54 SYNCHRONOUS MOTORS 



mission, and let 1=2200 volts be the generator E.M.F. The internal 

 resistance of each machine is 3 ohms and its reactance at 100 cycles 

 is 43 ohms, as previously stated. 



(>) Let us first suppose the line to have no resistance and no react- 

 ance. The total circuit will have the following constants resistance 

 6 ohms, reactance 86 ohms and impedance 86.20 ohms. 



The maximum power 



_. (2200) 2 



P= =201,660 watts, 

 4X6 



could only be obtained by giving to the motor E.M.F. the value 



2= - = 1 5,800 volts, 

 0.0695 



and it could only be obtained with a current 



2200 



/= = 183 amperes. 

 2X0 



It is therefore unattainable from all points of view. 



If we limit the E.M.F.'s to E^=Ei = 220Q volts, the possible 

 maximum will be 



f 22OO^ 



CP2)max= g 62 p (l -0.0695) =52,000 Watts; 



i.e. about 3/2 times the normal output. The stability will therefore be 

 sufficient provided the machines are not subjected to variations of load. 



Every increase in voltage will here produce an increase of (Pz) m;ai - 

 If, for example, we take 2=3000 volts, 69 k.w. instead of 52 is 

 found to be the maximum output possible without causing the machine 

 to fall out of step. The stability is then excellent at the normal load 

 of 37.5 k.w. If, on the contrary, the voltage is reduced, so high a load 

 could no longer be attained. 



(2) Suppose now the resistance of a line to be interposed between 

 the two alternators. Stability will evidently become impossible as soon 

 as the maximum power P approaches the effective power P 2 . If we 

 take, for the coefficient of load, the figure 3/2 already mentioned, the 

 maximum power P should not be less than 3/2X37.5=56 k.w., which 

 corresponds to a line-resistance of about 16 ohms. 



In his experiments Mordey (Proc. Inst. of Electr. Eng., 1894) was 

 able to increase the resistance to very much higher values (140 ohms), 



