Vaporization/Restrike Characteristics of Buried Insulated Conductors

The vaporization/restrike characteristics of buried insulated conductors have been measured for four metals (Al, Fe, stainless steel, and Inconel 600), each with four sample geometries and a range of pulser voltages up to 205 kV across 40-cm-long samples. Another sample composed of three twisted strands of graphite-fiber cable with only a minimal dielectric coating was also tested in air. For all of these samples, restrikes occurred when the peak pulser voltages were greater than about 60 kV (¿ 150 kV/m across the sample). For the dielectrically-wrapped samples, the dielectric cover was either shattered or punctured by the expanding metal vapor, and there was very little difference in the curves of resistivity versus time or specific action [¿(I/area)2 dt] with and without soil around the dielectric. The resistivity-versus-action curves differ significantly with and without the dielectric wrap, and as a function of geometery (mainly cross-sectional area), pulser voltage, and metal (Al is the most different). The effect of these differences on the protection provided to a ground installation by different R-wire cables is discussed.