62 



chosen, as sufficiently small to avoid a 

 sensible disturbance of the working ma- 

 chines when a new machine is switched 

 on, and this gives the dotted curve, 

 marked k ' — 10 amperes," in Fig. 11. The 

 interpretation of this diagram is obvious. 

 The normal terminal pressure of this 

 machine is 2,000 volts, and by drawing 

 the corresponding horizontal line, its 

 points of intersection with the curves 

 m s g fix the exciting power in each 

 case. In order that the machine may 

 work as a generator, giying its maximum 

 current of 30 amperes, the exciting power 

 must be O G. If the machine is merely 

 to run without producing or absorbing 

 current, it must be excited to an amount 

 represented by O S, and if running idle 

 as a motor, and allowing not more than 

 a 10 ampere current to pass, the excita- 

 tion must be O M. The ratio between 

 the length of the lines O M and O G 

 gives, therefore, in a rough-and-ready 

 way, an indication of the degree of safety 

 when working in parallel. 



The formulas and diagrams given above 



