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Steve Riddle
06-10-2006, 02:33 PM
Would someone be kind enough to explain the practice of "thumping through"
Thanks :)

scammy
06-10-2006, 03:53 PM
are you talking about locating primary faults underground?

topgroove
06-10-2006, 03:54 PM
Thumping a cable refers to using a machine to thump a underground piece of cable. When you first hook up the thumper it will megger the line out and tell you if its good or bad. If its bad you isolate it and begin thumping. Each thump sends current down the line to the fault is and you can actually hear and feel the thump through the ground. The spot where the thump is loudest is directly above the fault.

BigClive
06-10-2006, 07:33 PM
What sort of voltage is being dumped across the cable under test? I guess it's just a large capacitor bank that is charged up then discharged across the cable?

Viperexaf
06-10-2006, 10:13 PM
depends on what you have the machine set at and what the voltage the cable is set for. you set the machine too high then that cable will just burn. One we had out in cali was pretty nice, didn't get to play with it all that often. Majority of the thumpers anymore have gone computerized and some are a pain in the butt to try and operate, unless you go to a class on that particular machine and learn how to use it.

edski104
06-11-2006, 09:53 AM
here we set it at 15 kv to thump the primary. you can set it to 7.5 but 15 is better in that it is louder in the ground. it is also DC voltage so just the ends of the cables are burnt a little,but your cutting those off now anyways,aren't you? we also thump seconary services and it is a whole lot faster than with any other machine.

hifihaxor
06-11-2006, 10:26 AM
i believe thumping THROUGH refers to trying to locate a fault on a loop, going to the NO or end point and thumping THROUGH the loop connected transformers. then on the tdr display, youll see deflections where the transformers are and a deflection where the fault is (they look different) so you can see what section the fault is on and then go to that section and test again to get a better footage, or isolate that section and reswitch the loop

the voltage out of a thumper is around 20kv DC, from what ive seen, could be higher or lower, since its dc, its ok to go through transformers because the transformer wont turn it in to secondary voltage

dbrown20
06-11-2006, 10:54 AM
I've never experienced thumping through, nor have any of the manufactors of the thumpers we've used recommend it. We have always been taught to locate the section of line that contains the fault, stand it off on either side of the fault and thump that section. We've gotten one of those new brands of thumper that gives the line on a screen and gives the footage distance to the fault. Have only used it a few times but it's very accurate as to the distance etc.

Did know some guys once who were using one on secondary. It was supposed to be okay to use it as they had reduced the voltage to the manufactors recommendation for secondary. The funny thing was they neglected to remove the customer's meter and so they damaged some of the customer's appliances. Pretty funny. Anyway it was to me. dbrown20

Orgnizdlbr
06-11-2006, 11:00 AM
I've never experienced thumping through, nor have any of the manufactors of the thumpers we've used recommend it. We have always been taught to locate the section of line that contains the fault, stand it off on either side of the fault and thump that section. We've gotten one of those new brands of thumper that gives the line on a screen and gives the footage distance to the fault. Have only used it a few times but it's very accurate as to the distance etc.

Did know some guys once who were using one on secondary. It was supposed to be okay to use it as they had reduced the voltage to the manufactors recommendation for secondary. The funny thing was they neglected to remove the customer's meter and so they damaged some of the customer's appliances. Pretty funny. Anyway it was to me. dbrown20

Ive seen it damage inside equipment with the meter PULLED. Leaving the neutral in the pan, thumping the bad leg when the neutral is bad or exposed in the same place introducing the voltage into the house neutral and burning up recepticles.......

scammy
06-11-2006, 12:53 PM
our thumper was designed by a guy from DPand L named (vaughn) we us it on primary cable only, you can put up to 90000volts on it DC. but as mentioned ,you go too high you will blow another hole in it. go too low you cant here it. workes pretty good ,every fault has different conditions to deal with.... moistier content,sometimes its in conduit,,rocky ground , ect,,cable must be disconnected from apperatus at both ends,,,,,,,,its a must have for us,,,,,,,,,,also guys remember ,when you work underground your alreaddy grounded! test it and ground it before you touch it,,,,,be carefull,,,,,,its not dead untill its grounded,,,,,,,,,scammy

dbrown20
06-11-2006, 01:02 PM
our thumper was designed by a guy from DPand L named (vaughn) we us it on primary cable only, you can put up to 90000volts on it DC. but as mentioned ,you go too high you will blow another hole in it. go too low you cant here it. workes pretty good ,every fault has different conditions to deal with.... moistier content,sometimes its in conduit,,rocky ground , ect,,cable must be disconnected from apperatus at both ends,,,,,,,,its a must have for us,,,,,scammy

