I know this is a topic that seems to regularly surface here, not really
surprising I suppose, but I have a question that seem rather to go
against what I think I understand.
Recently I have started to see a number of 'protection systems'
installed on towers that are very different from anything that I have
seen in the past. So far I have found little independent analysis to
show what they do and how they work.
In essence the system seems to comprise an air terminal, mounted at the
top of the tower. In some cases these look like a pole with a sphere at
the top, about a foot in diameter, in other cases they look like a more
traditional 'pointed, almost' air terminal. In both cases the terminals
are attached to a heavy conductor, typically a 1" pvc insulated cable,
multi strand, totally isolated from any conductive connection to the
tower and running down to the ground system.
The 'claim' seems to be that these systems provide a way to prevent the
top of the tower from 'looking' electrically any different from the
surrounding earth and that any buildup charge in the area will be prevented.
I don't really think I understand this. What is the difference between
such a system and one utilising the tower structure as the down
conductor? I can understand that during a surge event the voltage
increases at a rate whereby the down conductor inductance plays an
important part but this scenario suggests that there should not be a
surge event with a fast rising edge and hence resistance rather than
inductance really is the significant factor and further that no current
should be allowed to flow in the tower or any of it's connected parts.
What's going on here? Snake oil or 'new science'?
Martin, HS0ZED
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