Here's a sample. The important thing is to decide what variable you're going to use to walk through %conductordata -- in the snippet below, I used $_ -- then use that in your format. Of course, I don't know what your data looks like, so I faked it. Also, please note that using a format doesn't matter if you're printing. The only thing that is affected by format is write.

use strict;
my $i;
my %conductordata;


format =
# Conductor
@>>>>>>>>>>@>>>>>>>>>>
$conductordata{$_}{radius},$conductordata{$_}{length}
.

for ($i=1 ;$i<=10 ; $i++){
    $conductordata{"conductor$i"}{radius}="radius$i";
    $conductordata{"conductor$i"}{length}=$i**2;
}

foreach (sort keys %conductordata){write}
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