SWITCHING EQUIPMENT 



583 



switch. The operating mechanism can be thoroughly grounded 

 to prevent any danger to the operator. 



A suspension-type switch for mounting directly in a trans- 

 mission line at the point of support of a tower is shown in Fig. 375. 

 The blades are suspended underneath a string of strain insulators 



FIG. 375. 90,000-volt Outdoor Disconnecting Switch with Strain Insulators. 



and open downward. The end of the switch with its T-shaped 

 casting is supported from the suspension insulators, and the L- 

 shaped casting on the opposite end is connected directly to the 

 span and is dependent on this to support it in an approximately 

 horizontal position. The blade guide serves also as a safety 

 catch to hold the blade closed. 



Signal Systems. In large power stations it becomes essential 

 to provide some means of communication between the switch- 

 board operator and the machine attendants, and different systems 

 of illuminated dials, bells or whistles are used. It is important 

 that this apparatus should be located in a position most convenient 

 to the operators, so as to save time and avoid possible errors at 

 critical moments. Direct visual signals between these persons 

 are practically impossible, without a moving or turning by the 

 switchboard operator from his position before the instrument 

 and control apparatus. This should not be expected of him, as it 

 would mean relocating himself with reference to the switchboard 

 equipment for every signal received or sent. 



In stations of moderate size it may be sufficient to install one 

 common large illuminated sign which is visible from any place in 

 the station. It contains the unit numbers and the most important 



