OVER-VOLTAGE PROTECTION 



619 



The arcing ground suppressor, as described in the following, 

 is intended to be used with non-grounded systems. It is also 



Condensers 



FIG. 395. Elementary Diagram of Arcing Ground Suppressor. 



limited to steel tower lines, as on a wood-pole line the resistance 

 of the pole is liable to prevent sufficient current flowing to ground 

 to reduce the potential sufficiently to operate the relay. 



The arcing ground suppressor, as generally built, consists 

 of three single-pole, independent, motor-operated oil switches, 

 electrically and mechanically 

 interlocked, to prevent more 

 than one operating at the 

 same time. Each switch is 

 connected to ground on one 

 side and to the line on the 

 other. The suppressor is con- 

 trolled by a phase-selecting 

 relay, which remains inactive 

 while the system is balanced, 

 but when unbalanced, due to a 

 ground on one phase, it oper- 

 ates the corresponding phase 

 of the suppressor, which, in 

 turn, grounds the same phase 

 of the line, thus shunting the 



current and extinguishing the FlG ' 396 --Phase-selecting Relay for 



Ardng Ground 



arc. The switch is then auto- 



matically opened and will remain so provided that the ground was 



only temporary, such as an insulator spilling over. If the ground 



