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Wednesday, October 7, 2009

Must-See Video of Line Fault and Reclose

Check this out:

If you've read over the previous two tutorials, you'll note how far above the three phase feeder these wires are, which makes this at least subtransmission voltage. I am guessing by what I can see that the involved circuit is probably 69kV - but don't hold me to that.

These people are entirely too close to this action. If the conductor were to melt and break from the heat of the arcing, the wire would recoil quite a long ways, and fall into the feeder, making more fireworks. These people are living out 'If Only We Knew How Stupid We Were'.

The extended duration of the fault is clear evidence that you cannot always depend on transmission or distribution circuits to clear quickly after a fault. We'll get into system protection and fault clearing in a future tutorial.

In any case, you spent most of your time watching that clip with the sustained arc in the tree, imagining how much power is in there. But then, when it finally 'flashed' at 4:02, that's when the full force of the 69,000 (?) volts coursed through the tree. You can see that I am not overstating the force when I make snippy comments about arms getting blown off.

Finally, it's dead, it's safe. Wrong. You saw it yourself, the line came back to life 10 seconds later through automatic reclosing, and carried the fault current for an additional 5 seconds. In addition, though it didn't seem to happen here, chances are excellent that after the second clearing event, a dispatcher may have waited a minute or so and then manually tried it one more time in case whatever was wrong had time to fall away.

That's all..... 'nuff said.

Thanks to Dave Statter for bringing this to my attention through his blog.

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