"288 APPENDIX C 



The practice of designing the synchronous motor portion of 

 motor-generator sets with special reference to their use as " synchro- 

 nous condensers " has become quite general in America. Many 

 articles and papers have appeared on the subject. A partial list 

 of the authors is given at the end of the book. 



The following item, taken from The Electrical World, refers to 

 an interesting case where synchronous condensers have been used 

 to great advantage: 



(From the Electrical World, March g, 1912, p. 548) 



Overrating of Motor-generator Sets to Improve Power-factor. 

 All motor-generator sets installed by the Detroit Edison Company 

 are now specified with their motor-elements sufficiently larger than 

 the generators to insure that, fully loaded, the motors can be operated 

 at a leading power-factor of 80 per cent to improve the power-factor 

 of the system. Operators are instructed to increase the field-excita- 

 tion of their machines until the motors take full load current at the 

 leading power-factor. As the result of this practice, power-factors 

 approaching within 97 per cent of unity have been observed at the 

 bus of the generating plant. 



The Detroit Edison Company, through its Engineering Depart- 

 ment, has kindly placed at the disposal of the Translator the follow- 

 ing detailed information regarding this case: 



(From the Engineering Department of the Detroit Edison Co.} 



The motor-generator sets referred to in the above item are 

 synchronous machines installed in the substations. They are sup- 

 plied with 4600 volt A. C., and deliver 600 volt D. C. for railway, 

 and 250 volt D. C. for the lighting, service. All are over-excited 

 more or less; and the station operators are instructed to adjust the 

 field so that the motors always take the full load current at a leading 

 power-factor. This power-factor varies from 50 to 95 per cent. 



The total induction-motor load on the systems is about 19,000 KW. 

 with a power-factor varying from 60 to 85 per cent, lagging. The 

 lagging current of such a load would lower the power-factor at the 

 power-house bus considerably, but by means of the over-excited 

 machines in the substations a leading current is provided to counter- 

 act the lagging one, and a very good power-factor is thus main- 

 tained. 



