Supplemental grounding of extending EMP collectors

The external conductors of a facility, particularly long, above ground types, pose a severe EMP threat. A primary purpose of this program was to investigate the premise that supplemental ground connections in these types of conductors could serve to reduce this threat. To support this investigation an External Collector Analysis Model (ECAM) was developed. ECAM was applied to analyzing the EMP-induced current levels appearing at a facility under various conditions of line length, line height, and number of grounds. From the results, approaches to the treatment of external collector penetrations are suggested. In addition to the external collector assessments, preliminary studies of internal collector responses are reported. Supplemental studies of techniques for measuring the responses of earth electrode systems over the EMP power spectrum are described, A successful technique utilizing currently available instrumentation was used to validate a test probe and to evaluate scaled models of various commonly used earth electrode geometries. From the measurements, observations relating to the behavior of various geometries up to 500 MHz are made.