SYNCHRONOUS MOTORS 15 



ing, but lagging, and the machine at that time does not 

 behave as a condenser, but would more accurately be 

 called a " synchronous reactor." Since the chief value 

 of the machine in the constant-voltage system is not its 

 ability to operate with leading current, but rather its 

 ability to change from leading to lagging as desired, it 

 would seem more appropriate to use the name "synchro- 

 nous phase modifier," which is recommended in the 

 " Standardization Rules of the American Institute of 

 Electrical Engineers." In this book, all three names are 

 used for a synchronous A. C. machine driven by alter- 

 nating current, and no essential difference is intended 

 when the different names are used. 



One of the most severe handicaps in the commercial 

 application of synchronous motors has always been the 

 low starting effort developed by the machine, and the 

 trouble in synchronizing it. The use of a cage winding 

 on the field has greatly improved matters, so that now 

 synchronous motors can develop about 30 per cent 

 starting torque with one and one-half times full load cur- 

 rent, and they synchronize themselves. The above 

 starting torque is sufficient for a great many motor 

 applications. In Fig. 3 is shown the rotor of the 6,000 

 Kva. phase modifier, illustrated in the frontispiece. The 

 cage winding, consisting of copper bars in the pole face 

 and heavy end rings, may be clearly seen. 



