I9 8 POLYPHASE CURRENTS. [Exp. 



3. Methods of Connecting Phases. Generating or receiving 

 coils or circuits may be combined in various ways, the common 

 ones being shown* diagrammatically in Figs. I and 2. In Figs, 

 i and 2, the relative positions of the various coils represent the 

 relative phase positions of their several electromotive forces. f 

 The black dotsj may be taken as line wires in cross-section. On 

 paper the distance between any two dots is the difference of 

 potential between them ; phase, as well as magnitude, is shown in 

 this way. 



To the same polyphase system, a number of differently con- 

 nected polyphase generators and receivers may be connected at 

 the same time ; thus, on a 3~phase system, some apparatus may be 

 delta- and some star-connected. From a 4-wire 2-phase system, 

 induction motors may be run simultaneously when connected as 

 (a), (c) or (d), Fig. I. Connection (b) can be combined on 

 the same system with (a), but not with (c) or (d). This is an 

 objection to 3-wire 2-phase distribution, inasmuch as synchron- 

 ous motors and converters as well as generators are frequently 

 wound quarter-phase and so cannot be run from a 3-wire system. 

 A further objection, that the line drop in the common wire makes 

 the voltages unsymmetrical, is discussed later, 14. 



4. Object. In performing this experiment, the object is to 

 gain a knowledge of the connections of polyphase circuits and 

 polyphase apparatus, and to understand their electrical relations 

 and various diagrammatic methods for representing them. 

 Make a study of whatever polyphase supply circuits are available 

 and by means of transformers obtain, so far as possible, all the 

 systems indicated in Figs. I and 2. 



* (3a). The arrangement of Fig. 2 (a) is never used for independent 

 3-phase circuits ; it is used only for connecting transformer secondaries to 

 so-called 6-phase synchronous converters, 27. 



t(3b). Although the diagram of connections can not in general be 

 taken as the vector diagram of electromotive forces, this can be done in 

 the simpler cases and makes the introduction to the subject more clear. 



t(3c). This representation by dot's is called by Steinmetz the topo- 

 graphic method. 



