are you talking about locating primary faults underground?
Would someone be kind enough to explain the practice of "thumping through"
Thanks
are you talking about locating primary faults underground?
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.
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?
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.
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.
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
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.......Originally Posted by dbrown20
"It is not the critic who counts:The credit belongs to the man who is actually in the arena" Teddy Roosevelt
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
Last edited by scammy; 06-11-2006 at 12:57 PM.