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Iclp 2008 Aau

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Lightning protection for a OHL/UC connected GIS

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Iclp 2008 Aau

  1. 1. <ul><li>Lightning Simulation of a Combined Overhead Line/Cable Connected GIS </li></ul><ul><li>by </li></ul><ul><li>Jakob Kessel, Ví ðir Már Atlason and Claus Leth Bak </li></ul><ul><li>Aalborg University, </li></ul><ul><li>Institute of Energy Technology </li></ul><ul><li>and </li></ul><ul><li>Jesper Lund </li></ul><ul><li>NV Net A/S </li></ul>
  2. 2. Introduction <ul><li>170 kV transmission system for year 2014 </li></ul><ul><ul><li>Mainly underground cable and GIS </li></ul></ul><ul><li>Follow up on 9th semester project </li></ul>
  3. 3. Introduction <ul><li>Only Area 3 showed overvoltages </li></ul><ul><li>Modelling </li></ul><ul><ul><li>Lines, cables and outdoor busbars </li></ul></ul><ul><ul><ul><li>Transmission lines </li></ul></ul></ul><ul><ul><li>GIS busbars and transformers </li></ul></ul><ul><ul><ul><li>Equivalent capacitances </li></ul></ul></ul><ul><ul><li>Tower model </li></ul></ul><ul><ul><li>Grounding resistance </li></ul></ul><ul><ul><li>Surge arrester </li></ul></ul>SA
  4. 4. Modelling <ul><li>Tower model </li></ul><ul><ul><li>Tower surge impedance </li></ul></ul><ul><ul><li>Insulator model </li></ul></ul><ul><ul><li>Grounding resistance </li></ul></ul>Cite: Fast Front Task Force of the IEEE, and Sargent et al.
  5. 5. Modelling <ul><li>Insulator model </li></ul><ul><ul><li>Voltage-time characteristic </li></ul></ul>Cite: Fast Front Task Force of the IEEE, and Yadee et al.
  6. 6. Modelling <ul><li>Grounding resistance </li></ul><ul><ul><li>Dynamic grounding resistance </li></ul></ul><ul><ul><li>Where: </li></ul></ul><ul><ul><ul><li>R 0 is low current grounding resistance </li></ul></ul></ul><ul><ul><ul><li>I g is the critical current causing ionization of the soil </li></ul></ul></ul><ul><ul><ul><li>I R is the current to ground </li></ul></ul></ul><ul><li>Surge arrester model </li></ul><ul><ul><li>Simplified IEEE model </li></ul></ul>Cite: Fast Front Task Force of the IEEE, and Crisholm et al. Cite: Pinceti et al.
  7. 7. Simulation <ul><li>Simulation parameters </li></ul><ul><ul><li>Shielding failure </li></ul></ul><ul><ul><li>Back flashover </li></ul></ul><ul><ul><li>The lightning surge is estimated with double exponential function </li></ul></ul><ul><li>Parameter investigation </li></ul><ul><ul><li>Lightning front time </li></ul></ul><ul><ul><ul><li>Only for shielding failure </li></ul></ul></ul><ul><ul><li>Soil resistivity (at the overhead line/cable transition point) </li></ul></ul><ul><ul><li>Cable length (between transformer and surge arrester in GIS) </li></ul></ul>Soil resitivity Crest magnitude Time to half Front time [ Ω m] [kA] [µs] [µs] 92,5 -200 350 10 Back flashover 92,5 -41,8 350 1,4 Shielding failure
  8. 8. Results <ul><li>Simulation results </li></ul><ul><ul><li>Varying lightning </li></ul></ul><ul><ul><li>front time, SF, </li></ul></ul><ul><ul><li>closed breaker </li></ul></ul><ul><ul><li>Varying lightning </li></ul></ul><ul><ul><li>front time, SF, </li></ul></ul><ul><ul><li>open breaker </li></ul></ul>U tf
  9. 9. Results <ul><li>Simulation results </li></ul><ul><ul><li>Varying soil </li></ul></ul><ul><ul><li>resistivity, SF, </li></ul></ul><ul><ul><li>closed breaker </li></ul></ul><ul><ul><li>Varying soil </li></ul></ul><ul><ul><li>resistivity, SF, </li></ul></ul><ul><ul><li>open breaker </li></ul></ul>U tf
  10. 10. Results <ul><li>Simulation results </li></ul><ul><ul><li>Varying cable </li></ul></ul><ul><ul><li>length, SF, </li></ul></ul><ul><ul><li>closed breaker </li></ul></ul><ul><ul><li>Varying cable </li></ul></ul><ul><ul><li>length, SF, </li></ul></ul><ul><ul><li>open breaker </li></ul></ul>U tf
  11. 11. Results <ul><li>Evaluation of critical lightning current </li></ul><ul><ul><li>Varying front time </li></ul></ul><ul><ul><ul><li>Only evaluated for shielding failure </li></ul></ul></ul><ul><ul><ul><li>No overvoltages with closed breaker </li></ul></ul></ul><ul><ul><li>Varying soil resistivity </li></ul></ul><ul><ul><ul><li>No overvoltage for SF with closed breaker </li></ul></ul></ul>
  12. 12. Results <ul><li>Evaluation of critical lightning current </li></ul><ul><ul><li>Cable length </li></ul></ul><ul><ul><ul><li>No overvoltages with closed breaker </li></ul></ul></ul><ul><ul><li>The MTBF is found based on the lightning current </li></ul></ul>
  13. 13. Modelling <ul><li>Risk assesment </li></ul><ul><ul><li>Back flashover </li></ul></ul><ul><ul><ul><li>MTBF closed = ( P (closed) P (current) N flashes ) - 1 </li></ul></ul></ul><ul><ul><ul><li>MTBF open = ( P (open) P (current) N flashes ) -1 </li></ul></ul></ul><ul><ul><ul><li>P (open) ≈ 1/365 </li></ul></ul></ul><ul><ul><ul><li>P (closed) = 1 - P (open) </li></ul></ul></ul><ul><ul><li>Shielding failure </li></ul></ul><ul><ul><ul><li>MTBF closed = ( P (closed) P (sf) P (current) N flashes ) -1 </li></ul></ul></ul><ul><ul><ul><li>MTBF open = ( P (open) P (sf) P (current) N flashes ) -1 </li></ul></ul></ul><ul><li>Mean Time Between Failure </li></ul>
  14. 14. Conclusion & Discussion <ul><li>Conclusion </li></ul><ul><ul><li>The steepness of the lightning surge </li></ul></ul><ul><ul><li>Limited effect on the overvoltages. </li></ul></ul><ul><ul><li>The soil resistivity at the overhead line/cable transition point </li></ul></ul><ul><ul><li>Great effect on the overvoltages. </li></ul></ul><ul><ul><li>The cable length between the transformer and the surge arrester in the GIS </li></ul></ul><ul><ul><li>Increased cable length yielding increased voltage magnitude at the transformer. </li></ul></ul><ul><ul><li>MTBF > 2000 years </li></ul></ul><ul><ul><li>The surge arrester at the overhead line/cable transition point provides adequate protection for the substation. </li></ul></ul><ul><ul><li>Further protection in form of a surge arrester at the GIS busbar is not necessary. </li></ul></ul>

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