CHAPTER III 



14. Polyphase currents 15. Rotating field produced by polyphase currents 

 16. Connections of polyphase systems 17. Comparison of single-, two-, and 

 three-phase systems 18. Simple alternating wave of magnetic flux 19. 

 Analysis of alternating into two rotating waves, and vice vend 20. Production 

 of rotating waves of magnetic flux by means of polyphase currents. 



14. Polyphase Currents 



IN connection with many important practical applications, the 

 alternating currents employed consist not of simple or single-phase 

 currents, but of a system of several currents of the same frequency 

 but differing in phase. Such a system is termed a polyphase system. 



The only two polyphase systems of practical importance are those 

 known as the two-phase and the three-phase systems.* 



FIG. 19. Graphs of Two-phase Currents. 



A two-phase system consists of two currents of the same frequency 

 differing in phase by 90. 



A three-phase system consists of three currents of the same 

 frequency differing 120 in phase. 



Fig. 19 shows the graphs of the currents (sire waves being 



* A six-phase system is frequently used in the armature windings of rotary 

 converters. But the transmission of power to the converter takes place by means of 

 three-phase currents. 



