410 ALTERNATING CURRENTS 



oil so that it is occasionally necessary to renew the oil. During 

 short-circuits, the switch may be called upon to absorb a large 

 amount of energy in a very short time. The resulting pressure 

 within the switch compartments may be very high, so that it is 

 necessary to construct the tanks of heavily riveted or welded 

 steel. Even so, explosions of switch cells are not uncommon. 



Due to the fact that carbonized oil may form a conducting 

 path between switch contacts, there is always a possibility of 

 injury to persons working on the supposedly dead side of the 

 switch. Therefore, it is always desirable to have an air-break 

 disconnecting switch in each phase. The disconnecting switch 

 may form a part of the switch, as in Fig. 373, or it may be in- 

 stalled on a separate outside mounting. (See wiring diagram, 

 Fig. 372.) The disconnecting switch is not called upon to 

 interrupt the circuit under operating conditions, but is opened 

 only after the oil switch has interrupted the circuit. 



Practically all oil switches operating at high voltages, or 

 connected in circuits of considerable power, are operated by 

 remote control. Both solenoids and motors, energized from a 

 low-voltage circuit and controlled from the switchboard by low 

 voltage, are used to operate the oil switch. 



The switch of Fig. 373 is motor-operated. The motor winds a 

 spring immediately after the switch has operated, leaving 

 the spring ready to open or close the switch, depending on what 

 the next operation is to be. Two separate compartments per 

 pole are used, Fig. 373, one for each contact. This makes the 

 energy per cell half that which would exist if a single tank were 

 used. The oil baffles shown in Fig. 373(6) are particularly 

 important. 



176. Arrangement of Apparatus in Sub-stations. The purpose 

 of the sub-station building is to protect the equipment and the 

 operator from the weather. . The incoming high-voltage lines 

 are brought in either through the roof, by means of roof-bushings, 

 or through the sidewalls by means of wall-bushings, Fig. 365, 

 page 401. The incoming wires are bent to form drip loops so 

 that water will not run down the wires into the station. 



The high-voltage bus-bars are usually located near the roof 

 of the station so as to be out of the way. It is also desirable to 

 place other high-voltage equipment, such as lightning arresters, 



