http://electrical-engineering-portal.com/how-to-locate-underground-faults-on-cable

Are you familiar with Hi Pot testing? 10 kv from the kit will not produce enough energy to allow you to find the fault. You would normally require about 40 kv along with a shunt capacitor. Suggest you locate some one who does this for a living.

In all the previous test, we are successful by injecting 10kv, But this is the first time we are struggling to locate the fault.Our project is going on in Oman. Last month also we locate some 5 faults with the same kit(Shrila Kit). And the lenght of the cable was 465m, 550m, all above 450m...In all these case we are just able to locate within 1hr.

I will take your suggestion to my tseting head and try it out...Do you think that the fault will be in the cable(Because the leakage current was too small 0.3mA)...

You need a cable fault locator such as those manufactured by the VON Corporation (I don't work for them, but have used their equipment). Commonly called a "thumper," it charges a capacitor and then discharges it into the cable to arc the fault. The one I have used senses the electrical "echo" of the pulse and calculates the distance to the faulted location (time-domain reflectometry, TDR). Sometimes it can also be found using an acoustic transducer/sensor to listen for the audible "thump" made when the faulted location arcs over.

VON's web site for such a unit is:

http://www.voncorp.com/products/fault/XF16.htm

It would be worth your while to hire a qualified and experienced testing consultant who has the equipment, because sometimes locating the fault is as much an art as a science. He will have the know-how to properly connect and operate the test set, and isolate the location of the fault.

Good luck!

If it's de-energized, maybe you could try a TDR, Time Domain Reflectometer.

I agree - TDR is the way to go if the other usual methods have failed. We used these in the military to ring out antenna cables. It will show you exactly how far down the cable the break (or short) occurs.

At only 160M wouldn't it be best to replace the cable? To repair it you will have to introduce two joints.

Since you are not getting proper results from your cable test equipments my feeling is the fault may be at the termination. XLPE cable joint failure is the most probable reason for the cable failure than a fault in the cable as the lenth of the cable is short and normally laid safely . The cheapest test that you can do is make a visulal check of the joints see for any partial discharge. If you have a good cable jointer and good quality XLPE cable termination kits available try to replace the end joints .

The OP has not stated, but I am assuming the fault is in only 1 of the 3 phase cables, and his test data is for multiple tries on the same conductor.

I agree that terminations are a common failure point if improperly installed. They also can give much difficulty in locating the fault with methods that look for distance. However, with HV cable terminators such as at 132kV, a visual inspection won't show you much since the probable failure point is so buried in its structure. Partial discharge may show something.

TDR, as several people including myself suggested, can have a difficult time with a fault at the end of the cable, since you normally get a reflection there anyway. It takes careful reading of the waveform, and comparison to the unfaulted phases.

If the fault is somewhere along the length of the cable, then using a splice is probably the cheapest repair. Even 160m of 132kV cable plus two new terminations is going to cost much more than one splice kit. Depending on whether the cable is direct-buried or in conduit, replacing it could mean a lot of excavation, again considering that there are 2 other phases running parallel.

Dear rajugerman,

Please note that for location of cable fault,close inspection of the cable is required e.g; terminations of the cable, laying condition, earthing system, age of the cable(for newly laid cable, detail commissioning test report is required to see whether there is some inherent weakness in the cable due manufacturing defects or deformation of the cable during laying process ). Also various informations should be collected from concerned personnel to detect/ indentify some happening of things like occurence of arc/flash, sound, under which protective relay tripped, etc.

Now, we may consider to adopt fault detection method and selection and deployment of equpments related for particular cable fault location.

First measure the IR value of the cable with designated insulation tester compatible with voltage rating of the cable. Then, measure the value of fault resistance preferably by analog multimeter from both ends of the cable(source end and load end after the cable is fully isolated). Depending on the value of fault resistance, selection of fault loacting equipments to be done. For example, for very low resistance fault(bolted ground fault),where the value of fault resistance is less than surge impedance of the cable, you may deploy TDR for pre-location of the fault; you may even use, fault loation bridge(Murrey Loop test)using inverted loop technology. For medium and high resistance fault(where value of fault resistance is more than five times of the surge impedance and upto several megohms), you should deploy Surge Generator coupled with TDR(set the TDR in SIM,secondary impulse mode) to pre-locate the fault.After pre-location of the fault, please use Surge Generator and Acoustic cum Magnetic Amplifier to pinpoint location of the fault. In case if the cable route is not available with you, you should use cable route tracer to identify the cable route.

Hope these informations may be useful you to fault location.

Thanks,

Manindra.