TESTS OF SYNCHRONOUS MOTORS 



137 



Fig. 68 gives an idea of the manner in which the power-factor 

 id the efficiency vary as a function of the load in a synchronous 

 lotor. 



Experimental Tests. It is interesting to compare the results 

 experiments with those of calculation. The methods which can be 



for that purpose will now be indicated. 



It should be understood that a satisfactory agreement between 

 leory and practice can only be hoped for when working with machines 

 laving E.M.F.'s of the same wave-form, and as nearly as possible 

 sinusoidal. Owing to the want of this precaution, certain authors 

 (Bedell and Ryan, loc. cit.) have found discontinuities in operation 

 are inexplicable by the ordinary theory 



FIG. 69. 



The factors to be measured experimentally are the E.M.F.'s induced 

 in the generator and the motor, the current in amperes, and the phase- 

 angles between these various quantities, and also the electrical and 

 mechanical powers applied or developed. The investigation can be 

 more or less complete according to the apparatus available. 



The author published, in 1893 (" Theory of the Coupling of Alter- 

 nators" Bulletin de la Societe des Electriciens, 1893, p. 9), a method, 

 based on that of Hopkinson for D.C. dynamos, which has the advantage 

 of requiring only a small amount of mechanical power (Fig. 69). 



The two machines, generator A^ and motor A\, are placed end to 

 end, and the two shafts are joined together by a flange-coupling or a 

 torsion dynamometer C (of type such as used by Mascart, Rateau, 

 Bedell, etc.) so arranged that they can be set in various positions for 

 changing the angle of phase of the two shafts with respect to each 

 other. This phase-angle is known, at rest, and all that is necessary is 

 to add to it the angle of torsion of the dynamometer to have the phase- 



