CHAPTER VI. 

 POLYPHASE CURRENTS. 



EXPERIMENT 6-A. A General Study of Polyphase Cur- 

 rents.* 



PART I. 



i. Introductory. In a polyphase system, several single- 

 phase currents differing in phase from each other are combined 

 into one system. The circuits for each phase may be independ- 

 ent, without electrical connection, or interconnected. The phase 

 difference between the currents of the several phases is usually 

 90 or 120, the corresponding systems being called two-phase 

 or three-phase. 



A' 



(a) 



FIG. i. Two-phase connections for generator or receiver circuits, a, 4-wire 

 system with independent phases, b, 3-wire system, c, Quarter-phase, star- 

 connected ; or, 4-wire system with interconnected neutral, d, Quarter-phase, 

 mesh-connected ; or, ring-connected. 



To form a polyphase system we must have several sources of 

 single-phase electromotive force which differ in phase by proper 

 amounts. For a symmetrical polyphase system these electro- 

 motive forces must be equal and differ from each other by equal 

 phase angles, as in the 3-phase and quarter-phase systems soon 



* ( ia). In making polyphase measurements, some form of voltmeter 

 and ammeter switches will be found convenient, so that all readings can be 

 made with one voltmeter and one ammeter. The same switches will serve 

 to transfer one wattmeter from one circuit to another. 



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