110 



SYNCHRONOUS MOTORS 



former through a rheostat which limits the amount of current. The 

 motor starts and attains synchronous speed in from 20 to 30 seconds. 

 The field-excitation circuit is then closed, and the counterweight of 

 the circuit-breaker is lifted, which enables the triple-pole switch to be 

 brought to the second position. The motor then receives the current 



At Rest: 



The belt is on the loose pul- 

 ley A. The circuit-breaker 

 / is open. The switch C is 

 to the left. 



Starting: 



1. Throw switch C to the 

 right. 



2. Close circuit-breaker 7. 



3. \Yhen synchronism is 

 reached throw switch C 

 to the left. 



4. Shift belt from pulley A 

 to pulley B. 



Stopping: 



1. Shift belt to pulley A. 



2. Open circuit-breaker /. 



N. B. 



To change direction of 

 rotation transpose wires a 

 and b, and c and \d. (Fig. 51.) 



FIG. '52. 



directly, and it attains full speed. The belt can then be transferred 

 gradually from the idler pulley to the driving pulley B. 



To stop the motor we proceed in inverse order. The belt is shifted 

 to the idler pulley A, the counterweight is dropped (which causes the 

 three-pole switch to open), and finally, the circuit-breaker D of the 

 field-excitation circuit is opened. 



For motors of 25 to 50 H.P. the single resistance is replaced by a 

 variable rheostat and the switches have but one step. Once the speed is 



