DETAILED STUDY OF OPERATION WITH NORMAL LOAD 89 



To overcome the difficulty, it will be sufficient to move the load- 

 point to ai, because the power will be that needed (the active current 

 being Ai'ai) without requiring that the total current, Aa'\, should 

 materially exceed the predetermined current. This only requires 

 that 49 amperes of reactive current should be eliminated from the 

 67 which exist. The most advantageous method of obtaining this 

 result consists in replacing a few induction-motors by synchronous 

 motors. If the change is made, for example, with a certain number 

 of motors representing 0.75X2100 voltsX25 amperes=39.5 k.w. of 

 mechanical power, the reactive current suppressed is already 25 amperes; 

 and it is sufficient, then, to produce an equal current in the opposite 

 direction, by means of synchronous motors. If we assume the latter 

 to have the same efficiency, they will also absorb 25 amperes of active 

 current, so that their total current will be about 35 amperes (same as 

 that of the induction-motors which they replace. 



Their E.M.F., calculated, in the manner above indicated, with 

 the object of producing the 25 amperes of reactive current, will be 

 only 2660 volts, if a single motor of 35 amperes be used, and 2525 

 volts if two motors of 17.5 amperes each are used, etc. These voltages 

 can be attained, as a rule, with motors bought for running at 2000 

 volts. 



These motors will necessarily be working under imperfect condi- 

 tions, since they will be only partly loaded. The installation, as a 



3525 

 whole, will, therefore, be losing an output of - X 4 16 k.w. 



25 

 But, on the other hand, it will be gaining, in the generator-output, 



(6731)2100=76 k.w.; hence there should be no hesitation in 

 adopting this method. 



The conditions taken, in this example, are not exaggerated, con- 

 sidering the apparatus which has been used until recently, and in which 

 a drop of voltage of 30 per cent in the alternators under full load on 

 a dead resistance was a frequent occurrence. These conditions 

 occurred at Bockenheim, where, according to Lahmeyer, the output 

 of the generators was doubled by introducing synchronous motors. 

 These conditions would occur on many of the actual distribution sys- 

 tems if induction-motors were extensively introduced. 



With the more recent types of alternators the conditions are better, 

 and, consequently, the use of synchronous motors may be less advan- 

 tageous. Nevertheless the reduction of generator-output by the use 

 of synchronous motors can still, easily, amount to as much as 25 to 



