Direction Expertise et Support Technique de Transport Lignes, Câbles et environnement. Prepared by : Richard Lehoux, ing.

Transcription

1 CALCULATION OF ELECTRICAL INDUCTION NEAR POWER LINES Direction Expertise et Support Technique de Transport Lignes, Câbles et environnement Prepared by : Richard Lehoux, ing. richard_lehoux@hydro.qc.ca May 2008

2 Scope of the presentation 1. Calculation of Electric Field 2. Electric field induction in a human body 1. IEEE Std (Guide for Safety in AC Substation Grounding) 2. EPRI (Electric Power Research Institute) 3. CSA (Canadian Standard Association) 3. Design criteria 1. CSA 2. HQTÉ (Hydro-Québec TransÉnergie) 4. Methods of determining induced current 1. Empirical 2. Boundary Element Method (BEM) 5. Comparison results: Empirical versus BEM 2

3 Electric field induction in a human body Range of tolerable current in a human body IEEE Std , Article 5.2 "Effect of magnitude and duration" 1mA: threshold of perception 1-6 ma: unpleasant to sustain 10.5 ma: threshold for women let-go currents 16 ma: threshold for men let-go currents Note: the duration of the fault is infinite Range of tolerable current in a human body EPRI "TRANSMISSION LINE REFERENCE BOOK", Chapter 8, "Field effect of overhead transmission lines and stations", Article 8.10 "Electric-field induction in people", paragraph "Response to steady-state Currents" 5 ma: let-go values for children for a probability of 0.5% have been conservatively estimated as equal to 5 ma threshold of perception 3

4 Electric field induction in a human body CSA C22.3 No.1-06, Article A "Vertical desing clearances of wires and conductors above ground or rails and Tables 2 and 4" 5 ma: let-go currents 4

5 Design criteria Height of conductors CSA calculation criteria Article : A5.3.1 Based on the worst-case condition : Vehicle is insulated from the ground by rubber tires Person contacting the vehicle is touching or standing on a well-grounded surface Induced current in all cases is below 5 ma (Let-go currents) Maximum line to ground voltage 23 m 5 ma 4,15 m HQTÉ Use CSA design criteria 5

6 Methods of determining induced current Two methods are available at HQTÉ to determine the induced current (5 ma let-go) in a human body Empirical method (EPRI) Easy, fast, cheap, approximate Boundary Element Method (Maxwell's Equations) Expensive, accurate 6

7 Empirical method Method of approximating induced current in objects close to ground EPRI "TRANSMISSION LINE REFERENCE BOOK" Chapter 8, "Field effects of overhead transmission lines and stations" Method of approximating calculation of current induced on objects close to the ground Empirical method for rectangular shape Figure "Shape for a rectangular solids" (The shape is collecting electrical charge) Many others shape available Horizontal / Vertical cylinder Flat plate House Horse Etc. 7

8 Empirical method Sizes of vehicles (m) Length Width Height Article C HQ HQ HQ Truck A , ,15 Large farm A * Train A5.3.1 (example 4) * : Height used by HQTÉ

9 Empirical method - Exemple : Truck Calculation with EPRI method to get 5 ma induced in a human body S/(AB) H/B A/B Size of the truck : Length (A): 23 m Width (B) : 2.6m Height (H) : 4.15m Center : 4.15/2 = 2.08 Ratio : A/B : 23/2.6=9.62 H/B : 4.15/2.6=1.6 With abacus : S/(A*B)=S/(23*2.6)=5.1 S= mA=S*E/300 (E: Electric field) E=(5mA*300)/304.9=4.9kV/m at 2.08m (center of vehicle) See slide 14 to determine height of conductors

10 S/(AB) Empirical method - Exemple : Large Farm vehicle - HQTÉ Calculation with EPRI to get 5 ma induced in a human body Size of the Large Farm Vehicle : Length (A) : 7.6 m Width (B) : 2.4m Height (H) : 4.5m (HQTÉ - Study) Center : 4.5/2=2.25m H/B Ratio : A/B : 7.6/2.4=3.2 H/B : 4.5/2.4= A/B With abacus : S/(A*B)= 8 S=8(7.6*2.4)=146 5mA = S*E/300 (E: Electric field) E=(5mA*300)/146=10.3kV/m at 2.25m (center of vehicle) See slide 14 to determine height of conductors

