616 



ELECTRICAL EQUIPMENT 



in Fig. 391 provides three gaps which may be so set as to provide 

 three paths for the discharge. All low-frequency discharges 

 would form corona and ionize the gap between the horns, passing 

 across the same and to ground through the resistance and the 

 cells while a high-frequency discharge would pass through the 

 upper of the two sphere gaps and similarly to ground. The 

 lower sphere gap has a wider setting than the upper sphere gap, 

 but if the quantity of the discharge is too great to be dissipated 

 through the upper paths, the discharge automatically shunts to 



FIG. 392. 90,000-volt Choke Coil for Station Service. 



the main gap, where it is not impeded by the resistances, and goes 

 directly through the cells to ground. The resistance is of low 

 value and consequently all but the heaviest discharges are taken 

 care of by the auxiliary paths. 



A knowledge of all discharges is of immense value to operating 

 engineers in studying conditions of abnormal voltage on trans- 

 mission and cable systems. For this purpose a discharge recorder 

 has been developed, which will register the time and nature of dis- 

 charges through an arrester. This recorder consists of four spark 

 gaps so arranged that the discharges between lines or between 

 lines and ground pass through the gaps. The spark gaps are 



