SYNCHRONOUS MOTORS 13 



at a iked value. The other property, of giving easy ad- 

 justment to the power-factor, making it sometimes 

 leading and sometimes lagging, is really distinct from 

 the first property, and is of far greater value, as will be 

 pointed out later. In order to make use of it, the extra 

 trouble of making continual adjustment of the field cur- 

 rent is necessary, but when the great advantages of con- 

 tinual adjustment of the power-factor are generally un- 

 derstood, the present common practice of leaving the 

 synchronous motor field current at a fixed strength will 

 be largely done away with. 



An electric motor is a machine capable of absorbing 

 electric energy and doing mechanical work, and syn- 

 chronous motors are generally used for this purpose. 

 They have also often been used in connection with steam- 

 power plants, merely to be run idle with over-excited 

 fields and to correct low power-factor of the load, thus 

 reducing the current in the generators and feeders. When 

 machines were designed for this purpose, economies were 

 effected by using smaller bearings and omitting any 

 mechanical connection such as pulley or coupling. Such 

 special features of design and application warranted a 

 distinctive name, and the name "synchronous con- 

 denser" was applied. This name is quite appropriate 

 for the case just described, for with a strong field current, 

 which is always necessary for raising the power-factor, the 

 machine has the electrical characteristics of a condenser, 

 since its armature current is leading. 



The name "synchronous condenser," however, is not 

 quite so appropriate when the machine is used with a 

 constant-voltage transmission line, because for a large 

 share of the time the current in the machine is not lead- 



