# [RFI] Power Lines

David Robbins K1TTT k1ttt at arrl.net
Sun Dec 23 14:23:01 EST 2007

```If the line uses the common porcelain or glass 'bell' type insulators shaped
like these:
http://www.berkshireinsulatorgallery.org/catalogimages/mvc-017f.jpg or
http://www.berkshireinsulatorgallery.org/catalogimages/mvc-042f.jpg.

Just count the number of insulator 'bells' in each string and multiply by
20kv, then pick the next lower value from this list of common voltages:
69kv, 115kv, 230kv, 345kv, 500kv, 765kv

so 7 bells would be 7*20kv=140kv so would likely be 115kv.

If there are 2 strings in parallel only count one of them.  It is the
overall length that really matters.

Note, some areas of the country use slightly different voltages like 131kv
instead of 115kv, so this will only get you in the ballpark.  There is also
the chance that the line was constructed with bigger insulators than it is
actually being used at.  For instance they could have put on insulators to
handle 230kv, but are only running it at 115kv until they upgrade the
substation equipment at both ends in the future.

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net

> -----Original Message-----
> From: rfi-bounces at contesting.com [mailto:rfi-bounces at contesting.com] On
> Behalf Of Jim Miller
> Sent: Sunday, December 23, 2007 19:00
> To: RFI Reflector
> Subject: [RFI] Power Lines
>
> Thanks Guys,
>
> Two large poles together with a single cross piece with all three
> "wires"(cables) hanging from the dangling insulators.  Sounds like AC
> then.  The power company maintains a cleared right-of-way width of 130 ft.
> The pole sets probably average about 5-600 ft separation.  Often wondered
> what the voltage was.
>
> Tnx es 73, de Jim, KG0KP
>
> ----- Original Message -----
> From: W0UN -- John Brosnahan
> To: Jim Miller
> Sent: Sunday, December 23, 2007 8:22 AM
> Subject: Re: [RFI] Power Lines
>
>
> At 08:02 23-12-07, you wrote:
>
>   Does the RFI from DC lines tend to be less or more than that from AC
> lines?
>   Is there a way to tell if the lines are DC or AC?  Can you "listen" to
> them
>   or something?  I have HV lines running across my property in the
> country.
>
>   Tnx es 73, de Jim, KG0KP
>
>
> Jim--
>
> Looks to me like the DC lines only have TWO main conductors (and maybe a
> third, smaller wire that is ground for lightning) while much of the AC has
> THREE
> conductors for the 3-phase that is usually transmitted (and maybe a fourth
> wire that is ground for lightning).
>
> I am no expert by any means but I'll be that if there are THREE big
> insulators
> on each tower it is AC and if there are just TWO it is PROBABLY DC.
>
> At least that would be my best guess.
>
> John  W0UN
>
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```