SWITCHING EQUIPMENT 503 



before the cover of the oil vessel is reached and, therefore, its 

 tendency to be thrown out is reduced. 



For each vessel there are two insulating bushings. The upper 

 one is clamped to the oil vessel cover and serves as guide to the 

 movable contact rod and also insulates the rod from the oil vessel. 

 The bottom bushing is fastened to the base supporting the oil 

 vessel by means of a metal clamp which holds it in proper align- 

 ment. Generally these switches are bottom connected but can 

 be obtained for combination bottom and back connection. 



The operating mechanism is located above the cell structure 

 and connected to the contacts by operating rods of specially 

 treated wood. Direct-current motor drive is recommended for 

 use whenever possible, and when no other suitable source of direct 

 current is available, a storage battery with motor generator for 

 charging may be installed. (See " Oil Circuit Breaker Bat- 

 teries.") Alternating-current motors can be furnished if for any 

 reason direct-current operation is not practicable. It should be 

 borne in mind, however, that with alternating-current motor 

 operation, a constant source of alternating current should be 

 available unless it is agreeable to close by hand some oil circuit 

 breaker, which would provide the necessary operating current. 



This type of breaker is, of course, always controlled by the 

 control switch on the main switchboard. It may be non-auto- 

 matic or automatic, the latter feature being obtained by circuit- 

 closing relays, with the relay contacts connected in multiple with 

 the contacts of the opening button of the control switch. When 

 the relays operate, they close a direct-current auxiliary circuit 

 through the tripping magnet of the oil circuit breaker and it 

 immediately opens. 



Fig. 310 illustrates a line of tank-type oil circuit breakers which 

 is used for stations of moderate and large capacity for voltages 

 from 35,000 to 110,000. Indoor and outdoor breakers are prac- 

 tically similar. The only difference consists of the addition to the 

 indoor breaker of a few parts to enable it to be serviceable both 

 from a mechanical and an electrical standpoint under all weather 

 conditions. 



A noteworthy advance in these breakers consists of mounting 

 them on framework and in the handling of the tanks by a tank- 

 lifting device. Such a construction, however, is limited to 

 switches below 110,000 volts. The lifter consists of a detachable 



