Power cables: pre-locating faults using echometry

Simply connecting a shockwave generator to the faulty phase of a damaged cable and setting up a listening point every 5 m or so is a possible technique for finding the fault and indicating where to start the excavation required for repair... when the link is short (a few dozen meters at most).

More reasonably, the choice of a pre-location method based on fault characteristics should enable a listening zone to be positioned on the cable drawing.

Echometric methods, based on the analysis of a cable's response to an electromagnetic pulse, enable pre-location.

The measurement taken gives the center of this listening zone, and the care taken in implementing the chosen method reduces the uncertainty to around 5% of the measurement. With accurate mapping in good condition, and a carefully calibrated echometer, you can obtain a measurement to within 1 or 2%. With a "standard" setting, the uncertainty can reach or even exceed 10% of the measurement.

This first step enables the operator to get to the presumed fault zone, thus reducing the time needed for shockwave searches once on site.

In this section, we will only deal with the various echometric methods. Theoretical notions will be gathered in .

This booklet is part of a series on fault finding in power cable networks:

• "Power cables: fault location and identification" ;

• "Power cables: fault prelocation using echometry";

• "Power cables: echometry theory" ;

• "Power cables: fault location methods";

• [Doc. D 4 545] "Energy cables. Find out more".