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MeerKAT Lightning Protection, Earthing and RFI Mitigation

MeerKAT Lightning Protection, Earthing and RFI Mitigation. 01 December 2010 Dr. Gideon Wiid Post-Doctoral Fellow Host: Prof. Howard Reader. Engineering Search: Nearby Galaxies and Pulsars. Galaxy nearby: Cape Town Pulsar serviced, no more timing problems. Acknowledgements.

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MeerKAT Lightning Protection, Earthing and RFI Mitigation

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  1. MeerKAT Lightning Protection, Earthing and RFI Mitigation 01 December 2010 Dr. Gideon Wiid Post-Doctoral Fellow Host: Prof. Howard Reader

  2. Engineering Search: Nearby Galaxies and Pulsars • Galaxy nearby: Cape Town • Pulsar serviced, no more timing problems

  3. Acknowledgements EM research group at SU: Prof. Howard Reader, Joely Andriambeloson, Dr. Braam Otto, Dr. Paul van der Merwe, Philip Kibet SKA SA Teams for support in measurements: Japie Ludick, Richard Lord, Carel van der Merwe, Luyanda Boyana, Siya Tshongweni NRF and SKA SA Sponsorship TESP funding for equipment

  4. Menu • RFI Background • Reverberation Chamber and cable transfer impedance • Lightning Protection • RFI Mitigation • Earthing

  5. Background to RFI Contrary to popular belief: • RFI ≠ Black magic NB: Electrons and Energy • Opposite charges attract • Electric field in between two polarities • Electron experiences force in E-field RFI ≠

  6. Background – Electrons • Free electrons – sneaky little rascals • Always takes the path of least resistance! • Very Excitable – especially with time-varying E-field applied • Electron E-field lines: stationary vs. moving

  7. Background – Making Waves

  8. Reverberation Chamber • Joely Andriambeloson – Transfer impedance of cables • Reverberation chamber – Stirring or mixing waves • Characterise avg or max • Confirm field uniformity • Standard radiator • Compare to calibrated data • Compare to GTEM • Future: OATS

  9. Cable Transfer Impedance • Cable transfer impedance vs shielding effectiveness • 15 SKA cables and metal braided sheath • GPS cable compromises Shielding chamber • Influence on overall shielding effectiveness

  10. Lightning Protection 1 • Elevation Motor assembly • Lightning current levels • Bonding efforts • Path of least resistance • Dirt road vs highway • Traffic jam!

  11. Lightning Protection 2 • Rogowski coil used for current measurement (pool noodle) • Structure currents spread out • LDC and Elevation currents concentrated • Bearings grease changes impedance • FEKO simulations currently busy

  12. Lightning Protection 3 Impedance: ZC = 1/jωC ZL = jωL ; HF Currents more concentrated

  13. RFI Mitigation 1 - Shoes • Azimuth bearings • Shoes and LDC conductor • Misaligned 2 vs 4 • FEKO during PhD • Measurements Nov. 2010

  14. RFI Mitigation 2 - Measurements • LDC two extra connections • Clamped on other LDC and plate • Measurements inside and outside • Current levels outside higher on avg for 4 vs 2 connections • Less current toward inside of pedestal • Path of least resistance!

  15. RFI Mitigation 3 - Shielding

  16. Chiller Plant Earthing 1 • Chiller plant no earthing philosophy – floating • Cables going through to pedestal interior • Possible path for induced currents • Consider optimal earthing options

  17. Chiller Plant Earthing 2  No redirection of current  Shunted connection redirects current

  18. Conclusion • Reverberation chamber method – relatively quick for testing cable shielding effectiveness or transfer impedance • Lightning protection measures can be incorporated at MeerKAT design stage • Elevation assembly might be reconsidered • Pedestal RFI can be mitigated with correct shielding and cable terminations • Correct earthing and terminations will aid in redirection of induced currents • Electrons are sneaky!

  19. T H E E N D Thank you for your time Any Questions? Veni, Vidi, Velcro ( I came, I saw, I stuck around )

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