Page 12 - EngineerIt April 2021
P. 12

MEASUREMENT AND INSTRUMENTATION


        Cable locator for failsafe cable




        fault diagnostics




                                By Lourenco Menezes, Comtest Sales Account Manager




                                  Accidentally hitting a power cable during a project can lead to costly
                                  repairs and create seriously hazardous safety situations. Digging in the
                                  wrong place can also lead to significant and unnecessary delays, not to
                                  mention run-on costs for the project.









             he Amprobe rugged and durable   Features of the AMPROBE UAT-600 series
             UAT600 series is specifically   The locating kit comes complete and ready for use with a transmitter, receiver, test lead kit,
        Tdesigned to accurately pinpoint     batteries and additional fuses, all in a mobile, protective duffle bag. The UAT-620 kit also
        underground utilities and buried services up   includes a Signal Clamp for transmitting a signal when it is not possible to make electrical
        to 30m deep and has accuracy to a depth   contact with the cable to be traced. For applications where ground fault locating is required,
        of 6m - ideal for locating pipes and cables.  the UAT-600 Transmitter can be used in combination with the optional A- Frame accessory.
           Mines generally use Thumper
        technology for cable fault location - a   Main applications
        portable high voltage (+25kV) surge   •   Locates energised 50/60 Hz cables carrying current
        generator into the cable. At the fault, a   •   Identifies the location of all metallic utilities: pipes*, energised and de-energized cables
        high-current arc makes a thumping sound.   •   Traces individual pipes* or cables (energised or de-energized)
        Disadvantages of thumping are that it is very
        time-consuming, and the cable, exposed to   Three testing modes for wide range of applications
        high voltage surges, may be degraded and   •   Passive power mode (50/60 Hz) – tracing energised lines conducting current (no
        will definitely require re-insulation.  It also   Transmitter necessary)
        can’t find short circuit faults.     •   Passive radio mode (RF) – using surrounding radio waves to trace underground
           In December 2020, a Free State Gold   utilities (no Transmitter necessary)
        Mine had a damaged cable incident,   •   Active mode using UAT-600-T Transmitter
        and the breach needed to be pinpointed
        urgently.  An external Thumper contractor
        was called in and the eventual diagnosis
        was that the damaged cable was at a length
        of 120m.  An excavation team was called
        in and dug to that length.  Unfortunately,
        no breach in the cable was found.  A new
        channel was then dug at 60m and still
        no fault was found.  On the third tracing
        attempt they located the breach across the
        road and on a different cable.
           The consequence of the cable breach/
        fault was numerous days of lost production,
        and the cost of the Thumper analysis.  For
        the cost of an AMPROBE UAT600 cable
        locator, the mine would not only have
        reduced the risks associated with the test,
        but have an instrument that is able to give
        an accurate reading, location diagnosis and
        solution within a day.



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