104 



ELEMENTS OF ELECTRICAL ENGINEERING. 



94, are arranged so that the current c flows towards the generator 

 in main No. 3 when a and b flow away from the generator in 

 mains No. I and No. 2, then the current in main No. 4 will be 

 zero, since a -f b c at each instant. Therefore, when the re- 

 ceiving circuits x, y and z are similar, main No. 4 may be dis- 

 pensed with if the windings are properly connected. The proper 

 connections are shown in Fig. 95. This arrangement of the 

 windings of a three-phase armature is called the Y-connection. 



(b) The ^-connection. Suppose the three armature windings 

 of a three-phase alternator to be connected so as to form a closed 

 circuit, and let the three lines A, C and B in the clock diagram, 

 Fig. 97, represent the electromotive forces of the respective wind- 

 ings. The electromotive 

 force C is equal to A -f B, 

 and therefore, if the windings 

 are properly connected, the 

 electromotive force around 

 the closed circuit of the three 

 windings will be zero. Each 

 junction of two windings 

 may then be connected to a 

 collector ring so that the 

 three windings can deliver current to three-wire mains. This 

 arrangement of the windings of a three-phase armature is called 

 the ^-connection. 



53. Conventional diagrams. Choice of signs to give symmetri- 

 cal clock diagrams, (a) Y-connection. The three armature wind- 

 ings of a three-phase armature branch out from a common junc- 

 tion, the so-called neutral point N t Fig. 94, when the windings 

 are Y-connected. The essential features of this scheme of con- 

 nections are best shown by a symmetrical diagram like Fig. 98. 

 // is desirable to consider the current (and voltage) in each winding 

 as positive when it flows away from the neutral point and the arrows 

 in Fig. 98 show these positive directions* On the basis of this 



*It must not be imagined that the arrows in Figs. 98 and 100 represent the actual 

 directions of the currents at any given instant. 



