330 ELECTRICAL MACHINERY 



Effect of Overload. Now no matter how great the twist 

 of C may be, P r and P revolve at the same speed, P' falling 

 farther behind P with increasing load on E. But if so 

 much load is put on E that the strength of C is exceeded, 

 then it will twist into two pieces and the set becomes inop- 

 erative. This corresponds to the opening of the circuit 

 breakers when a synchronous motor is overloaded. 



Illustration of Hunting. The hunting of a motor has 

 an exact analogy in the arrangement of Fig. 214. D, in 

 combination with C, has a certain natural period of oscil- 

 lation. But, while D is revolving with the same r.p.m. as 

 A, it may be executing, also, natural oscillations so that 

 P' is oscillating back and forth with respect to P. If 

 the belt on E flaps with a period equal to the natural period 

 of the system D-C, D will quite likely oscillate more and 

 more violently until the shaft C breaks. 



