GENERAL PRINCIPLES OF SYNCHRONOUS MOTORS 



SINGLE-PHASE AND THREE-PHASE SYNCHRONOUS MOTORS OF 

 THE "SOCIETE L'ECLAIRAGE ELECTRIQUE" 



Experimental Properties. As already stated, it is an experimental 

 fact that synchronous motors can only be run after they have first been 

 brought to synchronous speed by some external means. As will be 

 seen later the motors themselves can run indifferently in either direc- 

 tion, but the direction of rotation selected in bringing them to syn- 

 chronism should be that which is suitable for the brushes of the motor 

 or of the exciter. 



Case of Equal Electromotive Forces. Let us suppose that the 

 electromotive forces of the generator and motor are equal, and, to 

 simplify matters, let us take, as generator and motor, two machines 

 whose excitations are regulated to approximately the same value. 

 Let the two machines be driven by belts (Fig. 5) ; and, when they have 

 attained the same speed, let them be coupled together (experiment 

 of Hopkinson and Grylls- Adams). Let us, moreover, make use of an 

 apparatus of the kind described in Chapter VII, whereby the difference 

 of phase between the two machines may be determained. 



It will be noted, in the first place, that as soon as the two machines 

 are brought to the same speed, the current which passes from the one 