I've used the one you speak of. I believe it's VON, although the inventor may be named Vaughn, I don't know. I know the one I was acquainted was manufactored by the VON Corporation. The one we currently have, I don't even know the brand name. It is superior to the last VON I used. It has the screen that shows a line with a blip at the fault and gives you a footage figure. If you know the cable route it is very accurate. I have never witnessed anyone use them on secondary. Our servicepeople use a different type on secondary. They have good luck with it and routinely repair secondary faults with it. I try not to get very expert with URD stuff as much as possible. dbrown20

scammy
06-11-2006, 01:21 PM
we have to do both overhead and underground , soon they will make us (stick a broom),,,nevermind,,,,anyway we use the dinatell for secondary faults and the thumper for primary

CHICAGO HAND.
06-11-2006, 03:06 PM
i believe thumping THROUGH refers to trying to locate a fault on a loop, going to the NO or end point and thumping THROUGH the loop connected transformers. then on the tdr display, youll see deflections where the transformers are and a deflection where the fault is (they look different) so you can see what section the fault is on and then go to that section and test again to get a better footage, or isolate that section and reswitch the loop
WHY WOULDNT YOU ISOLATE THE BAD PIECE FIRST, RESTRORE SERVICE TO THOSE NOT EFFECTED AND THEN THUMP.
SEEMS LIKE ALOT OF PEOPLE SITTIN ON A LOOP WITHOUT LIGHTS WAITING FOR SOMEONE TO GET THERE HEAD OUT OF THERE ---.

dirtdobber
06-11-2006, 03:24 PM
with you Chicago restore power to all that you can isolate the fault then start thumpin away so repairs can be made. we've used radar machines also to locate faults they work pretty well also.

BigClive
06-11-2006, 03:42 PM
Do the TDR units (Time Domain Reflectometry) use a high voltage pulse?

These are the machines that display a trace of the result if applying a pulse onto the cable. Any fault or conection will reflect back a small pulse that shows as a blip on the display.

Very accurate for fault location finding. "Dig the hole right here."

CenterPointEX
06-11-2006, 03:42 PM
I have many years experience with the radar equipment. Some of the loops here on CenterPoint property have twenty or more transformers on them. Trying to thump cable one span at a time would be very time consuming as most of our xfmrs are in the easement. The first thing you do upon arrival is hook up the radar which sends a signal down the line. At each point of resistance the radar bounces back and shows up as a refelction on the screen. A reflection as in an up or down spike on a flat line on the screen. The coils on a xfmr show up as an up and down spike. The further away you get from each xfmr lessens the intensity of the spike. I got pretty good at reading the screen and could differentiate the reflections... I could tell ya how many xfmrs you were looking at, I could see a splice, and I could pretty much tell ya what kind of fault you were looking at... Bad elbow xfmr, etc... The sound of the Thump also became readable so to speak. Kinda in the way a Submariner listens to sonar.
...A open shows up as an up spike and a ground as a down spike. So you measure the distance and then look at the map to see if the open is at the right distance for the length of the loop which you can determine by measuring the scale on the maps of the URD service. If you you see a short distance you can go to that point and look for it either in an xfmr or test that piece of wire. If you see a ground same principle... If Everything checks out You send a DC Charge down the line with the thumper. If it grounds out you will see the down spike on the screen and then you can find the location. Some pin hole faults will not take the radar signal to ground But the DC Charge will... The Problem with thumping is that all cable has micro holes in it. The DC Charge kind of makes them microly bigger aka breaks down the cable. Thumping thru is thumping the whole loop xfmrs and and all.
........... When I worked nights I worked with a lazy Trouble shooter. He used a hand held radar, took a picture of the loop in memory. Then Thumped the loop with the biggest fuse he could find on the truck. Then when you reattached the radar the big fuse would almost always change the picture. So it was easy to locate on the screen by comparing the two pictures. He blew a lot of stuff up doing this not to mention that cable using this method got comprimised. The xfmrs also were also stressed by this thump. Fault current bounces back just like the radar signal. The electrons bounce at the fault and head back to the feed in effect doubling the voltage while it is faulting. This doubling of the voltage really tears stuff up. That is why lighting arrestors on URD stuff are made differant... The blow faster to interupt the fault current before to much damage is done.
........On occasion voltage spikes are generated by something that goes awry at the generator... These spikes are microscopic in durration but they would cause weak URD arrestors to fail simotaniously. Four or five loops would go out at one time... I discovered the micro spikes by talking to some folks on the generation side. Also charged clouds sometimes had the same effect. There would be no lighting in the area, only low fast moving charged clouds passing thru. The cloud current passing over the conductors would induce an over current on the line. This momentary overvoltage is normally taken to ground by lighting arrestors doing their job. A blown arrestor is one that failed. The arrestors have inulators in them which bleed over when a certain voltage is reached and then shut off the bleed when the voltage drops back down. Failed arrestors don't shut off when the voltage drops below the threshhold and thats when the blow...

