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Can we make mining operations immune from lightning induced explosions darren woodhouse

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Can we make mining operations immune from lightning induced explosions Darren Woodhouse

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Can we make mining operations immune from lightning induced explosions darren woodhouse

  1. 1. 27th Electrical Engineering Safety Seminar Can we make mining operations immune from  lightning induced explosions?  Copyright © Safearth Consulting 2017 Sydney 2017 1/12 Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse ELECTRICAL ENGINEERING SAFETY SEMINAR 2017 November 2017 Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse Bold Statement #1 Lightning is pretty cool … … until it hits you!
  2. 2. 27th Electrical Engineering Safety Seminar Can we make mining operations immune from  lightning induced explosions?  Copyright © Safearth Consulting 2017 Sydney 2017 2/12 Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse Isokeuranic Charts Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse Ground Flash Density
  3. 3. 27th Electrical Engineering Safety Seminar Can we make mining operations immune from  lightning induced explosions?  Copyright © Safearth Consulting 2017 Sydney 2017 3/12 Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse During one storm which lasted just over two hours 5295 strokes! Roughly 1 strike every 2 seconds! Lightning Stroke Density Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse • UQ MISHC  Minerals Industry Safety and Health Centre, Uni of Queensland • Makes 16 “considered important” conclusions • Makes overwhelming use to Capitalisation of the First letter of a word Randomly Within a Sentence • No.1 Conclusion “… in most cases lightning voltages generated at the bottom of vertical metallic pipes … are small enough for normal thicknesses of dielectric such as PVC ...” ACARP Research Project C22003 Lightning in UG Coal Mines – UQ MISHC
  4. 4. 27th Electrical Engineering Safety Seminar Can we make mining operations immune from  lightning induced explosions?  Copyright © Safearth Consulting 2017 Sydney 2017 4/12 Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse 10. Attenuation of the lightning current and voltage on buried vertical pipes increases as soil resistivity decreases and mine depth increases. 12. The soil resistivity profile (number of layers and layer thickness) has a strong influence upon the scalar potentials that can appear underground. However, when the top layer thickness is relatively small compared to the mine depth, the overriding factor is still the “infinite” soil resistivity below the top layer(s). 13. For a direct strike to the origin of the sloping pipe (above ground), the voltages seen underground are considerably smaller than those for a vertical pipe (since there is a longer distance over which attenuation occurs). … and on Attenuation Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse What changes the voltage on the structure? • The strike • The soil resistivity • The borehole length and material • Connection (earthed) to the borehole 11 When lightning hits a buried conductive structure … ?
  5. 5. 27th Electrical Engineering Safety Seminar Can we make mining operations immune from  lightning induced explosions?  Copyright © Safearth Consulting 2017 Sydney 2017 5/12 Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse • Direct Injection of Current • Electric Conduction • Magnetic Induction • … and combinations thereof! Mechanisms for Transfer Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse • Doesn’t have to be vertical! Models Considered
  6. 6. 27th Electrical Engineering Safety Seminar Can we make mining operations immune from  lightning induced explosions?  Copyright © Safearth Consulting 2017 Sydney 2017 6/12 Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse Lightning strike characteristic microseconds Amps Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse Soil - homogeneous Pipe - homogeneous Video – Uniform Borehole
  7. 7. 27th Electrical Engineering Safety Seminar Can we make mining operations immune from  lightning induced explosions?  Copyright © Safearth Consulting 2017 Sydney 2017 7/12 Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse Transients don’t behave like power frequency Surge or characteristic impedance of a path vrs Terminating impedance • Don’t make fast/severe changes to path type • Divide and Conquer Travelling waves Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse If lightning doesn’t like something it gets upset! Remember, by definition, any increase in voltage induced by lightning leads to a flash. Petulant Child
  8. 8. 27th Electrical Engineering Safety Seminar Can we make mining operations immune from  lightning induced explosions?  Copyright © Safearth Consulting 2017 Sydney 2017 8/12 Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse The old vanguard of earthing, to separate or not! And what does it mean? Beware that segregation, aka no interaction between systems, is almost impossible! Separation or Bonded, not Segregated! Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse The Ideal Solution … Now what could it be?
  9. 9. 27th Electrical Engineering Safety Seminar Can we make mining operations immune from  lightning induced explosions?  Copyright © Safearth Consulting 2017 Sydney 2017 9/12 Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse • Low resistivity ‘soil’ or cover. • Protection for the ‘lip’ of the entrance. • Flat unattractive surface. • Attractive elements can be located elsewhere. Ideal solution Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse • High resistivity ‘soil’. • No protection for the work area. • Irregular surface. • Attractive elements located in close proximity. Non-ideal Circumstances
  10. 10. 27th Electrical Engineering Safety Seminar Can we make mining operations immune from  lightning induced explosions?  Copyright © Safearth Consulting 2017 Sydney 2017 10/12 Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse • Could solve the borehole transfer problem, but is it practical? • Doesn’t solve the magnetic coupling scenario. Insulated Boreholes? Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse 29 Video – Well earthed borehole at depth
  11. 11. 27th Electrical Engineering Safety Seminar Can we make mining operations immune from  lightning induced explosions?  Copyright © Safearth Consulting 2017 Sydney 2017 11/12 Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse 1. Isolation is not always the answer – • It can fail! • Can be hard to implement and maintain! 2. Bonding is a possible answer in some circumstances. 3. Lightning can’t be controlled but it can be cajoled, hindered & encouraged! 4. Choose wisely! 30 Conclusions Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse The rules are: 1. Don’t be attractive to lightning! 2. Make, or encourage, something else to be more attractive! 3. Assume that you are attractive … aka your asset will get hit! 4. Make sure it can take the attention … aka current/energy. 5. Make sure it can jettison the attention … aka current/energy. 6. “Lightning doesn’t read standards!” – Prof. M. Darveniza The ‘Vogue’ rules of Lightning Protection
  12. 12. 27th Electrical Engineering Safety Seminar Can we make mining operations immune from  lightning induced explosions?  Copyright © Safearth Consulting 2017 Sydney 2017 12/12 Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse • Further research required into … • … a standard protocol for measuring soil resistivity, … • More analysis could be undertaken to better quantity quantify the effect of the gaps in the roof mesh, the size required and the spacing required. • … computer model calculations should be validated against low level in situ measurements … • The key currents and voltages necessary to ignite methane need to be better characterised … ACARP Research Project C22003 Lightning in UG Coal Mines – UQ MISHC Electrical Engineering Safety Seminar 2017 - Sydney Can we make mining operations immune from lightning induced explosions? Dr Darren Woodhouse 1. Identifying better rules for separation and bonding. 2. Looking at ways to attenuate voltage in metallic services before reaching workings. 3. Quantifying response of services in workings. 4. Increasing the understanding of transients, in particular lightning! 5. Understanding how to limit power transfer in the first place. 6. How to test/verify mitigation is effective. 7. … Alternative Suggestions for Further Work

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