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What are they doing?

Discussion in 'Electrics UK' started by viewer, 24 Jun 2013.

  1. viewer

    viewer

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  3. westie101

    westie101

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    Live line repair team, using a fully insulated platform. In the a lot of countries they operate live at these voltages, sometimes using helicopters to access the cables.

    http://www.youtube.com/watch?v=GxDKVAYJ_t4

    We have teams in the UK doing this at 11kV.
     
  4. viewer

    viewer

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    Ah, so insulated platform. Many thanks.
     
  5. SimonH2

    SimonH2

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    And key point is that those white suits they wear are conductive - wires woven into the fabric. Part of the pre-work safety checks is to ensure full connectivity between different sections (there are (for example) press studs linking gloves to sleeves). That gives the operator a full faraday cage to work inside.

    According to some goggle box programmes I've watched in the past.
     
  6. Porque223

    Porque223

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    The helicopter has a tiny capacitance to ground and so there will be AC current flowing in an arc between the heli and the line. The current may not be enough to be fatal but from the look of the arc that I've seen drawn it looks to be pretty nasty.
    To figure the capacitance you need to know the area of the helicopter footprint and the height above ground, then the 50 Hz gives you the reactance, then the line megavolts gives you the current in the arc.
     
  7. JohnW2

    JohnW2

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    If the platform is fully insulated, is the current in those arcs to their gloves getting to ground solely via the capacitance to ground?

    Kind Regards, John
     
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  9. westie101

    westie101

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    I expect so.

    On the lower voltages as clearances are smaller the conductive suits are not worn, rather they use insulated gloves & garments
     
  10. bernardgreen

    bernardgreen

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  11. JohnW2

    JohnW2

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    That would certainly seem the only explanation.
    If the platform really is 'fully insulated', do I take it that the capacitance from the workers to ground sufficiently high that they need protection (of any sort)? ... I think I would probably have guessed not.

    Kind Regards, John
     
  12. westie101

    westie101

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    At 11kV the phase to phase clearance can be about 0.8m so the risk of contact between two phases has to be taken into account, so a metallised suit would be a "risk" hence the use of insulated gear
     
  13. JohnW2

    JohnW2

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    Right. That makes sense. Thanks.

    Kind Regards, John
     
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