What sytems or methods are used for cable fault location within different countries and how good is the success rate??

In Auckland NZ in general we use the POPIE ( pool of potential in earth ) for single and multicore non screened cables.

The thumper or HV capacitor discharge is used on Ø to Ø faults or Ø to screen faults in LV and HV cables.

A-frame and signal generator used to pre locate a screen fault on long HV cables and confirmed afterwards with the Popie.

The dart is used for pre analysis of the approx fault distance.

In daylight, we look for the smoke. At night, we look for the flame. When we get close, we sniff for the ozone. But seriously, we have a gizmo with a 600V contactor and a bank of lights. We place it between our DC bus and the load side of an open bridge feeder or traction power breaker. It flashes the lights through the fault. Then we clamp on in various manholes and see the current pulses before the fault, and not after. For signal or control cables I'll give it a shot with a metallic TDR. Guessing the velocity of propagation is always fun but not really that important.
Joe

The pics that RODALCO submitted can be found here, by clicking right here .

The park that I manage is filled with defence contractors and one day one of them observed me trying to track down a underground fault in my outside lighting. Seems they were testing some equipment that was designed for this purpose to track electrical faults in tanks and aircraft wiring harnesses. They hooked up this small hand held gismo and entered the wire size into the parameters and vada bing it told me which wire had the fault and how many feet it was to the fault from the point that the gizmo was attached, it worked great. I am sure we will be seeing this in civilian applications real soon.

Mshaw,
The device you mentioned sounds like a TDR. I guess I should have mentioned that TDR stands for Time Domain Reflectometer. They work by sending pulses down conductors or fiber for Optical TDRs. When you get to an impedance change, some energy couples forward, while some reflects back. It works similar to SONAR or RADAR where they gate on a sensitve receiver after the pulse is sent and time the round trip. They calculate the distance to the fault by using the time, speed of light, and the velocity of propagation percentage correction to the speed of light. The guess work I mentioned is because those characteristics vary alot with power conductors and paired cables when compared to coax, and especially fiber. I usually just check a known length of the closest cable I can find and adjust the VP to jive with my sample.
Joe

We did TDR with a garden variety O scope. You have to do a little math but if you start thinking 2ns a foot and use a little Kentucky windage by causing faults at known locations to get your bearings, you can usually get to the general area of the break/short.

Bump! Boy, that felt good!

Bump!!

It did

Basic tests prior to fault loaction are:

1. cable safely isolated from supply.
2. both cable ends completely disconnected, including screen earths if used.
3. insulation test Ø to Earth.
4. insulation test Ø to Ø.
5. insulation test screen to earth if applicable.
6. continuity test.

Fault loaction for most screened cables:

7. If possible get the cable route traced with a cable locator if listening devices in conjuntion with a thumper are used.
8. A TDR or Dart can give approximate distance prior to thumping a cable.

For single core non screened cables

9. POPIE, pool of potential in earth can be used very accurately within < 5 cm to pinpoint the fault.

How Do you use an O-Scope as a TDR? It Sounds like something that could come in handy Someday.

How Do you use an O-Scope as a TDR? It Sounds like something that could come in handy Someday.

I didn't say anything at the time but I'm thinking our friend probably had a pulse generator from his laundry room and some kind of gated amplifier from his attic to go with his garden variety O-scope.
Joe

Using a tektronix we used the little jumper cable to a BNC "T" fitting. Go from the "B Gate" out on the side to the input. This gives you a pulse, then crank down the sweep until you are looking at nanoseconds and you will see the pulse go out and any reflections coming back. Generate a fault at a known location, usually the far end of the cable if it is working at all, to get your bearings. We mostly used it to find problems on 3270 coax or AS/400 Twinax.

Oh, I see, the garden variety Tektronix scope. If those are the scopes you keep in your garden, I can't wait to see the ones in your Florida room. I bought an old Dumont scope at a hamfest once and still have a 15MHz triggered Griefkit scope that I usually use in the garden.

I could use the Tek scopes in the lab at work in the clever way that you describe but they aren't as light and portable as the Tek TDR on the shelf. I can certainly see how you would have a good quality scope and not a TDR if you're fixing computers though. I wonder if I wasn't fixing minis back in the day when you were doing this?
Joe

Good to see the discussion re the options with a "garden variety" scope.
It is true that you see a deflection from the impulse at the end of the cable.

In case of utility mains, especially in 230/400 volts the cables there are a lot of joints and sometimes different sizes used mixed together.
These will all cause a deflection in the readings and the crew who digs up the fault will tell you quick enough if it's at the wrong location.
Hence the Pool of Potential is 99.9% accurate within ± 5 cm of the actual fault and my preferred method on non-screened cables.

With the HV cables as mentioned before, on long runs 2kms or more we use the dart to give us an approx. distance, then thump and listen for the noise generated at the fault.
quite often you can hear it above ground, and sometimes a Biddle listening set is used to pick up the magnetic flux and noise on your headphones and lcd display.
Cheers Ray

I have a 453 I will send you for the postage.