34 



will at full output require more exciting 

 current, and if the resistance of its field 

 be the same, this circumstance will in- 

 fluence the electrical efficiency unfavora- 

 bly. On the other hand, a sensible 

 amount of self-induction, although it 

 does reduce the j>] ant- efficiency, is indis- 

 pensable for the safe working of alterna- 

 tors in parallel, and must, therefore, be 

 regarded as rather an advantage than 

 otherwise. 



The problem of parallel working is of 

 the greatest importance for central 

 stations, as only by such an arrangement 

 of machines can absolute continuity of 

 the service and the greatest economy at 

 all times be ensured. Alternate current 

 distribution should, if possible, be carried 

 on in the same simple manner as direct- 

 current distribution, that is to say, the 

 number of machines at work should corre- 

 spond as nearly as may be to f he output at 

 any time ; the addition or with drawn 1 of 

 machines should not even momentarily 

 interrupt the supply of current to any 

 part of the system of distribution. These 



