TRACING POWER LINE NOISE DANGER! THIS PORTION OF THE ARTICLE IS FOR INFORMATIONAL PURPOSES ONLY! DO NOT ATTEMPT ANY PHYSICAL CONTACT WITH POWER LINE EQUIPMENT INCLUDING POLES OR GUY WIRES TO LOCATE SOURCES OF RFI! LEAVE THIS TO THE ELECTRIC COMPANY. IT IS THEIR RESPONSIBILITY.....NOT YOURS! ASSIST THEM ONLY WITH TRAINED POWER COMPANY PERSONNEL SUPERVISING YOU. DO NOT ATTEMPT STATEMENTS IN RED IN THE ARTICLE BELOW CONCERNING ELEVATED POWER LINES! ELEVATED POWER LINES If you can identify the exact pole that is having the problem, you can normally get things fixed pretty easily. Power companies have a legal requirement to not radiate noise so normally have special funding to fix these problems that is outside the normal maintenance accounts. The thing to remember is that most power company forms and documents list any form of power line interference as TVI. You will have good success using a cheap aircraft band portable. 108 to 136 MHz aircraft communications uses AM so receivers for that band have AM detectors. Line noise is much shorter range on VHF so you normally have to be much closer to a noise source to detect it. My best results was with a home-brew tunable HF am detector but the aircraft band receiver is almost as good. What you are looking for is loose hardware on the poles. The primary noise source is usually slack bell insulators. Those bell shaped insulators you see at the ends of power line runs have metal parts which, if not electrically bonded, will arc at a 120Hz rate. Without sufficient tensioning, a thin oxide layer builds up in metal joints. They arc simply because they are in such close proximity to high voltage (usually 4, 7.5, or 12 KV!). You can spot slack bells quite easily since they usually sag under their own weight. If the line they are on was properly tensioned, they wouldnt sag. Bell insulators are supposed to have metallic spring clips or soldered on jumper wires to prevent arcing but occasionally these things are damaged and no longer make contact. Another common source of pole top arcing is just loose hardware. Any kind of metal-to-metal contact, such as nuts, bolts, brackets, and braces, can loosen from the shrink and swell of poles with weather changes. When loose, oxide layers build up and arcing begins. Even though not directly connected to the power lines, these arcs can be so powerful that they couple into the line and propagate for miles. It is not uncommon for loose nuts and bolts on a pole top to loosen and arc so badly that the pole catches fire. Obviously, noise that goes away when the poles are wet and comes back when the poles are dry is a good candidate for loose hardware problems. It is a common task for a line maintenance crew to tighten hardware on pole tops. Transformers are rarely the source of line noise. I actually found only one noisy transformer and it was simply a loose high voltage connection to the top of the transformer. I could wiggle the guy wire on that pole a little and see the wire wobble. Noise burst were produced as the wire wobbled. What you do to locate a bad pole is to first narrow the search area down to a few poles. Carefully inspect the poles with binoculars for obvious loose or broken hardware. Then lightly kick suspect poles to see if the noise is changed or modulated by pole vibration. Unless the base is really stout, just turn your back to the pole and give it a mule kick. Some louder sources could ravel several miles on the lines though. If you are having trouble narrowing the search down, try another trick. Go to a convenient pole guy line and gently wiggle it to get the power lines to start swaying a little. THE IMPORTANT THING TO REMEMBER IS DONT TOUCH POWERLINE EQUIPMENT EVER. BE SAFE NOT DEAD! Sometimes, loose hardware on a conductor run would show up from the line movement. One thing to watch out for, aside from the obvious danger of just being around power lines, is that you are not fooled by the noise peaks you will find near pole ground lines, guy lines, and other conductors running down poles. These things bring power line noise right down to you so might make you think you have found a source when all you have is a noise antenna. Go out one dark night and walk along under the lines and listen by ear as well as radio and watch carefully at each pole. If there is a leak across an insulator (usually a cracked insulator) it may have a visible arcing. Once you find a bad pole, write its address and any identifying numbers you can spot on it and turn a TVI report into the power company. The thing to watch though, is that your report may not be written down correctly, The folks you talk to at the power company dont normally understand RF or think that anyone besides their own technician is incapable of understanding such an arcane subject. Try to get them to contact you and, preferably, allow you to be present when the work is done. If your problem report is just handed to a utility line repair foreman, he is likely to simply go to your home address and decide that he can hear the ball game on his truck radio just fine so not bother checking any further. You want to be able to give him the correct repair information so he will actually work on the real problem.
Posted on: Wed, 04 Jun 2014 02:21:00 +0000
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