Questions on different practices?

[tramp67]

A thumper van? Wow, that brings an image to mind! Picture a brown chevy van, with the tinted bubble windows on the sides, the interior wall to wall, floor to ceiling brown and gold shag carpeting, a striped mattress on the floor, covered with stains from who knows what.... Sorry, LA, I just couldn't pass that one up!!!

But really, always new things to learn. A thumper van sounds like a WWII vintage piece of equipment, I think I saw a picture of one in about the 3rd or 4th edition of the Lineman's and Cableman's Handbook. Do you really have any equipment nowadays to test underground primary cable that requires it's own van? It would be interesting to see, as it's something I've never run across yet.

As far as thumping through transformers, the few thumper manuals that I've actually read cover to cover state that it is perfectly safe to thump through transformers, and it is basically a waste of time to disconnect each transformer, stand off the primary, move the thumper, .......

Back to the AC or DC question - I guess maybe that's where the thumper van comes into play? I never tested or thumped cable using AC, and really don't understand how it would work well or the reasoning behind it, not to mention the tremendous stress it must impose on a cable. After all, underground primary cable is basically a long capacitor, and to subject it to an alternating current under fault conditions is proven by the cable manufacturers and EPRI to be very damaging to the cable, much more so than the DC current. Maybe that's where the exploding thumper vans come into play? I don't know everything, never claim to, but this one just seems too far out for someone to be doing, with all the technology out there today.

[lewy]

We always TDR the cable before we thump & we will TDR through transformers but once we have a good idea where the fault is ( TDR will tell you approx how far away fault is ) We will then thump the cable between the open points, do not see why you would thump through a transformer, if your thump-er is DC would it not go to ground through the winding? I have never heard of a thump-er powered by a 12 volt battery , we power ours either with a cheater cord or a generator. We also put it on a voltage low enough to just jump across the fault , I have thumped a lot of cable & when standing over it you can sometime hear it & feel it & have never had or heard of a problem with step potential.

[Mike Honcho]

I have worked for four different utilities, They have all had thumper vans where the equipment is installed in them, new and old, there are also portable unit's same equipment, portable unit's has a battery back up for remote location's, but all are run of a 120V inverter or portable generator, portable generator's are alway's the last resort because they are loud, hard to here the thump. As Lewy states you scope it in the Arc Reflection Mode, Yes you can see through transformers, but you have laterals alot of times, fault indicator's if installed should have already been looked at prior as part of the trouble shooting. As far as AC or DC, Your newer devices have a DC HI POT feature, you can also use you phasing set with the DC hipot adaptor for trouble shooting, but you should Isolate lightning arrestor's and transformer's when doing so. When putting your thumper in the direct mode or Thump mode to hear your fault it is actually an AC Voltage with a Square sine wave, again check with your manufacture of the thumper being used. I would also reiterate that no manufacture will approve the use of a thumper when eneregized cable's are in the same trench. A utility will not purchase a piece of equipment and say it is alright to use against manufacture's recommendation's. Again going back to Ryan's original post, there was a faulted cable in a trench with energized cable that was spliced 3" away, now to me a couple of thing's could have happened there, either when the first cable faulted, when thumping that cable, it damaged the integrity of the wire next to it, causing it to fault later, or when excavating the first fault they damaged it when digging it up or back filling it with out useing proper fill. There are other example's but that would be my guess. As far as step potental, you must work in place's where your concenrtic neutral is in good shape, again I will state that is not always the case. I have been on many faults where the concentric is completely corroided, as certain soil's are extremely corrosive to unjacketed primary that was plowed in 30 to 50 year's ago. When can you tell if your concentric is bad, when scoping it, your radar dosen't give you a good siganal, even when you try from both end's. If you have thumped a cable, and not isolated your transformer, and not seen light's go on and off everytime you thump, again consider yourself lucky, I have seen it happen, don't take my word for it, talk to your equipment's trainer's, dig as deep as needed, but ask about these question's, ask about step potental. Or keep on doin what your doin, it's your call.

[tramp67]

I have worked for four different utilities, They have all had thumper vans where the equipment is installed in them, new and old, there are also portable unit's same equipment, portable unit's has a battery back up for remote location's, but all are run of a 120V inverter or portable generator, portable generator's are alway's the last resort because they are loud, hard to here the thump. As Lewy states you scope it in the Arc Reflection Mode, Yes you can see through transformers, but you have laterals alot of times, fault indicator's if installed should have already been looked at prior as part of the trouble shooting. As far as AC or DC, Your newer devices have a DC HI POT feature, you can also use you phasing set with the DC hipot adaptor for trouble shooting, but you should Isolate lightning arrestor's and transformer's when doing so. When putting your thumper in the direct mode or Thump mode to hear your fault it is actually an AC Voltage with a Square sine wave, again check with your manufacture of the thumper being used. I would also reiterate that no manufacture will approve the use of a thumper when eneregized cable's are in the same trench. A utility will not purchase a piece of equipment and say it is alright to use against manufacture's recommendation's. Again going back to Ryan's original post, there was a faulted cable in a trench with energized cable that was spliced 3" away, now to me a couple of thing's could have happened there, either when the first cable faulted, when thumping that cable, it damaged the integrity of the wire next to it, causing it to fault later, or when excavating the first fault they damaged it when digging it up or back filling it with out useing proper fill. There are other example's but that would be my guess. As far as step potental, you must work in place's where your concenrtic neutral is in good shape, again I will state that is not always the case. I have been on many faults where the concentric is completely corroided, as certain soil's are extremely corrosive to unjacketed primary that was plowed in 30 to 50 year's ago. When can you tell if your concentric is bad, when scoping it, your radar dosen't give you a good siganal, even when you try from both end's. If you have thumped a cable, and not isolated your transformer, and not seen light's go on and off everytime you thump, again consider yourself lucky, I have seen it happen, don't take my word for it, talk to your equipment's trainer's, dig as deep as needed, but ask about these question's, ask about step potental. Or keep on doin what your doin, it's your call.

