Damaged MV Voltage Buried Cable

There are devices called "pingers" or "thumpers" that send a signal down the cable. The signal reflects back from the fault, and the time gives the distance to the fault. This may be what you need.

Do not energise the cable.

• Should the cable become energised inadvertently, after the circuit protective device has operated, simply enlarge the hole where the explosion happened, and the damaged area will be found.

Do you think if I put 380 v (from a generator)between phases I might get an explosion where the cable is damaged ? (the cable is buried 1m into the ground)

Right, and where the gophers pop up, dig there....

The official name for the "pinger / thumper" is a Time Domain Reflectometer, also known as a TDR. It sends a pulse down the conductor and times it's reflection. Wherever there is a leak to ground, that is where it reflects and by timing the speed of the pulse and reflection return, the TDR tells you how far down the conductor the leak is. This however is a linear measurement, it cannot compensate for turns and curves so it is approximate but it's the best method available. There is nothing you can do with a VOM that will be of any use.

By the way, once you fix the first one, you do the test again, and again, and again, until you end up with a result that equals your known conductor length.

Once you find the leak(s), use a heat shrink repair sleeve rated for your voltage and for underground use.

I was just wondering ... using ohms´s law and the megohmeter (megohmeter tells me the current that is leaking) and knowing the resistance of the cable wouldn´t there be a formula around to help get the approximate distance where this thing is damage? In the past we did not have TDR around ...

Depends on the type of fault. A fault will not alter the cable's characteristics in a predictable manner so once its wallaby ted then the absolute resistance is moot.

Indirect or comparative detection is really the only way to find the fault without visible inspection and all the joys of getting up close to it.

I don't think that OP has access to a TDR where he is.

Rough and ready, might work....measure the resistance to ground form each end (I'm assuming the cable is in ground fault condition). They should be different due to conductor's resistance. Compare the two values. If they are the same then the hole is in the middle section, if they are different then the hole is closer to the end with the lower resistance. That could cut your digging down by half.

He/She might be able to "wing it". See this article: http://www.eetimes.com/electronics-blogs/engineering-investigations-blog/4212190/It-s-cold--It-s-dark--And-the-TDR-you-need-is-missing-

I was thinking similarly but figured a CRO and a pulse generator might also be a bit of a tall ask in Angola.Then how to work out the V_p.....

Who knows? Maybe he can get his hands on a CRO and some parts and build his own cable radar.

He has options now.

Great story thanks.

I will try theses options today if does not work, we are probably running a 15KV aerial line due to several pipes buried around(also people dig too much in that area). Thanks guys!

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With CR4 having issues, I didn't get to post this: http://adslm.dohrenburg.net/troubleshoot/bridgetaps.php and in particular, this article: http://www.epanorama.net/circuits/tdr.html

Cable fault location can be done by using cable fault locating machine/ system comprising of TDR, SURGE GENERATOR/ THUMPER, MAGNETIC CUM AUIDBLE AMPLIFIER with SEARCH COIL etc. This system is costly and special expertise is required to use and finding/pinpointing underground cable faults. Alternatively High Resistance cable fault locator bridge(based on Wheatstone Bridge principle) can be used if there is a healthy core in the faulty cable and cable length is known. You may also adopt a very cheap method if you have a current or voltage sensor which may be used overground and if there is no other live cable running in the close vicinity of the faulty cable. From the source end of the cable you may connect a welding machine to the faulty core and earth and start welding process. The current through the faulty core travels upto the ground fault location point and returns back to the source through ground( if gound fault resistance is low value ,say,few hundred ohms) and if you move the current/voltage sensor during welding process, the sensor will not glow beyond fault point.

Thanks,

Manindra.