You could try and E-field detector.  Basically a simple whip antenna, with
a FET amplifier stage.  I guess a loop antenna would be more directional
and disctriminating.

To make this specific to power lines, you would need a 60Hz filter of some
sort.  This could be implemented with a PIC A/D easily enough.

Good examples of suitable circuitry (without the filter) can be found by
search the web for VLF , VVLF receivers.  People use them for listening to
RF being given off by the Aurora Borealis (SP), and other interesting things.

Cheers,
Don

At 06:32 PM 11/28/98 +0200, you wrote:
>Hi there all
>
>a bit of a question, who knows how to detect high voltage AC power lines
(overhead ones) from 30meters and above? I need to know when I am near one
and have enough time to react.
>
>Regards
>Richard Parsons
>
>