SWITCHING EQUIPMENT 529 



solenoid, for example, it is necessary to use a control relay with its 

 operating coil connected across the closing contacts of the con- 

 trol switch and the relay contacts in series with the solenoid closing 

 coil. This relay is illustrated in Fig. 332 and the connections in 

 Fig. 351. 



Switchboards. The switchboard of the modern large power 

 station is, strictly speaking, not a switchboard in the original sense 

 of the word. While for small stations the entire instrument and 

 switch equipment may be mounted directly on the board, for 

 large stations the oil circuit breakers and bus-bars are always 

 mounted at some distance from the same, the location being deter- 

 mined by convenience of wiring and safety. In such a case the 

 switchboard is rather a control board and contains only the con- 

 trol switches, instruments and the various other auxiliary devices 

 such as indicating lamps, plugs and receptacles for measuring 

 the voltage and for synchronizing, etc. 



The design of a switchboard involves a careful consideration 

 of the apparatus to be controlled, the system of connections, 

 arrangement of cables and other wiring, and on the general design 

 of the station. The various apparatus on the board should be 

 arranged so as to facilitate the operation, and for this reason the 

 board is always divided up in panels corresponding to the machin- 

 ery or circuits which are to be controlled. The exciter and the 

 regulator panels are generally located at one end, then the generator 

 panels, station panel, transformer and outgoing line panels in order 

 mentioned. This arrangement may, of course, be different so as 

 to more closely correspond to the arrangement of the apparatus. 

 Blank panels should preferably be provided for future machinery 

 from the beginning. The expense of such panels is very little and 

 it facilitates the addition of instrument equipments for future 

 units considerably. In such a case it will only be necessary 

 to remove the blank panels, have the necessary instruments and 

 wiring mounted thereon, then replace them on the framework 

 and make the necessary remaining connections, thus causing the 

 least disturbance to the rest of the equipment. 



Pipe framework is now almost universally used for support- 

 ing the panels on account of neatness and simplicity. The material 

 of the panels may be slate or marble. Where live parts are 

 mounted indirectly thereon, slate should not be used if the voltage 

 is higher than 1200, and marble is limited to about 3300. Natural 



