CHAPTER II 



METHODS OF TESTING ALTERNATORS ACCORDING TO THE 

 THEORY OF TWO REACTIONS 



BY PROF. ANDRE BLONDEL, Ecole des Fonts et Chaussees. 



THE author described in the Bulletin de la Societe des Electriciens 

 in 1892 a method of testing alternators similar to that of Hopkinson 

 for direct-current machines, which permits of studying both their 

 efficiency and their armature reactions, under the same conditions 

 of operation and without a large expenditure of power, under the 

 sole condition that the two alternators shall be similar. This method 

 depends upon the rigid coupling of two similar alternators. Later 

 the author published a variation of the method which does not call 

 for the rigid coupling between the alternators, but which consists 

 in operating the alternator on test as a synchronous motor, by the 

 aid of an auxiliary alternator. 2 The alternator under test revolves 

 on no-load, as a motor, under the normal current. This method has 

 been designed particularly to determine the efficiency with greater 

 precision than by separating the various losses. The object of the 

 present paper is to complete and yet further perfect this method by 

 pointing out how it may be likewise used for measuring armature- 

 reactions (especially by the employment of two reactions, set forth 

 in the preceding chapter). 



Method No. i. When the Rigid Coupling of the two Alternators 

 is Possible. When two similar alternators are available, and when 

 they can be placed side by side so as to be connected rigidly by a 

 short coupling, the following tests may be carried out (Fig. i): 



First a certain difference of phase a is provided between the 

 alternators (for example, a phase-difference of 30, that is to say, 

 one-sixth of a pole, or 45, that is to say, one-fourth of 



1 A paper presented by the author before the International Electrical Congress 

 at St. Louis in 1904. Reprinted from the Transactions, Vol. I, pp. 620-634. 

 1 See La Lumitre tlectrique, 1893. 



270 



