Patent ID: 7439747
Filing Date: 2008-10-21
Classification: G01R

Abstract:
1. A method of detecting high resistance ground faults of a resistance of greater than 250 K-ohms in an underground electric power cable including a central conductor with a dielectric material surrounding the central conductor and a ground return conductor surrounding the dielectric material, the method comprising: transmitting into a length of the said cable a signal that is connected across the central conductor and the ground return conductor, said signal comprising a primary oscillating waveform at a predetermined frequency and of a predetermined peak to peak voltage; tracing the length of the said cable with a receiver arranged to detect an electromagnetic field emitted by the said cable in response to the said signal; selecting the peak to peak voltage and the predetermined frequency to produce in the said high resistance ground faults fault currents from the central conductor to the ground return conductor through the said faults, said fault currents being of sufficient magnitude to generate detectable changes in the magnetic fields around the areas of the said faults; wherein the said primary oscillating waveform has a frequency between 0.200 Hz and 2.0 Hz. wherein the said signal includes a second frequency component superimposed on the said primary oscillating wave form to provide an unmistakable marking and/or identification frequency detected by the receiver.