THE SYNCHRONOUS MOTOR 



323 



motor necessary to raise the lygtem power-factor to unity. Tin- 

 synchronous motor is to run without load. 



olve the current / into two components, an energy compo- 

 nent /i = /cos 0i and a quadrature component 7 2 = / sin 61. 

 The energy current of the synchronous motor is small compared 

 with its quadrature current, when the motor is operating without 

 load, and is added at right angles to the quadrature current . 

 Therefore, in determining the total current taken by the syn- 

 chronous motor, this energy current may be neglected. For 

 unity power-factor, the motor current will then be substantially 

 equal to the quadrature current 7 2 , but leading. Therefore, the 



-/Cos 0, X ^ 



-/Cln e>, 



Fio. 296. Raising power-factor to unity by means of synchronous condenser. 



rating of the synchronous motor is 17 - 17.. volt-ampere- 

 phase. 



If it 1..- d'-iied to rai<e the power-factor to some value less than 

 unity, a smaller synchronous motor can be used. In practice. 

 it usually does not pay to raise the power-factor above ().*> 



15, M little is gained by any increase above these values. 

 Moreover, these l.-,st few per cent, of improvement in the power- 

 factor require a much greater proportionate increase in motor 

 capacity. 



In 1 'lie load power-factor is cos B\. The load on the 



synchronous tnotOI i- assumed to b.- /.-m and its losses are 

 ted. The load current / i- resolved int.. two com|)onents 

 I / M [t il di'-ired to deiei-mine th 



chronous mo' sary to raise th- factor to cos ^ . 



