THE ALTERNATING CURRENT GENERATOR 237 



Three-phase ^-connection. The other method of con- 

 necting the coils is called the delta connection, so named 

 because its schematic diagram resembles the Greek letter A. 

 In this connection the end of coil 1 is connected to the 

 beginning of coil 2, the end of coil 2, connected to the 

 beginning of coil 3, and the end of coil 3 is connected to the 

 beginning of coil 1. Then the three junction points are 

 connected to the three slip-rings, as shown in diagram (6) 

 of Fig. 141. The A-con ection is not used as frequently as 

 the Y-connection. 



Equality of Voltages in a Three-phase System. The 

 three-phase system is peculiar in that the voltage measured 

 between any pair of wires is the same, and this is true no 

 matter whether the generator armature is A or Y-connected. 

 Having a given three-phase winding on an armature, the 

 output capacity will be just the same whether the A or Y 

 connection is employed, but the Y-connected machine will 

 give a higher voltage between lines than the A-connected 

 machine. The possible current output of the latter machine 

 is greater than that of the Y-connected machine in the same 

 ratio as its voltage is smaller, so that the two outputs are 

 equal. 



A discussion of the voltage and current relations and 

 of the power and power measurement of three-phase circuits 

 will be taken up in detail in Chapter XIV. 



Of course the armature windings of an alternator are 

 not arranged as shown in the simple diagram given in 

 Figs. 138-141; there are generally several pairs of poles 

 on an alternator and there is always more than one coil 

 per pair of poles, per phase. 



A Typical Armature, to be Connected in Various Ways. 

 Let us consider a four-pole alternator having twenty-four 

 slots on the armature, so that there are six slots per pole. 

 The first thing to note about the winding of an a-c. arma- 

 ture is that there is generally only one coil side placed in any 

 one slot. (This is different from the c-c, armature which 



