Advantages of TDR Compared to Thumping in Underground Cable Troubleshooting

Megger PFL22M1500 Power Cable Fault Locator SystemCommon methods of finding faults in direct buried cables is arc reflection or simply thumping. Thumping is a method that is performed by discharging a large amount of energy into a cable. This electrical energy will seek to arc across the path of least resistance to ground, which in this case would be the electrical insulating material that separates the center conductor from the outer shield, or concentric neutral.  When that arc occurs it often makes an audible thumping sound in the vicinity of the arc. If thumping is being performed where there is high ambient noise, or for some reason cannot be heard, directional acoustic detectors can be used in pinpointing the fault location. However, this method may require the cable to be thumped for a lengthy period of time while walking the path of the cable and listening.  If a TDR (Time Domain Reflectometer) is incorporated into the test, along with a thumper, then when the arc occurs, the TDR will reflected the change to the impedance of the insulation at the location of the fault. This would be the Arc Reflection method and can significantly reduce the thumping time necessary to locate the fault.  It can be used to localize the fault and if necessary pinpointed using an acoustic fault detector.

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However, there are other underground electric power cable fault locating techniques you can try. One convenient method is using a time domain reflectometer (TDR).  In situations where a very low impedance fault, such as a short circuit, or a very high impedance fault, such as an open circuit, has been identified, it may not be necessary to use previously mentioned techniques that incorporate the use of a thumper to break down the fault.  In this case it may only require the use of a TDR to find the place at which the impedance of the cable insulation is substantially different from the rest of the cable. If cable conditions are such that only the use of a TDR is required for locating the point at which the cable is damaged or defective, this low voltage technique is much safer, more economical and less complex than previously mentioned techniques. The additional use of a thumper  would not be required in this case.

Related electrical test equipment available for rent from Protec:

High Voltage TDR1669 Time Domain Reflectometer

Megger CFL510G Hand-held Time Domain Reflectometer

Megger PFL22M1500 Power Cable Fault Locator System

Megger PFL40A Power Cable Fault Locator System

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Editor’s Note: This post was originally published July, 2011 and has been updated freshness, accuracy and comprehensiveness.