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BELL SYSTEM BECHNICAL JOURNAL 



simulative surge tests had been made three years before to obtain data on 

 voltages in the cable due to surge currents, and tests had also been made 

 of the dielectric strength of the thermoplastic insulation between the sheath 

 and the copper shield. These latter tests disclosed low dielectric strength 

 in the thermoplastic insulation at the location of the antenna referred to 

 above, a defect which was repaired at the time. The voltage curve in Fig. 



5 



16 q 



12 o 



LU 



10 ^ 



7654321 01 234567 



DISTANCE ALONG CABLE (FROM ESTIMATED STROKE POINT) IN KILOFEET 



Fig. 9 — Variation in crest current, voltage, and charge along cable for an extrapolated 

 stroke current of 50 ka, having an estimated time to half-value of 190 microseconds. 

 Dashed curve shows theoretical variation of current for this time to half-value and an 

 earth resistivity of 1700 meter-ohms. 



8 indicates that breakdown of the thermoplastic insulation occurred as a 

 result of excessive voltage between the sheath and the copper jacket, but no 

 other damage to the cable resulted. In Fig. 8 is also shown the theoretical 

 variation in crest current along the cable, for a uniform earth of 1200 meter- 

 ohms resistivity, for a stroke current reaching its half-value m 130 micro- 

 seconds, as obtained from the crest current and charge at the stroke point. 



In Fig. 9 are shown similar curves for an extrapolated stroke current of 

 50 ka and 190 microseconds to half -value, together with the theoretical 



