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Neutral problems

Discussion in 'Safety' started by David Ashton, May 24, 2008.

  1. David Ashton

    David Ashton Active Member

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    Occupation:
    truck driver
    Location:
    perth W Australia
    It was 1988 and I got the contract to light the premiere of Peter Brooks Mahabharata at a quarry in the hills outside Perth, this was the headline act of the festival and a big deal with 3 areas all lit and 8 hour performances.
    The State government chipped in and ran a 5 kilometre 3 phase[250V] 100A power feed out to the quarry, after a week or more of rigging we started to plot when we started getting random flickering on the dimmers, I took them back to the factory and they worked fine, so we figured it must be a power problem and called in the S.E.C. engineers who came out with their new DMM and checked it out, they had run the 3 phases up from the substation but no neutral, they had connected the neutral to an earth plate and put it in a little pond in the quarry, but I was measuring phase voltages and they were drifting all over the place and the neutral currents were impossibly high over 100% more than the phase currents and the DMM was reading 150hz.The engineers departed saying the power was OK and the silly readings were a meter fault, meanwhile opening night is 4 days away the lights are still flickering and I'm having a nervous breakdown.
    Three o'clock in the morning I realize whats happening, when the dimmers are down low below about 35% the phases are not canceling because they are on at different times and so the neutral is being pulled to the phase that is drawing current and then the next phase and is whizzing around at 150 times a second, but why isn't being held at earth potential its in a bloody pond.
    Well I ring the Production Manager who wasn't very receptive at 4 in the morning but the next day up at the quarry I discover that the pond is in a granite dip and is actually insulated from real earth, so we ran a cable down to some wet ground much lower and got a better earth but still not enough to stabilize the neutral.
    However now we had an understanding of the problem it was possible to overcome it by putting on as much balanced load as possible, air conditioners and lights and modifying the light cues to a degree by bringing lights to higher levels and if that light was too bright by taking it down with ND.
    The show went on but after that experience I sold up the business, bought a boat and sailed the world for a couple of years with my 9 yr old daughter.
    Which was the wisest thing I ever did.
     

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