3 02 



INDUCTION MACHINES. 



[Exp. 



brought up approximately to speed (the exact speed is not neces- 

 sary) the two machines are connected together by closing the 

 switch- S 2 , the power supply used in bringing the converter to 

 speed being cut off. 



1 8. No-load Excitation Curve. The load switch S 3 is open. 

 Vary the field current of the converter and measure watts, amperes 

 and volts. The induction generator is driven so as to give rated 



frequency at rated voltage; 

 hold speed, or frequency, con- 

 stant during the test. 



The converter may be sepa- 

 rately or self excited. When 

 the field current is reduced be- 

 low a certain value, the con- 

 verter goes out of step and 

 stops; the induction generator 

 then gives no voltage. 



19. For various field cur- 

 rents, plot voltage as in Fig. 4 ; 

 also / sin 0, the wattless compo- 

 nent of line current. It is the 

 increase in /sin* that increases 

 with the excitation of synchronous the excitation of the induction 



machine. 



generator and so increases the 



generated voltage. This relation will be seen by plotting voltage 

 for different values of 7 sin 6. 



20. No-load Speed Characteristics. Separately excite the field 

 of the converter and keep the field current constant. Vary the 

 speed of the induction generator and measure line voltage and fre- 

 quency. Begin with a speed of say 10 per cent, above normal and 

 decrease speed until the converter stops. Converter speed may 

 be measured instead of frequency. 



21. Results are plotted as in Fig. 5. The lower curve shows 



.2 .4 .6 .8 1.0 



Field current of Synchronous Converter 



