

DETAILED STUDY OF OPERATION WITH NORMAL LOAD 55 



because he made his machines run -without load. This proves nothing, 

 however, in regard to their operation under load. Moreover, these 

 conditions were absolutely exaggerated, since lines of such high resist- 

 ance would never be used in practice. 



QS- 



Finally, when we attain a resistance of approximately R= =7=50 



V 3 



ohms, we have cos <}>=%. The maximum power for E^=E\ being 

 then no longer 22,550 watts, the output of the motor can scarcely 

 exceed 15 k.w. Besides, it is sure that every increase of the E.M.F. 

 E 2 above 2200 volts will diminish the stability. This will be all the 

 more true if R is higher. We can thus understand that in using machines 

 of 50 k.w. with an external or line resistance of 63 ohms, Mordey could 

 only operate these machines without load, and that the slightest 

 increase of the voltage E 2 above E\ (20 per cent) would cause the 

 machines to fall out of step. 



The preceding analysis therefore explains perfectly the anomalies 

 of Mordey's experiments. 



We would be brought to analogous conclusions by the considera- 

 tion of sudden overloads and of oscillating changes of load, which 

 will be discussed later. t 



[The amounts of sudden overloads allowable are discussed in 

 the author's preceding work, " The Coupling of Alternators," and 

 also in La Lumicre Electrique, Vol. XLV, p. 474.] 



III. COMPARISON OF POSSIBLE OUTPUTS AT CONSTANT LOAD 

 WITH VARIOUS EXCITATIONS. CONSTANT POTENTIAL 

 SUPPLY 



Existence of a Current- Minimum. There exist several values of 

 current and E.M.F. which permit a motor subjected to an external 

 constant E.M.F. EI to develop a given electrical power P 2 . These 

 are all values for which the point A 2 (Fig. 27) falls on the line of 

 equal power corresponding to that value P 2 . 



These values differ from each other by the values of the E.M.F. E 2 

 necessary to produce them, and also by the phase-angles 6 and < of 

 the corresponding current /, and, particularly, by the reactive current. 



If, to simplify matters, we suppose the motor to be supplied from a 

 constant potential source whose impedance is negligible, the diagram 

 in Fig. 27 will give the solution. 



The current being represented by the vector A iA 2 according to 

 the scale of amperes, its minimum evidently corresponds to the point 