11 S/(AB) Empirical method - Exemple : Large Farm vehicle - CSA Calculation with EPRI to get 5 ma induced in a human body Size of the Large Farm Vehicle : Length (A) : 7.6 m Width (B) : 2.4m Height (H) : 4.15m (CSA) Center : 4.15/2=2.08m H/B Ratio : A/B : 7.6/2.4=3.2 H/B : 4.15/2.4= A/B With abacus : S/(A*B)= 7 S=8(7.6*2.4)=129 5mA = S*E/300 (E: Electric field) E=(5mA*300)/129=11.6kV/m at 2.25m (center of vehicle) See slide 14 to determine height of conductors

12 Calculation of Electric Field The electric field is determined by these parameters : 1. Voltage 2. Distance between phases 3. Diameter of conductors 4. Number of conductors per bundle 5. Presence of overhead ground wire 6. Distance of conductors from the ground Software available to calculate the electric field : CDEGS of SES (Package : MultiField - 38 k$ - Available on market) Coulomb (3D Electric Field Solver Used by IREQ - Available on market) Expomag (In house software HQ) 12

13 Calculation of Electric Field FAA TOWER kv Ø/Ø Electro-mechanicals specifications 1 circuit Conductors 4 per bundles Ø : cm Distances between Ø Voltage max 765 kv Overhead ground wire Quantity : 2 Ø : 1.27cm 13

14 Calculation of Electric Field Electric field 735 kv (FAA Tower) Conductors at rest kv/m 735 kv Electric Field Max. Elec. field: 10.3 kv/m Large Farm Vehicle 8 6 Max. Elec. field: 4.9 kv/m - Truck 4 Height of conductors 21.0 m 13.4 m Center of the ROW m HQTÉ ROW (80 m) < 2 kv/m

15 Boundary Element Method (BEM) Equivalent circuit of a truck near a power lines Isc = 5 ma Human body Represented by a 1 kω Modelization done by IREQ (Alain Turgeon) 15

16 BEM Example Truck parallel to the line Capacitive induction simulation for a truck located at 17 meters of the center line and parallel to conductors 735 kv ØØ with FAA towers 5 kv/m Height of conductors simulation : Height of conductors m Example of an electric profile field ma 2,6 m 4,15 m ROW 15,7 18,3 m

17 BEM Example Truck parallel Height of conductors Capacitances Current in a human body To limit the current in a human body at 5 ma the height of conductors must be higher than 23.2 m (m) Ca-t (pf) Cb-t (pf) Cc-t (pf) Ct-g (pf) ISC (ma) 21 3,03 15,8 43,4 1,46 5, ,19 15,4 40,6 1,46 5, ,33 15,0 38,0 1,46 5, ,45 14,6 35,6 1,46 4,71 17

18 BEM Exemple Truck perpendicular to line Capacitive induction simulation for a truck located perpendicular to conductors 735 kv ØØ with FAA towers Height of conductors simulation : Height of conductors 6 kv/m Example of an electric profile field ma 23 m 4,15 m ROW 5,5 28,5 m

19 BEM Example Truck perpendicular Height of conductors Capacitances Current in a human body (m) Ca-t (pf) Cb-t (pf) Cc-t (pf) Ct-g (pf) ISC (ma) To limit the current in a human body at 5 ma the height of conductors must be higher than 20.5 m 17 4,19 21,2 49,1 1,44 6, ,36 20,3 45,9 1,45 6, ,52 19,5 42,9 1,45 5, ,65 18,7 40,3 1,45 5,18 19

20 Comparison results: Empirical versus BEM Height of conductors 735 kv ØØ FAA tower Empirical Method (m) BEM Method (m) perpendicular 23.2 parallel HQTÉ chose empirical method for it's in house standard BEM method permitted HQTÉ to check the accuracy of empirical method 20

21 Empirical method HQTÉ results Nominal Voltage (kv) TOWER MINIMUM HEIGHT OF CONDUCTORS (m) TRUCK (Electric Field : 4.9 kv/m) LARGE FARM VEHICULE (Electric Field : 10.3 kv/m) FAA Single circuit EOA Double circuit 9.7 <7.25 * 315 EFK Single circuit DPD Double circuit 6.7 <6.2 * 230 DAD Single circuit 3.8 <6.2 * 161 BBA Double circuit 5.1 <5.8 * * : Height of conductors are determined by "Flashover-to-ground" not by induced current

22 ACKNOWLEDGEMENTS Daniel Goulet, Ph. D. Alain Turgeon, P. Eng. M. Sc. A. 22