ET201 - ELECTRICAL CIRCUIT (THREE PHASE PART 6)

1.1.2        Interconnection of three phase.

If the three armature coils of the 3-phase alternator are not interconnected but are kept separate  as shown in Figure 1.1.3 (a), then each phase or circuit would need two conductors, the total number of conductors, in that case, being six. It means that each transmission cable would contain six conductors which will make the whole system complicated and expensive.

 

Hence, the three phases are generally interconnected which results in substantial saving of copper. The general methods of interconnection are;

(a)                Star or wye connection

(b)               Delta or mesh connection

(a)        Star or wye (Y) connection

In this method of interconnection, the similar* ends say, ‘start’ ends of three coils (it could be ‘finishing’ ends also) are joined together at point N as shown in Figure 1.1.3(b). The point N is known as star point or neutral point. The three conductors meeting at point N are replaced by a single conductor known as neutral conductor. Such an interconnected system is known as 4-wire, 3-phase system as shown in Figure 1.1.3(c).  

 

         Figure 1.1.3 (b) and (c)  Interconnected system for Star connection

b)         Delta or mesh (D) connection

In this form of interconnection, the dissimilar* ends of three phase windings are joined together i.e. the ‘starting’ end of one phase is joined to the ‘finishing’ end of the other phase and so on as shown in Figure 1.1.3(d). In other words, the three windings are joined in series to form a closed mesh as shown in Figure 1.1.3(e).  

 

         Figure 1.1.3 (d) and (e)  Interconnected system for Delta connection