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E Field Modeling

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Topics

• Why E Field Modeling
• What is E Field Modeling
• Case Studies
• Questions

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Why E Field Modeling

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E Field Modeling

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• Mechanical design of transmission lines has become very robust thanks to

technology advancements in structures, conductors, hardware, and insulators

• Nearly all mechanical design is done by Computer Aided

Engineering (CAE) software

• Can’t we do the same for electrical

design?

YES

• Advancements in computers and software designed specifically

for electric field design and analysis make this a reality

WHY E FIELD MODELING

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As designers, you should want a better understanding of the electrical performance of a design No more “That’s the way we have done it in the past” Know what you are designing and using is achieving the desired result Make actual lab time as productive as it can be

Test what you can’t test in the lab THREE PHASE ASSEMBLIES

What is E Field Modeling

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What is E Field Modeling

• A representative model of a

transmission assembly that visually indicates the electric field intensity on or near the assembly

• For Polymer or Non Ceramic Insulators

(NCI) it provides a visual indication of the voltage stress on the sheds and sheath of the insulator

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What Do You Need

• Model of assembly – using customer specs

and inputs

• Computer Aided Engineering (CAE)

software

– Coulomb, Comsol, Maxwell 3D, and Flux 3D

• Create a simulation in 3D
• Computer to run simulation – min 512G of

RAM

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Model of the Assembly

• 3D Model of the Transmission

Assembly

• Typically created with SolidWorks

Software

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MacLean Power Systems uses Integrated Engineering Software’s Coulomb

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Computer Aided Engineering Software

Computer Aided Engineering Software

• Coulomb uses the Boundary Element Method (BEM) to solve the model simulations
• BEM is a numerical method for solving linear partial differential equations which

have been formulated as integral equations

• A good choice when the model being solved has a large air space around the

assembly and that has to be included in the model. BEM makes solving this a simple matter

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Simulation

The insulation medium is defined on insulator volumes

• Glass (shown)
• Polymer (NCI)

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Simulation

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• Voltages are assigned to the

hardware

• Traditional method is single phase

voltage

• Now 3 phase is available
• Hardware in contact with the

conductor, the tower, and all ground planes are assigned a voltage or boundary condition

• Conductive components not directly

in contact with conductor or tower are assigned a floating voltage

Simulation

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• Mesh elements are then created on

the 2D surfaces

• These are referred to as “triangles”
• The finer the elements or triangles the

more detailed the output

• More triangles means longer time to

solve

• Requires large amount of memory on

the computer

Analyze the Simulation

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• An E Field plot is generated for the entire

assembly

• Stress points are identified by visual

inspection

• Additional plots are made for any stress

points found

• These plots are reviewed and compared

with acceptance criteria provided by the end user

Corona Inception – E Field Modeling Example

Shield

Butterfly Predicted Value = 680 Halo Type Predicted Value = 720

• Min. Estimated Passing Values * = 510-525

Hardware (Clamp)

Butterfly Predicted Value = 640 Halo Type Predicted Value = 730

• Min. Estimated Passing Values* = 510-525

Insulator

Butterfly Predicted Value = 585 Halo Type Predicted Value = 750

• Min. Estimated Passing Values* = 510-525

*Min. test criterion will be determined based on calibration at time of test

PLOTS – Line End

• Plots can be contour or equipotential plots

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Highest Field Probed 0.9110-1.282 kV/mm Highest Field Probed 0.9056-1.570 kV/mm Note: Corona Rings are not required at the tower end as stresses do not exceed 0.42kV/mm along the sheath

MPS C-8850-TAN-V-1

E-field: Tower End

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Left Insulator Right Insulator

Case Studies

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Western US Utility

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Background

• Existing line constructed in the 1970’s
• Rated voltage was 230 kV
• Assembly/structure configuration is I-V-I
• Insulator strings are comprised of 52-3 porcelain disks
• Over 1,000 miles and elevation at times greater than 6,000’
• Two conductor vertical bundle of 795 Drake
• In early 2000’s, line voltage was uprated to 345 kV
• Soon after RIV became very noticeable – indicator of corona on the line
• Nuisance trips began occurring

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Questions to ask

• Is the leakage distance for the original 230 kV design sufficient for the 345 kV design

given contamination levels of the environment?

• Can the leakage distance be increased without drastically affecting the dry arc

distance of the assemblies?

• What is the solution to mitigate corona on the system?

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Potential solutions

• First two questions can be addressed together
• Leakage distance is more than likely insufficient for the voltage level and

environment

• Line is located in an arid environment with little rain or snowfall to clean the

insulators

• Nuisance trips are possibly being caused by contamination on the insulators
• Solution is to increase the leakage distance
• How can this be done without affecting dry arc distances?

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Leakage = 17.5 in. Leakage = 12.6 in. Note: 52-3 & 52-5 disks share the same dimensions

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52-5 Regular Glass Disk 52-5 Fog Glass Disk

Insulators

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Front View of V String Contour Plot of V String

V String Assembly

V String Pin

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First Glass Pin

V String Pin – Cross Section

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• Enhanced contour plot of 1st Glass Pin
• Stress is 2.77 kV/mm
• Corona Inception = 227 kV (±5%) at less than

1,000’

• Inception Voltage at 6,000’ = 209 kV
• Less than 10% over nominal operating voltage

New V String Options

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Final V String Option

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V String Split Halo

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• Enhanced contour plot of 1st glass pin
• Voltage Stress = 1.84 kV/mm
• Corona Inception = 341 kV (±5%) at less than

1,000’ of elevation

• Inception voltage at 6,000’ = 314 kV
• Excellent shielding performance

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Front View of I String Contour Plot of I String

I String Assembly

I String Pin – Cross Section

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First Glass Pin

• Enhanced contour plot of 1st Glass Pin
• Stress is 3.03 kV/mm
• Corona Inception = 207 kV (±5%) at less than

1,000’

• Inception Voltage at 6,000’ = 190 kV
• It is in corona at rated voltage

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Front View of I String Contour Plot of I String

I String with 17” Corona Ring

Cross Section of 1st Pin

Eastern US Utility

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230 kV Assembly Drawing

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MacLean Catalog Number H291094VA03

230 kV Full Assembly Plot

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230 kV Close up of highest stress area

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Average Voltage at corona ring: 1.801kV/mm Average Voltage at End Fitting: 1.903kV/mm

H291094VA03

230 kV – Graph along the Sheath

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H291094VA03

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

E (KV/MM) DISTANCE (MM)

PLOT ALONG INSULATOR SHEATH

230 kV Fully Assembly Plot – 12” Corona Ring

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H291094VB03

230 kV Close-up of highest stress area

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H291094VB03

with 12” Corona Ring

Average Voltage at corona ring: 1.732kV/mm Average Voltage at End Fitting: 1.608kV/mm

230 kV – Graph along the Sheath

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0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

E (KV/MM) DISTANCE (MM)

PLOT ALONG INSULATOR SHEATH

H291094VB03

with 12” Corona Ring

230KV Line Post with 6” Corona Ring

230KV Line Post with 6” Corona Ring

(Not Shown)

0.83 kV/mm 0.52 kV/mm 0.47 kV/mm 0.32 kV/mm

230KV Line Post with 12” Corona Ring

230KV Line Post with 12” Corona ring

(Not Shown)

0.39 kV/mm 0.58 kV/mm 0.52 kV/mm 0.27 kV/mm