116 



SYNCHRONOUS MOTORS 



through the wires 7, II, enters into the armature by the terminal A, 

 leaves by the terminal B and passes through the secondary-winding 

 S\ t 82 of the transformer E, called compensator, which plays the role 

 of self-inductance for throwing the armature-current out of phase. 



FIG. 57. 



The field-circuits are wound for a low voltage (25 volts) supplied by 

 the secondary circuit Si, 5*2 of another transformer F. 



At the time of starting, to overcome the induction of the field- 

 circuit, the potential-difference at its terminals is raised by the primary 

 winding of the compensating transformer E, whose secondary has the 



armature-current passing through it, 

 as already stated. The field-current 

 also passes through a fixed resist- 

 ance, ab, in the rheostat, R, the 

 object of which is to reduce the lag 

 in the field-circuit, and to put it in 

 phase with the armature-current. 



The motor starts. When it at- 

 tains synchronism, the current in the 

 field is commutated ; the connections 

 are then changed by means of the 

 double-throw switch D, which short- 

 circuits the secondary of E, connects 

 the two neighboring brushes together 

 and sends the secondary current of 

 FIG. 58. F into the variable resistance cd 



before it reaches the field-coils. 



A motor of the same kind was put on the market some years 

 .ago by the firm of Brown-Boveri (Fig. 58). The motor starts by simply 

 coupling in parallel the armature and the field-circuit and a resistance 



