Underground Electric Power Cable Fault Locating Techniques

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Even with the proper equipment and experience, cable fault locating can present challenges. These challenges are minimized significantly by understanding the equipment and techniques available and perhaps most important adhering to a disciplined step-by-step procedure.  Most cable fault locating failures and wasted time can be attributed to technicians not properly interpreting test results, selecting the wrong test equipment for the job or taking short cuts in the process.  Protec’s knowledgeable staff can help with product selection and interpreting results, but only discipline will correct wasted time and effort due to taking short cuts.  Popular CFL techniques include:

Time Domain Reflectometer:  TDR can be used to localize low resistance faults (short circuits or bolted faults) were the insulation resistance measures less than approximately 200 ohms.  The technique is equally successful in localizing series faults such as open conductors due to dig-ins, blow-outs or splice failure.  The TDR may be a separate unit or part of an integrated arc reflection system, such as the Megger PFL20-1500 or PFL40-2000.

Arc Reflection:  This technique incorporates both low voltage TDR and high voltage of the capacitive discharge, or “thumper” technique.  It is ideal for localizing high resistance faults on medium voltage power cable. Caution: Arc reflection systems are typically rated by output voltage and energy of the high voltage device, “thumper”.  An under-rated “thumper” can hamper performance of this technique.  Protec Equipment Resources stocks a range of complete CFL systems including the IUP Fault Wizard, Megger PFL20-1500 and PFL40-2000.