Check out this link. Maybe you should talk to your utility about moving into the 21st century in equipment. I have used this particular unit, and similar ones made by Biddle, etc., all battery powered. I have taken them to remote areas on the back of an atv, by boat, and by bush plane, not to mention wheeling them into back lot lines in town. They perform very well, have always been able to locate faults in thump mode, and have had pretty good luck with the TDR capability of these units. And yes, the manufacturer specifically states that their equipment is designed to thump through transformers, as the specs on this link state. The manufacturer rep that I have done training with years back claims there is no problem with using these units to thump near adjacent energized cables. I'm still not sure why you would have an entire vehicle devoted entirely to fault locating, unless it was someone's full time job?? I've never seen any modern equipment large enough to require a van to carry it, not even hipot and ratio testing equipment for station transformers - the equipment for testing station transformers that I've had experience with fits in those neat hard sided "suitcases". Usually seems like the cables take up more space than the test equipment. But, I'm sure there's all kinds of equipment out there that I've never seen or used, just as you must not have run across equipment like this.

http://www.hipotronics.com/pdf/5250brochurenewpic.pdf

http://www.iupcorp.com/iupcorp/iup2003.htm

I'll stand by my experience with thumping through transformers and near energized cables unless I'm working somewhere that a company safety manual prohibits it, as I've never had a problem and have been trained by manufacturer reps that it is an acceptable practice, at least with the types of equipment I'm familiar with. Maybe your truck mounted test equipment does not allow testing this way, it's the stuff you are familiar with. As always in linework, there's always more than one way to do a job, and more than one tool to do it with.

[Mike Honcho]

I do not see anything in that link that recommend's or approve's thumping cable next to energized cable's. I am familiar with unit's like you have posted.
http://www.cablemasterinc.com/produc...martthump.html

I never stated you can not look thru transformer's, I do not know why you would actually thump thru them when in the Direct mode. Loop feed's in my experience have normal open's, fed from different sources, thus only having a partial outage, but I am confussed on your methods, Do you go to your first transformer or switch cabinet, shoot the hole line, then thump it leaving custmers out til you find your fault?

But getting back to the original post, an apprentice splicing a faulted cable with engergized cable's 3"to6" away. If it is your recommendation to thump cable next to energized cable that is your call, if it is your recommendation to splice faulted cable in an energized trench again that is your call, if your supplier recommend's thumping cable in an energized trench with multiple cables, again that is there call.

If my recommendation's are opposite, that is my call. As I stated before do as you see fit.

[Ski_Digger]

Mike H.
Like you said, I totaly agree with ya.
You got to find the fault what ever way a company does it.
Splicing cable with other cables energized in the same trench, Man a lot of bad things can go wrong real fast. I can not see any reason to do that.
We always open and ground on both ends and isolate the cable.
Like you said I also have seen the cable burnt right off and glassed over, or the other end of it just a pin hole in the cable.
If there is three open concentric cables in the trench you could have a lot of current flow in the ground. With two "Hot" you could have a difference path for that neu. conductor.
I have spliced cable were you moved it and the Neu. has fallen apart. That is why we never splice with energized cable in the trench.
What it comes down to is urd sucks builder overhead
Work safe and wear your glove.
Ski

[Mike Honcho]

Ya Ski, I have done it myself, did'nt like it, multiple circuit's Sub get away's, I have also seen guy's do it. don't want to take the time to switch it out, But they were Journeyman, not some apprentice.

[linehandjlc]

i was working for a coop (1st mistake)who has a pretty nice urd system (all swithes are under oil) and is 70% u/g (2nd mistake) due to the resort area they are in (3rd mistake). i swapped crews for the first time after six months of being employed moving over to the maint. crew, (which was run by a six year journeyman who hasn't worked anywhere but there and thinks nobody does any linework but there) i knew there were going to be problems when i realized the lack of equipment this foreman had @ his disposal, (most likely because the company dosen't trust him not to destroy it). i was comfortable with my previous foreman recognizing that he was a lineman of 20+ years who had applied himself. he warned me about some of the practices there were not up to industry standards, especially the foreman that i was preparing to rotate to. it only took one week for me to see what he was talking about. what do you all think about a company pulling and snapping elbows then floating them never actually grounding and then working on the cable bare handed, claiming that due to the high resistance here in the mountains it creates more of a danger to ground????? yet this only pertains to their u/g system, their procedure for o/h grounding is legite. i didn't buy it @ all, stood my ground. but, i'm an apprentice who's obviously lacking confidence due to exposure. comments?