Smithsonian Report, 1925. —Peek 



Plate 9 



-1 /, r 



Fig. 27. -Sixty-Cycle Spark-Over of Suspension Insulator Strings 



.1, Dryspark-over on a nonshieldod string. Note that arc cascados badly along the entire 

 length of string. B, Dry spark-over on a string shielded with the ring shield. Note that arc 

 clears string. C, Wet si)ark-over on a string shielded with the ring shield. Arc starts 

 through drip tlien immediately transfer itself clear of string 



Fig. 23.— Lightning Spark-Over of Suspension Insulator Strings 



A, Dry spark-over on a nonshielded string. Note that the arc cascades badly along the entire 

 length of string. Voltage= 1.200,000 volts, h, Dryspark-over on a string shielded with the 

 ring shield. Note that the arc clears the string. Voltage=l, 200,000 volts. C, Wet spark-over 

 on a string shielded with the ring shield. Note that arc clears the string. Voltage=]. 200,000 

 volts. Note, also, the drip along the string a.nd the raindrops which appear stationary in 

 space since the light of the arc lasted less than a millionth of a second 



