Power Influence problem

tel601 · Posted: Tue Mar 02, 2010 7:24 am Post subject: Power Influence problem

What is the best way to narrow down the area that a power influence problem is originating from? I have a cable run that starts at the cross box as a 300 and breaks down into 8 side legs. The total length of all of the is about 25 miles if you add the length of the side legs and main cable together. Main cable is about 13,000 feet, side legs vary in length. All pairs are unloaded and adsl service is provided in this cable.

Everything in this 300 pr cable has a hum on it and shows a high power influence measurement but no other trouble. The pairs show great long. balance, but you can measure ac voltage from tip or ring to ground. We use a 965 and a sidekick to do measurements.

Any recomendations as a way to locate the area, or side leg this power influence is coming instead of having to go pole to pole? Is there a way to find if it is starting in one count and then bleeding into the other counts?

Jim Weston · Member Joined: 19 Oct 2009 Posts: 13 Location: NEBRASKA

Tel601,
I have written a procedure that might help you. Power influence can be a real pain in the butt and run you in circules. I know because I've been there over the years. Rather than posting the whole text if you would send me your email address and I will forward the documentation to you or you can call me at 402-533-3342.
Hope this helps
jw

mrfabulous · Member Joined: 31 Dec 2001 Posts: 68 Location: Oregon

I don't know of any EASY way to find the problem, but fixing it is going fun! The best feeling I've had in telco work is finding the "magic bond" and fixing 300 customer's phone problems by tying down one nut.

Just for fun, drive the power leads with your radio on AM 540, 600, or 1080. Listen for increases in interference. If you get massive noise in one area, you may have a power company problem. (You'll still need to do all your due diligence with bonding the cable, but an unbalanced power system can cause problems anyway.)

good luck

Jim Weston · Member Joined: 19 Oct 2009 Posts: 13 Location: NEBRASKA

It's nice to see someone else enjoys working on PI issues. Most of the techs in my company just thought I was not right in the head for finding fun while dealing with issue. I will say that's it's more fun today than it was 30 years ago. Why? For one thing, in the past if Uncle Joe could shave, fix his toast, and listen to the radio in the morning the power companys would reply " We can't have a problem". When they started running their own communications systems over the power lines and were dealing with the same issues as the telco they started paying more attention to us. Meters of today such as the "Mitigator" and the 965AMS also make the task much more enjoyable and many times less time restraining.
Thanks and keep having fun!!
jw

tel601 · Posted: Sun Mar 07, 2010 8:22 pm Post subject: update

Update : I went by one of the local power company's engineering offices for a sit down with them. They agreed to go out and check the area with a IR camera and a noise detector and said they would call me if they found anything. After a few days of not receiving any call I went back to check on the problem and found that the issue is gone. There has not been anymore work done on the phone cable so I can only guess that the power company fixed something.

Thanks for the help Jim.

Does anyone know where I can get some info on using a Megger DET10C clamp on Ground Resistance meter?

mrfabulous · Member Joined: 31 Dec 2001 Posts: 68 Location: Oregon

Nice! We had trouble on one lead, and we knew it was an unbalanced power load. In one location we used jumper wire and tied it between an MGN and the cable sheath, to see if we could draw current. We did...

Have you ever seen 14 amps run on jumper wire? Very impressive. The power company kept insisting nothing was wrong with their plant.

The problem continued until a wind storm blew tree limbs down on power lines all over the area and power had to make repairs...

Dave72 · Posted: Tue Mar 09, 2010 6:48 pm Post subject:

Dont forget that it's normal in a lot of situations to have current flow on the sheath. Current generated in the hydro grid must be a 'loop' from the hot phases at the generator back to the neutral/ground at the generator (simple way of looking at it, but its ok for here).
Only a small portion of the current flows back on the hydro neutral wires.. most flows in the earth and other conductive things like our nice telco network sheaths and ground wires.
The balancing of our pairs rejects most of the a/c fields (cancellation).. an unbalance can cause a/c current flow in the pair.
60hz is common, and is filtered out in the telco system, no worries (well, to a point. lol)
Its those other harmonics that can mess us up (360, 540 etc). Once they find some way into the pair (unbalance), then we get complaints. If the hydro system is blasting enough of a harmonic into us, there's only so much balancing and bonding/grounding you can do (in the real world).. then you have to hope for someone in the hydro util to help you out (or help point it out to them with a Mitigator etc)