APPENDIX C 



USE OF SYNCHRONOUS MOTORS FOR IMPROVING 

 POWER-FACTOR IN AMERICA 



IT is well known that the power-factor of a system supplying 

 current to rotary converters at various substations can be mate- 

 rially improved by over-exciting the field of the rotary converters. 

 In some cases this benefit was considered of enough importance to 

 warrant the use of rotary converters which are shunt-wound only and 

 consequently can produce no compounding effect. 



In a motor-generator set composed of a synchronous motor 

 driving a continuous current generator the compensating effect due 

 the over-excitation of the synchronous motor-element is retained 

 without sacrificing the compounding effect of the combination. 

 This is one reason why motor-generator sets have been preferred 

 in many cases to rotary converters. 



Owing to the fact that the compensating effect is the same as 

 that produced by a condenser the synchronous motor producing the 

 " condenser effect " is often called a " synchronous condenser " or 

 a " rotary condenser," and also a " synchronous compensator." 

 The Standards Committee of the American Institute of Electrical 

 Engineers gives the preference to another term, " phase- modifier," 

 as appears from the following definition given in the " Standardiza- 

 tion Rules " : 



" A Synchronous Phase-modifier, sometimes called a Synchronous 

 Condenser, is a synchronous motor, running either idle or under 

 load, whose field-excitation may be varied so as to modify the power- 

 factor of the circuit, or through such modification to influence the 

 voltage of the circuit." 



287 