The thumper has a dial on it that allows you to increase the DC Voltage. Ideally you start at a low setting to reduce the damage to the cable. I once thumped a cable that was attached to a step down on the Pole... The gas produced by over heated xfmr oil is acetylene... The top of the pot got launched into the primary. Luckly it clered itself from the xfmr before it energized the Radar van.... When I did this it was brand new technology and the only folks who really understood it was the German engineers did not speak linemanease... So, we learned by trial and error and somehow lived thru it. Also stay off the Van when they are thumping... Once when the Van ground was not hooked up and the ground in the xfmr had worked loose a Lineman who was leaning on the van discovered the sensation of taking the DC Thump to ground thru his body...

For weak thumps we also had a listening device... It was a set of head phones connected a sort of microphone with a metal tip in it that you stuck in the ground... A meter attached would tell if you were getting further or closer to it... I never had much luck with that contraption... Settin a road cone in the ground an puttin my ear to it worked better... The meter more often than not lied to me and sent me on wild goose chases... For a while they sent me out by myself to work a loop. I used a bycycle to ride out the loop listening for the thump.... This was insanity... But they were trying to get more done with less...

hifihaxor
06-11-2006, 04:34 PM
chicago, if you have a very long loop with a lot of TXes you can take hours to find the bad section and bang a bunch of fuses. if you use the radar at one end of the lop you can find the faulted section very fast and isolate and restore, thump the cable andf repair later

read centerpoints post, he explained it the way i know it.. everything ive heard and experiences matches with what hes saying...

dbrown20
06-11-2006, 08:27 PM
You guys are too damn expert for me. I was always used to the old method of using one of those chance phase testers and just checking it out one piece at a time and closing behind until you located the bad part and then standing it off and going to the NO and closing it in. No, you guys are way ahead of me. Ah well, 8 months and you'all can have it all. dbrown20

toptie
06-11-2006, 11:37 PM
By the time you have a crew deliver a VON you could install fault indicators on primary, find faulted bad span, restore service by switiching feed around. Then maintenance crew can thump and repair fault next day?

toptie
06-11-2006, 11:50 PM
by the time you called out a man or crew, could'nt you put fault indicators on up to the open-point, then identify the faulted section, switch it out to restore power, then let maintenance crew thump, find, and restore the bad section back to service?

hifihaxor
06-12-2006, 06:11 AM
down here there are a few trouble trucks in each service center that have thumpers built in to one of the bins.. its pretty cool. we also have portable thumpers on hand carts which can be deployed fairly easily if needed... so if someone doesnt have a thumper on their truck and they expect to do a lot of urd, they can bring one.

the facility im at now actually builds, repairs and maintains the thumpers and radars... as well as a ton of other stuff.

dbrown20
06-12-2006, 07:02 AM
by the time you called out a man or crew, could'nt you put fault indicators on up to the open-point, then identify the faulted section, switch it out to restore power, then let maintenance crew thump, find, and restore the bad section back to service?

Yeah, that's the way we did it one place I worked. Haven't even seen a fault indicator at my current job. dbrown20

scammy
06-12-2006, 07:13 PM
fault indicators dont work that well

CenterPointEX
06-13-2006, 12:23 AM
Fault indicators sometimes lie... Like I said, some of our loops have twenty or more xfmrs on them... I could usually have most of the loop back on in under an hour after I rolled up with the radar van... I worked nights and a lot of the time shot trouble out of the Van... So they did not have to call anyone out to work the loops... we were there twentyfour seven.. I often worked loops by myself... After we isolated, the bad span might sit for weeks or months before it got repaired...
By the time you have a crew deliver a VON you could install fault indicators on primary, find faulted bad span, In order to do make the fault indicators work you would have to install the indicators then refuse the switch and close in on the fault... Closing on a fault with AC damages the cable and equipment far more than the DC thump current... The purpose of the Radar equipment is to preserve the cable and equipment giving it a longer lifespan.. About half the time you do not even hacve to use the thumper... Just the radar finds it... Then you isolate without ever applying more fault current... In these cases you can get the loop back on in under thirty minutes after rolling up...

Steve Riddle
06-13-2006, 01:21 PM
Most greatfull thanks to all you guys, lots of information, I'm a lot wiser now.