77/ /: i.\i>rrrio\ . 



diametrically opposite each other and each section occupies 

 approximately one-fourth the winding space of the ring. The 

 two windings a re called the A-phaseand the B-phase, respectively. 

 Care must be taken to connect the two sections of each winding 

 correctly, the correct method being shown in Fig. 219. 



Curves I A and I B show the variation with time of the currents 

 in phases A and B, respectively. As these are two-phase cur- 

 rents, they differ in time-phase by 90 or one-fourth of a cycle. 



At the instant marked (1), the current in phase A is zero and 

 that in B is negative maximum. With the method of connecting 

 the wine I ings, and the direction of the currents as shown, two 

 S-poles are formed on the upper ends of the B-windings and two 

 N-poles on the lower ends. These four poles combine into two 

 poles, a single S-pole and a single N-pole, each of these last being 

 twice the magnitude of the individual poles which combined to 

 form them. The resultant field is vertical and is dii 

 upwards, as indicated by the arrow F beneath diagram (1). In 

 (2) the current in B is still negative, hut of lessor magnitude than 

 in (1). The current in A has increased positively until its mag- 

 nitude is equal to that of B. Two S-poles and two N-poles 

 again combine to form a single S-pole and a single X-jx)le, each 

 of double the magnitude of the individual poles forming them. 

 The direction of the resulting field is 45 clockwise from its 

 position in (1). It is to be noted that while the two currents 

 are passing through 45 electrical time-d- 'he resulting 



field in the gramme ring advances !."> space-degrees. Diagrams 

 (3), (4), (5), (6), (7), and (8) show at different instants the posi- 

 tion- of the gramme-ring field resulting from the combined mag- 

 netic effects of phases A and B. The diagram for (<M would be 

 identical with that for (1). The rotating magnetic field has 

 passed through Ml) space-degrees while the two-phase currents 

 through MO electrical lime-degrees or one cycle. This 

 constitute.- M t \\n-pole rotating field and its speed in revolutions 

 per second is 1 he >ame as the frequency. O r the c\ cli cond, 



of the currents. l-'or example, it" the currents had a frequency 

 veins per second, the field would make 00 revolutions per 

 second, or :>.()()() r.p.m. 



The gramme-ring winding need ! necessarily of the 



mdings shown in 1 IL:. JP.). but may Lea mesh-con- 



