GENERALIZED CIRCLE DIAGRAM 



223 



used as a motor; and the constructions for electrical power, 

 slip, and torque remain unaltered ( 110). 



Such a complete circle diagram, embracing every possible condition 

 of operation of the machine, whether as generator or motor, is shown 

 in Fig. 142.* Thus, O'P represents a certain value of the stator 

 current. Its projection O'P' on the line of phase p.d. is proportional 

 to the useful output of the generator outside its terminals.! If we 

 draw BT, the intercept RV on the line of slip represents the negative 

 slip of the generator to the same scale as that to which RS represents 



IMEFUL POHH Of CE*ERATOIl~ : 



POWIR, ABSORBED BY MOTOK 



FIG. 143. Curves Derived from Circle Diagram. 



a slip of unity for the motor. Again, the perpendicular TT' gives 

 the value of the torque which is actually instrumental in generating 

 electrical energy, excluding the additional torque which must be 

 provided to compensate for rotor friction. The power factor is given 

 by the cosine of the angle P'OT. 



If, using such a complete circle diagram, we determine the 

 relations connecting power supplied to terminals of motor, or power 



* The experimental data required for the construction of the diagram have already 

 been fully considered in Chapter XIII. 



t Total useful output = O'P' x phase p.d. X number of etator phases. 



