Electrical Engineering ⇒ Topic : Star or Wye Connected System

Star or Wye Connected System

In this method, similar ends (start or finish) of the three phases of the alternator are joined together to form a common junction N as shown in Fig.(a). The common junction N is called the *star point or neutral point.The three line conductors are run from the three ends (finish ends F in this case) and are as R, Y and B. This constitutes a 3-phase, 3-wire star-connected system. The voltage between any line and the neutral point (i.e., voltage across each winding) is called the phase voltage while the voltage between any two lines is called the line voltage. The currents flowing in the phases are called the phase currents while those flowing in the lines are called the line currents. Note that the phase sequence is RYB.Sometimes, a 4th wire, called neutral wire, is run from the neutral point as shown in Fig. (b) This gives 3-phase, 4-wire star-connected system.

                                     figure (a)                                                              figure (b)

The 3-wire star-connected system is used for balanced loads (i.e. load in each phase of the alternator has the same impedance and power factor) because then current in the neutral conductor is zero and no neutral conductor is required. However, 4-wire star-connected system is used for unbalanced loads because in that case, neutral current exists and the neutral conductor provides the return path as shown in Fig. (b)