Electrical Engineering ⇒ Topic : Interconnection of Three Phases
Interconnection of Three Phases
In a 3-phase alternator, there are three windings or phases. Each phase has two terminals viz, start and finish If a separate load is connected across each winding as shown in Fig. (a), 6 conductors are required to transmit power. This will make the whole system complicated and expensive. In practice, the three windings are interconnected to give rise to two methods of connections viz.
(1) Star or Wye (Y) connection (2) Mesh or Delta (Δ) connection
(1) In Y-connection, similar ends (start or finish) of the three phases are joined together within the alternator and three lines are run from the other free ends as shown in Fig. b (i). The common point N is called neutral point. In Y-connection, neutral conductor (shown dotted) may or may not be brought out. If a neutral conductor exists,the system is called 3-phase, 4-wire system. If there is no neutral conductor, it is called 3-phase, 3-wire system.
(2)In Δ-connection, dissimilar ends (start to finish) of the phases are joined to form a closed mesh and the three lines are run from the junction points as shown in Fig. b(ii). In a A-connection, no neutral point exists and only 3-phase, 3-wire system can be formed.
The Y or delta connection serves substantially all the functions of three separate single phase circuits but with one important advantage that the number of conductors required is reduced. This results in the saving of conductor material and hence leads to economy.
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