LIGHTNING CURRENTS IN BURIED CABLE 



295 



attenuation curve for the current for 1700 meter-ohms, which appears to 

 provide a fairly satisfactory check on the extrapolation. The maximum 

 observ^ed voltage obtained l^y extrapolation is about 8 kv, which com- 

 pares with 5.6 calculated as outlined in Section 1.3. The higher observed 

 voltage may be due to a long duration tail current of small value, which 

 mav increase the voltage appreciably because of its slow rate of attenuation 

 along the cable. 



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 DISTANCE ALONG CABLE (FROM ESTIMATED STROKE POINT) IN KILOFEET 



Fig. 10 — Variation in crest current, voltage, and charge along cable for an extrapolated 

 stroke current of 50 ka, having a time to half-value of 140 microseconds. Dashed curve 

 shows theoretical variation of current for an earth resistivitj' of 1200 meter-ohms. 



In Fig. 10 are shown similar curves for an extrapolated stroke current of 

 50 ka, reaching its half-value in 140 microseconds, together with theoretical 

 attenuation curve for the current, for an earth resistivity of 1200 meter- 

 ohms. The maximum extrapolated voltage is in this case about 3.5 kv, 

 as compared with 4.1 calculated for 1200 meter-ohms. 

 '• ■ The curves in Fig. 11 are for a fairly low extrapolated current, 16 ka, 

 reaching its half- value in 190 microseconds. Again satisfactory^ agreement 

 between observed and calculated attenuation is obtained. The maximum 

 observ^ed voltage of 1.5 kv in this case agrees with that calculated for an 

 earth resistivity of 1200 meter-ohms. 



