400 



ALTERNATING CURRENTS 



In time, the film dissolves and it is necessary to re-form it 

 about every 24 hours. This is done by closing the auxiliary gap 

 (lower gap, Fig. 363), which allows the arrester to charge through 

 a carbon-rod resistance and so re-forms the film. The purpose of 

 the carbon rod is to limit the charging current and to damp out 

 high-frequency disturbances that might otherwise occur when 

 the arrester is being charged. 



In arresters whose rating exceeds 12 kilo volts, there are three 

 stacks for a grounded 3-phase system, each stack being connected 



Line Conductors, 



Ground Stack/ 



FIG. 364. Connections of aluminum-cell arresters on 3-phase, ungrounded 



system. 



between its respective conductor and ground. In a non- 

 grounded system, the three line stacks are connected in a common 

 Y, and a fourth stack, called the ground stack, is connected 

 between the neutral of the Y and ground, Fig. 364. In Fig. 364, 

 No. 3 is the ground stack. By revolving the transfer switch 

 through 180 in a horizontal plane, No. 2 becomes the ground 

 stack and No. 3 is connected between the middle conductor and 

 the system neutral. 



PROPLRTY OF ELK- I'JHY, 



FACULTY OP APPI IFD 



