Locating an Electrical Tree (Pinhole) fault in a buried electrical power cable …
Electric trees or pin holes are the most common fault found in underground electrical power cable. The fault starts through a process of water ingress or small defects in the dielectric. Through age these defects begin to grow taking on the pattern of tree branches. Eventually one of these branches will breach the cable insulation and become a fault.
After discharge from the surge generator (thumper) the voltmeter will give a strong kick back, nearly reaching zero volts while the ammeter gives a strong kick forward. The pulse echo or TDR signature prior to discharging the surge generator will show the end of the cable under test. The cable end will be seen as a positive reflection indicating an open termination. Refer to the signature below with a solid line. After the Arc Reflection test a negative reflection will be captured from the point of the arching fault. The fault will be shown as a negative reflection indicating the short circuit created by the arc (thump).
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