California Institute for Energy and Environment (CIEE)

This report describes the final results from the project “Concentric Neutral Degradation and Failure Analysis: Sensors and Methods for In-Service Diagnosis” in which we investigated three on-line techniques for probing the concentric neutrals (CNs) of underground distribution cables. We have shown that both the surface-guided RF wave (Goubau Wave – GW) and the amorphous magnetoresistive (AMR) sensing technique produces a signature that can be used to detect failed CN wires. In the case of the AMR method, we demonstrated the detection of a faulty CN from at least 200 feet away from the location of the break. Similar result was found with respect to the GW method, however the GW is heavily attenuated by the surrounding soil, and hence further experiments have to be conducted to establish its practicality. The two-wire transmission line technique was shorted by the Semicon, and hence no signal was detected over the distance of a typical underground distribution cable.