E Field Modeling 1
Topics • Why E Field Modeling • What is E Field Modeling • Case Studies • Questions 2
Why E Field Modeling 3
E Field Modeling • 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 YES design? • Advancements in computers and software designed specifically for electric field design and analysis make this a reality 4
WHY E FIELD MODELING 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 5
What is E Field Modeling 6
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 7
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 8
Model of the Assembly • 3D Model of the Transmission Assembly • Typically created with SolidWorks Software 9
Computer Aided Engineering Software MacLean Power Systems uses Integrated Engineering Software’s Coulomb 10
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 11
Simulation The insulation medium is defined on insulator volumes • Glass (shown) • Polymer (NCI) 12
Simulation • 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 13
Simulation • 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 14
Analyze the Simulation • 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 15
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 17
MPS C-8850-TAN-V-1 E-field: Tower End Left Insulator Right Insulator Highest Field Probed Highest Field Probed 0.9056-1.570 kV/mm 0.9110-1.282 kV/mm Note : Corona Rings are not required at the tower end as stresses do not exceed 0.42kV/mm along the sheath 18
Case Studies 19
Western US Utility 20
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 21
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? 22
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? 23
Insulators 52-5 Regular Glass Disk 52-5 Fog Glass Disk Leakage = 12.6 in. Leakage = 17.5 in. Note : 52-3 & 52-5 disks share the same dimensions 24
V String Assembly Front View of V String Contour Plot of V String 25
V String Pin First Glass Pin 26
V String Pin – Cross Section • Enhanced contour plot of 1 st 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 27
New V String Options 28
Final V String Option 29
V String Split Halo • Enhanced contour plot of 1 st 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 30
I String Assembly Front View of I String Contour Plot of I String 31
I String Pin – Cross Section • Enhanced contour plot of 1 st 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 First Glass Pin 32
I String with 17” Corona Ring Front View of I String Contour Plot of I String Cross Section of 1 st Pin 33
Eastern US Utility 34
230 kV Assembly Drawing MacLean Catalog Number H291094VA03 35
230 kV Full Assembly Plot 36
230 kV Close up of highest stress area Average Voltage at corona ring: 1.801kV/mm Average Voltage at End Fitting: 1.903kV/mm H291094VA03 37
230 kV – Graph along the Sheath PLOT ALONG INSULATOR SHEATH 0.70 0.65 0.60 0.55 0.50 0.45 0.40 E (KV/MM) 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 DISTANCE (MM) H291094VA03 38
230 kV Fully Assembly Plot – 12” Corona Ring H291094VB03 39
230 kV Close-up of highest stress area Average Voltage at corona ring: 1.732kV/mm Average Voltage at End Fitting: 1.608kV/mm H291094VB03 with 12” Corona Ring 40
230 kV – Graph along the Sheath PLOT ALONG INSULATOR SHEATH 0.45 0.40 0.35 0.30 0.25 E (KV/MM) 0.20 0.15 0.10 0.05 0.00 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 DISTANCE (MM) H291094VB03 with 12” Corona Ring 41
230KV Line Post with 6” Corona Ring
230KV Line Post with 6” Corona Ring (Not Shown) 0.52 kV/mm 0.32 kV/mm 0.83 kV/mm 0.47 kV/mm
230KV Line Post with 12” Corona Ring
230KV Line Post with 12” Corona ring (Not Shown) 0.58 kV/mm 0.52 kV/mm 0.39 kV/mm 0.27 kV/mm
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