033.5kcmil 1192.5kcmil 1351.5kcmil 1590kcmil

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7. Financial Modeling – Iteration 2

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7. Financial Modeling – Iteration 2795kcmil 1033.5kcmil 1192.5kcmil 1351.5kcmil 1590kcmil1113kcmil

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Conclusions

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• To perform a conductor optimization numerous input variables must be defined including:• Physical characteristics of the transmission line• Electrical properties of the conductor • Cost estimates of the T-Lines that support different conductors• Financial variables from the client/utility

• The smallest conductor that meets the electrical requirements does not generally yield the lowest total lifecycle cost.

• Performing a conductor optimization can create the largest value-added engineering to a transmission line project.

• As the length of the line increases the value of performing a conductor optimization design also increases.

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• IEEE Std 738TM – IEEE Calculating the Current-Temperature Relationship of Bare Overhead Conductors, New York: Institute of Electrical and Electronic Engineers, Inc., 2012.

• IEEE - Economic Incentives for Larger Transmission Conductors. Ian S. Grant, Vito J. Longo, Vol. PAS-100, No 9 September 1981.

• The Aluminum Association – The Evaluation of Losses in Conductors, Washington D.C., 1982.

• Southwire – Overhead Conductor Manual 2ND Edition. Ridley Thrash, Amy Murrah, Mark Lancaster, Kim Nuckles, Southwire Company, 2007.

References

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Questions?